Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
  • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
  • F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
  • F28D15/043—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure forming loops, e.g. capillary pumped loops

Definitions

• the present invention relates to a capillary pumped heat transport loop comprising at least one evaporator, at least one condenser and a tank arranged to store a heat-transfer fluid, said evaporator comprising an outlet connected by a vapor line to an inlet of the condenser, an outlet of the condenser being connected to the reservoir, said evaporator comprising an evaporator body and being provided with a porous material arranged to produce a capillary pumping pressure inside the loop and exert it on said heat transfer fluid from the surface of the material in contact with the evaporator body, said evaporator also being arranged to evaporate the heat transfer fluid by heat absorption.
• Such a capillary pumping loop is known from the publication "Computer Model of satellite Thermal Control System Using a controlled capillary pumped loop" by KA Goncharov, E. Yu Kotlyarov and GP Serov published in SAE Technical Paper Series No. 932306.
• Such loops are for example used in satellites and allow the thermal transfer of a heat source, for example electronic equipment, to the condenser where the removed heat is dissipated.
• the loop is of course not limited to weightless applications because it also works in the presence of gravity.
• the porous material present in the evaporator has an axial channel which makes it possible to supply the porous material with heat-transfer liquid. The liquid saturation of the porous material allows the creation of capillary pressure.
• the loop configuration allows circulation of the evaporator to the condenser and then to the tank, which in turn supplies the evaporator with heat transfer liquid.
• the capillary material of the evaporator is thus supplied with heat transfer liquid and is therefore constantly saturated with liquid. In this way the capillary material makes it possible to develop capillary pumping pressures capable of compensating for the pressure drops in the loop.
• the capillary pressure obtained with the currently known capillary materials makes it possible to pump the heat transfer fluid from the condenser to the evaporator even over a height of several meters under a gravity field.
• the heat transfer fluid completely fills the liquid line, the steam line and the condenser, and partially the evaporator assembly.
• the liquid from the steam line and the condenser will be pushed by the steam generated by the evaporator to the tank.
• This thrust comes from a pressure difference between the evaporator and the tank caused by the external heat flow applied to the evaporator, which flow increases the temperature of the evaporator first.
• the volume of liquid vis-à-vis the volume of vapor contained by the tank therefore depends on the volume of the vapor vis-à-vis the volume of liquid contained in the vapor line and the condenser.
• This phase change and capillary pumping loop is called "auto-start” because it does not require any associated device or special start-up procedure. It is indeed the heat flow applied to the evaporator which causes the start of the loop.
• a disadvantage of the known loop is that the evaporator and the tank are connected to form an indivisible whole.
• the tank temperature is mainly dictated by the parasitic heat flux flowing from the evaporator to the tank.
• the pressure in the tank depends on the temperature and thus the pressure and the vaporization and condensation temperature at which heat transport occurs in the loop is equal to the tank temperature.
• the temperature of the heat source is thus not sufficiently regulated, since it depends on the thermal balance of said parasitic flow and on the heat losses from the tank to the atmosphere.
• the solution applied by the state of the art lies in active thermal control of the tank via a Peltier cell which links the tank to the evaporator or to other related devices which make it possible to regulate the temperature of the tank and thus the temperature of the entire heat transport loop.
• This solution however makes the loop more complex.
• the temperature of the tank equals that of the surface of the evaporator and there is no circulation of vapor.
• the invention aims to remedy these drawbacks.
• a capillary pumped heat transport loop is characterized in that the reservoir and the evaporator are thermally isolated from one another and connected together by a pipe comprising a first part. formed by a capillary connection arranged to pump the heat transfer fluid from the reservoir to the porous material and a second portion arranged to evacuate bubbles of gas and / or steam formed in the evaporator towards the reservoir, which reservoir being arranged for be kept at a temperature lower than that of the evaporator.
• the isola- The thermal effect of the tank and the evaporator has the consequence of thermally decoupling them and thus making it possible to condition the tank at a temperature independent of that of the evaporator.
• the direct parasitic heat flow from the evaporator to the tank is thus stopped.
• the temperature of the tank is thus mainly given by the temperature of the liquid coming from the condenser and by the temperature of the environment. These two temperatures are also stable and low, the tank and consequently the evaporator (s) are kept at a minimum temperature. This result is very widely desired because it allows a heat exchange with a minimum temperature difference between the heat source and the condenser.
• the capillary connection which brings the heat transfer liquid from the reservoir to the evaporator ensures that the porous material of the evaporator is always sufficiently supplied with heat transfer liquid and therefore that the capillary pumping pressure can be developed to maintain circulation in the loop.
• the second part makes it possible to evacuate towards the reservoir the vapor and the non-condensable gas formed by the parasitic heat flow which crosses the capillary material of the evaporator. Since the tank is at a temperature lower than that of the evaporator, it is the difference in temperature between the tank and the evaporator which will ensure the circulation of gas and steam in said second part towards the tank.
• a first preferred embodiment of a capillary pumping heat transport loop according to the invention is characterized in that in said pipe which connects the evaporator to the reservoir, the first part comprises at least a first channel and the second part of at least a second channel, the diameter of the first channel being less than that of the second channel. Thanks to this configuration, any gas or vapor in the second part does not hinder the circulation of the heat transfer fluid from the reservoir to the capil ⁇ lar material of the evaporator, because the smaller diameter of the first channel allows greater pumping pressure.
• a second preferred embodiment of a capillary pumped heat transport loop according to the invention is characterized in that the pipe which connects the evaporator to the reservoir extends in the central axis of the evaporator, said porous material of the evaporator being coaxially arranged relative to the pipe. This ensures an adequate supply of the capillary material with heat transfer liquid and allows the evaporator to operate on all of its external envelope.
• a third preferred embodiment of a loop according to the invention is characterized in that the reservoir is thermally connected to at least one of the evaporators by a thermoelectric cell with Peltier effect arranged to regulate the temperature of the reservoir.
• This configuration makes it possible to vary the temperature difference between the tank and the evaporator, while keeping the temperature of the tank lower than that of the loop, and thus to influence the circulation in the loop.
• This configuration also allows active control of the tank temperature and consequently of the vaporization and condensation temperature of the loop.
• This embodiment has the advantage of using an evaporator as the cold source of the tank rather than an additional heat transport device.
• it includes an auxiliary evaporator connected to a line of fluid leaving the condenser.
• This configuration has the advantage of avoiding a capillary link between the auxiliary evaporator and the tank.
• the performance of the capillary link no longer limits that of the auxiliary evaporators.
• the distances between the evaporator and the tank are no longer limited.
• the return line of the condensed fluid from the condenser thus ensures the circulation of steam and non-condensable gas. These will be transported to the tank using existing circulation in the loop.
• said auxiliary evaporator is connected to the line of fluid by a capillary connection.
• the auxiliary evaporator thus operates in the same way in relation to the fluid line as that in which the evaporator operates in relation to the reservoir.
• the end of the capillary connection in contact with the fluid line is thermally connected to the auxiliary evaporator by a thermoelectric cell with Peltier effect arranged to cool the line with respect to the auxiliary evaporator. It is therefore possible to regulate the temperature of the fluid line.
• Figure 1 schematically illustrates a first embodiment of a loop according to the invention
• FIG. 2 illustrates a longitudinal section of the surface of the capillary material
• FIG. 3 a respectively b and c shows a view in longitudinal cross section respectively of the capillary connection which connects the evaporator to the tank;
• FIG. 4 schematically illustrates the operation of the evaporator
• Figures 5 and 6 show a pressure diagram respectively temperature
• FIG. 7 schematically illustrates a second embodiment of a loop according to the invention
• FIG. 8 schematically illustrates a loop according to the invention provided with a Peltier cell.
• FIG. 1 schematically illustrates a first embodiment of a capillary pumped heat transport loop.
• This loop comprises a reservoir 1 in which a heat transfer liquid is stored.
• the tank 1 is thermally isolated from an evaporator 2. This keeps the tank at a temperature lower than that of the evaporator as will be described below.
• the connection between the tank 1 and the evaporator 2 is provided by a pipe 3 which carries a first part 18 formed by a capillary connection and a second part 4 formed by an axial channel.
• the evaporator 2 comprises a porous capillary material 5 arranged to produce a capillary pressure within the evaporator.
• An outlet of the evaporator is connected by a vapor line 6 to an inlet of a condenser 9.
• An outlet of the condenser is connected by a line 10 for the fluid which returns the fluid in the form of liquid condensed in the condenser towards the tank thus closing the loop.
• the fluid line can also be directly connected to the evaporator.
• the loop can contain one or more evaporators.
• the loop includes a second evaporator 8 connected by a pipe 7 to an outlet from the tank 1.
• the second evaporator 8 is also thermally dissociated from the tank.
• the evaporator 2 comprises an evaporator body 13 which forms the external envelope of this last.
• the evaporator body is in contact with the capillary material 5 which is arranged coaxially with respect to the central axis of the evaporator.
• the capillary material 5 contains heat transfer liquid from the reservoir.
• the capillary material 5 is provided with vapor collecting grooves 12 at the interface between this material and the evaporator body 13.
• the grooves 12 are in contact with the vapor line 6 to allow the evacuation of the vapor formed in the evaporator towards the vapor line.
• the heat Qe evaporates the heat transfer liquid contained in the capillary material 5.
• the vapor 15 thus produced will be released towards the grooves 12 steam collectors to then enter the vapor line 6.
• This liquid / vapor interface has a radius of curvature. The value of the radius of curvature of the liquid meniscus contained between the particles 16 of solid material of the porous material gives rise by the surface tension of the heat-transfer liquid to the capillary pressure P E - P D.
• FIG. 5 represents a pressure diagram.
• This capillary pumping pressure is exerted on the heat transfer fluid.
• the liquid is under vacuum in the porous material at the interface 17, which causes suction of the liquid upstream of the porous material.
• the vapor is overpressure relative to the liquid and will therefore direct the latter from the interface 17 towards the vapor line.
• capillary pressure a circulation of the heat transfer fluid is produced in the capillary material and in the whole of the loop. This pressure is such that it can overcome all the pressure drops in the loop as long as the capillary material remains supplied with liquid.
• the reservoir is connected to the evaporator by the pipe 3, a sectional view of which is illustrated in FIG. 3c.
• Figures 3 a + b illustrating a sectional view through the evaporator.
• the pipe comprises a first part 18 formed by a capillary connection whose structure is comparable to that of the capillary material 5 present in the evaporator but whose permeability and pore size of the capillary material is greater than that of the porous material 5
• the porous material 5 and the capillary material are preferably arranged coaxially with respect to the channel 4.
• the capillary material 18 joins the porous material 5 of the evaporator.
• the heat transfer fluid contained in the réser ⁇ see 1 circulates by capillarity in the capillary connection 18 to reach the porous material 5 of the evaporator.
• the continuity between the capillary connection and the porous material ensures a supply of heat transfer liquid over the entire length of the connection.
• the first part of the pipe 3 has at least one first channel formed between the particles of solid material of the capillary material 18.
• the second part 4 has at least one second channel. The diameter dl of the first channel being smaller than that of the second channel d2 to allow greater capillary pressure in the first channel and therefore ensure the supply of liquid to the evaporator.
• the tank 1 is thermally isolated from the evaporator does not prevent the circulation of the fluid towards the evaporator. Indeed, it is the capillary pressure produced by the porous material 5 supplied with liquid by the material 18 which ensures circulation in the loop.
• the insulation of the tank with respect to the evaporator makes it possible to maintain the tank at a temperature T A lower than that of T F of the evaporator as illustrated in FIG. 6.
• the tank being in connection with the condenser it receives the condensed fluid which is at a temperature T ⁇ when it leaves the condenser.
• T ⁇ when it leaves the condenser.
• the lower temperature of the tank relative to the evaporator also allows a large amount of non-condensable gas to be stored in the tank.
• a large quantity of non-condensable gas produced after several years of operation of the loop generates a significant partial pressure.
• the increase in partial pressure must be compensated by a decrease in the partial pressure of the heat transfer fluid. The latter can be obtained by a decrease in the temperature of the reservoir relative to that of the evaporator.
• the external heat flow Q e will not only cause the evaporation of the heat transfer liquid at the liquid / vapor interface 17 but also a production of vapor at the level of the pipe 4 at the other interface between the first and the second part of the pipe up to its extension in the evaporator.
• the heat flow Q E also causes a parasitic heat flow Q p which passes through the capillary material 5 of the evaporator and evaporates the heat transfer liquid present in the capillary connection 18 connecting the tank and the evaporator and more particularly in the evaporator. This is schematically illustrated in FIG. 4.
• the presence of a capillary material 18 in the pipe 3 within the evaporator will cause a capillary pressure P c - P B (FIG. 5) on the vapor produced by Q p in l 'evaporator.
• the temperature T A of the tank being lower than that T c at the level of the second part of the pipe a heat pipe will form between the evaporator and the tank.
• the capillary link 18 will operate as a heat pipe if T c reaches a temperature equal to or greater than the saturation temperature. Otherwise the channel 4 of the evaporator is filled with liquid and there is no risk of drying of the capillary material. If non-condensable gas is dissolved in the fluid conveyed by the capillary link, bubbles of non-condensable gases emerge from the liquid by the contribution of parasitic heat Q p .
• This difference in saturation pressure will cause the vapor and non-condensable gas to be transported from the evaporator to the tank via the channel 4 formed by the second part of the pipe 3.
• the vapor condenses on contact with the cooler fluid present in the reservoir 1.
• the non-condensable gas is transported to the reservoir by the vapor.
• the gas bubbles then escape to the top of the tank left free by the liquid.
• the drying out of the capillary link is caused both by the parasitic heat flow Q p and the flow Q E - Q P.
• This drying gives rise to capillary pumping pressures which cause a depression of the liquid in the capillary link 18 and an overpressure of the gas and the vapor in the channel 4 relative to the reservoir 1 (P B ⁇ P A ).
• This pressure difference then causes pumping by the capillary link 18 of the fluid from the reservoir to the evaporator. It is therefore thanks to the fact that the temperature of the tank is lower than that of the evaporator that the non-condensable gas and the vapor produced by Q p is transported to the tank.
• the pressure P B at the inlet of the evaporator must be less than the pressure P E at the outlet of the evaporator. It is the porous material 5 which makes it possible to support this pressure difference thanks to the capillary pressure which it can generate.
• the pressure P A at the tank is dictated by the temperature T A and the pressure P E at the evaporator is dictated by its temperature T E according to the saturation curve of the heat transfer fluid, it is thanks to the fact that the temperature of the tank is lower than that of the evaporator that the circulation of the fluid in the loop can be realized.
• the flow of gas and vapor in the counter-current channel 4 does not prevent the circulation of the fluid towards the evaporator due to the presence of the capillary link 18.
• the configuration of the capillary link 18 is preferably that described in Belgian patent n ° 903187. This configuration has the advantage of releasing gas bubbles towards the center of the channel.
• T ⁇ - T ⁇ temperature increase in the fluid line to the reservoir P x - P A : pressure drop in the fluid line
• Point J in Figure 6 represents a situation where the fluid has been further cooled before entering the tank.
• an auxiliary evaporator is connected to the fluid line which connects the condenser 9 to the reservoir 1.
• the auxiliary evaporator 21 can be connected to the fluid line by a capillary link. It is also possible to mount the auxiliary evaporator 21 on the fluid line 10 so that the fluid passes through the auxiliary evaporator.
• FIG. 8 shows a preferred example of a capillary pumped heat transport loop according to the invention.
• the configuration of the evaporator and reservoir assembly compared with FIG. 1 is more particularly dedicated to applications of heat transport in weightlessness for spacecraft.
• the evaporator assembly comprises, according to the example, three evaporators 2, 31 and 32 connected in parallel.
• the capillary links 3 guarantee the supply of coolant from the reservoir 1 to the evaporators.
• the supply of coolant to the evaporator B located slightly above the tank is carried out thanks to the capillary pumping pressure developed by the capillary link 3.
• the heat flow q e produces a flow of steam which is conveyed by the steam line 6 to the condensers 9 and 30.
• the heat flow q e absorbed by the evaporators by vaporization of the heat transfer liquid is transferred to the condensers by condensation of the steam flow.
• the reservoir 1 is thermally controlled by a cell thermoelectric (Peltier effect) 33.
• a sole 34 connecting the Peltier cell to the evaporator 2 allows the supply or extraction of thermal energy 35 from the tank to the evaporator. It is the Peltier cell 33 which realizes the temperature difference between the tank 1 and the soleplate 34 to direct the heat energy in the desired direction.
• the tank temperature control is thus achieved.
• the pressure in the tank is a function of the temperature of the tank according to the saturation curve of the heat transfer fluid and consequently, the pressure and the temperature of vaporization and of condensation in the loop is identical to that of the tank.
• the reservoir 1 contains a capillary structure 37 in order to manage in weightlessness the location of the heat-transfer liquid vis-à-vis the vapor or non-condensable gases contained by the reservoir.
• non-condensable gas If non-condensable gas is generated in the loop, it will be collected by the reservoir 1. Due to the partial pressure of non-condensable gas in the reservoir, the temperature of the latter must be maintained at a temperature below that of vaporization in evaporators in order to maintain a pressure equality between the tank and the rest of the loop.
• thermoelectric cell with Peltier effect can also be applied to the auxiliary evaporator in order to cool the fluid line relative to the auxiliary evaporator.
• the end of the capillary connection connecting the auxiliary evaporator to the fluid line is connected by the cell to the auxiliary evaporator.
• the cooling of the fluid line thus obtained makes it possible to condense the vapor produced by the heat flow supplied to the auxiliary evaporator and to limit the size of the bubbles of non-condensable gases. Too large an increase in the size of the gas bubbles compared to the speed of circulation of the fluid towards the tank could cause the draining of the line of fluid to the condenser and therefore cut off the liquid supply to the evaporator.

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• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)

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• 1995
  • 1995-06-14 BE BE9500530A patent/BE1009410A3/fr not_active IP Right Cessation
• 1996
  • 1996-06-13 AU AU61169/96A patent/AU6116996A/en not_active Abandoned
  • 1996-06-13 WO PCT/BE1996/000061 patent/WO1997000416A1/fr not_active Ceased
  • 1996-06-13 DE DE69606296T patent/DE69606296T2/de not_active Revoked
  • 1996-06-13 EP EP96918533A patent/EP0832411B1/de not_active Revoked
• 1998
  • 1998-01-28 US US08973981 patent/US5944092C1/en not_active Expired - Lifetime

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