GB2439557A

GB2439557A - A heat exchanger and heat exchanger assembly

Info

Publication number: GB2439557A
Application number: GB0607646A
Authority: GB
Inventors: Michael Massey
Original assignee: Vent Axia Group Ltd
Current assignee: Vent Axia Group Ltd
Priority date: 2005-04-16
Filing date: 2006-04-18
Publication date: 2008-01-02
Also published as: GB0507729D0; GB0607646D0

Abstract

A heat exchanger 17 comprises a plurality of first fluid channels 21 on the exterior of the heat exchanger 17 having inlets adjacent a longitudinal axis of the heat exchanger 17 and outlets radially spaced from the inlets, a plurality of second fluid channels 23 on the interior of the heat exchanger 17 having outlets adjacent the longitudinal axis of the heat exchanger 17 and inlets radially spaced from the outlets, and the first 21 and second 23 channels sharing a common dividing wall through which heat is exchanged. Channels 21, 23 may curve between the inlets and outlets, may be circular in cross section, may be equispaced around the heat exchanger 17, may be disposed on opposite sides of the heat exchanger 17 and staggered in relation to each other, may diverge as the channels extend away from the longitudinal axis or may be constant in cross section. Channels 21, 23 are formed by a plurality of exterior vanes 19 and interior vanes 18 respectively. Heat exchanger 17 forms part of a heat exchange assembly 1 comprising of a pump assembly (61, fig 3) comprising first and second pumps having concentrically mounted impellers (65, 71, fig 14) for pumping fluids through the channels 21, 23.

Description

I

A HEAT EXCHANGER AND HEAT EXCHANGER ASSEMBLY

The present invention relates to a heat exchanger and heat exchanger assembly and particularly but not exclusively relates to a heat exchanger and heat exchanger assembly for use with, or comprising part of, an extractor fan assembly.

Extractor fans are well known for extracting stale or damp air from inside a building or the like and it is desirable for such extractor fans to be relatively compact, quiet and low maintenance.

Existing extractor fans can suffer from the problem that heat contained in the stale or damp air, as may have been provided by a central heating or air conditioning system, is pumped out of the building with the stale or damp air. Additionally it is desirable to be able to replace the stale air pumped from the building with fresh air.

According to a first aspect of the invention there is provided a heat exchanger comprising first fluid channel means having inlet means adjacent the longitudinal axis of the heat exchanger and outlet means radially spaced from the inlet means, the heat exchanger further comprising second fluid channel means having outlet means adjacent the longitudinal axis of the heat exchanger and inlet means radially spaced S...

: 20 from the outlet means, the fluid channel means sharing a common dividing wall such that, in use, heat is exchanged through the dividing wall from fluid in one channel means to fluid in the other channel means.

Preferably the inlet means and outlet means of each channel means are axially spaced apart in the direction of the longitudinal axis.

Preferably each channel means curves between the respective inlet means and the respective outlet means.

Each channel means can curve about the longitudinal axis of the heat exchanger such that the radially inner end of the channel means is not aligned with the radially outer end of the channel means, when the heat exchanger is viewed along its longitudinal axis.

Each channel means can curve along substantially its entire length.

Preferably the thermal transfer surface area of each channel means is substantially constant along the length of the channel means.

Preferably the heat exchanger is substantially circular when viewed along the longitudinal axis of the heat exchanger.

Preferably each fluid channel means of the heat exchanger comprises a plurality of channels, each channel having a respective inlet and outlet. * . * .**

Preferably each channel means extends between a position adjacent the **.

axis of the heat exchanger and a position adjacent the radially outermost S... *S * : periphery of the heat exchanger.

S..... * S

Preferably the inlet means of the first fluid channel means, and the outlet * means of the second fluid channel means, are adjacent but spaced from S..

the axis of the heat exchanger so that the heat exchanger comprises a central tubular space at the heat exchanger axis.

Preferably the channels of each channel means are equispaced around the heat exchanger.

Preferably the first fluid channel means is adjacent one surface of the dividing wall such that fluid in the first fluid channel means is in contact with said surface of the dividing wall, the second fluid channel means being adjacent an opposed surface of the dividing wall such that fluid in the second fluid channel means is in contact with said opposed surface of the dividing wall.

Preferably the fluid channel means on one side of the dividing wall is non-aligned with the fluid channel means on the other side of the dividing wall.

Most preferably the fluid channel means on one side of the dividing wall is staggered from the fluid channel means on the other side wall, when the heat exchanger is viewed along its longitudinal axis.

Preferably the first fluid channel means is provided on one side of the heat exchanger, the second fluid channel means being provided on an opposed side of the heat exchanger. I...

s..., Preferably the heat exchanger comprises a plurality of hollow vanes each comprising a base surface and two opposed dividing walls, each channel *ISSSS * being defined between a respective two opposed dividing walls.

S..... * .

*:::: Preferably a first plurality of vanes are provided on one side of the heat exchanger and a second plurality of vanes are provided on the other side of the heat exchanger.

Preferably the inlets of the channels of the first fluid channel means are radially aligned, that is, each inlet is spaced the same distance from the heat exchanger axis.

Alternatively the inlets of the channels of the first fluid channel means are radially staggered, that is each inlet is spaced a different distance from the heat exchanger axis to the adjacent inlet.

Preferably the outlets of the channels of the second fluid channel means are radially aligned, that is, each outlet is spaced the same distance from the heat exchanger axis.

Alternatively the outlets of the channels of the second fluid channel means are radially staggered, that is each outlet is spaced a different distance from the heat exchanger axis to the adjacent outlet.

In one embodiment the cross sectional area of the or each channel varies along the length of the channel, such that the walls of each channel diverge. Preferably the walls of the or each channel diverge as the channel extends away from the axis of the heat exchanger.

In an alternative embodiment the cross sectional area of each channel is substantially constant along the length of the channel such that the walls of each channel are substantially parallel.

* Most preferably the walls of each channel are substantially parallel over *s.I* * substantially the entire length of each channel. *. S. * . *

In this embodiment the channels can be arranged in sets, each set I..

comprising a predetermined number of channels, the sets being equispaced around the heat exchanger.

According to a second aspect of the invention there is provided a heat exchanger assembly comprising a heat exchanger comprising first fluid channel means having inlet means adjacent the longitudinal axis of the heat exchanger and outlet means radially spaced from the inlet means, the heat exchanger further comprising second fluid channel means having outlet means adjacent the longitudinal axis of the heat exchanger and inlet means radially spaced from the outlet means, the fluid channel means sharing a common dividing wall, the assembly further comprising pump means to pump fluid through the first and second fluid channel means such that, in use, heat is exchanged through the dividing wall from the fluid pumped through one channel means to the fluid pumped through the other channel means.

Preferably the heat exchanger is substantially circular, when viewed along the longitudinal axis of the heat exchanger.

Preferably each fluid channel means of the heat exchanger comprises a * plurality of channels, each channel having a respective inlet and outlet.

S..... * S

* S Preferably each channel means extends between a position adjacent the axis of the heat exchanger and a position adjacent the radially outermost periphery of the heat exchanger.

Preferably the inlet means of the first fluid channel means, and the outlet means of the second fluid channel means, are adjacent but spaced from the axis of the heat exchanger so that the heat exchanger comprises central tubular space at the heat exchanger axis.

Preferably the pump means is mounted adjacent the central tubular space.

Most preferably the fluid channel means on one side of the dividing wall is staggered from the fluid channel means on the other side of the dividing wall, when the heat exchanger is viewed along its longitudinal I',.

* u axis. **..

Preferably the first fluid channel means is provided on one side of the heat exchanger, the second fluid channel means being provided on an opposed side of the heat exchanger. * *

Preferably the heat exchanger comprises a plurality of hollow vanes each comprising a base surface and two opposed dividing walls, each channel being defined between a respective two opposed dividing walls.

Preferably a first plurality of vanes are provided on one side of the heat exchanger and a second plurality of vanes are provided on the other side of the heat exchanger.

Alternatively the inlets of the channels of the first fluid channel means are radially staggered, that is, each inlet is spaced a different distance from the heat exchanger axis to the adjacent inlet.

is Alternatively the outlets of the channels of the second fluid channel *:::: means are radially staggered, that is each outlet is spaced a different distance from the heat exchanger axis to the adjacent outlet.

*S.S.. * S

S

SI....

* . In one embodiment the cross sectional area of the or each channel varies *:::: along the length of the channel, such that the walls of each channel diverge. Preferably the walls of the or each channel diverge as the channel extends away from the axis of the heat exchanger.

In this embodiment the channels are arranged in sets, each set comprising a predetermined number of channels, the sets being equispaced around the heat exchanger.

Preferably the pump means comprises a first pump having a first pump chamber comprising an inlet, and an outlet in communication with the inlet of the first fluid channel means, and a second pump comprising a second pump chamber comprising an inlet in communication with the outlet of the second fluid channel means and an outlet, the first and second pump chambers being separate such that, in use, the fluid pumped through the first pump and through the first fluid channel means is separate to the fluid pumped through the second pump and through the second fluid channel means.

Preferably the first and second pumps comprise respective impellers.

Preferably the pump means comprises a single motor that drives both S...

impellers.

S

S.....

* Preferably both impellers rotate about a common axis.

*SS.S.

S S

Preferably the first and second impellers are concentrically mounted on *:. the pump means, such that one pump chamber is radially outward of the other pump chamber.

Preferably a radially innermost cylindrical wall of the first pump chamber comprises the radially outermost cylindrical wall of the second pump chamber.

The total active surface area of the blades of the radially innermost impeller may be greater than the total active surface area of the blades of the radially outermost impeller.

The blades of the radially innermost impeller may be angled away from the rotational axis of the impeller to a greater extent than the blades of the radially outermost impeller.

Preferably the size of blade and speed of rotation of each blade is arranged such that the flow rate of fluid pumped through each impeller is substantially equal for a given motor speed.

Preferably the heat exchanger assembly comprises part of an extractor fan assembly for a building or the like, the inlets and outlets of the fluid channel means, and the pump means, being arranged such that the pump means, in use, pumps stale air from the building or the like and through one of the fluid channel means of the heat exchanger, and pumps fresh * SS air into the building or the like through the other fluid channel means, heat being exchanged from the stale air to the fresh air. * SSS * .

* SI...

* S According to a third aspect of the invention there is provided pump means for pumping fluid through a heat exchanger, the pump means comprising a first pump having a first pump chamber comprising an inlet and outlet, and a second pump comprising second pump chamber comprising an inlet and outlet, the first and second pump chambers being separate such that, in use, the fluid pumped through the first pump is separate to the fluid pumped through the second pump.

Preferably at least one pump comprises a radial inlet or outlet, that is, an inlet or outlet spaced from the axis of rotation of a pump impeller.

Preferably the pump assembly comprises duct means in communication with the heat exchanger for transferring fluid to and from the heat exchanger.

Preferably the duct means comprises an inlet duct and an outlet duct.

Preferably the inlet and outlet ducts are concentrically mounted.

Preferably the first and second pumps comprise respective impellers.

Preferably the pump means comprises a single motor that drives both impellers.

Preferably both impellers rotate about a common axis.

Preferably the first and second impellers are concentrically mounted in the pump means.

* S. I Preferably a radially innermost impeller wall of the first pump chamber comprises the radially outermost impeller wall of the second pump : chamber. * S S...

: 15 Preferably the total active surface area of the blades of the radially innermost impeller is greater than the total active surface area of the blades of the radially outermost impeller.

Preferably the blades of the radially innermost impeller are angled away from the rotational axis of the impeller to a greater extent than the blades of the radially outermost impeller.

Other aspects of the present invention may include any combination of the features or limitations referred to herein.

The present invention may be carried into practice in various ways, but embodiments will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a side view of a heat exchanger assembly in accordance with the present invention; Figure 2 is a front view of the heat exchanger assembly of Figure 1; Figure 3 is an exploded side view of the heat exchanger assembly of Figures 1 and 2 with parts of the exchanger shown in phantom; Figure 4 is a front view of a heat exchanger comprising part of the assembly of Figures 1 to 3; Figure 5 is a sectional view from one side taken on line A-A of Figure 4; Figure 6 is a view of the heat exchanger taken from the other side; *4s Figure 7 is a part sectional side view of part of the heat exchanger assembly of Figures 1 to 6; Figure 8 is a part cut away front view corresponding to Figure 7; Figure 9 is a sectional view on line A-A of Figure 8; Figure 10 is a sectional view on line A-B of Figure 8; Figure 11 is a sectional view on line C-C of Figure 7; Figure 12 is a sectional side view of a duct assembly of the heat exchanger assembly of Figures 1 to 3; Figure 13 is a sectional side view of a pump assembly comprising part of the duct assembly of Figure 12; Figure 14 is an end view of the pump assembly of Figure 13; Figure 15 is a sectional side view of the heat exchanger assembly of Figures 1 to 3, with the detail of the heat exchanger omitted for clarity; and Figure 16 is a front view of a modified heat exchanger comprising part of the assembly of Figures 1 to 3. S. * *

Referring initially to Figures 1 to 6 a heat exchanger assembly 1 *5S* comprises a heat exchanger housing sub assembly 3 in communication with a duct assembly 5. *

*S.SI. * I

The housing sub assembly 3 comprises a circular cross section, hollow : outer casing 6 comprising a planar back plate 8 having a curved outer SI.

peripheral wall 9 leading to a radially outwardly flared circular mouth 10. The back plate 8 of the casing 6 is formed with a circular, axially aligned aperture 13.

A circular cross section shallow cup shaped inner seal 14 is received within the outer casing 6 and is of toroidal form comprising a circular, axially aligned aperture 15 and a curved outer margin 16 which forms an air tight seal between the inside surface of the curved wall 9 of the casing 6 and the outer periphery of a circular cross section radial heat exchanger 17.

The heat exchanger 17 is operative to allow two flows of air to flow in opposed directions through the heat exchanger 17.

As can be seen from Figures 4 to 6, the heat exchanger 17 is of generally circular cup shape having a central through bore 20 which is concentric with the heat exchanger axis. The heat exchanger 17 comprises a plurality of spaced apart vanes 18 on the interior of the cup, and a plurality of spaced apart vanes 19 on the exterior of the cup. The vanes 18 on the interior of the cup are formed, when the exchanger 17 is viewed along its axis, in the spaces between the vanes 19 on the exterior of the cup. The vanes 18 on the interior are thus staggered from the vanes 19 on the exterior.

The vanes 18, 19 appear to be solid but are in fact hollow so that each *::::* 15 vane 18 on the interior of the heat exchanger 17 defines a fluid channel 21 on the exterior of the heat exchanger 17. Likewise each I.....

* vane 19 on the exterior of the heat exchanger 17 defines a fluid S. IS * channel 23 on the interior of the heat exchanger 17. S.'. * a S

In the example described the channels 21 on the interior of the heat exchanger 17 (the left hand side when viewing Figures 3 and 5) comprise inlet channels. The channels 23 on the exterior of the heat exchanger 17 comprise outlet channels. In this embodiment, the channels 21, 23 extend radially outwardly from the heat exchanger axis and comprise straight channel side walls that are arranged such that each channel 21, 23 flares outwardly as it extends away from the heat exchanger axis.

The heat exchanger 17 is preferably injection moulded using a plastics material such as polypropylene. Any other suitable manufacturing technique or material could alternatively be used. For example the heat exchanger 17 could be manufactured from pressed aluminium, or fabricated, folded card or paper. The heat exchanger could also be manufactured using a die casting technique using a metal material such as Zinc.

The technique and material used will be a balance between achieving the desired channel wall thickness so as to be as thin as possible to ensure efficient heat transfer; achieving the desired number of channels 21,23 and the desired channel width; and achieving the tool draft angles required to effectively manufacture the heat exchanger 17.

A toroidal outer seal 25 is inserted into the inside of the heat exchanger 17. The outer seal 25 comprises a radially innermost hollow tubular boss 27 of curved profile which abuts, and seals against, the Ia..

vanes 18 on the inside of the heat exchanger 17. The tubular boss 27 does not extend fully axially into the heat exchanger 17 and thus there is S.....

* a gap 28 defined between the end of the boss 27 and the inner ends of the * vanes 18. This gap 28 comprises an inlet air outlet. S... * a * *5 *

The heat exchanger 17 is closed off by a circular closure 31. The closure 31 comprises an inner circular element 33 comprising a solid boss 35 which curves radially outwardly from its axis so as to be of generally mushroom shaped cross section. The tubular boss 35 is dimensioned to be received in, and to seal against, the tubular boss 27 of the outer seal 25.

The outer periphery of the inner circular element 33 is joined, by suitably spaced ribs or the like (not shown), to an outer closure plate 37, so as to define, there between an inlet air inlet slot 38. A circumferential outlet air outlet slot 39 is defined between the outer closure plate 37 and the mouth 10 of the casing 6.

Referring additionally to Figures 7 to 11 the sealing between the heat exchanger 17 and the inner and outer seals 14, 25 is shown.

It can be seen from Figure 7 that the inner seal 14 forms an airtight seal between the inner surface of the casing 6, and the outer margins of the vanes 19 on the exterior of the heat exchanger 17. Thus outlet air can flow through the central aperture 13 of the heat exchanger 17, along an outlet flow path as indicated by arrows 41 and as defined in the channels 23 between the vanes 19 on the exterior of the heat exchanger 17 as shown in Figure 9, before exiting the heat exchanger 17 through outlet slot 39 defined between the closure plate 37 and the mouth 10 of the casing 6.

S * .5.

The outer seal 25 forms an airtight seal between the boss 35 of the *5ma closure 31 and the outermost margin of the vanes 18 on the interior of S.....

* the heat exchanger 17. This enables inlet air to flow through inlet ISS* dS * slot 38 along an inlet flow path as indicated by arrows 43 and as defined in the channels 21 between the vanes 18 on the interior of the heat me * *. 20 exchanger 17 as shown in Figure 10, before exiting the heat exchanger 17 through the gap between the boss 35 of the closure and the closure back plate 8, and through the central aperture 13 of the back plate 8.

Referring additionally to Figures 12 to 14, the duct assembly 5 comprises a circular cross section outer pipe 51 and a concentrically mounted circular cross section inner pipe 53 so as to define an outlet flow duct 55 between the outer and inner pipes 51, 53, and an inlet flow duct 57 within the inner pipe 53. The duct assembly 5 is sealingly connected to the circular aperture 13 on the back plate 8 of the casing 6 so that the outlet flow duct 55 is in communication with outlet flow path 41 and the inlet flow duct 57 is in communication with the inlet flow path 43.

A pump assembly 61 is mounted within the end of the duct assembly 5 that is connected to the casing 6. The pump assembly 61 comprises an outer tubular impellor housing 63 in which an outer impellor 65 is rotatably mounted. The outer impellor 65 comprises an inner hollow hub 67 provided with a plurality of radially outwardly projecting impellor blades 69. An inner impellor 71 is rotatably mounted within the hollow hub 67 and comprises a central hub 73 provided with a plurality of radially outwardly projecting impellor blades 75. Motor means and transmission means (not shown) are provided to drive the impellors 65, 71 and may be provided within, or external to, the impellor housing 63.

The impellors 65, 71 are arranged such that air flows through impellor 65 in an opposite direction to the flow of air through impellor 71. This can be achieved using suitable relative orientation of the impellor blades 69, 75, or by driving each impellor 65, 71 in :" 20 opposite directions of rotation. Thus the outer impellor 65 drives air from right to left referring to Figures 3, 4 and 13, whilst the inner : impellor 71 drives air from left to right. **

Referring to Figure 15, the heat exchanger assembly 1 described above defines two separate air flow paths 41, 43.

The inlet air flow path 43 extends from the inlet slot 38 defined between the inner circular element 33 and the outer closure plate 37 of the closure 31, enters the radially outermost inlets of the channels 21 on the interior of the heat exchanger 17, flows along each flow channel 21 on the interior of the heat exchanger 17 towards the axis of the heat exchanger 17 before exiting the heat exchanger 17 at a radially inner position so as to enter the inlet duct 55 of the duct assembly 5.

The outlet air flow path 41 extends from the outlet duct 57 and initially flows from a radially inner heat exchanger inlet, along each outlet channel 23 of the heat exchanger 17, through a radially outermost heat exchanger outlet before exiting the assembly 1 through the outlet slot 39 defined between the inner surface of the flared mouth 10 of the casing 6, and the outer periphery of the outer closure plate 37 of the closure 31.

It will be appreciated that the inlet flow channel 21 of the heat exchanger 17, is formed on an opposed side of the heat exchanger 17 to the outlet flow channel 23, the inlet and outlet channels 21, 23 being sealed from one another by the vane walls to prevent cross contamination of the two air flows.

The inlet air thus inlets the heat exchanger 17 in an axial direction S.* through the radially outer peripheral slot 38 defined between the outer periphery of the outer seal 25, and the outer periphery of the outer

S

closure plate 37. The inlet air then flows radially inwardly and exits the

S

heat exchanger 17, in an axial direction, at a radially inward position, 5I5* : namely through the central aperture 13 of the heat exchanger 17.

The outlet air inlets the exchanger 17 in axial direction through a radially inward space defined between the outer surface of the central exchanger aperture 13, and the innermost surface of the boss 27 of the outer seal 25. The outlet air then flows radially outwardly and exits the heat exchanger 17, in a radially outward direction, at a radially outward position, namely through the peripheral slot 39 defined between the inside surface of the mouth 10 of the casing 6, and the outermost periphery of the outer closure plate 37 of the closure 3 1.

It will be appreciated that the flow paths 41, 43 could be inlet or outlet flow paths as desired. The heat exchanger 17 could be used with any fluid whether gaseous or liquid.

Referring to Figure 16, a modified heat exchanger 117 is provided for use with the heat exchanger assembly 1 described above, instead of the heat exchanger 17.

The heat exchanger 117 is of generally circular cup shape and comprises a plurality of spaced apart vanes 11 8 on the interior of the cup and a plurality of spaced apart vanes (not shown) on the exterior of the cup.

The vanes 118 on the interior of the cup are formed, when the exchanger 117 is viewed along its axis, in the spaces between the vanes on the exterior of the cup. The vanes 118 on the interior are thus staggered from the vanes on the exterior.

S *S.

S

The vanes are hollow so that each interior vane 118 defines a fluid * channel (not shown) on the exterior of the heat exchanger 117 and each .S IS

S * exterior vane defines a fluid channel 123 on the interior of the

heat

S

exchanger 117. sasS * I *5 I

In this embodiment the fluid channels radiate out from the central circular bore 120 so as to curve around the bore 120 as each channel extends radially outwardly from the bore 120 to the outer periphery of the exchanger 117. Each channel is thus semi-involute in that each channel initially extends radially outwardly from the bore 120 before curving generally back on itself. The radially inner end of each channel is thus not axially aligned with the radially outer end of each channel.

It will be appreciated that the cross sectional area of each channel is substantially uniform along its length. Additionally each channel has a greater thermal transfer area than if each channel extended in a straight line from the bore 120 to the heat exchanger periphery. Thus thermal transfer efficiency can be improved.

The channel uniformity enables a more constant fluid flow to be achieved and can improve thermal efficiency.

Additionally, balancing of the dual fluid flows between the bore 120 and the heat exchanger periphery is more readily achieved. * . S.* **SSS

S P.S..

S S... * S 5 *I5

Claims

CLAIMS

1. A heat exchanger comprising first fluid channel means having inlet means adjacent the longitudinal axis of the heat exchanger and outlet means radially spaced from the inlet means, the heat exchanger further comprising second fluid channel means having outlet means adjacent the longitudinal axis of the heat exchanger and inlet means radially spaced from the outlet means, the fluid channel means sharing a common dividing wall such that, in use, heat is exchanged through the dividing wall from fluid in one channel means to fluid in the other channel means.

2. The heat exchanger of claim 1 wherein the inlet means and outlet means of each channel means are axially spaced apart in the direction of the longitudinal axis.

3. The heat exchanger of claim 1 or claim 2 wherein each channel means curves between the respective inlet means and the respective outlet means.

4. The heat exchanger of claim 3 wherein each channel means curves about the longitudinal axis of the heat exchanger such that the radially inner end of the channel means is not aligned with the radially outer end of the channel means, when the heat exchanger is viewed along its . 20 longitudinal axis. *SS

5. The heat exchanger of claim 4 wherein each channel means curves along substantially its entire length.

6. The heat exchanger of any one of claims 3 to 5 wherein the thermal transfer surface area of each channel means is substantially constant along the length of the channel means.

7. The heat exchanger of any one of the preceding claims wherein the heat exchanger is substantially circular when viewed along the longitudinal axis of the heat exchanger.

8. The heat exchanger of any one of the preceding claims wherein each fluid channel means of the heat exchanger comprises a plurality of channels, each channel having a respective inlet and outlet.

9-. The heat exchanger of any one of the preceding claims wherein each channel means extends between a position adjacent the axis of the heat exchanger and a position adjacent the radially outermost periphery of the heat exchanger.

10. The heat exchanger of any one of the preceding claims wherein the inlet means of the first fluid channel means, and the outlet means of the second fluid channel means, are adjacent but spaced from the axis of the heat exchanger so that the heat exchanger comprises a central tubular space at the heat exchanger axis. SI*

11. The heat exchanger of any one of claims 8 to 10 wherein the * channels of each channel means are equispaced around the heat . . S *

S

* exchanger. S...'

12. The heat exchanger of claim 1 wherein the fluid channel means on S. one side of the dividing wall is non-aligned, when the heat exchanger is viewed in a direction along its longitudinal axis, with the fluid channel means on the other side of the dividing wall.

13. The heat exchanger of claim 12 wherein the fluid channel means on one side of the dividing wall is staggered from the fluid channel means on the other side wall, when the heat exchanger is viewed along its longitudinal axis.

14. The heat exchanger of any one of the preceding claims wherein the first fluid channel means is provided on one side of the heat exchanger, the second fluid channel means being provided on an opposed side of the heat exchanger.

15. The heat exchanger of claim 14 wherein the heat exchanger comprises a plurality of hollow vanes each comprising a base surface and two opposed dividing walls, each channel being defined between a respective two opposed dividing walls.

16. The heat exchanger of claim 15 wherein a first plurality of vanes are provided on one side of the heat exchanger and a second plurality of vanes are provided on the other side of the heat exchanger.

17. The heal exchanger of any one of claims 8 to 16 wherein the inlets of the channels of the first fluid channel means are radially aligned, that I..

is, each inlet is spaced the same distance from the heat exchanger axis.

18. The heat exchanger of any one of claims 8 to 16 wherein the inlets S..', of the channels of the first fluid channel means are radially staggered, that is each inlet is spaced a different distance from the heat exchanger axis to the adjacent inlet.

19. The heat exchanger of any one of claims 8 to 18 wherein the outlets of the channels of the second fluid channel means are radially aligned, that is, each outlet is spaced the same distance from the heat exchanger axis.

20. The heat exchanger of any one of claims 8 to 18 wherein the outlets of the channels of the second fluid channel means are radially staggered, that is each outlet is spaced a different distance from the heal exchanger axis to the adjacent outlet.

21. The heat exchanger of any one of claims 8 to 20 wherein the cross sectional area of the or each channel varies along the length of the channel, such that the walls of each channel diverge.

22. The heat exchanger of claim 21 wherein the walls of the or each channel diverge as the channel extends away from the axis of the heat exchanger.

23. The heat exchanger of any one of claims 8 to 20 wherein the cross sectional area of each channel is substantially constant along the length of the channel such that the walls of each channel are substantially parallel.

24. The heat exchanger of claim 23 wherein the walls of each channel are substantially parallel over substantially the entire length of each channel.

25. The heat exchanger of claim 23 or claim 24 wherein the channels 0I* are arranged in sets, each set comprising a predetermined number of channels, the sets being equispaced around the heat exchanger.

26. A heat exchanger assembly comprising a heat exchanger comprising first fluid channel means having inlet means adjacent the longitudinal axis of the heat exchanger and outlet means radially spaced from the inlet means, the heat exchanger further comprising second fluid channel means having outlet means adjacent the longitudinal axis of the heat exchanger and inlet means radially spaced from the outlet means, the fluid channel means sharing a common dividing wall, the assembly further comprising pump means to pump fluid through the first and second fluid channel means such that, in use, heat is exchanged through the dividing wall from the fluid pumped through one channel means to the fluid pumped through the other channel means.

27. A heat exchanger assembly according to claim 26 wherein the inlet means and outlet means of each channel means are axially spaced apart in the direction of the longitudinal axis.

28. A heat exchanger assembly according to claim 26 or claim 27 wherein each channel means curves between the respective inlet means and the respective outlet means.

29. The heat exchanger assembly of claim 28 wherein each channel means curves about the longitudinal axis of the heat exchanger such that the radially inner end of the channel means is not aligned with the radially outer end of the channel means, when the heat exchanger is viewed along its longitudinal axis.

S II.

* 30. The heat exchanger assembly of claim 29 wherein each channel 5.5 * means curves along substantially its entire length. 55SS

5. 31. The heat exchanger assembly of any one of claims 28 to 30 wherein the thermal transfer surface area of each channel means is substantially constant along the length of the channel means.

32. A heat exchanger assembly according to any one of claims 26 to 31 wherein the heat exchanger is substantially circular, when viewed along the longitudinal axis of the heat exchanger.

33. A heat exchanger assembly according to any one of claims 26 to 32 wherein each fluid channel means of the heat exchanger comprises a plurality of channels, each channel having a respective inlet and outlet.

34. A heat exchanger assembly according to any one of claims 26 to 33 wherein each channel means extends between a position adjacent the axis of the heat exchanger and a position adjacent the radially outermost periphery of the heat exchanger.

35. A heat exchanger assembly according to any one of claims 26 to 34 wherein the inlet means of the first fluid channel means, and the outlet means of the second fluid channel means, are adjacent but spaced from the axis of the heat exchanger so that the heat exchanger comprises central tubular space at the heat exchanger axis.

36. A heat exchanger assembly according to claim 35 wherein the pump means is mounted adjacent the central tubular space.

37. A heat exchanger assembly according to any one of claims 33 to 36 Is a wherein the channels of each channel means are equispaced around the heat exchanger.

 IS a

38. A heat exchanger assembly according to any one of claims 26 to 37 wherein the fluid channel means on one side of the dividing wall is non-as * aligned with the fluid channel means on the other side of the dividing wall.

39. A heat exchanger assembly according to claim 38 wherein the fluid channel means on one side of the dividing wall is staggered from the fluid channel means on the other side of the dividing wall, when the heat exchanger is viewed along its longitudinal axis.

40. A heat exchanger assembly according to any one of claims 26 to 39 wherein the first fluid channel means is provided on one side of the heat exchanger, the second fluid channel means being provided on an opposed side of the heat exchanger.

41. A heat exchanger assembly according to claim 40 wherein the heat exchanger comprises a plurality of hollow vanes each comprising a base surface and two opposed dividing walls, each channel being defined between a respective two opposed dividing walls.

42. A heat exchanger assembly according to claim 41 wherein a first plurality of vanes are provided on one side of the heat exchanger and a second plurality of vanes are provided on the other side of the heat exchanger.

43. A heat exchanger assembly according to any one of claims 33 to 42 wherein the inlets of the channels of the first fluid channel means are radially aligned, that is, each inlet is spaced the same distance from the heat exchanger axis. S. * 4,S

44. A heat exchanger assembly according to any one of claims 33 to 42 p55*$

S

wherein the inlets of the channels of the first fluid channel means are 5.' I radially staggered, that is, each inlet is spaced a different distance from the heat exchanger axis to the adjacent inlet. 5.

45. A heat exchanger assembly according to any one of claims 33 to 44 wherein the outlets of the channels of the second fluid channel means are radially aligned, that is, each outlet is spaced the same distance from the heat exchanger axis.

46. A heat exchanger assembly according to any one of claims 33 to 44 wherein the outlets of the channels of the second fluid channel means are radially staggered, that is each outlet is spaced a different distance from the heat exchanger axis to the adjacent outlet.

47. A heat exchanger assembly according to any one of claims 33 to 46 wherein the cross sectional area of the or each channel varies along the length of the channel, such that the walls of each channel diverge.

48. A heat exchanger assembly according to claim 47 wherein the walls of the or each channel diverge as the channel extends away from the axis of the heat exchanger.

49. A heat exchanger assembly according to any one of claims 33 to 46 wherein the cross sectional area of each channel is substantially constant along the length of the channel such that the walls of each channel are substantially parallel. S... * S S...

50. The heat exchanger assembly of claim 49 wherein the walls of each **SS*5 ... channel are substantially parallel over substantially the entire length of * the channel. * SS

51. A heat exchanger assembly according to claim 49 wherein the channels are arranged in sets, each set comprising a predetermined number of channels, the sets being equispaced around the heat exchanger.

52. A heat exchanger assembly according to any one of claims 26 to 51 wherein the pump means comprises a first pump having a first pump chamber comprising an inlet, and an outlet in communication with the inlet of the first fluid channel means, and a second pump comprising a second pump chamber comprising an inlet in communication with the outlet of the second fluid channel means and an outlet, the first and second pump chambers being separate such that, in use, the fluid pumped through the first pump and through the first fluid channel means is separate to the fluid pumped through the second pump and through the second fluid channel means.

53. A heat exchanger assembly according to claim 52 wherein the first and second pumps comprise respective impellers.

54. A heat exchanger assembly according to claim 53 wherein the pump means comprises a single motor that drives both impellers.

55. A heat exchanger assembly according to claim 52 or claim 53 wherein both impellers rotate about a common axis.

56. A heat exchanger assembly according to claim 55 wherein the first and second impellers are concentrically mounted on the pump means, * such that one pump chamber is radially outward of the other pump chamber.

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57. A heat exchanger assembly according to any one of claims 54 to 56 wherein a radially innermost cylindrical wall of the first pump chamber comprises the radially outermost cylindrical wall of the second pump chamber.

58. A heat exchanger assembly according to any one of claims 54 to 57 wherein the total active surface area of the blades of the radially innermost impeller is greater than the total active surface area of the blades of the radially outermost impeller.

59. A heat exchanger assembly according to claim 58 wherein the blades of the radially innermost impeller are angled away from the rotational axis of the impeller to a greater extent than the blades of the radially outermost impeller.

60. A heat exchanger assembly according to claim 58 or claim 59 wherein the size of blade and speed of rotation of each blade is arranged such that the flow rate of fluid pumped through each impeller is substantially equal for a given motor speed.

61. A heat exchanger assembly according to any one of claims 26 to 60 wherein the heat exchanger assembly comprises part of an extractor fan assembly for a building or the like, the inlets and outlets of the fluid channel means, and the pump means, being arranged such that the pump means, in use, pumps stale air from the building or the like and through one of the fluid channel means of the heat exchanger, and pumps fresh air into the building or the like through the other fluid channel means, heat being exchanged from the stale air to the fresh air.

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* : 62. Pump means for pumping fluid through a heat exchanger, the pump S...., * means comprising a first pump having a first pump chamber comprising an inlet and outlet, and a second pump comprising second pump chamber comprising an inlet and outlet, the first and second pump chambers being separate such that, in use, the fluid pumped through the first pump is separate to the fluid pumped through the second pump.

63. The pump means of claim 62 wherein at least one pump comprises a radial inlet or outlet, that is, an inlet or outlet spaced from the axis of rotation of a pump impeller.

64. The pump means of claim 62 or claim 63 wherein the pump assembly comprises duct means in communication with the heat exchanger for transferring fluid to and from the heat exchanger.

65. The pump means of claim 64 wherein the duct means comprises an inlet duct and an outlet duct.

66. The pump means of claim 65 wherein the inlet and outlet ducts are concentrically mounted.

67. The pump means of any one of claims 62 to 66 wherein the first and second pumps comprise respective impellers.

68. The pump means of claim 67 wherein the pump means comprises a single motor that drives both impellers.

69. The pump means of claim 67 or claim 68 wherein both impellers rotate about a common axis. s.

70. The pump means of any one of claims 67 to 69 wherein the first and second impellers are concentrically mounted in the pump means. I...

71. The pump means of any one of claims 67 to 70 wherein a radially innermost impeller wall of the first pump chamber comprises the radially outermost impeller wall of the second pump chamber.

72. The pump means of any one of claims 67 to 71 wherein the total active surface area of the blades of the radially innermost impeller is greater than the total active surface area of the blades of the radially outermost impeller.

73. The pump means of any one of claims 67 to 71 wherein the blades of the radially innermost impeller are angled away from the rotational axis of the impeller to a greater extent than the blades of the radially outermost impeller.

74. A heat exchanger substantially as described herein with reference to the accompanying drawings.

75. A heat exchanger assembly substantially as described herein with reference to the accompanying drawings.

76. A pump assembly substantially as described herein with reference to the accompanying drawings. * *.. S... * S *5P*

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