EP0076079A2

EP0076079A2 - Improvements in or relating to heat pipes

Info

Publication number: EP0076079A2
Application number: EP82304956A
Authority: EP
Inventors: Lars Erik Larsson; Michael James Graveney
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1981-09-25
Filing date: 1982-09-21
Publication date: 1983-04-06
Also published as: EP0076079A3

Abstract

A heat pipe assembly, principally an assembly including a heat pipe in the form of a conformable garment acting as a heat receiver or cooling element, and wherein the liquid return to the heat pipe is actively pumped, thus permitting remoting of receiver and sink with minimum assembly bulk, and independance of geometrical configuration requirements.

Description

The present invention relates to heat sources-cum-sinks, and especially to heat pipes constituted as thermal conditioning clothing for humans.
In UK Patent Specification 8106782 there is described a flexible or conformable heat pipe assembly in sheet form and suitable for use as a thermal conditioning garment, the assembly having a reticulated structure including wicking and void continua, an impermeable plastics film envelope surrounding the structure, and a valve in the envelope by which the assembly may be outgassed and evacuated and liquid introduced thereto.
According to the present invention a heat pipe assembly for use when heat source and heat sink are remote, comprises a heat receiver element of heat pipe form, that is having an encased reticulated structure including wicking and void continua, a heat sink element, a liquid pump, a vapour duct connecting the heat receiver element and the heat sink element, and a liquid duct connecting the heat sink element with the heat receiver element via the liquid pump.
In traditional heat pipe assemblies, the wicking constitutes a liquid duct and the void continuum a vapour duct. In circumstances where the heat sink and the heat source have to be remote, and/or the thermal conditions require a higher liquid flow rate than a given bulk of wicking can fulfil (for example there may be a requirement to minimise weight) a hollow liquid duct without wicking can have advantages. Indeed the provision of a liquid pump and an unwicked liquid duct can enable quite small ducting to be employed in supplying a heat receiving heat pipe of considerable heat receiving surface area. Moreover the operation of assemblies in accordance with the invention can be independent of orientation, ie the heat sink may be sited well below the heat receiver element.
The invention confers yet another advantage when heat sinks in the form of heat pumps are employed, if not in other situations, in that the liquid pump performs the function of a non-return valve preventing back-flow of the water.
The invention is thus particularly suitable for use when the heat receiving heat pipe element is in conformable garment form such as is described in UK Patent Specification 8106782, and it is therefore a feature of the invention that the heat receiver element may be in sheet heat pipe form, may be in conformable sheet heat pipe form, and may even be in conformable heat pipe thermal conditioning garment form, comprising a flexible reticulated structure including a wicking element, an impermeable flexible envelope containing the structure, there being vapour flow channels within the envelope and substantially coextensive with the wicking element. The wicking element may be on one face, the working or heat receiving face of the structure.
The flexible reticulated structure may, for example, be one formed in a three dimensional weaving process involving picking yarns out and thermosetting plastics warp and weft fibre elements, with the wicking perhaps constituting part or all of the weft or warp fibre or perhaps comprising non woven sheets attached to or interwoven by the structure.
In their preferred form, therefore, heat pipes according to the invention are of sheet construction. In some such embodiments of the invention it may be of value for elements of the structure which support the thickness of the heat pipe to have higher stiffness than the rest, and be, for example, formed of metal or metallised plastics. Whether the wicking forms part of the matrix or is introduced thereinto subsequent to formation thereof a suitable wicking may comprise glass fibre tow or cord., eg 'REFRASIL' (TM), or metal wick. It will be appreciated that for the purposes of the present specification the words 'wick' and 'wicking' refer to the liquid drawing function rather than to any particular wick structure or composition.
An alternative flexible reticulated structure may include an uncut velvet structure such as is described in UK Patent Specification 1028141. Typically this could be formed of nylon, polyester, or carbon or glass fibre, with or without a stiffening agent.
The envelope suitably comprises a heat sealable plastics film, and is preferably metallised, eg aluminised. It may be a laminate of various materials, eg Mylar (RTM).
In order to ensure liquid continuity between the liquid duct and the heat receiver element, liquid distribution means may be incorporated in the heat receiver element, the liquid distribution means comprising an elongate perforate tube contacting the wicking throughout its perforate length.
The elongate perforate tube may simply be a tube with discrete perforations throughout its working length and the contact between that and the wicking obtained by wrapping wicking around the tube and/or poking strands thereof through the perforation. Alternatively the perforation may be realised in a slit, and perhaps the wicking edge retained in the slit perhaps by tube resilience, or perhaps by thread sewn through the wicking and passing around the tube. Where the attitude of the receiver element is not likely substantially to alter whilst in use, in particular is not likely to be inverted more than momentarily, the perforation of the distribution tube is advantageously sited in a substantially uppermost part thereof. This can assist in preventing parts of the receiver element, particularly lowermost parts, from being swamped and ensuring that the liquid remains with the wicking. Moreover where the receiver element is to be used occupying a substantially vertical plane the liquid distribution means are preferably disposed substantially uppermost therein.
The tube may be endless, eg annular, and are preferably formed of resilient, flexible plastics material.
In the context of a thermal conditioning garment, in which the receiver element constitutes for example, a flexible poncho for being worn over the shoulders of a wearer the distribution means are therefore preferably disposed so that in use they will overlie the length of the wearer's shoulders, as epaulettes, with wicking emanating to either side thereof.
It will be appreciated that the distribution means of the present invention are particularly suitable for use in heat pipe assemblies where the heat sink element is not in heat pipe form but merely supplies cooled liquid, perhaps condensing vapour received from the receiver element to provide the liquid. In such qircumstances, where it may be advantageous for geography and weight reasons not to employ wicking in the transfer means, a liquid transfer means/wicking interface, such as is the subject of the present invention, will be required. These circumstances can readily prevail in the context of thermal conditioning garments, when separability of a receiver element in garment form and the heat sink can be highly desirable. The usual requirement for substantially a vacuum within the apparatus, and the exclusion of contaminants, may be met on the one hand by the provision of evacuation pump means as part of the heat pipe assembly and on the other by suitable isolating valve means in the connector by which elements to the assembly are disconnected. The assembly may include a liquid-pump for supplying the liquid to the liquid distribution means. The liquid pump and the evacuation pump may be gauged, and if the assembly includes heat sink means which include a heat pump this latter can also be gauged to the liquid pump. Use of a liquid pump allows operation of assemblies in accordance with the invention to be independent of orientation and minimises the bulk of the fluid transfer ducts.
Because the invention permits the remoting of the heat source and the heat sink a very wide variety of heat sinks may be suitable for use in the heat pipe assembly. Examples include the air blown wick assisted condenser system (ABWACS) described in copending UK Patent Application 8129027, the heat pump arrangement described in copending UK Patent Application 8129023, a thermoelectric heat sink of the type described in copending UK Patent Application 8129052, and heat sinks described in copending UK Patent Application 8129022, inter alia. These latter include a pack of ice or dry ice, perhaps in the portable cooler form described in UK Patent Specification 1376604, or of preheated liquid or mineral, and a rechargeable supply of cooled liquid and a distinct sink for vapour, incorporating for example molecular sieve material or zeolite, from which the vapour can subsequently be discharged.
If a thermoelectric heat sink is used the hot face thereof may be bonded directly to the heat pipe at a location designated as the condenser, which location includes a liquid collector for supplying the distributor, perhaps via a pump.
The liquid may be water. If however freon is employed a higher pressure (lower vacuum) may be permitted within the assembly.
An example of apparatus in accordance with the present invention will now be described with reference to the accompanying drawings, of which:

Figure 1 illustrates a thermal conditioning garment,
Figure 2 is a section at II in figure 1,
Figure 3 is a section at III in figure 1, and
Figures 4 and 5 illustrate alternative heat sinks,
Figure 6 illustrates a heat sink employing stored latent heat, and
Figure 7 and 8 show a refrigerator heat sink.

The thermal conditioning garment shown in figure 1 is a poncho style undergarment 10 shaped to overlie the shoulders of a person. It comprises plastics structure 20 supporting a perforated wick sheet 21 and surrounded by a non-rigid, impermeable plastics envelope 22. The structure 20 provides a continuous void behind the wick 21 and coextensive therewith. The garment carries an umbilical heat transfer lead 23 leading to a connector PEC. The garment is therefore substantially similar in construction to that described in UK Patent Specification 8106782.
- The garment is constructed as a heat receiver element, so that the umbilical lead 23 is arranged for the conveyance of cool liquid to and vapour from the garment. Thus the garment and lead 23 contain liquid distribution means in the form of a flexible plastics tube 24 leading from the lead 23 up one side of the garment, across the shoulders and around the neck of the garment. Across the shoulders, ie in the region II, and across the neck front and back, ie in region III, the tube 24 is slit in a substantially uppermost location. Edges 25 of the wick 21 are held in the slits by thread 26 sewn through the wicks and passed around the tube 24.
Figure 1 also illustrates in block form a servicing unit suitable for use with the garment 10. It comprises a liquid pump 31, a motor MPU, a compressor 32, an evacuator 33, an air blower pump 34, and a condenser unit ABWACS with a water reservoir 35. A liquid duct 40 connects the condenser ABWACS with the connector PEC via the pump 31, and a vapour duct 41 connects the condenser with the connector via the compressor 32. From the duct 41 between the condenser and the compressor a duct 42 leads to the evacuator 33, while the blower 34 communicate with the sink via a duct 43.
The motor MPU is arranged for driving the pump 31, the compressor 32, the blower 34 and the evacuator 33 intermittently. The pump 31 is a peristaltic pump to preserve ducting integrity, and serves as a non-return valve to the heat sink ABWACS. The compressor 32 serves partially to condense and to raise the temperature of the vapour to facilitate operation of the heat sink ABWACS, and is more particularly described in the copending UK Patent Application 8129023. The evacuator 32 is employed initially to evacuate the assembly and serves by intermittent operation to maintain a low pressure regime within the assembly. It is particularly described in copending UK Patent Application 8129028. The air blower 34 and the reservoir 35 associated with the heat sink ABWACS are more particularly described in the copending UK Patent Application 8129027.
The connector PEC includes valves by which the garment 10 is isolatable, so that it can be supplied for use already outgassed and perhaps partially evacuated.
The assembly is prepared for use by being connected as described and shown, when the connector PEC automatically establishes communication between ducts 24 and 40 etc, the poncho donned by someone about to enter a hot environment, and the heat sink ABWACS and the reservoir 35 charged with water. The motor MPU is switched on when the environment to the garment wearer has become hot. Then the pump 31 pumps water from the sink ABWACS via the ducts 40 and 24 into the garment 10 and the compressor 12, by compressing the vapour it receives from the garment via the duct 41, raises the temperature thereof while passing it to the sink ABWACS. In the sink ABWACS the vapour is condensed and the water so formed cooled. This is principally effected by means of thermal contact over an extensive area between the working fluid and a wick in the sink moistened with water from the reservoir 35 and dried by airflow from the blower 34 and duct 43. The evacuator 33 operates intermittently to maintain the evacuated state of the assembly interior.
Within the garment 10, upon reaching stations II and III - the liquid is absorbed from the tube 24 into the wick 21 and is distributed therethrough. As the liquid is vapourised by heat from the body the vapour is conveyed via the structure 20 and the leads 23 and 41 to the compressor 32.
Garments in accordance with the invention may be worn by personnel working in hot environments, such as military personnel, particularly tank crew and aircrew, and furnace operatives. They may be particularly useful in the aircrew context, for in the event of emergency egress over sea the connector PEC, which may be part of an ejector seat mounted personal equipment connector, may be arranged both to isolate the interior of the garment and to minimise the extent to which it and the lead 23 can act as a heat sink per se.
The heat sink illustrated in figure 4 is substantially that described in UK Patent Specification 1376604. It comprises a pressure vessel 50 with a tight-fitting screw-on cap 51. A coil 52 at the bottom of the vessel, has an inlet end connected by a pipe 53 to a connector PEGs and an outlet end connected by a pipe 54, via a liquid reservoir and air trap 55 and a pump 56 to the connector PECs.
An adjustable valve 57 is connected across the pipe 54 upstream of the reservoir 55 and downstream of the pump 56.
The vessel has a relief valve 58, set to a pressure of about 80 psia, in the cap 51 thereof, while a pipe 59 connected to the cap 51 communicates the interior of the vessel with the pump 56. As with embodiments described above the pump is arranged initially to evacuate the assembly.
For operation, the reservoir 55 is primed with a suitable coolant liquid, such as dimethyl silicone and, with the cap 51 off, the vessel 50 is filled with solid carbon dioxide, and the cap 51 tightly replaced.
When the vessels are subjected to environmental heat the pressure therein will rise and carbon dioxide gas will pass through the pipe 59 to drive the pump 56. The pump 56 then pumps the coolant liquid via the pipe 54 and the connector PECs and PECm to the garment 20.
When the pressure in the vessel 50 reaches the triple point pressure of carbon dioxide, about 75 psia, liquid carbon dioxide will start to form, and this will settle to the bottom of the vessel and surround the coil 56. Vapour passing through the coil 52 from the garment 20 via the pipe 53 will then be condensed and pass as liquid to the reservoir 55.
A stage will be reached when all the solid carbon dioxide has disappeared, leaving only the liquid and gaseous phases. Provided that the coil 52 is immersed in liquid the cooling unit will still operate efficiently, but the pressure in the vessel 50 will rise and some carbon dioxide gas may escape through the relief valve 58.
Temperature control of the garment 20 can be effected by adjustment of the valve 57 to vary the volume of liquid by-passing the garment.
The thermal reservoir illustrated in figure 5 comprises a liquid source 60 and a distinct vapour sink 61. The liquid source 60 is connected via a pump 62 and a duct 63 with the connector PECs, which is also connected via a vapour duct 64 with the sink 61. The source 60 is charged with a suitable quantity of water, and the sink 61 is filled with dried zeolite.
After assembly and evacuation as with the apparatus described above with reference to figures 2 to 5, in operation of the assembly water is supplied by the pump from the source 60 to the garment 20 via the connectors PEC and the ducts 33, 34 and 63, and vapour from the garment passes via the tube 64 and is absorbed in the zeolite in the sink 61.
The expression 'PEC' employed to indicate the connector in figures 2, 5 and 6, is that normally used to describe the connector means on an ejector seat by which various services, eg oxygen and intercom, are conveyed to an aircrewman. The PEC, which stands for Personal Equipment Connector, may have three parts; the aircraft connector, the seat mounted element, and the aircrewman connector, arranged so that the aircraft/seat connection is separated upon ejection and the seat element arranged to convey oxygen to the aircrewman from a seat mounted source until seat/man (aircrewman/seat element) separation. There may not be a need to condition thermally an aircrewman during that stage of an ejection that a man is attached to his seat, but the triple connector may readily be arranged not just as a normal connector/interchange heat exchanger for the thermal conditioning means of the present invention but in addition to allow or prevent as required during the said man/seat attachment stage of an ejection, normalisation of the pressure within the thermal conditioning garment to restrict the flow of body heat to the sea for example.
Of course the first heat exchanger need not be a garment and need not be for personal thermal conditioning, and as a garment need not be exclusively for aircrew use, certainly not only those in ejector seats. An advantage of apparatus such as that described with reference to figures 4 or 5 is that it does not require an external power source, and can be portable to a place of work so as to permit an operative to work in a hot environment for periods larger than he would otherwise have been able.
The assembly shewn in figure 6 comprises a latent heat storage (glycerol) reservoir 70 incorporating a working fluid heat exchanger 71, a cabin air inlet heat exchanger 72, a pump 73, and control means including a mixing valve 74, a thermostat 75, and a 2-way valve 76. A coupling 77 connects the apparatus with a garment 78 in heat pipe form as worn by an aircrewman in an aircraft cockpit. The mixing valve 74 includes a pressure relief valve, not shown.
The cabin air inlet heat exchanger 72 comprises a coiled liquid duct 80 having fins 81 and sited in an air inlet duct 82.
A description of the liquid circuit of the apparatus shown in figure 6 now follows. In the basic circuit the output of the pump 73 is connected via the 2-way valve 76, the tube 80 in the air inlet heat exchanger 72, the reservoir heat exchanger 71, the thermostat 75, the mixing valve 74, the coupling 77, the garment 78 and back to the coupling, the valve 74 and the pump. The second output of the valve 76 is connected to the input of the heat exchanger 71. The output of the pump 73 is also connected to the thermostat 75 and to the valve 74, and the pressure relief valve in the mixing valve 74 is arranged to permit return flow to the pump when the garment 78 is blocked.
The working fluid of the apparatus is a water glycerol mixture having a melting point of about 16°C; that of glycerol is about 20°C. Thus the garment can be supplied to its wearer with its working fluid pre-frozen to about 10⁰C₇ and this can supply cooling to him for a preliminary standby period prior to flight.
During taxi and flight, with the pump 73 in operation, working fluid is pumped via the valve 76 through the air inlet heat exchanger 72, then through the heat exchanger 71 where it cools the fluid in the reservoir 70 all the while the inlet air temperature is sensibly lower than that of the reservoir fluid (it usually is in flight). From there it passes via the thermostat to the mixing valve 74. If the fluid in the garment has melted the mixing valve will pass fluid through it, but due to operation of the thermostat 75 will mix fluid from the heat exchanger 71 with fluid from the pump output in an effort to pass fluid to the garment at a temperature no greater than 25^oC.
If after a flight the aircrewman has to stay with the aircraft for a further standby and environmental air is warm, the valve 76 will cause circulating fluid to by-pass the air inlet heat exchanger 72 and be cooled in the heat exchanger 71 by frozen glycerol in the reservoir 70.
The heat sink shown in figure 7 comprises a cylindrical chassis 90 housing the components of a vapour compression unit, viz a compressor 91, a condenser 92, an expansion valve 93 and an evaporator 94. It also includes a brushless motor 95, a fan 96, insulation means 97 for thermally insulating the evaporator from the condenser and a liquid pump 98.
The condenser 92 is in the form of a coil of finned tubing and surrounds the insulant 97 and the evaporator 94. The fan 96, for which the chassis acts as a shroud, is arranged for causing air to flow past the condenser fins.
The motor 95 is arranged to drive the fan 96, the compressor 91, and the pump 98, the compressor and the motor being mounted in and spaced from the chassis 90 by means of mounting air guide vanes 99.
The expansion valve 93 comprises a coiled capillary tube. The vapour cycle circuit connections are not illustrated, and are partly outside the chassis. The order of the circuit is as shown in figure 8, compressor, evaporator, expansion valve, condenser, compressor.
The heat pipe assembly illustrated in figure 8 comprises a vapour compression cycle heat sink 100 which is as shown in figure 7 but without a pump 98 therein, a heat exchanger 101 located in the cabin air inlet, a pump 102, a control valve 103 with an associated inlet selector 104, and a coupling 105 associated with a garment 106 in heat pipe form.
The heat exchanger 101 comprises a coiled finned tube located in the air inlet. The heat sink 100, with the valve 103 and the pump 102 are located in a ventilated bay in the vicinity of the cockpit.
The connections of the circuit are as follows. The output of the pump 102 is connected to the control valve 103 which now has three outlets, one connected to the input of the heat exchanger 101, one to the input of the evaporator 94, and one to the input of the coupling 105. The output of the heat exchanger 101 is also connected to the input of the evaporator 94, and the output of the evaporator 94 is also connected to the input of the coupling 105.
The operation of the assembly is as follows. On occasions such as during standby, that is when the pilot is seated within his aircraft on the ground and not receiving cool air via the cabin air inlet, the heat exchanger 101 thereof is bypassed and cooling of the liquid in the garment circuit obtained from the unit 100. Modification of the temperature of the garment liquid circuit is obtained by allowing an amount of liquid returning from the garment to by-pass the unit 100.
During flight when cool air is entering the cockpit via the cabin air inlet the heat exchanger 101 no longer assumes responsibility for cooling the liquid and the unit 100 is switched off.

Claims

1. A heat pipe assembly comprising a heat receiver element of heat pipe form, that is having an encased reticulated structure including wicking and void continua, a heat sink element, a liquid pump, a vapour duct connecting the heat receiver element and the heat sink element, and a liquid duct connecting the heat sink element with the heat receiver element via the liquid pump.

2. A heat pipe assembly as claimed in claim 1 and wherein the heat receiver element is in sheet heat pipe form.

3. A heat pipe assembly as claimed in claim 1 and wherein the heat receiver element is conformable.

4. A heat pipe assembly as claimed in claim 2 and wherein the heat receiver element is in conformable garment form.

5. A heat pipe assembly as claimed in claim 1 and wherein the heat receiver element incorporates liquid distribution means comprising an elongate perforate tube contacting the wicking throughout its perforate length.

6. A heat pipe assembly as claimed in claim 5 and wherein the elongate perforate tube is a tube with discrete perforations throughout its working length.

7. A heat pipe assembly as claimed in claim 6 and wherein strands of wicking are wrapped around the tube and extend through the perforation.

8. A heat pipe assembly as claimed in claim 6 and wherein the perforation is realised in a slit.

9. A heat pipe assembly as claimed in claim 8 and wherein the wicking is retained in the slit by tube resilience.

10. A heat pipe assembly as claimed in claim 5 and wherein the perforation is disposed for facing upwards.

11. A heat pipe assembly as claimed in claim 5 and wherein the tube is formed of resilient, flexible plastics material.

12. A heat pipe assembly as claimed in claim 5 having an evacuation pump.

13. A heat pipe assembly as claimed in claim 1 and wherein the heat sink comprises thermoelectric elements.

14. A heat pipe assembly as claimed in claim 1 and wherein the heat sink comprises

a reservoir of liquid having a melting point between 15⁰C and 30°C;

a reservoir heat exchanger in the reservoir and connected to the heat pipe;

an air heat exchanger, and

control means,

the assembly being arranged so that when the cabin air heat exchanger is operational liquid-therefrom cools both the liquid in the reservoir and effects cooling by the heat pipe and in periods when the air heat exchanger is non-operational heat pipe cooling is effected from the reservoir heat exchanger.

15. A heat pipe assembly as claimed in claim 1 and wherein the heat sink is arranged to operate on a vapour compression cycle and comprises

a cylindrical chassis

a condenser in coiled tube form contained in the chassis

a fan shrouded by said chassis and arranged for blowing air over the condenser

a compressor

an evaporator, and

an expansion valve.

16. A heat pipe assembly as claimed in claim 15 and wherein the expansion valve is a coiled capillary tube.

17. A heat pipe assembly as claimed in claim 15 and wherein the heat sink incorporates a brushless motor arranged to drive the compressor via a magnetic link.

18. A heat pipe assembly as claimed in claim 1 and wherein the heat. sink comprises a rechargeable supply of cooled liquid and a distinct sink for vapour.

19. A heat pipe assembly as claimed in claim 18 and wherein the vapour sink incorporates molecular sieve material.

20. A heat pipe assembly as claimed in claim 18 and wherein the vapour sink incorporates zeolite.

21. A heat pipe assembly as claimed in claim 1 and wherein the heat sink is substantially that described and claimed in UK Patent Specification 1376604.