DE102023000207A1 - Device for heating a medium - Google Patents

Abstract

The invention relates to a device for heating a medium. A primary circuit (1) heats an intermediate medium. A secondary circuit (2) carries the medium. A coupling device (3) transfers thermal energy from the intermediate medium to the medium. If the intermediate medium is not actively conveyed, the heat is given off to another medium (e.g. air) that is also coupled to the heat exchanger of the primary circuit (in the case of air, a fan is then running there, for example).

Description

The present invention relates to a device for heating at least one medium. The medium is, for example, a liquid such as water.

In the prior art, it is known to obtain thermal energy from the application of electrical current or from the combustion of, for example, propane, butane or diesel fuel converted into a gaseous state and to transfer it to a liquid, e.g. service water, via a heat exchanger. It is also known that such devices additionally serve as air heaters and, for example, heat room air.

If such a device is to be used in a caravan or mobile home, for example, it is usually necessary to guide and heat the medium through a circuit that is as small and compact as possible. This is intended to reduce the installation space and weight. The medium is therefore usually guided through relatively small pipes, etc. If special environmental conditions arise, such as frost or very high heat from direct sunlight, the medium reacting to the extreme outside temperatures can cause problems. For example, consider the increased volume of ice compared to liquid water or the significantly larger volume of steam compared to liquid. If the medium is, for example, service water, there is a particular risk of calcification of parts of the device that carry the medium. Such limescale deposits should be avoided as far as possible, as otherwise pipes can become blocked or units such as pumps or valves can be impaired in their function.

The object underlying the invention is to propose a device for heating a medium which differs from the prior art in that the problem of extreme temperature situations is addressed.

The invention solves the problem by a device for heating at least one medium, having a primary circuit, a secondary circuit and a coupling device, wherein the primary circuit is designed such that the primary circuit heats an intermediate medium, wherein the secondary circuit is designed such that the secondary circuit carries the medium, and wherein the coupling device transfers thermal energy from the intermediate medium in the primary circuit to the medium in the secondary circuit.

In the device according to the invention, there are two circuits in which an intermediate medium or the actual medium to be heated is guided. The intermediate medium is heated in the primary circuit. In one embodiment, this primary circuit is designed as a closed circuit for the intermediate medium guided in it. The thermal energy absorbed is transferred by the coupling device, which can also be considered a second heat exchanger, to the secondary circuit and thus to the medium. The secondary circuit is preferably designed as an open circuit in which the medium is taken, for example, as service water. In order to be able to easily remove the medium from a container in the second secondary circuit, for example, the medium to be heated is introduced in a lower area and the heated medium is taken from the container in an upper area. By splitting into two circuits, an intermediate medium can be selected that is better suited to the extreme ambient conditions than the medium. If the medium is (service) water, for example, the intermediate medium can be selected so that it only freezes at significantly lower temperatures.

One embodiment is that the intermediate medium is ethanol or consists partly of ethanol. Ethanol has a freezing point of -114 °C at ambient pressure, so there can be no danger from frost under normal application conditions.

One embodiment provides that the coupling device is designed as a condensation device in which the intermediate medium condenses. The intermediate medium thus liquefies in the coupling device and thereby releases thermal energy. Ethanol as an example of an intermediate medium has a condensation temperature of 78 °C at ambient pressure. This means that, for example, service water as a medium could be heated to a sufficiently high temperature. Preferably, the heat exchanger is designed and the primary circuit is operated in such a way that the intermediate medium in the heat exchanger at least partially evaporates.

One embodiment consists in that the secondary circuit has at least one medium storage device and that the coupling device is at least partially arranged in the medium storage device. In this embodiment, the secondary circuit has a type of container in which the medium is located. The coupling device protrudes into the container. Preferably, the coupling device absorbs thermal energy from the intermediate medium and releases it to the medium. In one embodiment The coupling device is connected to the primary circuit in such a way that the intermediate medium flows through the coupling device.

In one embodiment, the heat transfer to the medium occurs via natural convection.

In one design, the tank has the simplest possible geometry with large cross-sections for the flowing medium. Preferably, the tank can be easily emptied by gravity to protect against frost. Since the medium is only in the tank, the frost can only affect this and in particular not the much more complex components of the primary circuit, such as the heat exchanger.

One embodiment provides that at least one guide device is arranged in the medium reservoir, and that the guide device is designed and arranged in such a way that the guide device influences the flow behavior of the medium in the medium reservoir. The guide device has the task of ensuring that the heat transfer to the medium is as high as possible. Furthermore, the stratification of the heated medium in the medium reservoir is to be as optimal as possible. The guide device therefore influences the flow behavior of the medium. For example, the speed at which the heated medium circulates in the medium reservoir is reduced to such an extent that there is more time for heat transfer in the interaction area of the coupling device. Influencing the flow behavior can also prevent different temperature layers from mixing.

One embodiment includes that the guide device is designed and arranged in such a way that the guide device reduces a flow cross-section within the medium storage for the heated medium. If the cross-section for the heated medium is reduced, less medium can flow from the interaction area of the coupling device into the rest of the medium storage at a lower speed, thus ensuring less turbulence with colder medium there. In the area of the coupling device (i.e. the heat transfer), however, turbulence of the medium is advantageous in order to generate a high heat transfer coefficient there. This allows the necessary areas for the transfer of thermal energy to be reduced. Conversely, the inlets and outlets for the medium should lead to the lowest possible flow velocity so that as little turbulence as possible occurs at these points. This is for the purpose of layering the medium as well as possible, i.e. so that the thinnest possible jump/boundary layer is present between the heated and cold medium.

One embodiment provides that the primary circuit has a heat source, a heat exchanger, an intermediate medium container and a pump, that the heat source generates thermal energy, that the heat exchanger transfers the thermal energy to the intermediate medium, and that the pump moves the - preferably liquid - intermediate medium from the intermediate medium container through the heat exchanger. In this embodiment, a heat source in the primary circuit generates the thermal energy, e.g. by burning a fuel-air mixture or by applying electrical current. A heat exchanger transfers the thermal energy to the intermediate medium. This happens, for example, when the intermediate medium (partially or completely) undergoes a phase change and thus absorbs latent heat. In one embodiment, the coupling device is arranged downstream of the heat exchanger. A pump transports the intermediate medium from an intermediate medium container to the heat exchanger. Preferably, the intermediate medium returns to the intermediate medium container after contact with the coupling device. This leads to a closed circuit.

In one embodiment, the coupling device is designed as a pipe coil through which the intermediate medium is guided and which easily releases thermal energy to the outside.

Alternatively, the coupling device is formed by, for example, a meandering pipe structure which forms part of the wall - preferably mainly the bottom - of the container.

A further embodiment consists in that the primary circuit also has a fan, that the heat exchanger is designed in such a way that the heat exchanger transfers the thermal energy to the medium and to air, and that the fan is designed in such a way that the fan causes the air to interact with the heat exchanger. In this embodiment, either the medium - e.g. water - or air can be heated via the device. In this embodiment, it is therefore a device for heating a preferably liquid medium and air. The medium is heated indirectly by first heating the intermediate medium and then the medium. The air is heated directly by bringing it into contact with the heat exchanger itself. There are therefore two heat sinks between which switching takes place effectively, so that high power is taken from both heat sinks. In one embodiment, either the pump or the blower is operated.

One embodiment consists in that a control device is also present, and that the control device is designed in such a way that the control device can specify whether the medium or air is to be heated, and that the control device operates the pump in such a way that, in the case that only the medium and no air is to be heated, the intermediate medium leaves the heat exchanger as a two-phase mixture at the heat output of the heat source. In this embodiment, a control device is present that controls the pump based on data about the heat source. The control device can also consist of setting operating values and then not changing them. The control device is thus basically just a unit that starts and stops the pump and does not carry out any regulation. The pump output is specified in such a way that the intermediate medium leaves the heat exchanger as a two-phase mixture and therefore at boiling temperature after passing through the heat exchanger and after absorbing the thermal energy generated by the heat source. This has the advantage that with reduced heat output, the pump output can be maintained and does not have to be regulated. It may therefore be sufficient if the control device is limited to starting or stopping the pump. This applies to the case where the control device has been specified that only the medium - indirectly via the intermediate medium - and not the air is to be heated. This means that it is easy to switch between the air and the medium (or the intermediate medium) as a heat sink. If the air is to be heated, the control device starts up the fan, which guides the air past the heat exchanger.

One embodiment provides that the primary circuit further comprises at least one barrier, that the barrier is arranged in a flow direction between the pump and the heat exchanger, and that the barrier is arranged and designed in such a way that it prevents the intermediate medium from entering the heat exchanger from the intermediate medium container due to gravity alone. The barrier prevents the intermediate medium from flowing into the heat exchanger without the pumping power of the pump. This refers, for example, to an outlet of the intermediate medium container being so low that gravity pushes the intermediate medium through the pump into the heat exchanger. The barrier thus also blocks the flow of the intermediate medium to the downstream heat exchanger. This therefore prevents the intermediate medium from continuing to be heated when the pump is switched off. This is relevant, for example, if the thermal energy is not to be transferred to the medium, but rather to air, for example.

In one embodiment, the barrier is provided by a type of two tubes communicating with each other. In one embodiment, the barrier is at least partially designed as a pipe section, e.g. in the form of a bend, which has an uppermost region which lies above a maximum liquid level of the intermediate medium in the intermediate medium container.

In one embodiment, a second barrier is present. The second barrier is present in particular when the return from the coupling device to the intermediate medium container is installed below the liquid level of the intermediate medium in the intermediate medium container: The second barrier prevents the intermediate medium from passing backwards through the coupling device into the heat exchanger. The second barrier is preferably arranged between the heat exchanger and the coupling device.

One design is that the pump only has one conveying direction. The pump is, for example, a centrifugal or diaphragm pump. The design is based on the fact that it is not necessary to reverse the conveying device of the pump, for example to switch from medium heating mode to air heating mode (and vice versa): In air heating mode, the remaining intermediate medium in the heat exchanger evaporates. If the pump does not convey any further intermediate medium, the steam is not conveyed out of the heat exchanger either, but remains there, and thus no further heat is transferred to the intermediate medium or the medium.

One embodiment provides that a pressure relief valve is also present and that the pressure relief valve is connected to the intermediate medium container. Preferably, the intermediate medium container is not completely filled with liquid, but has a gas cushion above the intermediate medium. This reduces the pressure increase in the primary circuit when the intermediate medium evaporates in the heat exchanger. The pressure relief valve would only open as a safety valve in the event of a fault.

The return of the intermediate medium from the coupling device to the intermediate medium tank takes place in one embodiment below the liquid level of the intermediate medium in the intermediate medium tank. This means that intermediate medium that may not be completely condensed for a short time is briefly condensed due to the good contact with direct introduction and the larger mass of the liquid. The intermediate medium condenses there. This can reduce pressure peaks. In addition, direct introduction leads to good mixing of the intermediate medium so that it has as homogeneous a temperature as possible. During operation, the boiling temperature and the resulting pressure are linked. If complete condensation in the primary circuit is not achieved, the pressure and boiling temperature increase. This in turn results in higher heat transfer in the coupling element because there is a higher temperature difference. With this design, the pressure in the primary circuit can therefore rise within limits, which results in greater heat transfer to the medium. The safety valve would only come into action if the heat cannot be sufficiently dissipated into the medium - e.g. water.

An alternative design is based on the following consideration: Since the boiling pressure correlates with the boiling temperature and the temperature in the primary circuit is fairly homogeneous, the temperature can be measured at any point in the piping system or the intermediate medium tank in order to detect a pressure increase. In this design, the heat source and/or the pump are switched off if necessary.

• 1: eine schematische Darstellung der erfindungsgemäßen Vorrichtung und
• 2: drei Darstellungen eines Beispiels für einen Mediumsspeicher mit Koppelvorrichtung (a) räumliche Darstellung, b) Explosionsdarstellung und c) angeschnittene räumliche Darstellung).

In detail, there are a number of possibilities for designing and developing the device according to the invention. Reference is made to the following description of exemplary embodiments in conjunction with the drawing. They show:

• 1 : a schematic representation of the device according to the invention and
• 2 : three representations of an example of a medium storage device with coupling device (a) spatial representation, b) exploded view and c) cut-away spatial representation).

The 1 shows schematically the structure of a device for heating the medium which is located in the medium storage 20. The device consists of a primary circuit 1 and a secondary circuit 2, between which the coupling device 3 transfers the thermal energy.

In the primary circuit 1, an intermediate medium, which is ethanol, for example, is heated. The pump 13 conveys the intermediate medium from the intermediate medium storage 12 through the downstream heat exchanger 11. The heat exchanger 11 transfers the thermal energy generated by the heat source 10 to the intermediate medium. The intermediate medium then passes through the coupling device 3 to condense there and transfer the thermal energy to the medium in the medium storage 20. The re-liquefied intermediate medium then flows back to the intermediate medium storage 12.

Of the secondary circuit 2, in which the medium - in the case shown, domestic water - is conducted, only the lower supply line and the upper discharge line are shown here. An indicated guide device 21 is located in the medium storage tank 20. The coupling device 3, which in the embodiment shown serves to condense the intermediate medium, is located in the medium storage tank 20 and can thus transfer the thermal energy directly to the medium. The guide device 21 collects the medium heated at the bottom by the coupling device 3 and flowing upwards due to the lower density. The speed of the medium is reduced - in the example by a cross-sectional constriction - so that the medium is heated to a desired temperature on the one hand - by remaining in the lower area for a sufficiently long time - and on the other hand is introduced at the upper end of the storage tank 20 in such a way that the heated medium is layered with as little turbulence as possible. The coupling device 3 is therefore also arranged at the bottom of the storage tank 20 so that the entire contents can be heated and, if possible, only the coldest water is heated due to its highest density. The aim is therefore to achieve the best possible stratification, with only the thinnest possible transition/boundary layer between the cold and hot water and which, in the example shown, uses natural convection. In the example, the guide device 21 is designed as a bent sheet and has the clearly visible bottleneck.

In the primary circuit 1 there is also a barrier 14 in the form of two communicating tubes, which prevents the intermediate medium from entering the heat exchanger 11 and thus being heated even when the pump 13 is switched off. Flow even without pumping power would otherwise be possible due to the hydrostatic pressure within the intermediate medium tank 12, which is filled from above and emptied from below. In an additional variant - not shown here - there is a further barrier 14 in the flow direction behind the heat exchanger 11 to prevent backflow from the coupling device 3 into the heat exchanger 11. The intermediate medium tank 12 is also provided with a pressure relief valve 15 as a safety valve, which is only activated in the event of a fault.

The device has a control device 4, which operates the pump 13 with a constant pumping power or alternatively with a pumping power dependent on the heat output of the heat source 10. If no medium is to be heated in an operating case, the pump 13 is switched off. The thermal Energy from the heat source 10 is then dissipated by heating air. For this purpose, the control device 4 acts on the fan 16, which causes air to interact with the heat exchanger 11. For this purpose, the heat exchanger 11 has, for example, a rib structure on its outside and the fan guides the air over this outside. The following then happens: the remaining intermediate medium - e.g. ethanol - in the heat exchanger 11 evaporates, but remains (in a superheated state, i.e. with a temperature above boiling point) essentially in its position because the pump 13 is not running. Depending on an air bubble in the intermediate medium container 12, there is a slight increase in pressure in the primary circuit 1. The vaporous intermediate medium can move convectively within the pipeline and, for example, partially condense at the phase boundary layer to the liquid intermediate medium. However, these heat exchange surfaces are very small, so that only a very small heat transport to the liquid intermediate medium can be expected. The heat losses of the entire system to the outside should more than compensate for this heat input. Overall, it is therefore very easy and safe to switch back and forth between heating the medium and heating the air.

The 2 shows three representations of an alternative embodiment of the coupling device 3 in connection with the medium storage 20. The coupling device 3 is designed as part of the floor and has several pipe coils through which the intermediate medium flows and cools down in the process.

The 2 a) shows a view into the bottom of the medium reservoir 20, so that the pipe structure can be seen. In the exploded view of the 2 B) It can be seen in particular that the coupling device 3 in the embodiment comprises two components, e.g. made of sheet metal. The lower, essentially flat sheet metal component has a recess which, in conjunction with the upper component with the tube structure, serves as an introduction opening for the intermediate medium. The cut-away spatial representation of the 2c) shows how semicircular end pieces connect the tubes, which are arranged essentially parallel to each other.

List of reference symbols

1

Primary circuit

2

Secondary circuit

3

Coupling device

4

Control device

10

Heat source

11

Heat exchanger

12

Intermediate medium tank

13

pump

14

barrier

15

Pressure relief valve

16

fan

20

Media storage

21

Guidance device

Claims (10)

Device for heating at least one medium, with a primary circuit (1), a secondary circuit (2) and a coupling device (3), wherein the primary circuit (1) is designed such that the primary circuit (1) heats an intermediate medium, wherein the secondary circuit (2) is designed such that the secondary circuit (2) carries the medium, and wherein the coupling device (3) transfers thermal energy from the intermediate medium in the primary circuit (1) to the medium in the secondary circuit (2). Device according to Claim 1 , where the intermediate medium is ethanol or consists partly of ethanol. Device according to Claim 1 or 2 , wherein the coupling device (3) is designed as a condensation device in which the intermediate medium condenses. Device according to one of the Claims 1 until 3 , wherein the secondary circuit (2) has at least one medium reservoir (20), and wherein the coupling device (3) is at least partially arranged in the medium reservoir (20). Device according to Claim 4 , wherein at least one guide device (21) is arranged in the medium reservoir (20), and wherein the guide device (21) is designed and arranged such that the guide device (21) influences a flow behavior of the medium in the medium reservoir (20). Device according to Claim 5 , wherein the guide device (21) is designed and arranged such that the guide device (21) reduces a flow cross-section within the medium reservoir (20) for the heated medium. Device according to one of the Claims 1 until 6 , wherein the primary circuit (1) comprises a heat source (10), a heat exchanger (11), an intermediate medium container (12) and a pump (13), wherein the heat source (10) generates thermal energy, wherein the heat exchanger (11) transfers the thermal energy to the intermediate medium, and wherein the pump (13) moves the - in particular liquid - intermediate medium from the intermediate medium container (12) through the heat exchanger (11). Device according to Claim 7 , wherein the primary circuit (1) further comprises a fan (16), wherein the heat exchanger (11) is designed such that the heat exchanger (11) transfers the thermal energy - preferably indirectly via the intermediate medium - to the medium and to air, and wherein the fan (16) is designed such that the fan (16) brings the air into interaction with the heat exchanger (11). Device according to Claim 8 , wherein a control device (4) is also present, and wherein the control device (4) is designed such that the control device (4) can be specified whether the medium or air is to be heated, and that the control device (4) operates the pump (13) such that the intermediate medium leaves the heat exchanger (11) as a two-phase mixture at the output heating power of the heat source (10) in the case that only the medium and no air is to be heated. Device according to one of the Claims 7 until 9 , wherein the primary circuit (1) further comprises at least one barrier (14), wherein the barrier (14) is arranged in a flow direction between the pump (13) and the heat exchanger (11), and wherein the barrier (14) is arranged and designed such that it prevents the intermediate medium from passing from the intermediate medium container (12) through the pump (13) into the heat exchanger (11) due to gravity alone.

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