GB2602162A

GB2602162A - Apparatus and method for drying and styling hair

Info

Publication number: GB2602162A
Application number: GB2020306.3A
Authority: GB
Inventors: Alexander Weatherly Robert; Norfolk Andrew; Daniel Harrison Alexander
Original assignee: Jemella Ltd
Current assignee: Jemella Ltd
Priority date: 2020-12-21
Filing date: 2020-12-21
Publication date: 2022-06-22
Also published as: AU2021406047A9; CN116847756A; EP4262469A2; GB202020306D0; WO2022136866A2; US20240057740A1; WO2022136866A3; ZA202306653B; AU2021406047A1

Abstract

A device 10 for drying and/or styling hair through conduction and convection comprising a body portion 12 having a fan 24 and a heater 30 for generating a heated air stream, which flows into a head portion 16 that has a base portion 22 and a heat exchanger 44. Heat from the air heats up the heat exchanger, which in turn heats up the base portion. The user’s hair contacts an outer surface of the base portion and is heated by conduction. Vent holes (40; figure 1) could be provided in the base portion so that the heated air can also heat the user’s hair by convection. The head portion may comprise baffles to direct the heated air to the central portion of the heat exchanger. The heat exchanger at the proximal end to the head may have a lower heat exchanging efficiency than the rest of the heat exchanger, and/or a convoluted path. The device may also have a plurality of bristles 20 and thermally conductive elements 18 that guide the hair around the plurality of vent holes. The thermally conductive elements may be coupled to the heat exchanger.

Description

APPARATUS AND METHOD FOR DRYING AND STYLING HAIR

Field of the Invention

The present invention relates to an apparatus for styling the hair of a person (or conceivably an animal), for example after washing the hair or as part of a styling process. That is to say, the hair may be wet (or "towel-dry") prior to use of the invention, and may then be dried and styled using the invention. Alternatively, the device may be used to style dry hair. Such drying and styling of the hair may be performed by a user in respect of their own hair, for example, or by a hair stylist. It should also be noted that the term "wet" as used herein should be interpreted broadly, to encompass not only hair wetted by water, but also hair wetted by liquids other than water. For example, hair may be wetted by a solvent-based colourant, which the invention may be used to dry and/or style.

Background to the Invention

Conventional handheld hairdryers, that incorporate an electrically-powered motorised fan to blow a current of cool or hot air in order to dry a person's hair, are well known. The fan draws ambient air into the body of the hairdryer and blows the current of air towards the hair to be dried. When hot air is to be blown, typically an electric heating element, incorporated within the body of the hairdryer, is used to heat the current of air before it leaves the hairdryer. Optionally, the hairdryer may be equipped with a concentrator nozzle attachment to intensify and direct the current of air, or a diffuser attachment to deliver the air more gently.

However, conventional hairdryers can often be noisy, heavy and bulky. Moreover, they can be awkward to use, and it can be difficult for a user (in particular a domestic user attending to their own hair) to achieve desired results, particularly in respect of styling the hair whilst drying it. For instance, a hairdryer will often be used simultaneously with a hairbrush or comb, or another piece of styling equipment, to style the hair during drying. The styling process may be, for example, to straighten the hair, or to provide "body and volume" to the hair (if necessary, preceded or succeeded by the application of styling products such as mousse, gel, wax, hairspray, etc.). Simultaneously manoeuvring a hairdryer and a brush (or a comb, etc.) around the head can be awkward for the user, and often requires a degree of skill to achieve the desired results.

Thus, whilst using a conventional hairdryer is the fastest method to dry hair, it can be very difficult and/or time-consuming to create a desired end result in respect of styling. To do this the user has to use a brush and/or additional hair styling tools.

As an alternative to conventional hairdryers, some people may use so-called "wet to straight" hair straighteners. These are used to both dry and straighten hair, by drawing wet hair between a pair of heated plates mounted on opposing arms of the device. These devices tend to use conductive heating at high temperatures (typically 185-230°C) on wet hair but can be damaging to hair, and/or may be perceived to be damaging to hair, due to sounds of cavitation (sizzle) or the use of elevated temperatures around the denaturation temperature of wet hair.

Hot air brushes may also be used to dry and style hair. Whilst this type of product combines drying and styling capability in a single hand-held device, these devices tend to be relatively slow at drying hair. Users may first dry the hair using a conventional hair dryer before switching to the hot air brush to perform the final drying and styling of the damp hair. Therefore, there is a need for a more efficient hair-styling device that removes or reduces the need for a separate device to dry the hair, that provides more efficient drying and styling of the hair, and that can be easily operated by the user.

A further problem that occurs with hot air brushes is uneven temperature distribution across the outer surface of the device. For example, a portion of the device that is loaded with wet or damp hair may cool relatively quickly, whilst an unloaded section of the device remains relatively hot. This temperature imbalance can result in reduced drying and styling performance. Therefore, there is a need for a hair styling device that more effectively balances the temperature distribution across the device.

Summary of the Invention

The present invention provides an apparatus for drying and styling hair, the apparatus comprising: a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair; a fan for drawing air into the apparatus and for blowing air towards the head portion; and at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the head portion is configured to receive the heated air stream and the base portion is configured to be heated by the heated airstream and to store heat from the heated air stream for subsequent transfer of heat by conduction to hair that engages the hair contacting surface of the base portion.

The apparatus may control the heating of the air by the at least one heater in response to a change in temperature of the base portion. One or more temperature sensors may be provided to sense the temperature and a controller can then change the power applied to the heater, the number of heaters used to heat the air or the speed of the fan to increase or decrease the air temperature. For example, the apparatus may increase the heat output of the at least one heater when a temperature of the base portion falls below a predetermined threshold value. The heat output can be increased by increasing the heat provided by one heater or by powering an additional heater and/or by slowing down the fan so that the air takes longer to pass through the heater which results in the air being heated to a higher temperature.

The apparatus may also comprise: at least one sensor for sensing a temperature of the base portion; a first heater for heating the air drawn into or output from the fan to provide the heated air stream; and a second heater configured to provide a boost function to provide addition heat to the air stream; wherein the apparatus is configured to control the second heater in response to a detected decrease in the temperature of the base portion.

Typically, the base portion comprises at least one and preferably a plurality of vent holes to allow for flow of the heated air out of the base portion for transfer of heat from the heated air to the hair by convection. With this arrangement, the hair can be heated by both conduction and convection leading to a more efficient drying device.

The head portion may comprise a plenum chamber and the heated air flows from the plenum chamber to the at least one of vent hole.

In a preferred arrangement, the base portion comprises a plurality of thermally conductive elements on an outer surface of the base portion, wherein the thermally conductive elements are configured to be heated by the heated airstream and to store heat from the heated air stream for subsequent transfer of heat by conduction to hair that engages the hair contacting surface of the base portion. These thermally conductive elements increase the overall heated surface of the base portion -thereby increasing the amount of conductive heating the apparatus can provide. Typically, these thermally conductive elements can increase the overall surface area of the hair contacting surface by between 50% and 200%. In a preferred arrangement, the thermally conductive elements are integrally formed with the base portion, for example by cast moulding. The thermally conductive elements may have a fin-like or a blade-like shape which helps them cut through the user's hair without getting tangled up with the hair. The specific heat capacity of the base portion (including the thermally conductive elements is between 800 to 1000 J/kg °C (for example, 900 J/kg °C); and the thermal conductivity is between 90 and 200 W/mk. To provide a reasonable heat storage, the mass of the base portion is preferably greater than about 50 grams.

The mass of the base portion should not be too great -or the device will become too heavy to use for prolonged periods of time. The inventors have found that the mass of the base portion is preferably between about 100 grams and 140 grams.

By providing a base portion that has a relatively high thermal mass, the device can provide a significant portion of its heating effect by way of conduction instead of convection through the heated air. Specifically, with preferred embodiments of the invention more than 30% and preferably more than 50% of the heating effect provided by the apparatus is provided by conduction (through contact between the hair and the base portion) rather than convection via the heated air.

A heat exchanger may be provided that receives the heated air from the plenum chamber and that guides the heated air to the plurality of vent holes. The heat exchanger helps to transfer heat from the heated air to the base portion. In a preferred arrangement, the heat exchanger comprises a plurality of radial fins.

In a preferred arrangement, the heat exchanger comprises one or more air-inlet channels for receiving the heated air from the plenum chamber; and one or more air-outlet channels for guiding the heated air to the vent holes. The heated air flows along one of the air-inlet channels before flowing through one of the air-outlet channels. A mixing chamber may be provided that receives the heated air from the air-inlet channels, and the air-outlet channels receive the heated air from the at least one mixing chamber. Mixing chambers may be provided at each end of the heat exchanger. As those skilled in the art will appreciate, as the heated air flows along the air-inlet channel and then into the air-outlet channel, some of the heat is given up to the heat exchanger and in turn the heat in the heat exchanger flows into the base portion. The heat exchanger is preferably bonded to the base portion using a thermally conductive bonding agent to maximise the heat transfer from the heat exchanger to the base portion.

Mixing chambers may be provided at an end of the head portion that is proximal to the main body and the second mixing chamber is provided at an end of the head portion that is distal to the main body.

In a preferred arrangement heated air will flow towards the body portion along the one or more air-inlet channels, before flowing away from the body portion in the one or more air-inlet channels. Heated air will also flow away from the body portion along the one or more air-inlet channels, before flowing towards the body portion in the one or more air-inlet channels.

The thermally conductive elements mounted on the base portion are preferably arranged in rows and each row preferably aligns with a corresponding air-inlet channel. With this arrangement, the hottest part of the heated air is used to heat the parts of the base portion closest to the thermally conductive elements.

The head portion may take on one of a plurality of different shapes. For example, it can provide a generally cylindrical head or it can be flatter and provide head that is shaped more like a traditional paddle brush. The head portions can be detachable from the body portion -such that the function of the head portion can be changed for different drying or styling processes. The head portion may be made and sold separately from the main body portion (which typically houses the fan, heater and control electronics).

A plurality of thermally insulated bristles may be provided on the base portion for guiding the hair. These bristles help to prevent the user from touching the heated surface of the base portion or the heated thermally conductive elements. They also help to apply some tension to the hair during use which helps to pull the hair on to the heated surface -thereby increasing the conductive heating the device provides on the user's hair.

Typically, the fan and the at least one heater are provided in the body portion which may be shaped to facilitate gripping by the user. The heater preferably sits close to the head portion to reduce heating of the body portion.

The fan may be mounted to generate a generally longitudinal flow of air from the body portion into a plenum chamber in the head portion.

The invention also provides an apparatus for drying and styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair and a heat exchanger thermally coupled to the base portion, wherein the head portion has a proximal end and a distal end and is coupled to the body portion at the proximal end; a fan for drawing air into the apparatus and for blowing air towards the proximal end of the head portion; at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the proximal end of the head portion is configured to receive the heated air stream, wherein the heat exchanger extends between the proximal and distal ends of the head portion and wherein the head portion further comprises a baffle positioned at the proximal end of the head portion and configured to cause the heated air stream to enter a central portion of the heat exchanger located between said proximal and distal ends. The baffle prevents the heated airstream from entering the heat exchanger adjacent the proximal end of the head portion which prevents the proximal end of the heat exchanger (closest to the body portion) from getting too hot compared to other parts of the heat exchanger.

Typically, the baffle extends over between about 10% and 40% of the heat exchanger. The baffle may be formed of thermally insulating material.

Multiple baffles may be provided -one positioned at each end of the heat exchanger to force the heated air to enter the heat exchanger in a central region thereof.

As an alternative solution to using the baffles, the thermal efficiency of the heat exchanger may be reduced at the proximal end of the heat exchanger. This can be achieved by reducing the surface area of the heat exchanger in the proximal region or by providing some thermal insulation around the parts of the heat exchanger at its proximal end.

The invention also provides an apparatus for drying and styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair and having one or more vent holes; a fan for drawing air into the apparatus and for blowing air towards the head portion; at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; and a heat exchanger for exchanging heat between the heated air stream and the base portion, and wherein the heat exchanger forms a convoluted path for the heated air stream to follow to reach said one or more vent holes.

The heat exchanger may comprise one or more air-inlet channels and one or more air-outlet channels and the heat exchanger may cause heated air to flow along one of the one of more air-inlet channels and to change direction and travel along one of the one or more air-outlet channels to reach a vent hole. The heat exchanger is preferably arranged so that the flow direction of air in the air-outlet channel is opposite to the flow direction of the corresponding air in the air-inlet channel.

Typically, the heat exchanger comprises a proximal end and a distal end and a plurality of air-inlet channels and a plurality of air-outlet channels extending between the proximal and distal ends; and each air-inlet channel is configured to receive part of the heated air stream such that heated air flows along the air-inlet channel towards and into a first mixing chamber located at the proximal end of the heat exchanger and heated air flows along the air-inlet channel towards and into a second mixing chamber located at the distal end of the heat exchanger; and the air-outlet channels are configured to receive air from the first mixing chamber for air flow along the air-outlet channels away from the proximal end of the heat exchanger, and to receive air from the second mixing chamber for air flow along the air-outlet channels away from the distal end of the heat exchanger. The head portion may include a plenum chamber for receiving the heated air stream, a first baffle that isolates the first mixing chamber from the plenum chamber of the head portion and a second baffle that isolates the second mixing chamber from the plenum chamber of the head portion, whereby heated air from the plenum chamber cannot reach the mixing chambers without flowing along an air-inlet channel.

The base portion may comprise a plurality of thermally conductive elements extending from the hair contacting surface of the base portion and the air-inlet channels are aligned with the plurality of thermally conductive elements such that heated air flowing along the air-inlet channels is arranged to heat the base portion in the vicinity of the thermally conductive elements. In a preferred arrangement, the plurality of thermally conductive elements are arranged in rows on the surface of said base portion and the air-inlet channels are arranged in rows that are aligned with the rows of the plurality of thermally conductive elements.

Typically, the base portion comprises a plurality of vent holes and the air-outlet channels are aligned with the plurality of vent holes such that heated air flowing along the air-outlet channels is arranged exit the apparatus through the vent holes.

In a preferred arrangement, the plurality of vent holes are arranged in rows on the surface of said base portion and said air-outlet channels are arranged in rows that are aligned with the rows of vent holes.

The invention also provides an apparatus for drying and styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair; and a fan for drawing air into the apparatus and for blowing air towards the head portion; and at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the base portion comprises: a plurality of vent holes for venting the heated air from the apparatus; a plurality of bristles extending from the hair contacting surface of the base portion; and a plurality of thermally conductive elements extending from the hair contacting surface of the base portion; wherein the bristles and conductive elements are arranged to guide the hair around the vent holes to prevent, during use, the hair from blocking the vent holes.

The vent holes, the plurality of bristles and the plurality of thermally conductive elements are preferably arranged in rows, with the bristles being offset from the thermally conductive elements. The rows of bristles and the rows of thermally conductive elements may each form a regular array of bristles and thermally conductive elements. In a preferred arrangement, each thermally conductive element is surrounded by four bristles Similarly, each bristle is preferably surrounded by four thermally conductive elements. Typically, each vent hole is positioned between a thermally conductive element and two bristles. In a preferred configuration, the vent holes and the thermally conductive elements are aligned in a row that is transverse to a longitudinal axis of the head portion.

The invention also provides an apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion defining an inner space and having an outer hair contacting surface for engaging with a length of hair; a fan for drawing air into the apparatus and for blowing air towards the head portion; and at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the base portion has a plurality of thermally conductive elements extending from the outer hair contacting surface and wherein each of the thermally conductive elements is coupled to a heat exchanger mounted within the head portion and which is configured to transfer heat from the heated air stream to the thermally conductive elements.

The thermally conductive elements may be coupled to a common heat exchanger or multiple heat exchangers may be provided. The head portion also comprises a plenum chamber that receives the heated air stream from the heater and wherein the or each heat exchanger is configured to receive heated air from the plenum chamber.

The base portion may be formed of a sheet material (in which case it does not contribute in any significant way to the conductive heating of the user's hair (due to its lack of thermal mass) or it may be a casting -in which case it can have sufficient thermal mass to contribute to the conductive heating of the user's hair.

As before, the base portion may comprise one or more vent holes through which the heated air stream exits the apparatus. In this case, the or each heat exchanger is preferably configured to cause the heated air stream to follow a convoluted path to reach said one or more vent holes.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, and with reference to the drawings in which: Figure la is a perspective overview of a hair styler device; Figure lb shows the hair styler device of Figure la in use; Figure 2 shows a longitudinal cross section of the device of Figure la; Figure 3 shows an overview of a head portion of the device shown in Figure la; Figure 4 shows an overview of a base portion of the head portion shown in Figure 3; Figure 5 shows a perspective view of a heat exchanger of the head portion shown in Figure 3; Figure 6 illustrates the location of part of the heat exchanger inside the head portion; Figure 7 shows a longitudinal cross section of the head portion shown in Figure 3, illustrating the flow of air from the central plenum chamber and through the heat exchanger; Figure 8 shows a transverse cross section of the head portion shown in Figure 3; Figure 9 shows one half of the head portion of the device, with the heat exchanger removed; Figure 10 shows a transverse cross-section through the distal end of the head portion shown in Figure 3 illustrating a mixing chamber of the head portion; Figure 11 shows a flow diagram that schematically illustrates the flow of heated air through the device if mixing chambers are not provided; Figure 12 shows a flow diagram that schematically illustrates the flow of heated air through the device when mixing chambers are provided; Figure 13 shows a schematic longitudinal cross section of the head portion, illustrating the flow of air between the inlet channels, the outlet channels and the mixing chambers; Figure 14 shows an overview of an alternative configuration of the head portion; Figure 15 shows an example of a bristle insert that may form part of the head portion shown in Figure 3; Figures 16a and 16b show examples of dividers; Figure 17 shows a detailed view of the exterior surface of part of the head portion; Figures 18a and 18b show schematic diagrams of an arrangement of bristles and heated elements on the exterior surface of the head portion; Figure 19 shows a graph plotting pressure against flow rate for when the device is loaded with wet hair, dry hair and no hair; Figures 20a and 20b show schematic diagrams of exemplary shapes of the heated elements on the exterior surface of the head portion; Figure 21 is a diagram showing example curves having different values of a 30 parameter p; Figure 22 is a schematic diagram indicating three types of curve of a heated surface element; Figure 23 shows a schematic block diagram of the hair styler device of Figure la; Figure 24 shows a plot of temperate against time for the air temperature and surface temperature of the device; Figure 25 shows a graph of hair sample temperature against drying time, useful for understanding the technological background of the disclosure; and Figure 26 shows a cross section of a further alternative configuration of the head portion.

In the figures, like elements are indicated by like reference numerals throughout.

Detailed Description of Preferred Embodiments

The present embodiments represent the best ways known to the applicant of putting the invention into practice However, they are not the only ways in which this can be achieved.

Figure la is a perspective overview of a combined hair dryer/styler device 10 according to a presently-preferred embodiment. The device 10 is operable to dry wet or damp hair, whilst also being operable to style the hair. Figure lb illustrates the device when in use to dry and/or style hair. As illustrated in Figure 1 b, the device is a handheld and portable device. The styling process may be, for example, to provide "body and volume" to the hair (if necessary, preceded or succeeded by the application of styling products such as mousse, gel, wax, hairspray, etc.).

The device comprises a main body (handle portion) 12 and a head portion 16. A control button or switch 14 may be provided on the device 10, to enable it to be turned on or off, together with an indicator light to show whether the power is on.

A sound can also be played by a sound generator (not illustrated) when the device 10 is switched on and ready to use.

The head portion 16 comprises a base portion 22 that can be heated so that hair contacting the outer surface of the base portion 22 is heated to facilitate styling.

The base portion 22 has a plurality of thermally conductive surface elements 18 that extend from the outer surface of the base portion 22. Beneficially, a thermally conductive path is formed around the circumference of base portion 22, allowing more efficient balancing of the temperatures across the external surface of the base portion 16. The head portion also has a relatively high thermal mass so that the head can store the heat energy and deliver it to the user's hair when in contact with the head. The thermal mass of the head portion is typically between 180 to 220 J/K (for example, 205 J/K).

In the preferred embodiment, the thermally conductive surface elements 18 (also referred to as 'heated surface elements' 18 throughout this specification) are integrally formed with the base portion 22. The base portion and the heated surface elements may be formed from one or more parts that are made, for example, in a casting operation. However, it will be appreciated that the base portion 22 and the heated surface elements 18 may be formed using any other suitable manufacturing method. The heated surface elements 18 typically have a thermal conductivity of between 90 and 200 W/mk (for example, 160 W/mK). The head portion 16 typically comprises between 250 to 350 heated surface elements (for example, 304 heated surface elements). If the heated surface elements are not provided, the surface area of the external surface of the head portion 16 is approximately 15000 mm2. When the heated surface elements are provided, the external surface area of the head portion 16 is approximately 36000 mm2. It will be appreciated, therefore, that the heated surface elements provide a large increase in the surface area, of approximately 140%, enabling mor efficient heat transfer to the hair.

The head portion 16 also comprises a plurality of bristles 20 that protrude through openings in the base portion 22, and a plurality of vent holes 40.

In use, the outer surface of the base portion 22 and the heated surface elements 18 transfer heat to the hair of the user as the hair passes over the surface of the head portion 16, enabling the user to more rapidly dry wet or damp hair. Beneficially, the heated surface elements 18 increase the surface area of the base portion 22 that may engage with the hair, increasing the drying rate.

Heated air flows out of the vent holes 40, further increasing the drying rate. In use, the temperature of the outer surface of the base portion 22, including the heated surface elements 18, may be approximately 120 °C. The temperature of the heated air flowing out of the vent holes 40 may be between approximately 100 °C and 150 °C. This temperature enables efficient drying of wet or damp hair, whilst avoiding audible 'sizzle' and damage to the hair.

The bristles 20 guide the hair as is passes over the head portion 16 and enables the user to have greater control over the styling of the hair. Moreover, the combination of heat transfer from the base portion 22, the flow of heated air from the vent holes 40, and the use of bristles enables the user to more easily style the hair, and enables a greater range of styling techniques to be used. The bristles 20 may also prevent the user from touching the heated surface of the base portion 22 and the heated surface elements 18.

The combination of the heated external surface of the base portion 22 and the flow of heated air from the vent holes 40 enables the hair to be dried more efficiently. Therefore, a less powerful heater and/or fan assembly can be used whilst still achieving good drying performance.

Figure 2 shows a longitudinal cross section through the device 10. The dashed line L2 indicates the longitudinal axis of the device. As shown in Figure 2, the device 10 comprises a fan assembly 24 inside the main body 12, for delivering a flow of air along a generally longitudinal direction inside the device 10. The air passes from the main body 12 into a central plenum chamber 32 located inside the head portion 16. A heater 30 is provided between the fan assembly 24 and the head portion 16. The heater 30 heats the air before it passes into the central plenum chamber 32. It will be appreciated, therefore, that the central plenum chamber 32 receives a flow of heated air from the main body 12 of the device 10, as indicated by arrow Dl. Alternatively, the heater 30 could be provided before the fan assembly 24, such the fan assembly 24 generates a flow of the heated air.

However, providing the fan assembly at the distal end of the main body 12 (away from the head portion 16) allows the fan to generate a flow of air at ambient temperature (or near-ambient temperature) over the printed circuit board assembly 28, beneficially cooling the electronics. The temperature of the heated air flowing into the central plenum chamber 32 may be, for example, between 200 °C and 500 °C, typically about 200 °C. However, in a typical heater, in which a heating coil is used to form the air heater, the heater provides more heating towards the periphery of the air stream than at the centre of the air stream. The temperature of the air towards the centre of the plenum chamber (i.e. close to a central longitudinal axis of the device) may be significantly lower (e.g. close to ambient temperature) than the temperature of the air towards the radial edge of the plenum chamber 32 (e.g. 400 °C). Problems associated with such uneven heating can be reduced by creating turbulent flow inside the device to mix up the heated air before it reaches the plenum chamber of the head portion. For example, one or more mixing elements (e.g. turbulence inducing elements) may be provided between the heater 30 and the plenum chamber 32 (or inside the plenum chamber 32), to mix the heated air inside the plenum chamber 32.

The heater 30 may comprise an electrically-powered heating coil (or other electrical heating elements), operable to heat the air drawn in by the fan assembly 24. Allowing for the airflow heating coil (or other heater elements) as well as the fan 30, the overall power consumption of the device 10 is typically around 950 W, which is significantly less than a 2000 W conventional hairdryer. For example, the power usage required to maintain the base portion 22 at a temperature of 120 °C is approximately 600 W. A so called 'boost mode', described in more detail later, may use an additional 300 W (a total of 900 W). The fan assembly may have a maximum power of approximately 15 W. In the example illustrated in Figure 2, a printed circuit board assembly 28 is provided within the main body 12. Electrical power is provided to the device 10 by means of a power supply located at the end of the main body 12 distal from the head portion 16. In the presently-preferred embodiment the power supply is an AC mains power supply. However, in an alternative embodiment the power supply may comprise one or more DC batteries or cells (which may be rechargeable, e.g. from the mains or a DC supply via a charging lead), thereby enabling the device 10 to be a cordless product.

The fan assembly 24 has an impeller and is typically also provided with a filter. In this example, the air enters the inside of the device via an air inlet covered by a protective grille 26. Advantageously the fan assembly 24 may incorporate a brushless motor designed to operate at high speeds (e.g. over 30,000 revolutions per minute) and low power (e.g. 15W maximum, 3W during normal operation), and may be driven by a DC power supply. Such high-speed low-power parameters of the fan have been found to provide excellent drying performance, drying hair as quickly as a 2000 W conventional hairdryer, but using significantly less power.

The head portion 16 comprises a heat exchanger 44 arranged to receive the heated air from the central plenum chamber 32. Baffles 36 are provided at either end of the central plenum chamber 32 such that air is prevented from flowing into the heat exchanger 44 at proximal and distal ends (relative to the main body 12) of the central plenum chamber 32. The baffles 36 may be formed of a thermally insulating material to further inhibit the flow of heat into the proximal and distal ends of the heat exchanger 44. It will be appreciated, therefore, that heated air flows into the heat exchanger 44 in a generally central region, in the longitudinal direction, of the head portion 16.

Each of the baffles 36 may prevent air from flowing into between 5% and 40% of the heat exchanger. Therefore, the baffles 36 (the entire arrangement of baffles 36) may prevent air from flowing into between 10% and 80% of the of the heat exchanger, depending on the exact number and configuration of baffles 36 used.

The head portion 16 also comprises an end grip 38. The end grip 38 may be formed of a thermally insulating material so that a user can comfortably hold the end grip 38 even when the head portion 16 is heated by the flow of heated air into the head portion 16 from the main body 12. It will be appreciated that the outer casing of the main body 12 and the bristles 20 are also typically constructed of a thermally insulating material, such as a plastic having a low thermal conductivity.

Figure 3 shows an enlarged view of the head portion 16 of the device 10. Heated air enters the central plenum chamber 32 of the head portion 16 from the main body 12, as indicated by arrow Dl. As shown in the figure, the head portion 16 comprises a pair of base portions 22a and 22b that are connected together. Each base portion 22 is formed of a single respective piece of material. For example, each base portion 22 may be formed from a single respective cast piece of aluminium. The base portion 22 may be formed of about 120g of aluminium having a conductivity in the range of 90 -200 VV/mk, for example 160 VV/mk Beneficially, the use of a single piece of material allows heat to be efficiently transferred from one side of the base portion 22 to the other. For example, if a region of the base portion 22 is cooled by wet or damp hair, heat can efficiently flow into the cooled portion from the other regions of the base portion 22. The base portion is preferably made from multiple parts -as this facilitates the assembly of the bristles into the base portions 22. The multiple parts of the base portion may be screwed or glued together using a heat conducting glue to facilitate heat transfer from one base portion to another. However, it will be appreciated that the base portion 22 may be formed as a single piece, although that complicates the manufacturing process. Forming the base portion as a single piece does, however, enables highly efficient heat distribution throughout the base portion. Beneficially, therefore, the formation of 'hot spots' -localised regions of high temperature on the exterior surface of the head portion 16, is reduced.

Figure 4 shows one of the base portions 22 -without the bristles 20. As shown, the base portion 22 comprises a plurality of heated surface elements three of which are labelled 18a, 18b and 18c. The base portion 22 is also provided with a plurality of apertures 42. The apertures 42 are arranged in rows along the longitudinal axis of the base portion between rows of the heated surface elements 18. As can be seen from Figure 3, the bristles 20 protrude through some of the apertures 42. In this example, the bristles 20 protrude from every-other aperture 42 along each row of apertures 42. The cross sectional dimension of each bristle is smaller than that of the corresponding aperture 42 through which it protrudes, such that air may flow out of the head portion 16 around the bristle. The remaining apertures 42 will be referred to as vent holes 40 and are provided with dividers which divide each vent hole 40 into a pair of openings. Advantageously, the user may position the vent holes 40 to direct the outgoing air towards the roots of the hair, to dry the roots and create root lift.

Figure 5 shows a perspective view of a heat exchanger 44 of the head portion 16 that is used to transfer heat from the heated air into the base portions 22. Figure 6 shows a cross section through the head portion 16, and illustrates the location of the heat exchanger 44 inside the head portion 16. Figure 6 also shows the baffles 36a and 36b that ensure the heated air enters the heat exchanger 44 in a central area thereof As shown in Figure 5, in this example the heat exchanger 44 is formed of two heat exchanger parts 44a and 44b that are connected together at flanges 45. Whilst the use of two heat exchanger parts 44a and 44b allows the device to be manufactured more easily, it will be appreciated that the heat exchanger parts 44a and 44b may instead be provided as a single heat exchanger part 44.

The total surface area of the heat exchanger is typically between 50000 mm2 and 70000 mm2 (for example, 66000 mm2). The ratio of the surface area of the heat exchanger to the external surface area of the head portion is typically between 1.6 and 2.0 (for example, 1.82).

The heat exchanger 44 comprises a plurality of alternating air-inlet channels 46 and air-outlet channels 48. The air-inlet channels 46 are arranged to receive heated air directly from the central plenum chamber 32 inside the head portion 16 in a region between the baffles 36a and 36b. Each air-inlet channel 46 is aligned with a corresponding row of the heated surface elements 18 of the base portion 22 -so that heat from the heated air can be efficiently transferred into the heated surface elements 18. Each air-outlet channel is arranged adjacent to a corresponding row of the apertures 42 of the base portion 22, such that air can flow from the air-outlet channel and out of the apertures 42 to exit the head portion 16.

As illustrated in Figure 5, each heat exchanger part 44a comprises a set of radial fins, each connected at an outer end to a neighbouring fin by an outer heat transfer portion 50.

Each outer heat transfer portion 50 forms an outer connecting wall of a corresponding air-inlet channel 46. Each of the radial fins is also connected, at an inner end, to the other neighbouring fin, by an inner connecting wall 51. Each of the inner connecting walls 51 is a wall of a corresponding air-outlet channel 48. Whilst in this example all of the fins are constructed as part of the heat exchanger 44, this need not necessarily be the case. For example, for ease of manufacturing at least some of the fins may be formed as part of the base portion 22 (for example, in as part of a casting manufacturing method), for later assembly with the remaining parts of the heat exchanger. The inner connecting walls 51 prevent air from flowing directly from the central plenum chamber 32 into the air-outlet channels 48. As will be described in more detail below, the air-inlet channels 46 are in fluid communication with each other at the distal and proximal ends of the heat exchanger 44 -such that the air can travel along the air-inlet channels 46 and then into the air-outlet channels 48 before escaping from the device through the vent holes 40. The point at which each of the fins engages with the base portion 22 (and the outer heat transfer portion 50 engages with the base portion 22) helps to maintain uniform heat exchange and air-speed in the head portion 16.

Each of the air-inlet and air-outlet channels may have a uniform (or near-uniform) cross section.

Whilst in this example the heat exchanger part 44 comprises radial fins, it will be appreciated that the fins need not necessarily be radial, and that any other suitable shape and configuration of surfaces (e.g. fins or vanes) could be used for dividing at least one air-inlet channel from at least one air-outlet channel such that air flows through the air-inlet channel before flowing through the air-outlet channel.

The heat transfer portions 50 engage with the interior wall of the base portion 22 -specifically at the parts of the base portion 22 from which the heated surface elements extend. As heated air flows through the air-inlet channel, heat is transferred into the heat transfer portion 50, and heat is subsequently transferred (by conduction) from the heat transfer portion 50 to the base portion 22. In other words, the flow of heated air through the heat exchanger 44 causes heat to be transferred to the base portion 22, for subsequent transfer of heat from the base portion 22 to the hair of a user. In another variant, described in more detail later, the heat transfer portions 50 may be omitted and the heat may instead be transferred directly from the flow of heated air to the base portion 22.

Figure 7 shows a longitudinal cross section of the head portion 16, illustrating the flow of air from the central plenum chamber 32 and through the heat exchanger 44. Heated air flows from the main body 12 of the device 10 into the central plenum chamber 32 in the direction indicated by arrow D10, along a longitudinal direction of the device. As shown in the figure, the air flows in a generally transverse direction from the central plenum chamber 32 into the air-inlet channels 46 of the heat exchanger 44. For completeness, it should be noted that although the direction of the airflow entering air-inlet channels 46 may be said to be "generally transverse" to the length of the head portion 16 (i.e. substantially perpendicular to the longitudinal airflow into the central plenum chamber 32 from the main body 12), it will be appreciated that the airflow may be at least partially angled with respect to the transverse direction, for example as the air begins to turn to flow in the longitudinal direction along the length of the air-inlet channel.

Inside the air-inlet channels 46 the air flows longitudinally towards the ends of the head portion 16. Part of the air inside the air-inlet channel 46 flows towards the end of the head portion 16 that is proximal to the main body 12 and part of the air inside in the air-inlet channel 46 flows towards the end of the head portion 16 that is distal to the main body 12. As the heated air flows through the air-inlet channels 46, heat from the air is transferred to the corresponding heat transfer portions 50, and from the heat transfer portions 50 to the base portion 22.

The air flows out of the proximal and distal ends of each air-inlet channel 46 and into mixing chambers 54a, 54b. The air received into the mixing chambers 54a, 54b from the air-inlet channels 46 mixes inside the mixing chambers 54a, 54b.The air flows from the mixing chambers 54a, 54b into the air-outlet channels 48 of the heat exchanger 44. Each air-outlet channel is coupled to a corresponding row of apertures 42 of the base portion 22, for airflow from the air-outlet channel 48 out of the apertures 42. It will be appreciated, therefore, that the heat exchanger acts as an air-guiding structure for guiding air from the central plenum chamber 32 to the vent holes 40 via the air-inlet channels 46, the air-outlet channels 48 and the mixing chambers 54a, 54b. More specifically, the heat exchanger 44 guides the air to flow in a first direction along an inlet channel 46, along the longitudinal direction of the head portion 16, before being turned (inside the mixing chambers 54) to flow in the opposite direction along the air-outlet channel 48. This flow and counter-flow of heated air enables efficient and uniform heat transfer from the air to the heat exchanger 44.

Figure 8 shows a transverse cross section of the head portion at one of the distal or proximal ends thereof -illustrating the flow of air from the air-inlet to the air-outlet channels. The flow of air into the air-inlet channels 46 from the central plenum chamber 32 is illustrated by arrows Al and A2. The curved arrows illustrate the flow of air from the air-inlet channels 46 into a mixing chamber 54, and from the mixing chamber 54 into the air-outlet channels 48. As can be seen in the figure, each of the heat transfer portions 50 is arranged generally adjacent to a row of corresponding heated surface elements 18 on the outer surface of the head portion 16. Similarly, each of the air-outlet channels 48 is arranged generally adjacent to a corresponding row of bristles 20 and vent holes 40.

As illustrated in Figure 8, the transverse cross section of the head portion 16 has a generally oval or elliptical shape. It will be appreciated, therefore, that the head portion 16 comprises two regions (the upper and lower regions of the head portion in Figure 8) having a first curvature, and two further regions having a second curvature, greater than the first curvature (the regions on the left and right of the head portion 16 in Figure 8). The upper and lower regions (having the lowest curvature) are shaped to optimise drying of the user's hair and the left and right regions are (having the greater curvature) are shaped to optimise styling of the user's hair. As will be discussed in more detail later, the shape of the heated surface elements 18 is different in regions of different curvature of the head portion 16.

Figure 9 shows one half of the head portion 16 of the device, with the heat exchanger 44 removed. The lower surfaces 60 below the corresponding rows of heated surface elements 18, that engage with the heat transfer portions 50 of the heat exchanger 44 are shown. The outer walls 56a, 56b of the mixing chambers 54a, 54b are also shown. A dashed circle 61 indicating a particularly advantageous location for providing one or more temperature sensors is also shown. As will be described in more detail, the temperature sensor may be used to sense the temperature of the base portion 22. The indicated location is at the approximate centre of the thermal mass of the base portion 22. Since the indicated region 61 is at the approximate centre (along the longitudinal direction) of the base portion 22, this region of the base portion 22 is likely to transfer a large fraction of the heat transferred to the hair by conduction.

Figure 10 shows the distal end (relative to the main body 12) of the head portion 16, in which the outer wall 56 is not shown. The location of the mixing chamber 54 between the end of the head portion 16 and the heat exchanger 44 can been seen. In this example, the baffles 36 form an inner wall of the mixing chamber 54, and separate the mixing chamber 54 from the central plenum chamber 32. Alternatively, the mixing chamber may be separated from the central plenum chamber 32 by a transverse wall across the central plenum chamber 32. In other words, a cap may be provided to separate the central plenum chamber 32 from the mixing chamber 54.

Figure 11 shows a flow diagram that schematically illustrates the flow of heated air through the device if mixing chambers 54 are not provided. The flow of air is illustrated by the arrows. The width of the arrow indicates the corresponding temperature of the air -the hotter the air the wider the arrow. However, it will be appreciated the arrow widths are not necessarily proportional to the actual temperature of the air that would flow through the device, and are provided merely for illustrative purposes.

Firstly, the fan assembly 24 generates a flow of air over the heater 30 which produces heater air which is then passed into the central plenum chamber 32. The heated air flows out of the central plenum chamber 32 into the air-inlet channels 46 of the heat exchanger 44.

As described above, each air-inlet channel 46 is aligned with a corresponding row of heated surface elements 18 on the outer surface of the head portion 16, for transfer of heat from the air inside the air-inlet channel to the corresponding heated surface elements 18, via the heat transferring portion 50 of the heat exchanger. In use, when the user places wet or damp hair on the outer surface of the head portion 16, some of the heated surface elements 18 will cool after coming into contact with the wet/damp hair. This results in an increase in the amount of heat transferred from the air inside the corresponding air-inlet channel 46. Since the hair of the user is unlikely to be distributed evenly over the entire outer surface of the head portion 16, there can be significant differences in the temperature of the air inside each of the air-inlet channels 46. In the example illustrated in Figure 11, the heated surface elements 18 corresponding to the two central air-inlet channels 46 (indicated by the dashed rectangles) have cooled, resulting in a decrease in the temperature of the air flowing along those channels 46. A temperature imbalance may also occur due to differences in the temperature of the air entering each of the air-inlet channels 46 from the plenum chamber 32. For example, the air entering the plenum chamber may be unevenly heated due to the configuration of the heater 30 (as discussed above), resulting in some of the air-inlet channels 46 (e.g. the inlet channels 46 indicated by the dashed lines in Figure 11) receiving cooler air compared to the air received into the other air-inlet channels 46.

In the example shown in Figure 11, each air-inlet channel 46 is coupled directly to a corresponding air-outlet channel 48. No mixing chambers are provided. The cooler air from the central two air-inlet channels 46 flows directly into the corresponding air-outlet channels 48, and out of the corresponding vent holes 40.

Therefore, there is a central region of cooler air flowing out of the vent holes 40 on the external surface of the head portion 16. This region of cooler airflow is undesirable. For example, when the region of cooler airflow is in the same region as the user's hair on the surface of the head portion 16, the rate of drying of the hair is decreased.

Figure 12 shows a flow diagram that schematically illustrates the flow of heated air through the device 10 when mixing chambers 54 are provided. The flow of air from the fan assembly 24 to the air-inlet channels 46 is the same as for Figure 11, and will not be described again here. In this example, different from the example illustrated in Figure 11, the air from the air-inlet channels 46 flows into a pair of mixing chambers 54. As illustrated in the figure, the relatively low temperature air from the central air-inlet channels 46 mixes with the higher temperature air from the other air-inlet channels 46 inside the mixing chambers 54. The mixed air flows into the air outlet channels 46, and out of corresponding vent holes 40.

As the air flows through an air-inlet channel 46, heat is transferred to the air flowing through the neighbouring air-outlet channels 48. The cross sectional area and/or surface area of the air-inlet channels 46 and air-outlet channels 48 can be configured to obtain a desired level of heat transfer between the channels. The dimensions of the channels can also be configured to provide a desired rate of airflow out of specific vent holes 40 (or groups of vent holes 40), and to adjust the external surface temperature of the base portion 22 in different regions. In this way, different parts of the heat exchanger can be made to be more efficient than other parts thereby allowing different parts of the base portion to reach different operating temperatures. This may help, for example to a make the regions with higher curvature (and therefore useful for styling the hair) hotter than the regions with lower curvature that are better for drying the hair.

Whilst the temperature of air that exits some of the vent holes 40 is lower that the corresponding vent holes 40 of Figure 11, the temperature of the air exiting the head portion 16 is beneficially more uniform. This helps to reduce hotspots in the air flowing out of the vent holes 40, which could damage the hair. Accordingly, if the mixing chambers 54 are not provided, it may be necessary to reduce the hair heating power and therefore reduce the drying speed of the device.

It will be appreciated that since air flows from single air-inlet channel into both of the mixing chambers of the device 10 (at the proximal and distal ends of the head portion), each of the 'inlet channels' illustrated schematically in Figure 12 may be considered to represent one half of a physical air-inlet channel of the device 10, through which air flows into a single mixing chamber 54.

Figure 13 shows a schematic cross section of the head portion, illustrating the flow of air between the inlet channels, the outlet channels and the mixing chambers. As shown in the figure, relatively hot air (indicated by the wider solid arrows) flows from the central region of the air-inlet channels 46 towards the mixing chambers 54 provided at either end of the air-inlet channels 46. Since the air inside the air-inlet channels is thermally coupled to corresponding heated surface elements 18, the air inside the air-inlet channel 46 cools as is flows towards the mixing chambers 54, as heat is transferred to the heated surface elements 18. The cooling of the air inside the air-inlet channels is indicated by the decreasing width of the solid arrows towards the mixing chambers 54. The air from the air-inlet channels 46 mixes inside the mixing chambers 54 before flowing into the air-outlet channels 48. The mixed air, of relatively uniform temperature, flows through the air-outlet channels 48 and out of corresponding vent holes 40 provided between the bristles 20 on the external surface of the head portion. As previously described, air may also flow from the air-outlet channels through gaps provided around each of the bristles.

In use, the head portion 16 will typically receive a length of approximately 35 cm of hair. This corresponds to approximately 16 g of dry hair (for a large section of hair), and to approximately 25 g of wet hair. The mass of the head portion 16 is approximately 230 g, of which 144 g corresponds to the base portion. The ratio of the mass of the base portion to the mass of the wet hair engaged with the base portion is typically between 4 to 5 (for example, 4.5). The inventors have determined that this range of values for the ratio provides particularly effective drying and styling properties for the device 10.

Figure 14 shows an overview of an alternative (simpler) configuration of the head portion 16. In this example, different to the example illustrated in Figure 8, the heat exchanger 44 is not provided with the heat transfer portions 50. The heat exchanger simply comprises a plurality of radial fins 68. In this example, air flowing through the air-inlet channels is in direct contact with the inner surface of the base portion 22, to transfer heat to the heater surface elements 18. However, similar to the previous example, the heated air passes into the air-inlet channels 46 from the central plenum chamber 32 and flows into mixing chambers 54, before flowing into the air-outlet channels 48. Whilst this simpler configuration of the heat exchanger 44 has fewer parts, it is harder to manufacture compared to the configuration of the heat exchanger 44 illustrated in Figure 5, which can be made using a common extruding process.

Figure 15 shows an example of a bristle insert 21 that may be inserted into the base portion 22. The bristle insert 21 comprises a base 64 to which a plurality of bristles 20 and dividers 62 are secured. In this example, the bristles 20 and dividers 62 alternate in position along the length of the base 64. The bristle inserts 21 may be formed of a single piece of material. For example, the bristle inserts 21 may be manufactured using a plastic injection moulding technique. In order to assemble the head portion 16, the bristle inserts 21 are inserted into the base portion 22 from the inner surface of the base portion 22. Each bristle 20 and divider 62 is inserted into a corresponding aperture 42 of the base portion 22 so that the bristles 20 extends out from the outer surface of the base portion 22 and the dividers 62 create vent holes 40 in the base portion 22.

The bristles 20 may be flexible bristles. Beneficially, the use of flexible bristles enables a more uniform tension to be applied to the hair fibres as they pass across the surface of the head portion 16. Alternatively, the bristles 20 may be hinged or articulated. The angular range of a hinged bristle may be, for example, 20 degrees. Flexible or hinged bristles 20 beneficially reduce the tension applied to the hair (and reduce so-called 'snagging') when the bristle encounters a 'knot' of hair, and may also reduce the risk of damage to the device 10 if the device 10 is dropped.

The inventors have realised that the apertures 42 formed on the outer surface of the head portion 16 by casting the base portion 22 or by punching holes (or other suitable manufacturing techniques) into the base portion 22 are relatively large. These large apertures are not optimal for air speed and system resistance control when the hair is loaded. However, smaller apertures are difficult and costly to manufacture using casting or hole-punching techniques. Beneficially, each divider 62 of the bristle insert 21 splits the corresponding aperture 42 of the base portion 22 into two smaller openings. Therefore, the airflow properties of the apertures 42 are improved. Of course, the same result can be achieved by forming larger holes for the bristles and smaller holes for the vent holes 40 in the base portion 22.

However, such a solution increases manufacturing cost as it is less expensive to create apertures 42 of uniform size in the base portion 22.

Figures 16a and 16b show examples of dividers 62 that may be used. In the example shown in Figure 16a the divider 62a has a rectangular cross section. In the example shown in Figure 16b the dividing walls of the divider 62b are concave.

It will be appreciated that any other suitable shape of divider may be used to divide the aperture 42 into a plurality of smaller vent holes 40. It is also not necessary for each divider to form two holes. Alternatively, a divider 62 may be used to provide three or more openings or just a single opening. For example, the divider 62 may block the entire aperture 42 except for a small opening that passes through, for example, the centre of the divider 62.

Figure 17 shows a detailed view of the exterior surface of the head portion 16 of a particularly advantageous arrangement of heated surface elements 18, bristles 20 and dividers 62. In this arrangement, each divider 62 is positioned between a 5 corresponding pair of the heated surface elements 18 and between a corresponding pair of bristles 20. Each bristle is arranged between a corresponding pair of dividers 62, and generally in the centre of a set of four of the heated surface elements 18. In other words, for a row of bristles 20 and dividers 62 provided on a single bristle insert 21, each divider 62 is adjacent to 10 (sandwiched between) two of the heated surface elements 18, whereas each bristle 20 is adjacent to a space between the heated surface elements 18.

As the hair of the user passes over the external surface of the head portion 16, there is a risk that some of the vent holes 40 will become blocked or partially obstructed by the user's hair, reducing the drying efficiency. Whilst providing a more powerful fan could partially mitigate this issue, this would be an inefficient use of energy, would create additional noise, increase the size and cost of the device and reduce the lifetime and/or reliability of the motor. Beneficially, the arrangement of heated surface elements 18, bristles 20 and dividers 62 illustrated in Figure 17 reduces the risk that the vent holes will become blocked or obstructed, and therefore removes the need for a more powerful fan.

Figures 18a and 18b show schematic diagrams of this preferred arrangement of bristles 20 and heated surface elements 18 on the exterior surface of the head portion 16. The vent holes 40 created by the dividers 62 positioned in the apertures 42 are represented by the black dots labelled 40a and the openings formed around the base of the bristles 20 and the wall of the corresponding aperture 40 through which the bristle extends are represented by the hatched circles 40b.

Figure 18a is a schematic diagram that shows exemplary paths of strands or tresses of hair 80 as it passes over the surface of the head portion 16. As shown in the figures, the hair 80 curves around the bristles 20 and the heated surface elements 18. Beneficially, the arrangement of bristles 20 and heated surface elements 18 creates triangular regions 78 through which hair is less likely to pass.

Since the vent holes 40a and the openings 40b around the base of the bristles are positioned inside these triangular regions 78, the risk of these vent holes 40a and openings 40b becoming blocked by the hair is reduced, beneficially reducing the pressure build-up and reducing the load on the fan assembly 28. Moreover, since a relatively constant volume of air flowing out of the openings is maintained, the device is able to more efficiently dry the hair.

Figure 18b is a schematic diagram that illustrates preferred dimensions of the bristles 20, dimensions of the heated surface elements 18, and the relative arrangement of the bristles 20 and heated surface elements 18 that may be varied in order to control the size and shape of the regions through which hair is less likely to pass (in this example, the triangular regions 78): * Length L1: width of the heated surface elements 18 (substantially parallel to the longitudinal axis of the head portion 16) * Length L2: length of the heated surface elements 18 (substantially transverse to the longitudinal axis of the head portion 16) * Length L3: diameter of the bristles 20 * Length L4: spacing between the bristles 20 of a single bristle insert 21 (i.e. the spacing between adjacent bristles substantially parallel to the longitudinal axis of the head portion 16) * Length L5: spacing between adjacent bristle inserts 22 (i.e. the spacing between bristles substantially transverse to the longitudinal axis of the head portion 16). Length L5 is also the spacing between the rows of heated surface elements 18.

Length L1 is typically between 2 to 3 mm (for example, 2.7 mm). Length L2 is typically between 4 to 6 mm (for example, 5 mm). Length L3 is typically between 2 to 3 mm (for example, 2.3 mm). Length L4 is typically between 4 to 8 mm (for example, 6 mm). Length L5 is typically between 7 to 11 mm (for example, 9.2 mm). The length of the head portion is typically between 100 to 140 mm (for example, 120 mm). A width of the head portion is typically between 30 to 50 mm (for example, 40 mm). A height of the head portion is typically between 20 to 40 mm (for example, 30 mm).

Figure 19 shows a graph plotting pressure against flow rate for when the device is loaded with wet hair, dry hair and no hair. Beneficially, as shown in the figure, the particularly advantageous arrangement of bristles 20, apertures 40a, 40b and heated surface elements 18 illustrated in Figure 18b results in a relatively small increase in pressure when the device is loaded with wet hair or dry hair, compared to when the device is not loaded with hair. In other words, there is a relatively low change in the resistance when the device is loaded with hair. It is also noticed that the airflow properties of the device are beneficially not affected by whether the device is used to style wet or dry hair.

Figures 20a and 20b show schematic diagrams of exemplary shapes of the heated surface elements 18 on the exterior surface of the head portion. In the example illustrated in figure 20a, the heated surface element 18 has a triangular cross section and tapers to a point. Beneficially, the tapered shape of the heated surface element 18 allows the heated surface element 18 to 'cut' into the hair. This reduces the resistance of the hair being divided either side of the heated surface element 18. However, the inventors have realised that there is a risk of hair becoming trapped between the bristles 20 and heated surface elements 18 on the surface of the head portion 16, as illustrated by the 'trapped' hair 76 shown in figure 20a. The trapped hair is prevented from engaging with the surface of the base portion 22, and therefore the heat transfer to the hair 76 is reduced.

Another advantageous feature of the shape of the heated surface elements 18 is that they have a lower portion that has substantially parallel sides and an upper portion that tapers to a tip. This shape of the heated surface elements 18 helps to reduce the risk of hair becoming trapped between the bristles 20 and heated surface elements 18 compared to an arrangement where, for example the heated surface elements taper from the tip all the way to the surface of the base portion 22. This is illustrated schematically in Figures 20a and 20b. Specifically, Figure 20a illustrates the case where the heated surface elements 18 are tapered from the tip to the base at the outer surface of the base portion 22. As can be seen, because of the tapered sides, clumps of hair 76 are more likely to become wedged between the heater surface elements 18 and the adjacent bristles 20 -and not touch the heated outer surface of the base portion 22. In contrast, when the heated surface elements have substantially parallel sides, the clumps of hair can more easily fit between the heated surface elements and the bristles and touch the outer surface of the base portion 22. In this way, the surface area of the heated surface used to heat the user's hair is maximised, which leads to more efficient heat transfer.

As shown in Figure 8, the shape of the heated surface elements 18 is different in regions of different curvature of the head portion 16. For example, in the uppermost and lowermost parts of the head portion 16 in Figure 8 (the regions of the head portion 16 having the lowest curvature, which may be referred to as the 'brushing zone') the heated surface elements 18 are relatively elongate. In contrast, at the sides of the head portion 16 (the regions of the head portion having the highest curvature, which may be referred to as the 'styling zone') the heated surface elements 18 (and the bristles 20) are relatively short. Beneficially, the longer heated surface elements 18 in the brushing zone help to speed up the drying of the user's hair.

The reduced length of the bristles 20 and heated surface elements 18 in the styling zone beneficially reduces the risk of hair becoming tangled as it is passes between the bristles 20 and heated surface elements 18 when the brush is rolled around the hair. Alternatively, or additionally, this issue can be mitigated by providing flexible or articulated (e.g. hinged) bristles 20.

Figure 21 is a diagram showing example curves having different values of a parameter p. The parameter p is related to the dimensions X1 and X2 indicated in the figure. The dashed lines form a triangle. The solid lines indicate smooth curves that extend from the bottom two apexes of the triangle and towards the top apex. X2 is the height of the triangle. X1 is the distance from the base of the triangle to the peak of the corresponding smooth curve. The value of p is given by the following equation: X2.

As illustrated in the figure, curves for which p > 0.5 are hyperbolic, curves for which p = 0.5 are parabolic, and curves for which p < 0.5 are elliptical.

Figure 22 illustrates a schematic diagram indicating three types of curve that were used to define the preferred shape of the heated surface elements 18. As shown in the figure, the heated surface element 18 has three types of curve: a "root curve" 74, a "face curve" 72 and a "side curve" 70. The inventors have determined that particularly beneficial values of p for each of these curves are as follows: Root curve: 0.2 < p < 0.35 Face curve: 0.3 < p < 0.45 Side curve: 0.5 < p < 0.7 Beneficially, compared to simple parabolic curves, these values of p enable the following benefits: * Increased effective bristle spacing * Increased base conductive area * Increased sharpness of the tip of the heated surface element 18, to allow better 'slicing' into the hair * Higher 'shoulders' on the side curve, increasing the conductive area The device described above has been developed to provide a handheld portable device that can be used to dry wet/damp hair and that can also be used to style the hair once dry. The device provides a significant part of its heating effect by way of conduction. Typically, at least 30% of the heating is done by way of conduction.

The amount of conductive heating provided by the device depends on the overall area of the heating surface of the base portion (including the surface area of the thermally heated elements), the amount of hair loaded onto the device and the pressure between the hair and the heating surface. The bristles help to increase this pressure by gripping the hair and pulling the hair on to the heating surface of the base portion.

Control system Figure 23 shows a block diagram of a power/control system 500 for the device 10. The system comprises an AC/DC power supply 523 deriving power from a mains power supply input 502. Alternatively, power may be derived from a 12v lithium ion battery 505, in which case the mains power supply input 502 is used to charge the battery 505 via an AC to DC converter, which may be external or internal to the appliance. AC/DC power supply 523 may be configured to provide approximately 600 watts to a first heater 30-1 and 300 watts to a second heater 30-2.

The power supply unit 523 provides a 24 V supply to the fan assembly, for a maximum power of 15W.

Mains power is provided to a power/temperature control module 514, which in turn powers the heaters 30. Power/temperature control module 514 may employ one or more power semiconductor switching devices (triacs) to control application of the AC mains voltage to the heaters 30. During a heat-up phase, both heaters 30 may be powered to reduce the time taken for the device 10 to get up to the desired operating temperature. Similarly, if the surface temperature drops when wet hair is applied to the device 10, both heaters may be powered to provide a boost of heat (so-called "boost mode") to counter heat lost into the hair, and to increase the removal rate of bound water. At other times just the first heater 1 may be powered to maintain the device 10 operating at the desired operating temperature. The device may also include a mode in which both heaters 30 are switched off (disabled), and a stream of cool air (air at ambient or near-ambient temperature) out of the vent holes 40 is generated by the fan. This mode is a so-called "cool-shot" mode, which may be used to set a style of the hair. The cool-shot mode may also be used to cool the head portion 16 if overheating of the head portion 16 occurs.

Power from power supply 523 is also provided to a microcontroller/control means 506 via a DC/DC power supply 524. The microcontroller 506 is coupled to non-volatile memory 508 storing processor control code for a temperature control algorithm, and to RAM 510. The skilled person will appreciate that any of a wide range of different control algorithms may be employed including, but not limited to, on-off control and proportional control. Optionally the control loop may include a feed-forward element responsive to a further input parameter relating to the hair styling device, for example to use the operation of the apparatus to improve the temperature control. A user interface 512 is also coupled to microcontroller 506, for example to provide one or more user controls and/or output indications such as a light or audible alert. The output(s) may be employed to indicate, for example, when the surface of the base portion 22 or the airflow out of the vent apertures 40 has reached a desired operating temperature.

In order to perform effective control of the heaters 30 it is advantageous to have accurate measurements (either direct or indirect) of the temperature of the base portion 22 and the temperature of the air flowing out of the vent holes 40. However, in order to ensure the safety of the user, it is important that the base portion (which may be formed of an electrically conductive material) be isolated from the power electronics of the device (the power electronics driving the heaters 30). The inventors have realised that it is difficult to sense the temperature of the base portion 22 whilst also providing electrical isolation of the base portion 22, since physical sensors located on the base portion 22 could potentially form an electrical contact path.

A solution provided by the present work is to provide isolation 522 between the microcontroller 506 and the temperature sensors 340. This may be achieved using an optical isolator or by using a low voltage measurement circuit that is electrically isolated from the power electronics 523 driving the heaters 30.

Another alternative solution is to provide physical isolation between a sensor and the base portion 22 using an electrically insulating material. For example, an electrically insulating tape could be used.

A further alternative solution is to provide a non-contact sensor (for example, an infrared sensor) to sense the temperature of the base portion 22. The non-contact sensor could be provided in the main body portion 12 of the device 10 provided that the sensor has line-of-sight to the base portion 22.

A yet further alternative solution is to provide temperature measurements via conduction. For example, a heat pipe could be used to transfer heat from the base portion 22 to a sensor provided in the main body 12 of the device 10.

Heater control The device 10 has two operating modes -one for drying wet or damp hair and the other for styling dry hair. When drying hair, lower maximum air and surface temperatures are set to avoid user discomfort. When the device is used to style dry hair, higher maximum air and surface temperatures are set. Figure 24 shows a plot of temperate against time for the air temperature and surface temperature of the base portion 22 of the device when operating in the drying mode. The line labelled 'air temperature' indicates the temperature of the airflow leaving the vent apertures 40. The line labelled 'surface temperature' indicates the external surface temperature of the base portion 22. Two dashed lines indicating temperatures of 120°C and 150°C are also shown.

Region (1) of the graph illustrates an initial period when the device 10 is switched on and both heaters 30 are powered up, resulting in a steady increase in the surface and air temperatures. When the device is used with wet or damp hair (in a drying mode), the heater 30 and fan assembly are controlled to prevent the air temperature from exceeding approximately 150 °C, in order to prevent discomfort or damage to the hair of the user. The temperature of the base portion can be increased by either increasing the heat output of the heater, or by decreasing the fan speed. When the sensor detects that the air temperature has reached 150 °C, the microcontroller 506 switches off the second heater 30-2 (whilst the first heater 30-1 remains powered). As shown in the figure, the surface temperature of the outer surface of the base portion may be maintained below approximately 120 °C. When the device is used to style dry hair, the temperature of the outer surface base portion can be increased to a higher temperature of about 185 °C (by increasing the heat output of the heater 30, decreasing the fan speed of the fan assembly, or both. However, it will be appreciated that there will be a delay between increasing the heat output of the heater and the corresponding increase in temperature of the base portion as the heated air flows through the device 10). The inventors have found, however, that a lower temperature of around 145 °C is sufficient when operating in the styling mode.

Region (2) of the graph illustrates a period in which the air and surface temperatures have reached an equilibrium. The first heater 30 remains powered whilst the second heater 30-2 is switched off.

Region (3) of the graph illustrates a period in which wet or damp hair has been placed on the surface of the base portion 22, resulting in a decrease in temperature of the base portion 22. This decrease in temperature is detected from the temperature sensor signals and in response the microcontroller 504 switches on the second heater 30-2. As a result, the air temperature increases back up to the maximum 150 °C, and the amount of heat transfer from the air to the base portion 22 is also increased. As a result, the surface temperature rises back to the equilibrium state.

Region (4) of the graph illustrates a period in which the surface temperature has been restored to the equilibrium temperature. As a result, the second heater 30-2 is switched off and the air temperature drops to its equilibrium temperature.

Technical principles The expressions "to dry hair", "drying hair" and the like, as used herein, should be taken to refer primarily to the removal of "unbound" water that exists on the outside of hair when wet. Such "unbound" water should be contrasted with "bound" water, which exists inside individual hairs, and which can be interacted with when heat styling hair. There is no requirement to remove this "bound" water when drying hair in the context of the present invention, although removal of some bound water may occur during the drying process. Further removal of bound water usually occurs during the styling process.

Figure 25 shows is a graph of hair sample temperature against drying time, useful for understanding the technical principles associated with the present work. As the temperature of the hair is increased, the hair goes through a warming-up period and then first and second drying periods, as set out below. The first drying period relates primarily to the removal of unbound water, and the second drying period relates primarily to the removal of bound water.

* The "warming-up period": In this phase the heater is used to raise the temperature of the hair to that of the drying period where phase change of the liquid occurs (points A-B). The surface of the base portion and of the heated surface elements cannot operate over 100-135°C (nominally 120°C) before water cavitation (sizzle) occurs.

* The "drying period 1": This phase is supported by heated airflow to dry unbound water on the hair (points B-C). Without a freshly heated airflow supporting evaporation the hair will quickly cool and the drying rate will slow.

* The "drying period 2": This phase (points C-E) occurs when bound water on the hair evaporates and bound water is driven off from within the hair fibre.

* Styling/straightening can be achieved when forces are applied to the fibres and the bound and unbound water is driven off.

Additional Problems and solutions provided by the present work In the present work the inventors have considered the following problems (amongst others) and have provided the following solutions thereto: Problem I -achieving rapid temperature equalization across the outer surface of the hair styling device The inventors have determined that achieving rapid temperature equalization across the heated surface of the hair styling device beneficially reduces the occurrence of 'hot spots' that could damage the hair of the user, and enables more efficient drying of the hair.

The solution provided by the present work is to use heated air inside the head portion 16 of the device 10 to transfer heat to heated surface elements 18 having a relatively high specific heat capacity and thermal conductivity. The head portion also has a relatively high thermal mass so that the head can store the heat energy and deliver it to the user's hair when in contact with the head. When a region of the surface of the hair styling device is cooled after contacting wet or damp hair, heat is rapidly transferred from the heated air. The relatively high specific heat capacity enables a relatively large amount of heat to be transferred to the wet hair whilst minimising the decrease in temperature of the heated surface of the device.

Problem 2-minimising the range of air temperatures of the air directed at the hair of the user The inventors have determined that achieving uniform air temperature for air exiting the head portion 16 of the device 10 is beneficial to maintain drying efficiency. However, achieving uniform air temperature can be difficult due to the asymmetrical load of damp or wet hair on the outer surface of the device 10. On regions of the surface where the user has positioned a large amount of wet or damp hair, a local decrease in the surface temperature of the device and the temperature of the air exiting the vent holes 40 may occur.

The solution provided by the present work is to provide a heat exchanger 44 for balancing the thermal load across different regions of the surface of the device 10. Therefore, external surface temperature of the device can be balanced across the head portion 16, and the temperature of the airflow out of the vent holes 40 is more uniform.

Problem 3 -reducing the airflow resistance for the air flowing out of the device towards the user's hair.

The inventors have determined that hair, and wet hair in particular, has a large variation in airflow resistance, depending on the size and water content of the section of hair. A solution is therefore needed to prevent hair from blocking the vent holes and increasing the airflow resistance for the air flowing out of the device towards the user's hair.

The solution provided by the present work is to provide an arrangement of bristles 20, heated surface elements 18 and vent holes 42 that creates regions in which the hair less likely pass over the surface of the device. Air outlets are provided in these regions, and are therefore less likely to be blocked by the hair of the user.

This also helps to reduce the heater power and range in power requirements to regulate the air temperature, thereby increasing energy efficiency and reducing product size and cost.

By reducing the range of resistance in the airflow requirements of the system this also in turn enables lower speed motors/fans to be used, helping to increase the energy efficiency of the fan, and to reduce sound and cost.

Problem 4-drying the hair roots and creating root lift The inventors have determined that it is desirable to dry hair at the roots, e.g. with a view to creating root lift.

The solution provided by the present work is to provide vent holes 40 on the surface of the head portion 16, adjacent to bristles 20. These vent holes 40 can be orientated by the user to direct the outgoing heated air towards the roots of the hair, to dry the roots and create root lift.

Problem 5-to refresh hair on days when the hair is not washed The inventors have determined that users may wish to get a freshly washed and blow dry feeling to their hair on days when they do not have the time, ability or inclination to wash and dry their hair.

The present work provides a solution to this problem by enabling a fragrance to be emitted into the air stream generated by the device 10, to give the hair a fresh smell. To achieve this, a user-replaceable piezo-atomiser and/or a simpler fragrance reservoir and wick may be used to enable phase exchange (liquid to gas) into the air stream and thence onto the user's hair. For example, one or more fluid chambers, which may be re-fillable or replaceable, may be provided in the head portion 16 or main body 12 of the device 10, storing wet product that may be dispensed automatically or by user input. A delivery actuator and mechanism for dispensing the wet product may be provided. A sensor may be provided for sensing the amount of product remaining in the chamber and a user interface may provide feedback to the user informing the user of the remaining product in the chamber.

Problem 6-portability The inventors have determined that consumers desire products that are suitable for "on the go" use, e.g. away from home, or in any event away from plug sockets (e.g. in the bathroom) By virtue of the above-described compact configuration of the heater 30 and fan 30 assembly 24 in the main body of the device and the efficient usage of power, the present work enables a low voltage (LV) device 10 to be used for safe operation in the bathroom, and/or enables the device 10 to be used cordlessly (e.g. with a rechargeable battery) and/or a compact isolated power supply.

Problem 7 -preventing hair from being caught between the bristles and heated 5 surface elements The inventors have realised that there is a risk of hair becoming trapped between the bristles and heated surface elements on the surface of the head portion 16, if the shape of the heated surface elements is not carefully designed. The trapped hair is prevented from engaging with the base portion 22, and therefore the heat transfer to the hair is reduced. However, it is also beneficial for the heated surface elements to be tapered to 'cut' through the hair, to minimise the resistance of the movement of the hair through the bristles 20 and heated surface elements 18.

The solution provided by the present work is to provide heated surface elements having substantially parallel side-walls and a curved top portion. Beneficially, parallel side-walls reduce the risk of hair becoming trapped between the heated surface elements 18 and the bristles 20. The curved top portion enables the heated surface elements 18 to 'cut' through the hair, to minimise the resistance to the movement of the hair over the device.

Problem 8 -reduction of harmonic generation The inventors have realised that harmonic generation by the device should be minimised.

The solution provided by the present work is to interleave the driving of the heaters to reduce the times that the current supplied to the heaters is switched on and off or from one current level to another.

Problem 9-providing efficient airflow from the vent holes The inventors have realised that the apertures 42 formed on the outer surface of the head portion 16 by casting the base portion 22 or by punching holes into the base portion 22 are relatively large. These large apertures are not optimal for air speed and system resistance control when the hair is loaded. However, smaller apertures are difficult and costly to manufacture using casting or hole-punching techniques.

The solution provided by the present work is to provide bristle inserts comprising dividers 62 that split the corresponding apertures 42 of the base portion 22 into one or more smaller openings. Therefore, the airflow properties of the apertures 42 are improved.

Problem 10-providing thermal balancing between the proximal and distal ends of the head portion The inventors have realised that a temperature imbalance can occur between the proximal end of the head portion 16 (relative to the main body 12) and the distal end of the head portion 16. In particular, proximal end of the head portion 16 may become hotter than the distal end of the head portion 16. This may result in discomfort for the user, since the user grips the main body of the device near the proximal end of the head portion 16.

The solution provided by the present work is to provide a pair of baffles 36 between the central plenum chamber 32 and the heat exchanger 44. One of the baffles 36 is provided at the proximal end of the head portion 16 and the other baffle is provided distal end of the head portion 16. Since the baffles 36 only allow the heated air to enter the air-inlet channels 46 of the heat exchanger in a generally central region of the head portion, temperature imbalances across the length of the head portion 16 are reduced.

The pair of mixing chambers 54 provided at the proximal and distal ends of the head portion may also help to reduce temperature imbalances between the proximal and distal ends of the head portion 16 Reducing the size of the air-inlet channels 46 of the heat exchanger 44 at the proximal and distal ends of the head portion 16 may also help to reduce temperature imbalances between the proximal and distal ends of the head portion 16.

Beneficially, the reduction in temperature imbalances also increases the drying performance of the device. The maximum temperature limit for the external surface of the device (to ensure the safety of the user and to prevent 'sizzling' of wet hair) is approximately 120 to 125 °C. For maximum drying performance, the temperature of the outer surface of the base portion 22 should be maintained close to this temperature limit. If a peripheral region of the base portion 22 near the main body 12 is hotter than other parts of the base portion 22, that region would reach the upper temperature limit before other parts of the base portion 22, limiting the maximum temperature of the other parts of the base portion 22 (with which hair is more likely to engage) and reducing the drying performance.

Problem 11 -heating the outer surface of the head portion whilst minimising the weight, cost and complexity of the device The inventors have realised that whilst ceramic heater plates could, in principle, be used to heat the outer surface of the head portion 16, ceramic heaters are relatively costly and add a significant amount of weight to the device. Moreover, providing a thermal interface with a curved surface (such as the surface of the base portion 22) is relatively difficult, requiring a more complex arrangement of electrical connections and fuses.

The solution provided by the present work is to utilise a flow of heated air to heat the outer surface of the head portion, avoiding the need for ceramic heaters.

Problem 12 -reducing volume of fan airflow and heating power required to 5 produce a compact and efficient device The inventors have realised that drying hair with heated air is a very inefficient use of energy, since most of the energy is lost to the atmosphere rather than being transferred to the hair. Traditionally, hair dryers use high pressures and large volume flow rates to mitigate this issue. However, this requires high RPM motor and fan components, adding to the weight and cost of the device, increasing the noise level, and decreasing the energy efficiency. Alternatively, the diameter of the fan could be increased to increase the flow rates. However, this would result in an increase in the circumference of the device, which is not ideal for easy ergonomic use of the device. In contrast, conductive heating is very efficient at drying hair, and can be implemented in a fast-drying, compact and quiet product. However, the amount of heat transferred by the conduction is limited by the contact surface area. Whilst increasing the circumference of the head portion 16 would increase the contact surface area, this would make the device less compact and therefore reduce the portability of the device.

The solution provided by the present work is to provide heated surface elements 18 on the outer surface of the base portion 22. Beneficially, the heated surface elements 18 increase the surface area available for conductive heat transfer to the hair, increasing the energy efficiency and drying performance. The combination of the heated surface elements 18 with the heated air flowing out of the vent holes 40 provides particularly good drying performance. More specifically, the hair styling device of the present work achieves a drying rate of 0.57 g per pass of the device through the hair. The device is operable to dry 44 mm/s of large hair sections. This is a significantly better drying rate than the currently available air-brush style drying devices, and reduces the number of passes required to dry the hair by approximately half.

Modifications and alternatives Detailed embodiments and some possible alternatives have been described above. As those skilled in the art will appreciate, a number of modifications and further alternatives can be made to the above embodiments whilst still benefiting from the inventions embodied therein. It will therefore be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto.

Whilst in the above examples the head portion 16 of the device 10 is generally symmetrical in transverse cross-section. as illustrated for example in Figure 8, this need not necessarily be the case. For example, the head portion 16 may take the shape of a more traditional brush (e.g. a so-called "paddle" brush) with the bristles and heated surface elements provided on an upper surface of the device. In such and example, the bristles 20 and heated surfaced elements 18 may be provided only on the curved region of the head portion 16.

Whilst the heat exchanger 44 shown in Figure 5 has a 'corrugated' or 'square-wave' type shape, it will be appreciated that other suitable configuration of the heat exchanger that guides the airflow from the central plenum chamber 32 to transfer heat to the heated surface elements 18, before the air passes to the vent holes 40 (optionally via mixing chambers 54), could be used. For example, whilst the heat exchanger 44 shown in Figure 5 has straight air-inlet and air-outlet channels, curved channels could be used.

Figure 26 shows (in transverse cross section) a further alternative configuration of the head portion 16. In this example, as in the previous examples, heated surface elements 75 are provided for transferring heat to the hair. However, in this example the outer surface 73 of the head portion is not directly connected to the heated surface elements 75. Instead, the heated surface elements 73 protrude through corresponding holes in the surface 73. In this example, the outer surface 73 may be formed of a thermally insulating material 73 (e.g. plastic or insulating foil), or a thermally conducting material such as sheet metal. The heated surface elements 73 (which extend in rows along the head as before) still provide the head 16 with sufficient thermal mass (150 to 250 J/K) that the head 16 can provide conductive heating of the hair for sustained periods of time to allow for drying and styling of the hair. Heads that only comprise a relatively thin material 73 do not have the thermal mass required to store sufficient thermal energy to allow for conductive heating for drying or styling purposes.

The heated surface elements 75 extend from a structural support 77 inside the head portion 16. The heated surface elements 75 are connected to the structural support 77 by connecting members 79. The connecting members 79 form the walls of corresponding air-inlet channels 83 and air-outlet channels 81 that run along the length of the head 16 (into or out of the page) under a row of heated surface elements 75. The rows of bristles 20 are also supported by the support structure 77. As in the previous examples, heated air flows along the air-inlet channels 83 (transferring heat to the heated surface elements 75 adjacent thereto) before flowing along the air-outlet channels and out of vent holes (not shown) provided in the surface 73. As in the previous examples, mixing chambers may be provided at the proximal and distal ends of the head between the air-inlet channels 83 and the air-outlet channels 81. The walls 79 defining a single air-inlet channel 83 could form an individual heat exchanger that transfers heat to one or more of the surface elements 75 to which the heat exchanger is coupled; or individual heat exchangers may also be coupled together to form a similar heat exchanger structure to that shown in Figure 5 described above.

Whilst in the above embodiments, baffles were used to prevent the handle end (the proximal end) of the head portion 16 from getting too hot. The baffles helped to ensure that the heated air entered the heat exchanger in a central portion thereof. In an alternative arrangement, the efficiency of the heat exchanger at its proximal end could be reduced so that this end naturally heats up less than other parts of the heat exchanger. This could be achieved by reducing the surface area of the heat exchanger at the proximal end and/or by thermally insulating parts of the heat exchanger at its proximal end.

Any or all of the bristle inserts 21, base portion 22, heat exchanger 44 and main body 12 may be formed of a unitary structure, e.g. by 3D printing.

Whilst bristle inserts 21 comprising rows of bristles 20 and dividers 62 may be particularly easy to manufacture, it will be appreciated that individual bristles 20 and dividers 62 could instead be inserted into the apertures of the base portion 22.

Whilst the device 10 has been described above as comprising two heaters 30, this need not necessarily be the case. For example, three or more heaters 30 or only a single heater may be provided.

The device 10 may comprise one or more moisture sensors for determining a moisture content of the hair on the surface of the device 10. The operation of the fan assembly 24 and heater 30 may then be controlled based on the measurements of the one or more moisture sensors. Alternatively, the moisture content of the hair may be inferred from a change in temperature of the base portion 22 or a change in temperature of the air flowing out of the vent apertures 40.

The head portion 16 may be reversibly detachable from the main body 12. For example, the head portion 16 may be interchangeable with another styling or drying attachment for the device 10.

In alternative configurations of the device 10 the heated surface elements 18 may be omitted. The bristles 20 may also be omitted or may be provided as retractable bristles 20 (e.g. retracting inside the head portion 16 by mechanical movement, from the use of the device 10 or by electronic control).

In the above embodiment, the heat exchanger (and in particular the layout of the air-inlet and the air-outlet channels) was designed to achieve a desired heating profile of the base portion 22. In a more complex arrangement, each channel may be provided with a valve actuator that can be opened and closed to vary the restriction to air flow along each channel. The valves can then be controlled by the microcontroller based on the sensed temperature of different parts of the base portion 22. Thus if one area of the base portion is found to be hotter than another area, the microcontroller can open and close some of the valves to increase or decrease the heating provided to a particular are of the base portion 22.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "containing", means "including but not limited to", and is not intended to (and does not) exclude other components, integers or steps.

The present disclosure also includes the following numbered clauses: Clause 1. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair and a heat exchanger thermally coupled to the base portion, wherein the head portion has a proximal end and a distal end and is coupled to the body portion at the proximal end; a fan for drawing air into the apparatus and for blowing air towards the proximal end of the head portion; at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the proximal end of the head portion is configured to receive the heated air stream, wherein the heat exchanger extends between the proximal and distal ends of the head portion and wherein the head portion further comprises a baffle positioned at the proximal end of the head portion and configured to cause the heated air stream to enter a central portion of the heat exchanger located between said proximal and distal ends.

Clause 2. Apparatus according to clause 1, wherein the baffle is configured to prevent the heated airstream from entering the heat exchanger adjacent the proximal end of the head portion.

Clause 3. Apparatus according to clause 1 or 2, wherein the baffle extends over a portion of the heat exchanger.

Clause 4. Apparatus according to clause 3, wherein the baffle extends over 5 to 40 % of the heat exchanger.

Clause 5. Apparatus according to any of clauses 1 to 4, when the baffle is formed of a thermally insulating material.

Clause 6. Apparatus according to any of clauses 1 to 5, wherein the baffle is a first baffle and further comprising a second baffle positioned at the distal end of the head portion and configured to prevent the heated airstream from entering the heat exchanger adjacent the distal end of the head portion.

Clause 7. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair and having one or more vent holes; a fan for drawing air into the apparatus and for blowing air towards the head portion; at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; and a heat exchanger for exchanging heat between the heated air stream and the base portion, and wherein the heat exchanger forms a convoluted path for the heated air stream to follow to reach said one or more vent holes.

Clause 8. The apparatus of clause 7, wherein the heat exchanger comprises one or more air-inlet channels and one or more air-outlet channels and wherein the heat exchanger is arranged to cause heated air to flow along one of the one of more air-inlet channels and to change direction and travel along one of the one or more air-outlet channels to reach a vent hole.

Clause 9. The apparatus of clause 8, wherein the heat exchanger is arranged so that the flow direction of air in the air-outlet channel is opposite to the flow direction of the corresponding air in the air-inlet channel.

Clause 10. The apparatus according to any of clauses 7 to 9, wherein the heat exchanger comprises a proximal end and a distal end and a plurality of air-inlet channels and a plurality of air-outlet channels extending between the proximal and distal ends; wherein each air-inlet channel is configured to receive part of the heated air stream such that heated air flows along the air-inlet channel towards and into a 30 first mixing chamber located at the proximal end of the heat exchanger and heated air flows along the air-inlet channel towards and into a second mixing chamber located at the distal end of the heat exchanger; and wherein the air-outlet channels are configured to receive air from the first mixing chamber for air flow along the air-outlet channels away from the proximal end of the heat exchanger, and to receive air from the second mixing chamber for air flow along the air-outlet channels away from the distal end of the heat exchanger.

Clause 11. The apparatus according to any of clauses 8 to 10, wherein the base portion comprises a plurality of thermally conductive elements extending from the hair contacting surface of the base portion and wherein the air-inlet channels are aligned with the plurality of thermally conductive elements such that heated air flowing along the air-inlet channels is arranged to heat the base portion in the vicinity of the thermally conductive elements.

Clause 12. The apparatus according to clause 11, wherein the plurality of thermally conductive elements are arranged in rows on the surface of said base portion and wherein said air-inlet channels are arranged in rows that are aligned with the rows of the plurality of thermally conductive elements.

Clause 13. The apparatus according to any of clauses 8 to 12, wherein the base portion comprises a plurality of vent holes and wherein the air-outlet channels are aligned with the plurality of vent holes such that heated air flowing along the air-outlet channels is arranged exit the apparatus through the vent holes.

Clause 14. The apparatus according to clause 13, wherein the plurality of vent holes are arranged in rows on the surface of said base portion and wherein said air-outlet channels are arranged in rows that are aligned with the rows of vent holes Clause 15. The apparatus according to clause 10 or any clause dependent thereon, wherein the head portion has a plenum chamber for receiving the heated air stream, a first baffle that isolates the first mixing chamber from the plenum chamber of the head portion and a second baffle that isolates the second mixing chamber from the plenum chamber of the head portion, whereby heated air from the plenum chamber cannot reach the mixing chambers without flowing along an air-inlet channel.

Clause 16. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair; and a fan for drawing air into the apparatus and for blowing air towards the head portion; and at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the base portion comprises: a plurality of vent holes for venting the heated air from the apparatus; a plurality of bristles extending from the hair contacting surface of the base portion; and a plurality of thermally conductive elements extending from the hair contacting surface of the base portion; wherein the bristles and conductive elements are arranged to guide the hair around the vent holes to prevent, during use, the hair from blocking the vent holes.

Clause 17. The apparatus of clause 16, wherein the vent holes, the plurality of bristles and the plurality of thermally conductive elements are arranged in rows, with the bristles being offset from the thermally conductive elements.

Clause 18. The apparatus according to clause 17, wherein the rows of bristles and the rows of thermally conductive elements each form a regular array of bristles and thermally conductive elements.

Clause 19. The apparatus according to any of clauses 16 to 18, wherein each thermally conductive element is surrounded by four bristles.

Clause 20. The apparatus according to any of clauses 16 to 19, wherein each bristle is surrounded by four thermally conductive elements.

Clause 21. The apparatus of any of clauses 16 to 20, wherein each vent hole is positioned between a thermally conductive element and two bristles.

Clause 22. The apparatus of any of clauses 16 to 21, wherein the vent holes and the thermally conductive elements are aligned in a row that is transverse to a longitudinal axis of the head portion.

Clause 23. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion defining an inner space and having an outer hair contacting surface for engaging with a length of hair; and a fan for drawing air into the apparatus and for blowing air towards the head portion; and at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the base portion has a plurality of thermally conductive elements extending from the outer hair contacting surface and wherein each of the thermally conductive elements is coupled to a heat exchanger mounted within the head portion and which is configured to transfer heat from the heated air stream to the thermally conductive elements.

Clause 24. The apparatus of clause 23, wherein each of the thermally conductive elements is coupled to a common heat exchanger.

Clause 25. The apparatus of clause 24, wherein the head portion comprises a plenum chamber that receives the heated air stream from the heater and wherein the or each heat exchanger is configured to receive heated air from the plenum chamber.

Clause 26. The apparatus of any of clauses 23 to 25, wherein the base portion is formed of a sheet material or a casting.

Clause 27. The apparatus of any of clauses 23 to 26, wherein the base portion comprises one or more vent holes through which the heated air stream exits the apparatus.

Clause 28. Apparatus according to clause 27, wherein the or each heat exchanger is configured to cause the heated air stream to follow a convoluted path to reach said one or more vent holes.

Clause 29. A head portion for a hair drying or styling device, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair; and a plenum chamber; wherein the head portion is configured to receive a heated air stream into the plenum chamber; and wherein the base portion is configured to be heated by the heated airstream and to store heat from the heated air stream for subsequent transfer of heat by conduction to hair that engages the hair contacting surface of the base portion.

Clause 30. A head portion for a hair drying or styling device, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair and a heat exchanger thermally coupled to the base portion, wherein the head portion has a proximal end and a distal end and is connectable to a body portion of the hair drying and styling device at the proximal end; wherein the proximal end of the head portion is configured to receive a heated air stream, wherein the heat exchanger extends between the proximal and distal ends of the head portion and wherein the head portion further comprises a baffle positioned at the proximal end of the head portion and configured to cause the heated air stream to enter a central portion of the heat exchanger located between said proximal and distal ends.

Clause 31. A head portion for a hair drying or styling device, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair; wherein the base portion comprises: a plurality of vent holes for venting the heated air from the head portion; a plurality of bristles extending from the hair contacting surface of the base portion; and a plurality of thermally conductive elements extending from the hair contacting surface of the base portion; wherein the bristles and conductive elements are arranged to guide the hair around the vent holes to prevent, during use, the hair from blocking the vent holes.

Clause 32. A head portion for a hair drying or styling device, the head portion comprising a base portion having an outer hair contacting surface for engaging with a length of hair; a plurality of thermally conductive elements extending from the outer hair contacting surface of the base portion; a plenum chamber, wherein the head portion is configured to receive a heated air stream into the plenum chamber; and at least one heat exchanger mounted within the head portion and which is configured to transfer heat from the heated air stream to the thermally conductive elements.

Claims

CLAIMS1. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair; a fan for drawing air into the apparatus and for blowing air towards the head portion; and at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the head portion is configured to receive the heated air stream and the base portion is configured to be heated by the heated airstream and to store heat from the heated air stream for subsequent transfer of heat by conduction to hair that engages the hair contacting surface of the base portion.
2. Apparatus according to claim 1, wherein the apparatus is configured to control the heating of the air by the at least one heater in response to a change in temperature of the base portion.
3. Apparatus according to claim 2, wherein the apparatus is configured to increase the heat output of the at least one heater when a temperature of the base portion falls below a predetermined threshold value.
4. Apparatus according to any preceding claim, wherein the base portion comprises at least one vent hole for flow of the heated air out of the base portion for transfer of heat from the heated air to the hair.
5. Apparatus according to claim 4, wherein the head portion comprises a plenum chamber; and the device is configured for flow of the heated air from the plenum chamber to the at least one of vent hole.
6. Apparatus according to any preceding claim, wherein the base portion comprises a plurality of thermally conductive elements on an outer surface of the base portion, wherein the thermally conductive elements are configured to be heated by the heated airstream and to store heat from the heated air stream for subsequent transfer of heat by conduction to hair that engages the hair contacting surface of the base portion.
7. Apparatus according to claim 5 or 6, the apparatus further comprising a heat exchanger configured to receive the heated air from the plenum chamber and to guide the heated air to the plurality of vent holes.
8. Apparatus according to claim 7, wherein heat is transferred from the heated air to the base portion via the heat exchanger.
9. Apparatus according to claim 7 or 8, wherein the heat exchanger comprises a plurality of radial fins.
10. Apparatus according to any of claims 7 to 9, wherein the heat exchanger comprises one or more air-inlet channels for receiving the heated air from the plenum chamber; and one or more air-outlet channels for guiding the heated air to the vent holes.
11. Apparatus according to claim 10, wherein the heat exchanger is configured to guide the heated air through one of the one more air-inlet channels before the heated air flows through one of the one more air-outlet channels.
12. Apparatus according to claim 10 or 11, further comprising at least one mixing chamber, wherein the at least one mixing chamber is configured to receive the heated air from the one or more air-inlet channels, and the one or more air-outlet channels are configured to receive the heated air from the at least one mixing chamber.
13. Apparatus according to claim 12, wherein the apparatus comprises first and second mixing chambers, wherein the first mixing chamber is provided at an end of the head portion that is proximal to the main body and the second mixing chamber is provided at an end of the head portion that is distal to the main body.
14. Apparatus according to any of claims 10 to 13, wherein heated air flows towards the body portion along the one or more air-inlet channels, before flowing away from the body portion in the one or more air-inlet channels.
15. Apparatus according to any of claims 10 to 14, wherein heated air flows away from the body portion along the one or more air-inlet channels, before flowing towards the body portion in the one or more air-inlet channels.
16. Apparatus according to any of claims 10 to 15, wherein the base portion comprises a row of thermally conductive elements that is aligned with a corresponding air-inlet channel, for transfer of heat to the row of thermally conductive elements from the corresponding air-inlet channel.
17. Apparatus according to claim 16, wherein heat is transferred from the heated air to the thermally conductive elements via a thermally conducting member of the heat exchanger.
18. Apparatus according to claim 17, wherein the thermally conducting member forms a wall of the air-inlet channel.
19. Apparatus according to any of claims 16 to 18, wherein the total surface area of the thermally conductive elements is between 40% and 70% of the total external surface area of the base portion.
20. Apparatus according to any preceding claim, wherein the head portion is generally cylindrical.
21. Apparatus according to any preceding claim, wherein a plurality thermally insulated bristles for guiding the hair extend from the hair contacting surface.
22. Apparatus according to any preceding claim, wherein the specific heat capacity of the base portion is between 800 to 1000 J/kg °C.
23. Apparatus according to any preceding claim, wherein the thermal conductivity of the base is between 90 and 200 W/mk.
24. Apparatus according to any preceding claim, wherein heat is transferred directly to the base portion from heated air inside the head portion.
25. Apparatus according to any preceding claim, where the fan and the at least one heater are provided in the body portion.
26. Apparatus according to claim 25, wherein the fan is configured to generate a generally longitudinal flow of air from the body portion into a plenum chamber in the head portion.
27. Apparatus according to any preceding claim, wherein heat is transferred from the base portion to the hair by conduction, and from the heated air to the hair by convection.
28. Apparatus according to claim 27, wherein at least a majority of the heat transferred to the hair by the apparatus is transferred by conduction.
29. Apparatus according to claim 3 or any claim dependent thereon, further comprising at least one sensor for sensing a temperature of the base portion; a first heater for heating the air drawn into or output from the fan to provide the heated air stream; and a second heater configured to provide a boost function to provide addition heat to the air stream; wherein the apparatus is configured to control the second heater in response to a detected decrease in the temperature of the base portion.
30. Apparatus according to any preceding claim, comprising a plurality of base portions, each configured to be heated by the heated airstream and to store heat from the heated air stream for subsequent transfer of heat by conduction to hair that engages the hair contacting surface of the base portion.
31. Apparatus according to claim 30, wherein each base portion takes the form of a thermally conductive element that extends from an outer surface of the head portion.
32. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair and a heat exchanger thermally coupled to the base portion, wherein the head portion has a proximal end and a distal end and is coupled to the body portion at the proximal end; a fan for drawing air into the apparatus and for blowing air towards the proximal end of the head portion; at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the proximal end of the head portion is configured to receive the heated air stream, wherein the heat exchanger extends between the proximal and distal ends of the head portion and wherein the head portion further comprises a baffle positioned at the proximal end of the head portion and configured to cause the heated air stream to enter a central portion of the heat exchanger located between said proximal and distal ends.
33. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair and a heat exchanger thermally coupled to the base portion, wherein the head portion has a proximal end and a distal end and is coupled to the body portion at the proximal end; a fan for drawing air into the apparatus and for blowing air towards the proximal end of the head portion; at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the proximal end of the head portion is configured to receive the 20 heated air stream, wherein the heat exchanger has a proximal end adjacent the proximal end of the head portion that has a lower heat exchanging efficiency than the rest of the heat exchanger.
34. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair and having one or more vent holes; a fan for drawing air into the apparatus and for blowing air towards the head 30 portion; at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; and a heat exchanger for exchanging heat between the heated air stream and the base portion, and wherein the heat exchanger forms a convoluted path for the heated air stream to follow to reach said one or more vent holes.
35. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion having a hair contacting surface for engaging with a length of hair; and a fan for drawing air into the apparatus and for blowing air towards the head portion; and at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the base portion comprises: a plurality of vent holes for venting the heated air from the apparatus; a plurality of bristles extending from the hair contacting surface of the base portion; and a plurality of thermally conductive elements extending from the hair contacting surface of the base portion; wherein the bristles and conductive elements are arranged to guide the hair around the vent holes to prevent, during use, the hair from blocking the vent holes.
36. Apparatus for drying or styling hair, the apparatus comprising a body portion; a head portion coupled to the body portion, the head portion comprising a base portion defining an inner space and having an outer hair contacting surface for engaging with a length of hair; and a fan for drawing air into the apparatus and for blowing air towards the head portion; and at least one heater for heating the air drawn into or output from the fan to provide a heated air stream; wherein the base portion has a plurality of thermally conductive elements extending from the outer hair contacting surface and wherein each of the thermally conductive elements is coupled to a heat exchanger mounted within the head portion and which is configured to transfer heat from the heated air stream to the thermally conductive elements.