GB2263502A

GB2263502A - Blower unit.

Info

Publication number: GB2263502A
Application number: GB9200944A
Authority: GB
Inventors: John Leslie Mark; Ronald Brian Parker
Original assignee: Parker Mark & Associates Limit
Current assignee: Parker Mark & Associates Limit
Priority date: 1992-01-17
Filing date: 1992-01-17
Publication date: 1993-07-28
Also published as: GB9200944D0

Abstract

A blower unit (10) comprises a centrifugal impeller (12) rotatably mounted in a housing (11) and an outlet device (17) to accelerate and silence a flow of air centrifugally discharged by the impeller. The outlet device comprises a nozzle (20) which is clad with sound-absorbing material and has an entry portion (20a), which tapers inwardly in direction away from the housing and a straight-sided exit portion (20b). The taper of the nozzle entry portion and lengths of the entry and exit portions in that direction are selected so that the centre of pressure of air flowing through the nozzle is at a spacing from the exit portion. The nozzle configuration and sound-absorbing material attenuate noise at the discharge side, and attenuation at the intake side can be achieved by way of a cylindrical inlet silencer (14). The blower may be used in a vehicle washing installation. <IMAGE>

Description

BLOWER UNIT The present invention relates to a blower unit and has particular reference to a blower unit usable as drying apparatus or as part of such apparatus in a vehicle washing station.

Vehicle washing stations consist of booths into which a motor vehicle to be washed is driven and then, in one form of station, parked while washing apparatus and subsequently drying apparatus are moved over the vehicle to wash the vehicle by way of water jets and brushes and dry the vehicle by way of air streams of relatively high velocity. The air streams are provided by blower units with centrifugal fans, with the units moving closely past the vehicle surface to blow off residual water. In another form of station, the vehicle is conveyed along a path with batteries of washing, rinsing and drying devices. Blower units are disposed at the end of the path and are capable of limited movement relative to the vehicle.

The air drying steam from each unit issues from a nozzle which shapes and accelerates the centrifugally discharged air flow from the fan. The operation of such units is associated with the generation of a considerable amount of noise, which is produced by the fan itself, by the induction air flow of the fan and particularly by the nozzle.

The air intake and the nozzle are unsilenced and the nozzle configuration effectively promotes noise generation at the point of departure of air from the unit. The total noise output is a source of inconvenience in the environment of the station and also some discomfort to the vehicle driver, who remains in the vehicle during the washing and drying phases.

It is accordingly the principal object of the present invention to provide a blower unit, especially a unit of a kind suitable for use as or in drying apparatus, with attenuation of the noise emission by the unit but without significant increase in the dimensions of the unit at the discharge side. Other objects and advantages of the invention will be apparent from the following description.

According to the present invention there is provided a blower unit comprising a centrifugal impeller mounted in a housing to be rotatable about an axis and outlet means to accelerate and silence a flow of air centrifugally discharged by the impeller, the outlet means comprising a sound-damped nozzle having an entry portion which communicates with the interior of the housing at a terminating end of a centrifugal flow path therein and which tapers inwardly in direction away from the housing and towards a plane bisecting the impeller perpendicularly to the axis so as to be of reducing cross-sectional area in said direction and a substantially straight-sided exit portion which communicates with the entry portion and with the ambient atmosphere, the taper of the entry portion of the nozzle and the dimensions of the entry and exit portions in the direction of discharge air flow through the nozzle portion being so selected that in use the centre of pressure of such a discharge air flow is disposed upstream of and at a spacing from the exit portion.

By comparison with known blower units, the area of highest pressure of the discharge air flow through the nozzle in a unit embodying the invention is displaced back towards the start of the nozzle and preferably is located in the region of the communication of the nozzle entry portion with the impeller housing interior. Such a spacing of the area of highest air pressure from the nozzle outlet, in conjunction with sound damping of the nozzle, can result in an appreciable reduction in noise output at. the discharge side of the unit.

In a preferred configuration of the nozzle, the taper of its entry portion its defined by two mutually opposite walls each including an angle of more than substantially 40 with the mentioned reference plane. An optimum angle is substantially 450, thus providing a taper which is significantly more abrupt than in the case of prior art units, where the nozzle walls each include an angle of about 30 with the reference plane. Preferably, also, the stated dimension of the exit portion of the nozzle is at least equal to that of the entry portion. The discharge air flow is thus able to expand in controlled manner along the exit portion in almost laminar flow to achieve the desired increase in flow velocity without excessive noise generation.

In the prior art units, the nozzle has, by comparison with its tapered entry portion, a very short exit portion, with the result that the area of highest pressure of the air flow is located in the immediate proximity of the nozzle outlet and effective noise suppression is difficult or impossible.

The walls of the entry and exit portions of the nozzle may be provided by partition plates in a casing, with sound-absorbing material disposed in cavities between the plates and the casing and the plates defining the walls of the exit portion preferably perforated. The outlet means thus constructed forms a complete outlet silencer.

The dimensions of the nozzle in the mentioned reference plane and transversely to the direction of discharge air flow therethrough can be greater than the corresponding dimension of the terminating end of the centrifugal flow path, the nozzle upstream end being closed at regions thereof disposed laterally of the terminating end of the centrifugal flow path. The closed-off regions of the nozzle upstream end, which lie outside the direct range of the centrifugal flow path, result in high pressure areas ensuring that the discharge air flow occupies the entire exit portion of the nozzle, even though the nozzle entry portion has a greater cross-sectional area than the terminating end of the centrifugal flow path.By these measures the nozzle can be larger than the flow outlet of the impeller housing, so that the housing does not have to be increased in volume in order to provide the desired size of the finally issuing air stream. Equally, the nozzle does not have to taper outwardly, as in the known units, in a direction perpendicular to that of the inward taper.

To enhance noise attentuation, the blower unit preferably also comprises inlet means to silence a flow of air axially inducted by the impeller. The inlet means can comprise a cylindrical body with an axial inlet duct disposed coaxially with the impeller, such a cylindrical body conveniently being formed by a casing with soundabsorbing material disposed between the casing the wall of the inlet duct, in which case the duct wall can be perforated. The length of the inlet duct is preferably equal to substantially twice the diameter of an axial intake of the impeller.

An embodiment of the present invention will now be more particularly described with reference to the accompanying drawings, in which: Fig. 1 is a schematic side view of a blower unit embodying the invention; and Fig. 2 is a schematic front view of the blower unit of Fig. 2.

Referring now to the drawings there is shown a blower unit 10 which, in this instance, is intended to form part of drying apparatus in a motor vehicle washing station, drying being achieved by blowing a high velocity stream of unheated air onto the wet surfaces of a vehicle. The blower unit comprises a spiral housing 11 of sheet metal in which a centrifugal impeller 12 is mounted to be rotatable about an axis defined by a drive ouput shaft (not shown) of an electric motor 13 flange-mounted on one side of the housing. The impeller is mounted in the housing solely by way of the shaft.

Mounted on the other side of the housing is an inlet silencer 14, which consists of a cylindrical casing 15, a perforated tube 16 spaced from the casing and defining an axial inlet duct coaxial with the impeller axis, and a filling of sound-absorbing material, preferably a fibrous material such as rockwool or a foam material, between the casing and the tube. The length of the inlet duct is equal to about twice the diameter of the axial intake zone of the impeller and the diameter is such that the inducted air flow - indicated by arrows in Fig. 2 - remains at substantially constant pressure along the duct.

The air entry end of the duct in the tube 16 is closed by a filter mesh.

The air inducted by the impeller 12 is discharged along a centrifugal path in the interior of the housing as indicated by arrows in Fig. 1 and the termination of the path occurs at a junction of the housing with a flow accelerating and silencing outlet device 17. The outlet device consists of an elongate box-shaped sheet metal casing 18 provided in its interior with metal partition plates 19 forming a discharge nozzle 20 for air from the impeller housing, the cavities between the partition plates and the casing being filled with a soundabsorbing material the same or similar to that in the inlet silencer casing 15.

The nozzle consists of an entry portion 20a, which tapers inwardly in a direction away from the impeller housing 11 and towards a reference plane 21 bisecting the impeller 12 perpendicularly to its axis, and a straight-sided exit portion 20b. The entry portion 20a communicates directly with the terminating end of the centrifugal discharge path of the impeller and the exit portion 20b continues from the entry portion and opens into ambient atmosphere. Since the nozzle extends the entire length of the casing 18, the outlet of the nozzle, i.e. the downstream end of the exit portion, is in the form of a slot.

As will be apparent from the illustration of the nozzle configuration, the cross-sectional area of the entry portion 20a constantly reduces in direction away from the impeller housing, thus in the direction of discharge air flow through the nozzle, while the cross-sectional area of the exit portion 20b is unchanged between its inlet and outlet ends.

The partition plates 19 defining the nozzle walls consist of solid upper plates 19a which each include an angle of more than 400, preferably about 45 , with the reference plane 21, and perforated lower plates 19b parallel to each other. The angle of the upper plates 19a and the length of the lower plates 19b are such that, having regard to the available depth of the outlet device casing 18, the length of the nozzle exit portion 20b in the direction of the discharge air flow is somewhat greater than the length, in the same direction, of the nozzle entry portion 20a.

The outlet device 17 may be fabricated as a unit and secured to the impeller housing 11, but it may be more convenient to attach the nozzle upper plates 19a directly to the lower end of the housing 11 and then enclose the plates in the casing 18. The lowermost face of the casing 18 can be formed by perforated sheets which are additionally bent around to form the nozzle lower plates 19b and which close off the cavities receiving the sound-absorbing material.

The complete unit 10 forms part of drying apparatus, which may consist of several such units, in a vehicle washing station, and can be mounted on a travelling carriage intended to pass back and forth over a vehicle to be washed, or in a stationary location adjacent to a conveying path for the vehicle. In the latter case, the unit may be capable of limited movement and in both cases the unit is mounted with the air discharge slot at a small angle, for example 15 to 200, to be horizontal. Other uses for the unit are, of course, possible, particularly applications where the sensitivity to noise is such that attenuation of noise emission is desirable or even essential.

In operation of the blower unit, air is axially inducted by the impeller 12 through the inlet silencer 14 and centrifugally discharged so as to flow around the perimeter of the impeller and into the nozzle 20, from which it is issued as a relatively high speed narrow stream.

In the nozzle, the air flow is initially throttled by the tapered entry portion 20a and then accelerated by expansion in controlled manner along the exit portion 20b. The angle of taper of the entry portion 20a and the relative lengths, in the flow direction, of the entry and exit portions are such that the area of highest pressure of the centrifugally discharged air is located upstream of the exit portion, in particular in the region of the start of the entry portion. The thus controlled discharge of the air, in conjunction with the cladding of the nozzle with sound-absorbing material and resonance of the plates 19b permitted by the perforations, provides silencing of the discharge side of the unit but without significant increase in the overall depth of the outlet device 17. Although the nozzle is longer than the outlet of the impeller housing 11 in the direction shown in Fig. 1, i.e. in the plane 21 and transversely to the outflow direction, a relatively uniform distribution of air across the nozzle results from the presence of high presssure dead zones in the upper end regions of the casing 18.

The intake side of the unit is correspondingly silenced by the inlet silencer 14 and the cumulative effect of the silencing measures is a blower unit that may be appreciably quieter, for example by 12 to 14 decibels, in operation by comparison with similarly dimensioned unsilenced units.

Claims

1. A blower unit comprising a centrifugal impeller mounted in a housing to be rotatable about an axis and. outlet means to accelerate and silence a flow of air centrifugally discharged by the impeller, the outlet means comprising a sound-damped nozzle having an entry portion which communicates with the interior of the housing at a terminating end of a centrifugal flow path therein and which tapers inwardly in direction away from the housing and towards a plane bisecting the impeller perpendicularly to the axis so as to be of reducing cross-sectional area in said direction and a substantially straight-sided exit portion which communicates with the entry portion and with the ambient atmosphere, the taper of the entry portion of the nozzle and the dimensions of the entry and exit portions in the direction of discharge air flow through the nozzle being so selected that in use the centre of pressure of such a discharge air flow is disposed upstream of and at a spacing from the exit portion.

2. A blow unit as claimed in claim 1, wherein said centre of pressure is disposed in the region of the communication of the entry portion with the housing interior.

3. A blower unit as claimed in claim 1 or claim 2, wherein tne taper of the entry portion of the nozzle is defined by two mutually opposite walls each including an angle of more than substantially 40O with said plane.

4. A blower unit as claimed in claim 3, wherein the angle is substantially 45".

5. A blower unit as claimed in any one of the preceding claims, wherein said dimension of the exit portion of the nozzle is at least equal to that of the entry portion.

6. A blower unit as claimed in any one of the preceding claims, wherein the walls of the entry and exit portions of the nozzle are provided by partition plates in a casing and sound-absorbing material is disposed in cavities between the plates and the casing.

7. A blower unit as claimed in claim 6, wherein the plates defining the walls of the exit portion of the nozzle are perforated.

8. A blower unit as claimed in any one of the preceding claim wherein the dimension of the nozzle in said plane and transversely to the direction of discharge air flow therethrough is greater than the corresponding dimension of the terminating end of the centrifugal flow path, the upstream end of the nozzle being closed at regions thereof disposed laterally of the terminating end of the centrifugal flow path.

9. A blower unit as claimed in any one of the preceding claims, comprising inlet means to silence a flow of air axially inducted by the impeller.

11. A blower unit as claimed in claim 10, wherein the cylindrical body comprises a casing and sound-absorbing material disposed between the casing and the wall of the inlet duct, the duct wall being perforated.

12. A blower unit as claimed in any one of claims 9 to 11, wherein the length of the inlet duct is equal to substantially twice the diameter of an axial intake of the impeller.

13. A blower unit substantially as hereinbefore described with reference to the accompanying drawings.

14. Drying apparatus for a vehicle washing station, comprising a blower unit as claimed in any one of the preceding claims, the unit being mounted on a reciprocatingly movable carriage and arranged to discharge air from the nozzle into a region to be occupied by a vehicle to be dried.

15. Drying apparatus for a vehicle washing station, comprising a blower unit as claimed in any one of the preceding claims, the unit being mounted for limited movement at a stationary location and arranged to discharge air from the nozzle into a region to be occupied by a vehicle travelling past the unit.