Improvements in or relating to heat exchangers

Abstract

 A heat sink for use with a fluid containing garment and comprising a thermoelectric module array adapted to be connected to a suitable power source, a fluid duct in thermally conducting association with the cold junctions of the array, a gas duct in thermally conducting association with the hot junctions of the array and a fan for causing gas to pass in the gas duct, the fluid duct being adapted for connection to a fluid conditioning garment. The heat sink may incorporate a fluid pump, perhaps in tandem with the fan, for pumping fluid through the fluid duct.

Description

[0001] The present invention relates to heat exchangers, and is particularly concerned with a lightweight heat exchanger for cooling a fluid medium employed in conditioning clothing apparatus.

[0002] Liquid conditioning clothing, in which a cooled liquid is passed through a labyrinth of flexible tubing in a garment to cool a person, is described in UK Patent Specification 992929 and 1115414. More recently the application of conformable heat piping to conditioning clothing has been the subject of co-pending UK patent applications 8205747, and 8129022-8 The clothing, which may be in vest or combination form, can be of particular value to the crew of military aircraft and other vehicles and to industrial personnel in hot environments.

[0003] Heat exchangers for such a garment are described in UK Patent Specifications 1376604 and 1550351, the latter employing a heat pump principle in order to effect cooling but also integrally incorporating a heating facility, and the former being a rechargable device not using external power but with a limited period of use.

[0004] The present invention provides a powered heat sink suitable for use with a liquid conditioning garment.

[0005] According to the present invention a heat sink for use with a fluid conditioning garment comprises a thermocouple adapted to be connected to a suitable power source, a heat source fluid duct in thermally conductive association with the cold junction of the thermocouple, a heat dump fluid duct in thermally conductive association with the hot junction of the thermocouple, and pump means for causing fluid to pass in the heat dump fluid duct, the heat source fluid duct being adapted for connection to a fluid conditioning garment. The heat sink may incorporate a fluid pump, perhaps in tandem with the heat dump pump means, for pumping fluid through the fluid duct.

[0006] It will be appreciated that the invention relies on the Peltier or thermoelectric effect produced in a thermocouple, that is the production of cold and hot junctions when an electric current is passed through a non-homogeneous conductor, ie one in which there are junctions between dissimilar materials, in series. It has been found by the present inventor that a plurality of thermocouple modules, that is modules having an array of junctions and disposed so that the module has a hot face and a cold face, can be arranged in a device according to the present invention to give about 150 watts of cooling when air passed over the hot junction face is as hot as 40⁰C. This amount of cooling is sufficient to reduce the temperature of the liquid used in one liquid conditioned garment of the type described in UK Patent Specifications 992929 and 1115414, from 28°C to 25⁰C, and that this amount of cooling in these air temperature conditions renders acceptable such a working environment.

[0007] In one embodiment of the invention therefore the heat dump fluid is a gas, eg air, and the heat dump pump a fan. In an alternative embodiment it is a liquid arranged to dump heat in say an aircraft fuel tank.

[0008] In the aircraft context at least it is required that the weight and bulk of the heat sink are a minimum, and it is a feature of the present invention that the said 150 watts of cooling can be obtained in a heat sink measuring no more than about 50 x 100 x 200 mm and weighing no more than about 1.5 kg, if the heat source fluid duct is an elongate heat exchanger surrounded on both elongate sides by an array of thermocouple modules, on the outer elongate sides of which are located the heat dump fluid ducts, and if, in the case of the heat dump fluid being air, the air fan is a tangential fan extending substantially the length of the heat source fluid duct. Both the heat source and dump heat exchangers so formed preferably include corrugations formed of highly thermally conductive metal to maximise the heat transfer produced in a given volume. Similarly.heat transfer between the hot and cold faces of the thermocouples at the heat exchangers is maximised. In a typical module 20-30 thermocouples are sandwiched between ceramic plates of high thermal conductivity and low electrical conductivity, such as berillium oxide, and a thermally conducting link between the plates and the heat exchangers may be effected if low melting point solder is used as the medium giving structural integrity to the device.

[0009] Thermocouple heat sinks in accordance with the invention may be employed in hybrid heat sink apparatus to take advantage of other available cooling and to save power. In the aircraft context the cabin air supply has been found to be capable of supplying cooling in many cases during flight without the need for a power input to an intermediate device such as the thermocouple heat sink. Accordingly a hybrid heat sink according to a feature of the invention may be a thermoelectric heat sink, a cabin air inlet heat exchanger, a pump and control means, the heat dump to a thermoelectric heat sink comprising a liquid heat exchange means, and the control means being arranged to permit working fluid to bypass the cabin air inlet heat exchanger.

[0010] If the heat sink is to be employed with a heat pipe, particularly a sheet heat pipe in conformable, garment form of the type described, for example, in copending UK Patent applications 8205747, 8129022, 8129024, 8129025, 8129026, the heat source

[0011] fluid duct may be arranged as a condenser, and have a condensate collector with an associated outlet for connection, via a pump, to the heat pipe. The heat source fluid duct may also include an outlet for a vacuum pump.

[0012] Heat sinks in accordance with the invention will now be described by way of example with reference to the accompanying drawings, of which:

Figure 1 is a part sectioned isometric view of a thermoelectric heat sink associated with a liquid conditioned suit,

Figure 2 is a cross-section of the heat exchanger portion of the heat sink,

Figure 3 is a schematic diagram of a hybrid heat sink, and

Figure 4 is a schematic diagram of a heat sink associated with a conformable heat pipe.

[0013] As shewn in Figures 1 and 2 the thermoelectric heat sink comprises an elongate heat source liquid heat exchanger duct 10, two arrays of thermocouple modules 11, 11a, two banks of heat dump heat exchanger ducts 12, 12a, a tangential air fan 13, a liquid pump 14, a motor 15, and a housing 16.

[0014] The heat source duct 10 lies at the heart of a heat exchanger portion of the heat sink and the cold faces of the thermocouple module arrays 11, 11a are attached one array on either elongate side of the duct 10. To the outer, hot, faces of the module arrays 11, 11a are attached the banks of air ducts 12, 12a. The elements 10, 11, 11a, 12, 12a form the heat exchanger portion of the heat sink which is mounted at a mouth of the housing 16. The air ducts 12, 12a debouche onto the fan 13, from which therr is an exit in the housing 16. The fan 13 and the pump 14, which is a centrifugal pump connected to pump liquid through the liquid duct 10, are drivably connected in line to the motor 15. The liquid duct 10 contains metal corrugation 17 of the serrated plate fin type, and the air ducts 12, 12a metal corrugation 18 of the plain fin type.

[0015] The heat sink is illustrated as connected to a liquid conditioned suit (LCS) 20 of the type described in UK Patent Specification 1115414. It comprises a labyrinthe of flexible tubing 21 attached to a net fabric 22 in garment form, there being inlet manifolds 23 and outlet manifolds 24. As shewn in figure 1 the outlet manifold 24 of the suit is connected to the pump 14 of the heat sink, and the inlet manifold 23 of the suit is connected to the liquid ducts 10 of the heat sink.

[0016] In operation of the assembly, liquid coolant received at the pump 14 is urged through the liquid duct 10 and on to and through the garment 20 and back to the pump. DC electrical power supplied to the thermocouple array, 11, 11a sets up cold faces adjacent the liquid duct 10 and hot faces adjacent the air ducts 12, 12a, and air drawn through the ducts 12, 12a by the fan 13 cools the hot faces while the cold faces cool the liquid in the duct 10.

[0017] In a typical example of this embodiment of the invention, suitable for locating in an aircraft cockpit, a heat sink measuring 50 x 100 x 200 mm and weighing 1.5 kg and having 12 thermocouple modules of the type M1063 supplied by Marlow Industries Ltd, UK, is capable of cooling LCS liquid from 28 C to 25°C given an environmental air temperature of 40°C. The liquid customarily employed is a water based solution known as Methanol B.

[0018] In the hybrid heat sink apparatus shown in Figure 3 a thermoelectric heat sink 30 is coupled to a cabin air inlet heat exchanger 31 together with a control valve 32 and a heat exchanger input pump 33 and heat exchanger 34. Via a coupling 35 the hybrid heat sink is connected to a LCG 36.

[0019] The heat sink 30 incorporates the working fluid pump (not shown), and its output is connected to the coupling 35. It is substantially as hereinbefore described with reference to Figures 1 and 2 except that in place of the air heat exchangers 12, 12a and fan 13 the heat dump comprises liquid heat exchangers (not shown) and a liquid pump (not shown). The heat dump circuit heat exchanger is located in a bay accessible to shaded ambient air.

[0020] The cabin air inlet heat exchanger 31 comprises a coiled finned tube interposed in the path of incoming cabin air.

[0021] The control valve 32 is connected to the coupling 35 return and outputs thereof to both the cabin air inlet heat exchanger 31 inlet and the inlet to the thermoelectric heat sink 30. The outlet of the heat exchanger 31 is also connected to the inlet of the sink 30. Thus the valve 32 is operable to pass working fluid through the two heat exchangers in series, or to bypass the cabin air inlet heat exchanger.

[0022] In operation of the hybrid heat sink in flight conditions etc when the cabin air inlet has cooling available, the electrical input to the thermocouples in the thermoelectric heat exchanger 30 is switched off, and the sink 31 is relied on to cool working fluid for the LCG 36. In hot situations during for example standby on the ground the heat exchanger 31 can be bypassed, the power to the thermocouples in the heat sink 30 switched on, and the latter relied upon to cool the working fluid.

[0023] In the embodiment illustrated in figure 4 a heat sink 40 is associated with a heat source 41 which is in conformable sheet heat pipe garment form of the type described in co-pending UK Patent application 8205747; that is to say that the garment 41 comprises a flexible reticulated structure 42 including a wicking element 43, and an impermeable flexible envelope 44 containing the structure, there being vapour flow channels within the envelope and substantially co-extensive with the wicking element.

[0024] Concentric vapour and liquid conduits 45, 46 respectively lead from the garment 41 via a connector 47 to the heat sink 40. There is a liquid return pump 48 in the liquid conduit 46, and within the garment 41 the liquid conduit is connected to a diffuser 49 as described in co-pending UK Patent application 8129024, the diffuser comprising a perforated tube associated with the wicking element 43.

[0025] The heat sink 40 comprises a bank 50 of thermoelectric elements the cold faces of which are bonded to a condenser 51, and the hot faces of which are bonded to an air heat exchanger 52. The air heat exchanger has an associated fan 53 and comprises a labyrinthe of metal sheet. The condenser 51 has an outlet 54 for association with an evacuator, and the thermoelectric cell bank 50 is associated with a supply of electricity.

[0026] In operation of this embodiment of the invention, with an appropriate current supplied to the thermoelectric cell bank 50 and with the liquid circuit changed with water and evacuated of gas to a vacuum of the order of 10 ^{-4 -} 10^-2 Torr, and the pump 48 and the fan 53 operating, vapour from the conduit 45 condenses adjacent the cold faces of the bank 50 and is collected in the condenser, while the hot face of the bank 50 is being cooled by air drawn through the heat exchanger 52 by the fan 53. The liquid collected in the condenser is returned by the pump to the garment 40.

[0027] In an alternative form of this embodiment, the liquid includes freon, so that the vacuum required is less. In another a further bank of thermoelectric elements is bonded to the lower faces of the condenser, with a further air heat exchanger bonded to the hot face thereof, the fan 53 being constructed to draw air through both heat exchangers.

Claims

1. A head sink for use with a fluid conditioning garment and comprising a thermocouple adapted to be connected to a suitable power source, a heat source fluid duct in thermally conductive association with the cold junction of the thermocouple, a heat dump fluid duct in thermally conductive association with the hot junction of the thermocouple, and pump means for causing fluid to pass in the heat dump fluid duct, the heat source fluid duct being adapted for connection to a fluid conditioning garment.

2. A heat sink as claimed in claim 1 and incorporating a fluid pump.

3. A heat sink as claimed in claim 1 and wherein heat source fluid duct is an elongate heat exchanger surrounded on both elongate sides by an array of thermocouple modules, on the outer elongate sides of which are located the heat dump fluid ducts.

4. A heat sink as claimed in claim 1 and wherein the heat dump pump is a tangential fan.

5. A heat sink as claimed in claim 1 and wherein heat dump heat exchanger includes corrugations formed of highly thermally conductive metal.

6. A heat sink as claimed in claim 1 and wherein heat source heat exchanger includes corrugations formed of highly thermally conductive metal.

7. A hybrid heat sink comprising a heat sink as claimed in claim 1,a cabin inlet heat exchanger, a pump and control means, the heat dump to a thermoelectric heat sink comprising a liquid heat exchange means, and the control means being arranged to permit working fluid to bypass the cabin air inlet heat exchanger.

8. A heat sink as claimed in claim 1 and wherein the heat source fluid duct is associated with a heat pipe.

9. A heat sink as claimed in claim 1 and wherein the heat source fluid duct is connected to a liquid conditioning garment.

₁0. A heat sink as claimed in claim 8 and wherein the heat pipe is a conformable sheet heat pipe.

11. A heat sink as claimed in claim 10 and wherein the heat pipe is in garment form.

Drawing