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 evaporator for a two-phase energy transfer loop between a hot source and a cold source, of the type which comprises a) an enclosure made of a porous material having an inlet for a heat-transfer fluid in the liquid state. b) an envelope in which said enclosure is placed to define, around the latter a chamber for collecting said fluid in the vapor state, said envelope having an outlet through which the vapor collected by said chamber is evacuated.
• Such an evaporator is known in particular from French patent application No. 94 09459 filed on July 29, 1994 by the applicant.
• Such evaporators are part of two-phase loops such as that shown in Figure 1 of the accompanying drawing, which is used to transfer thermal energy from a zone A called “hot source”, to a zone B, at lower temperature, called “cold source”.
• the loop takes the form of a closed circuit in which circulates a heat transfer fluid which can be, according to the temperatures of use, water, ammonia, a "Freon", etc.
• This circuit includes evaporators "capillaries” 1, l ', .... connected in parallel, condensers 2, also connected in parallel (or in series-parallel), a vapor circulation duct 3 and a liquid circulation duct 4.
• the meaning fluid circulation is indicated by the arrows 5.
• An isolator 6 can be placed at the inlet of each evaporator, to prevent an accidental return of vapor in the duct 4.
• a sub-cooler 7 is placed on the duct 4 to condense steam which, accidentally, would not have been completely condensed at the outlet of all the condensers 2 and to lower the temperature so as to ensure security with respect to the risk of locally reaching the saturation temperature and thus generating vapor bubbles upstream of the evaporators.
• the operating temperature of the loop is controlled by a two-phase pressurizer tank 8 mounted on the duct 4. This tank is thermally controlled (by means not shown) so as to ensure control of the vaporization temperature.
• the hot source can be constituted by equipment releasing heat and mounted in a spacecraft, or installed on the ground, equipment the loop of which maintains the temperature at a value compatible with proper operation of this equipment.
• the maximum power that can be transported is conditioned by the maximum pressure rise that the capillary evaporators can provide and by the sum of the pressure drops in the circuit for the maximum power considered.
• ammonia pressure increases of the order of 5000 Pa can be achieved.
• Figures 2 and 3 show an evaporator 1 capable of being used in the loop of Figure 1. It is described in the document entitled "Capillary pumped loop technology development", authors: J. Kroliczek, R. Me Intosh, presented during from the ICES conference held at LONG BEACH (California) in 1987. Evaporators from this type are marketed by the company OAO in the United States of America.
• L 1 evaporator 1 comprises a metallic tubular casing 9 which is a good heat conductor, having an inlet 10 at one end and an outlet 11 at the opposite end.
• a cylinder enclosure 12 with a wall made of porous material is held by spacers 13 (see FIG. 3) coaxial with the envelope 9.
• the porous material called “capillary wick”, can be made of any material having pores of suitable dimensions and substantially homogeneous, for example metallic or plastic sintered materials (polyethylene) or even ceramics.
• the space 14 inside the enclosure 12 is filled with the heat-transfer fluid in the liquid state while the annular chamber 15 collects the vapor of this liquid which forms in this chamber under the effect of the heat given off by the hot source A.
• the pressure of the vapor is higher than the pressure of the liquid which allows the circulation of the heat-transfer fluid in the loop and the evacuation of the heat transported to the cold source B.
• the heat transfer fluid which circulates in the loop is almost never pure and often contains noncondensable gases in the loop, such as hydrogen.
• This gas can come from a decomposition of the heat transfer fluid, when the latter consists of ammonia, for example. It can also result from chemical reactions between this ammonia and parts metallic buckle made of aluminum, for example. In microgravity, this noncondensable gas can collect in a pocket 16 at the bottom of the enclosure 12, as shown in FIG. 2.
• the space 14 inside this enclosure 12 can also accommodate bubbles 17 of non-condensed vapor of the heat transfer fluid . This can result in a local stop of the circulation of this fluid and therefore a thermal runaway of the loop.
• FIG. 4 schematically represents an evaporator of another type, described in the document entitled “Method of increase the evaporation reliability for loop heat pipes and capillary puped loops", authors: E.Yu. Kotliarov, GP Serov, presented at the ICES conference held in Colorado Springs, USA, in 1994. Evaporators of this type are marketed by Lavotchkin of the Russian Federation.
• the evaporator of FIG. 4 differs from that of FIGS. 2 and 3 in that it incorporates a buffer tank 19 at the inlet of the evaporator proper, which comprises a casing 9 and an enclosure 12 made of material porous similar to those of the evaporator of Figure 2.
• the evaporator further comprises a tube 20 with a solid wall which passes axially through the pressurizing tank 19 and the enclosure 12, this tube opening near the bottom of this enclosure.
• FIG. 5 schematically represents an evaporator of yet another type, described in the document "Test results of reliable and very high capillary multi- evaporation condensers loops", authors: S. Van Ost, M. Dubois and G. Beckaert, presented at the ICES conference held in San Diego, California, USA, in 1995.
• the Belgian company SABCA markets evaporators of this type.
• the evaporator is placed. in one of the branches of a circuit which has one evaporator per branch, the same pressurizer tank 8 supplying all these branches.
• the evaporator comprises, like the previous ones, a casing 9 and an enclosure with a porous wall 12. Between the reservoir 8 and the evaporator, the connection is made by a tubular conduit internally lined with a "capillary link" 21 constituted by a tube made of a metallic fabric.
• the heat transfer liquid which arrives from the condenser 2 passes through the pressurizer tank 8 and fills the entire duct 3 as well as the space inside the enclosure 12.
• the incondensable gas s' In the presence of incondensable gas in the loop, but without generation of vapor in the core of the evaporator, situation characteristic of an operation with high thermal power (typically greater than 50 Watt for ammonia), the incondensable gas s' accumulates in the enclosure 12 of the evaporator inside the capillary link 21 only. The porous material of the enclosure 12 then always remains supplied with heat transfer liquid, which ensures the operation of the evaporator.
• the vapor which forms in this enclosure can, if its generating pressure is sufficient, return to the pressurizing tank 8 as shown schematically in Figure 5, and entrain the incondensable gas.
• the liquid As for the liquid, it circulates around the periphery of the capillary link 21 and allows the porous material of the enclosure to be supplied, which ensures the operation of the evaporator.
• the capillary link 21 present in the conduits 3 for supplying the evaporators makes them rigid and bulky (diameter of the order of 10 mm), drawbacks which can prove to be prohibitive when the loop must be placed in a limited space and complex shape, as is often the case in space vehicles, for example.
• the present invention therefore aims to achieve an evaporator for two-phase loop with capillary pumping, which is tolerant of the presence of incondensable gas or vapor inside its porous enclosure.
• the present invention also aims to produce such an evaporator suitable for integrating into a two-phase loop containing a plurality of such evaporators mounted in parallel, the geometry of this loop can be adapted to installation in a reduced space and / or complex shape.
• an evaporator of the type described in the preamble to the present description remarkable in that it comprises a tube which develops throughout the interior space of the enclosure with a porous wall, from one end of the tube constituting the inlet of the enclosure in heat-transfer liquid, said tube being pierced over its entire length with holes for injecting the liquid coolant in the wall of the enclosure.
• this tube makes it possible, in all circumstances, to supply the entire enclosure with a porous wall with heat transfer liquid, which ensures the necessary generation of vapor by the evaporator, even in presence of incondensable or uncondensed gas or vapor in said enclosure.
• FIG. 1 is a diagrammatic representation of a two-phase energy transfer loop comprising capillary evaporators, described in the preamble to this description
• FIGS. 2 to 5 represent capillary evaporators of the prior art, also described in the preamble to this description,
• FIG. 6 is a schematic representation of a two-phase loop comprising at least one capillary evaporator (in axial section) according to the present invention
• Figures 7 to 9 are schematic representations of one capillary evaporator according to the invention, similar to that of FIG. 6 and useful for the description of its operation.
• FIG. 6 of the appended drawing in which the essential parts of the two-phase loop of FIG. 1 are found, namely, in addition to one or more capillary evaporators 1,1 ', 1 ".... according to invention, conduits 3 of gas and 4 of vapor, a condenser 2 and a pressurizing tank 8.
• the evaporator according to the invention comprises, like the preceding ones, a tubular casing 9 and an enclosure with a porous wall 12 held in the casing 9 away from this casing by spacers such as the spacers 13 shown in FIG. 3 , or by grooves formed on the inner face of the casing 9, so as to define between the casing and the enclosure a chamber 15 for collecting the vapor formed in one evaporator.
• the evaporator also includes an inlet 10 for the coolant in the liquid state and an outlet 11 for the vapor of this fluid.
• the evaporator according to the invention, it comprises (see FIG. 16) a tube 22, for example of helical shape, developing axially throughout the interior space of the enclosure 12, to the bottom of it.
• the tube 22 is plugged at its end 22 'close to this bottom but it is pierced over its entire length with holes 23, for example regularly spaced.
• the helical tube 22 adjusts substantially to the inside diameter of the enclosure 12 so as to closely follow the porous wall of this enclosure.
• the holes 23 are drilled in front of this wall, to inject heat-transfer liquid into the space 14 inside the enclosure 12, by continuously spraying this wall, as will be seen below.
• the unplugged end 24 of the tube 22 passes through, and is carried by, a partition 25 of a sealed material mounted transversely in a chamber 26 interposed, according to the invention, between the inlet 10 of the evaporator and the assembly formed by the envelope 9 and the enclosure 12.
• the partition 25 divides the chamber 26 into a first compartment (26 x , 26 2 ), see FIG. 7, and a second compartment 26 3 , one of which (26 ⁇ , 26 ? ) contains a partition 27 made of a porous material similar to that constituting the wall of the enclosure 12.
• the partition 27 is transverse to the axis X of the evaporator, and it is therefore substantially parallel to the watertight partition 26. It divides the first compartment (261., 26 2 ) into two sub-compartments 261 and 26 2 .
• means 28 for cooling the chamber 26 are mounted thereon.
• these means 28 are used to condense heat-transfer fluid in the vapor state present, in certain types of operation of the evaporator, in chamber 26.
• these means 28 can be constituted by a Peltier effect cold source.
• a heat sink 29 can be placed between the means 28 and the metal casing 9.
• the evaporator according to the invention then operates as follows. In the absence of noncondensable gas and vapor in the enclosure or at the inlet of the evaporator, an ideal situation illustrated in FIG. 6, the heat transfer liquid which returns from the condenser 2 passes through the porous partition 27 and is then forced to borrow the perforated tube 22 which plunges into the heart of the evaporator. The liquid spurts through the holes 23 of the tube by injecting heat transfer liquid into the porous wall of the enclosure which faces these holes. The enclosure 12 of the evaporator is full of liquid and its porous wall is always supplied with liquid. The condensing means 28 are then useless and therefore inactive. The evaporator is operating normally.
• C ' is a situation encountered in high power operation of one evaporator (typically greater than 50 W for ammonia).
• the bubbles 30 of noncondensable gas are stopped by the porous partition 27 at the inlet of the evaporator, as shown in the figure.
• a certain quantity of noncondensable gas can accumulate in a part 31 of the enclosure 12 by desorption of the gas dissolved in the liquid.
• the porous wall of the enclosure 12 is always wetted by liquid even in this part 31 of the enclosure where the noncondensable gas has accumulated.
• the cold source 28 can remain inactive and the performance of the evaporator remains nominal.
• FIG. 8 to explain the operation of the evaporator according to the invention, in the presence of bubbles 30 of incondensable gas in the loop and with the formation of bubbles 32 of vapor in the enclosure 12.
• This is a situation encountered in operation at low thermal power (typically less than 50 W for ammonia).
• the porous partition 27 stops both the noncondensable gas 30 and the vapor 32 which enter the evaporator under the effect of the circulation of the heat transfer fluid.
• a certain quantity of noncondensable gas can accumulate at 31 in the enclosure 12 as in the previous case and this enclosure also contains, by hypothesis, steam 32 which is formed there, in small quantity in this hypothesis.
• the porous wall of the enclosure 12 remains wetted by heat transfer liquid, even in the part 31 where the noncondensable gas and the vapor have accumulated.
• the cold source 28 is activated according to the invention. Peltier to condense this vapor. Its cooling power must obviously be compatible with the power (very low, however) necessary for the condensation of the total mass flow rate of steam generated in the enclosure 12 of the evaporator and arriving at the inlet thereof. For example, the typical cooling power that must be installed for an ammonia evaporator is of the order of a few watts.
• FIG. 9 schematically illustrates an extreme operation of the evaporator according to the invention, in which the enclosure 12 is filled with vapor and noncondensable gas, only the perforated tube 22 remaining filled with coolant for watering the the internal face of the porous wall of this enclosure 12, so as to ensure the operation of one evaporator.
• the power delivered by the cold source 28 is exactly equal to that which is necessary for the condensation of all the uncondensed vapor arriving against the porous partition 27.
• This evaporator is also robust screw -with respect to the generation of noncondensable gas and vapor in the porous wall enclosure of the evaporator, unlike the evaporator of FIGS. 2 and 3.
• the connection of its input to a two-phase loop requires a simple flexible conduit and not rigid, unlike that of the evaporator of the prior art shown in Figure 5, which facilitates the integration of such a loop e in reduced spaces and / or of complex shape, as found in space vehicle equipment.
• the invention is not limited to the embodiment described and shown which has been given only by way of example.
• the invention is not limited to its implementation in thermal conditioning circuits for space vehicle equipment and can also find applications in equipment operating on the ground.
• one evaporator according to the invention can be integrated into any type of two-phase capillary pumping loops, whatever the level of the temperature to be regulated.
• the evaporator according to the invention can undergo a modification to facilitate its ground tests.
• the gravity gathers the liquid in the lower part and the gases in the upper part, both in the enclosure 12 and in the tube 22, the upper end of which is no longer supplied with heat-transfer liquid, the latter then no longer watering the part high of enclosure 12.
• a straight tube 33 with a solid wall can be placed in enclosure 12 so that the liquid entering this enclosure enters the tube helical by the end of this tube which is close to the bottom of the enclosure. In this case, it is obviously the other end of the tube 22, near the partition 25 which is blocked. It is understood that thus the heat transfer liquid entering the tube 22 sprinkles the wall of the enclosure, including at the level of a possible pocket of noncondensable gas such as that represented at 31 in FIG. 7.

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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)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
• Filling Or Discharging Of Gas Storage Vessels (AREA)

Applications Claiming Priority (3)

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• 1996
  • 1996-08-12 FR FR9610110A patent/FR2752291B1/fr not_active Expired - Fee Related
• 1997
  • 1997-08-08 CA CA002234403A patent/CA2234403A1/en not_active Abandoned
  • 1997-08-08 JP JP10509452A patent/JPH11514081A/ja active Pending
  • 1997-08-08 ES ES97936757T patent/ES2156398T3/es not_active Expired - Lifetime
  • 1997-08-08 DE DE69704105T patent/DE69704105T2/de not_active Expired - Lifetime
  • 1997-08-08 WO PCT/FR1997/001470 patent/WO1998006992A1/fr not_active Ceased
  • 1997-08-08 EP EP97936757A patent/EP0855013B1/de not_active Expired - Lifetime
• 1998
  • 1998-04-10 US US09/058,516 patent/US6058711A/en not_active Expired - Fee Related

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