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 purely passive thermal regulation device, comprising at least one heat transfer loop circulating a heat transfer fluid by capillary pumping, of the type also called capillary pumping fluid micro-loop, and used for cooling sources. hot, such as components or sets of electronic components (circuits).
• a heat transfer loop comprises an evaporator for extracting heat from a hot source, and a condenser, intended to restore this heat to a cold source.
• the evaporator and the condenser are connected by piping, in which circulates a heat transfer fluid in the liquid state in the cold part of the loop, and in the gaseous state in the hot part of this loop.
• the device of the invention relates more particularly to fluid loops, the pumping of the coolant is provided by capillarity (capillary loop).
• the evaporator is associated with a fluid reserve in the liquid state, and comprises a microporous mass (also called wick) ensuring the pumping of the fluid by capillarity.
• the fluid in the liquid phase present in the reserve associated with one evaporator evaporates in the microporous mass under the effect of heat from the hot source.
• the gas thus created is discharged to the condenser, in heat exchange contact with the cold source and where it condenses and returns to the liquid phase towards the evaporator, thereby creating a heat transfer cycle.
• One of the limitations of such a heat transfer loop in operation lies in the amount, more or less important, of thermal energy which is transferred to the liquid reserve, through the evaporator.
• a first effect of this parasitic phenomenon is to heat the liquid circulating in the loop or contained in the reserve 1 'evaporator.
• a second parasitic effect is to reduce the thermal performance of the transfer loop, which is very sensitive to the temperature of this liquid. Indeed, such a transfer loop carries the quasi-totality of the energy by phase change of the heat transfer fluid, and requires, in order to operate, a few frigories to maintain in the liquid state the fluid flowing from the condenser to the evaporator. Heating, even partial, of this liquid by any bias therefore significantly degrades the heat transfer performance of the loop, eventually leading to its total shutdown.
• the object of the present invention relates to passive capillary pumping micro-loop thermal control devices for cooling hot sources such as electronic components and / or circuits.
• components or electronic circuits are characterized by a reduced size (thickness 1 to 2 mm, surface 10 to 100 mm 2 , for example), and high power densities to be evacuated (more than 50 W / cm 2 , for example).
• the temperature variation between the junction of the component or electronic circuit and the housing of said component or circuit is very large (in a factor of 2 to 3) in front of the temperature variation of the component housing or circuit and the temperature of a soleplate of a card where the component or circuit is implanted.
• a capillary pumping heat transfer loop to the size of the component or circuit, called a micro-loop, advantageously reduces the temperature difference between the junction of the component or circuit and the sole of the card where it is implanted, and thus increase the reliability of the component or circuit, by increasing the power dissipated by this component or circuit.
• micro-loop capillary pumping is characterized in that its dimensions are reduced (typical thickness of 1 to 2 mm, typical surface from 10 to 100 mm 2 ), to allow its installation closer, see inside , component or circuit.
• the first disadvantage of the state of the art for producing such a device lies in the fact that the reduction in size of the said micro-loop promotes the parasitic transfer of heat towards the liquid reserve, which strongly degrades the performance of the loop.
• This disadvantage is one of the main limitations for reducing the size of the evaporator of a micro-loop according to the state of the art.
• a fluid loop device representative of the state of the art is that described in US7111394.
• the evaporator 11 is connected to a reservoir of liquid 15, and comprises a mass microporous 12 of generally cylindrical shape, pierced with a central artery 14, inside which circulates the liquid phase 19 of the fluid returning from the condenser 16 to the reservoir 15.
• this artery 14 at the periphery of the microporous mass 12, are pierced conduits 13 in which is collected the steam 18 resulting from the heat exchange taking place in the evaporator 11, between the mass 12 and the fluid in the liquid phase in the reservoir 15, and pumped by capillary action by the microporous mass 12. It is noted that the vapor phase 18 is confined to the periphery of the mass 12, as close as possible to the zone where the heat exchange takes place between the hot source (for example an electronic component in contact with the face external tube 10 at the evaporator 11) and 1 'evaporator 11.
• the hot source for example an electronic component in contact with the face external tube 10 at the evaporator 11
• the vapor phase is thus maintained at a sufficient distance from the central liquid phase, avoiding parasitic heat flow inevitably ably present in the mass 12 do not warm the liquid phase too much and affect the effectiveness of the loop.
• the vapor phase collected in the conduits 13 of the mass 12 is guided towards the condenser 16 by the annular space between the outer tube
• the peripheral ducts 13 will be very close to the internal artery 14 bringing the liquid " and all the more so that the diameters of the conduits 13 and 14 of the artery must be of sufficient size to ensure a fluid flow rate for efficient transport of heat to be evacuated. Large parasitic heat fluxes will then inevitably settle from the vapor to the liquid, the liquid will heat up and the efficiency of the loop will collapse.
• the invention proposes a device with at least one micro-loop, very simple to implement, limiting these parasitic effects and thus improving the thermal performance of each micro-loop.
• the device according to the invention is also advantageous for fluid loops of larger size and heat transfer capacity.
• the invention proposes a passive thermal regulation device, comprising at least one thermal transfer loop with capillary pumping of a heat transfer fluid, said loop comprising an evaporator comprising a microporous mass, and a condenser, intended to be in heat exchange relation with a hot source and a cold source respectively, and a pipe connecting the evaporator to the condenser and transporting the heat transfer fluid essentially in the vapor phase of the evaporator to the condenser and essentially in phase liquid from the condenser to the evaporator, the pipework comprising an outer tube, housing the mass microporous of substantially elongate shape, and which ensures the circulation of coolant fluid in the liquid phase by capillary pumping, which is characterized in that said liquid phase of said fluid is pumped by at least one end of the microporous mass which is turned towards the condenser, and circulates in at least one external pipe delimited between said outer tube and at least one inner tube
• said outer tube is closed on itself by forming a continuous loop, of which two substantially opposite portions, with respect to the center of said loop, are in thermal exchange relationship with each other.
• said outer tube is closed at its two ends, and its two ends are in thermal exchange relation with one of said condenser and the other with said evaporator and with said microporous mass housed in this end of the outer tube, said liquid phase of said fluid is pumped by the end of the microporous mass facing the condenser, and circulates in an external pipe delimited between said outer tube and an inner tube extending into said outer tube, and the vapor phase of said heated fluid at the level of the microporous mass of one evaporator is collected in a longitudinal central duct formed in said microporous mass and evacuated by the internal duct defined in said inner tube, said inner tube being connected at one end to one end of said central duct, while the vapor phase is vacated at the other end of said inner tube at the condenser.
• said other end of said at least one inner tube located at the condenser is fitted into a microporous mass annulus filling a defined space in said condenser between said other end of said inner tube and said outer tube.
• the liquid condensing at the condenser is drained to said annular microporous mass, preferably along the wall of said outer tube for example by a capillary drain or a microporous mass located along the wall said outer tube at said condenser.
• each of the evaporator and the condenser comprises at least one outer sleeve of a material which is a good conductor of heat, said at least one sleeve of one evaporator surrounding, at least partially , a portion of the outer tube which houses said microporous mass, and said at least one sleeve of the condenser surrounding a portion of the outer tube wherein at least one inner pipe releases the vapor phase fluid to said at least one outer pipe.
• At least one of the outer sleeves of the evaporator and the condenser comprises at least one sole of a material that is a good conductor of heat and by which said sleeve is intended to be placed in heat exchange relation with a source respectively hot or cold.
• said at least one inner tube has its walls made of at least one thermally insulating material, preferably a synthetic plastic material, in order to ensure good thermal insulation between the vapor phase flowing in the inner tube and the liquid phase flowing in the pipe (s) located (s) between the inner tube and the outer tube.
• said at least one internal vapor evacuation tube enters the interior of said microporous mass to ensure a greater seal between the vapor and liquid phases of the fluid at the level of the microporous mass.
• said inner tube comprises in its outer wall at least one capillary drain defined for example by at least one substantially longitudinal groove, at least at the portion of said inner tube which penetrates into the microporous mass, so as to bring the liquid phase deep inside said microporous mass by capillarity.
• the outer wall of said at least one inner tube comprises capillary drains defined for example by substantially longitudinal grooves extending preferably over the entire length of said tube.
• the outer wall of said at least one inner tube is in contact with the inner wall of said outer tube, except at at least one capillary drain defined by at least one substantially longitudinal groove dug in the outer surface of said inner tube and defining at least one outer pipe leading the liquid phase of said fluid.
• Said microporous mass advantageously has a substantially cylindrical outer shape, as well as the portion of said outer tube which houses it without radial play.
• said evaporator has a zone intended to be in thermal exchange contact with said hot source and whose dimension along the axis of said outer tube is significantly greater. small as the length of said microporous mass, preferably of the order of half of said length of said mass.
• said microporous mass has a length that is about 2 to 15 times greater than its diameter so as to create a large liquid reserve remote from the heat exchange zone with the hot source.
• said outer tube is in heat exchange contact with said microporous mass over the entire outer surface of said mass except one or both of its longitudinal end faces.
• said outer tube is of constant diameter section.
• the outer tube is advantageously made of a good heat conducting material, at least in part in heat exchange relation with said microporous mass, and in another part in heat exchange relationship with said condenser or constituent. this last.
• said outer tube is metallic, preferably made of stainless steel.
• said outer tube and said at least one inner tube are cylindrical of circular cross section, the diameter of said at least one inner tube being substantially half the diameter of the outer tube.
• the subject of the invention is also the application of a passive thermal regulation device to at least one heat transfer loop according to the invention and as defined above, to the transfer of thermal energy.
• a heat source such as a component or set of electronic components, in heat exchange relationship with the evaporator, to a cold source, in heat exchange relation with the condenser.
• FIG. 1 is a longitudinal sectional view of an exemplary fluid loop device according to US Patent 7,111,394;
• FIG. 2 is a cross-sectional view at the level of the microporous mass of the example of FIG. 1, according to US Pat. No. 7,111,394, FIGS. 1 and 2 being already described above;
• FIG. 3 is a schematic view in FIG. longitudinal section of a fluid micro-loop device according to the invention;
• FIG. 4 is a longitudinal sectional view on a larger scale of a detail of the device of Figure 3 around the microporous mass;
• FIG. 5 is a cross-sectional view along VV of Figure 4 at the evaporator;
• FIG. 6 is a view similar to FIG. 3 of a simplified variant of a fluid micro-loop device according to the invention;
• FIG. 7 is a diagrammatic view in longitudinal section, on a smaller scale than FIG. 3 and limited to the portions of the device including the evaporator and the condenser, of an alternative embodiment of the device of Figure 3;
• FIG. 8 is a cross-sectional view along VIII-VIII of Figure 7;
• Figure 9 is a schematic longitudinal sectional view at the evaporator, of another embodiment of the device of the invention; and
• FIG. 10 is a cross-sectional view along XX of FIG. 9.
• FIG. 3 A first embodiment of the passive thermal regulation device of the invention is illustrated in FIG. 3, representing the assembly of a double microboucle in longitudinal section, FIG. 4 showing a longitudinal section of the zone of the loop including the and Figure 5 showing a cross-section of the evaporator at its center. All the numerical values and technical characteristics relating to the materials and fluids given below are only indicative. These indications are compatible with an industrial embodiment of the invention with the current means of the art.
• the capillary pumping fluid micro-loop device 20 comprises an outer tube 21 with walls made of a good heat-conducting material, advantageously metallic, for example made of stainless steel, which is a tube, for example a cylindrical section tube. circular cross-section, with a constant outer diameter of 2 mm, and a wall thickness of 0.2 mm.
• This tube 21 is closed on itself in a continuous loop to form a closed circuit, in which circulates a coolant, which can be typically of ammonia, water, or any other two-phase fluid.
• a fill tube of the micro-loop connecting to the main tube 21 is not shown in Figure 3 to simplify the diagram.
• a microporous mass or wick 23 At the level of an evaporator 22, a microporous mass or wick 23, cylindrical in shape of circular section, is positioned without radial clearance inside a section of the tube 21.
• the outer diameter of the microporous mass 23 is therefore 1.6 mm, and its length is for example 20 mm.
• the microporous mass may be of a single block of the same constitution, with pores whose diameter or the main dimension is of the order of 1 to 10 microns.
• the pores may be of an optionally variable size, for example ranging from large pores to the axial end zones 23b of the wick 23 to promote the capillary pumping of the liquid and its insulation vis-à-vis stray heat flows from the hot source 27 and the central zone 23a of the wick 23, to small pores in the central zone 23a of the wick 23, where the vaporization of the pumped liquid fluid occurs, as explained below.
• the evaporator 22 also comprises a cylindrical sleeve 24, also of circular section, which is traversed axially and without substantial radial play by the portion of the outer tube 21, which surrounds the microporous mass 23, this sleeve 24 being made of a good conducting material heat, preferably metal, and possibly of the same nature as the outer tube 21, that is to say, stainless steel, the length of this sleeve 24 along its axis, which is also that of this section of the tube 21 and the microporous mass 23 (because these three elements are substantially coaxial) being about half the length of the mass 23.
• a good conducting material heat preferably metal, and possibly of the same nature as the outer tube 21, that is to say, stainless steel
• the sleeve 24 is in good thermal exchange relation with the outer tube 21, which is also in good heat exchange relation with the microporous mass 23 'over the entire external surface of the latter except for its two end faces.
• 23c longitudinal connected to each other by a central duct 25 cylindrical circular section, which passes through the mass 23 from one side.
• a sole 26 of the evaporator 22 is integral with a sole 26, and preferably in one piece with the latter, whose axial dimension may be preferably the same as that of the sleeve 24, and which constitutes a zone by which the evaporator 22 may be placed in heat exchange relation with a hot source 27, schematized in dashed lines in FIGS.
• a parallelepipedal body which may be a circuit or an electronic component to be cooled, and against which the sole 26 is in plane contact promoting thermal transfer by conduction of the hot source 27 to the sole 26 and thus to the sleeve 24, itself in good heat exchange relation, as already mentioned above, with the microporous mass 23 due to the coaxial assembly without radial clearance of this mass 23 in a section of the tube 21, and of the latter in the sleeve 24 of the evaporator 22.
• the sole 26 of the evaporator 22 in thermal contact with the hot source 27 thus has a dimension of approximately 10 mm along the axis of the outer tube 21, and this sole 26 is centered with respect to the microporous mass 23, so that the two zones and end faces 23b and 23c of the microporous mass 23 are remote from the central zone 23a of heat exchange with the hot source 27.
• the microporous mass 23 is assembled to the inner cylindrical wall of the tube 21, and the outer cylindrical wall of this tube 21 is itself assembled to the inner cylindrical wall of the sleeve 24 of the evaporator 22 by any means which ensures the best possible thermal contact, for example by gluing, sintering or any other means.
• the device also comprises a condenser 28 mounted, in this example, at a straight section of the outer tube 21 which is opposite to the rectilinear section of tube 21 passing through the evaporator 22, in the loop formed by this outer tube. 21 and in relation to the center of this loop.
• the condenser 28 comprises a cylindrical sleeve 29 made of a good heat-conducting material, preferably a metal material, which is in good thermal exchange contact with the section of tube 21 passing through it.
• a cold source 30 shown diagrammatically in FIG. 3 by a dotted rectangle, and which may be a heat sink, for example a metal element of a supporting structure.
• the sleeve 29 of the condenser may optionally comprise a sole (not shown) promoting the heat exchange contact with the cold source 30, and, as in the evaporator 22, measures can be taken to favor the contact thermal between the sleeve 29 of the condenser 28 and the outer tube portion 21 which passes through it.
• the device also comprises two inner tubes 31, which, in this example, are substantially identical to one another, cylindrical with a circular section, of a constant diameter which is substantially half of that of the outer tube 21, and which are made of a thermally insulating material, for example a so-called plastic synthetic material.
• their outer diameter is 1 mm
• their wall thickness is 0.1 mm.
• Each of these inner tubes 31 has a first end 32, through which it is fitted and fixed in one of the two longitudinal ends of the longitudinal central duct 25, for example with a diameter of 0.8 mm, of the microporous mass 23, as shown more precisely in FIG. 4, so that each of the inner tubes 31 is connected to the microporous mass 23 by fitting its first end 32 into one of the two longitudinal end zones 23b of this mass 23, respectively.
• connection of the inner tubes 31 with the microporous mass 23 must be sealed to prevent the liquid and vapor phases are in contact at this level.
• each of the two inner tubes 31 enters the section of the outer tube 21 passing through the sleeve 29 of the condenser 28, in which each second end 33 opens freely opposite the second end 33 of the other inner tube 31, so that the outer tube 21 and the two inner tubes 31 delimit an annular outer pipe 34, inside the outer tube 21 and outside the tubes 31, and two internal pipes 35 each inside one of the two inner tubes respectively 31.
• each of the inner tubes 31 may be advantageous to seal the end 33 of each of the inner tubes 31 in one of the two annular microporous masses 38 respectively, each filling an annular space delimited between a portion of the corresponding end 33 and a radially peripheral portion of the outer tube 21 in the condenser 28, and whose function is to capture the liquid phase by capillarity at the condenser 28, while avoiding a return of the vapor phase in the outer pipe 34. It is advantageous to extend these annular microporous masses 38 along the inner wall of the outer tube 21 at the condenser 28, in order to pump the liquid more efficiently at this level.
• This capillary drain may be produced by a cylindrical sleeve 39 of microporous mass, of radial thickness less than that of the masses 38, and connecting them to one another, and possibly in one piece with the two masses 38 in a microporous monolithic element 40.
• the cylindrical sleeve 39 may be replaced by a metal sleeve with grooves extending from one of its axial ends to its internal face, each groove forming a cape drain. link.
• the operation of this device is as follows.
• the sole 26 of the evaporator 22 collects heat generated by the hot source 27, and transmits it through conduction at the section of the outer tube 21 in contact with the microporous mass 23.
• This microporous mass 23 thus heated by the outer tube section 21 which surrounds it, essentially heats in its central zone 23a the fluid in the liquid phase coming from the external pipe 34 and which has been sucked and pumped by capillary action by the microporous mass. 23, at its longitudinal end regions 23b long enough axially to thermally isolate the liquid in the outer pipe 34 which can thus contain a liquid reserve near the wick 23.
• Each axial end face 23c of the wick 23 where the liquid phase arrives is also remote from the central zone 23a of this wick which is in heat exchange with the hot source 27. In other words, each end zone 23b of the microporous mass 23 moves the liquid away from the zone 23a hot central where the vaporization occurs.
• the fluid in the liquid phase pumped into the microporous mass 23 is vaporized in the central zone 23a and the vapor is collected in the central conduit 25 of the mass 23, where the vapor phase fluid is evacuated towards each of the two internal conduits 35, which guide the fluid in the vapor phase to the ends 33 of the inner tubes 31, in the condenser 28, where the vapor of this fluid condenses, and the liquid condensates are pumped by the microporous masses 38, 39 and guided by the external duct 34 from the condenser 28 to the evaporator 22, to supply liquid phase fluid to the microporous mass 23, by its two faces and end zones 23c and 23b longitudinal, as already mentioned above .
• the fluid in the liquid phase moves according to the arrows 36 of FIG.
• the liquid phase fluid reserve contained in the external pipe 34, the inside of the outer tube 21 and of the other microporous mass 23, is sufficiently far from the hot source 27, despite the reduced size of the evaporator 22, to minimize the flow of thermal energy parasitic towards this reserve of liquid, which improves the thermal performance of the device.
• the evaporator 22 and the condenser 28 each comprise a thermally conductive sleeve 24 or 29, but, in variants, as described below with reference to Figures 7 to 10, this sleeve may be constituted directly by a section of the outer tube 21 made of a good heat-conducting material, and which, alternatively also, may be made of such a good thermally conductive material only at the level of the two sections of the tube external 21 which, for one, surrounds the microporous mass 23 and, for the other, is surrounded by the sleeve of the condenser 28 or constitutes by itself this sleeve.
• FIG. 6 represents a simplified variant of the device of the invention, comprising a capillary pump elementary micro-loop, in which there is an outer tube 21 which connects an evaporator 22 to a condenser 28, being engaged and fixed by its two longitudinal ends closed in sleeves 24 and 29 respectively of the evaporator 22 and the condenser 28.
• the axial end portion of the outer tube 21 engaged in the sleeve 24 of the evaporator 22 surrounds the cylindrical microporous mass 23 which, in this example, has a central longitudinal duct 25, vapor collector, which opens only through the longitudinal end 23c of the mass 23 which faces the condenser 28, and in which is fitted and fixed an end 32 of a tube internal 31, thermally insulating, extending inside the outer tube 21, thermally conductive.
• the other end 33 of the inner tube 31 is fitted into an annular mass 38 of another monolithic microporous element 40 'making it possible to separate the liquid phase from the vapor phase at the condenser 28, and leads to the inside of the end portion of the outer tube 21 housed in the sleeve 29 of the condenser 28 and lined with this microporous element 40 ', for communicating the pipe 35, internal to the inner tube 31 and guiding the fluid in the vapor phase of the outlet of the duct 25 from the mass 23 to the condenser 28, with the annular external duct 36 guiding the condensed fluid in the liquid phase from the condenser 28 to the microporous mass 23 of the evaporator 22, which pumps this liquid by capillarity and vaporizes it under the effect of the heat received from the hot source 27, in heat exchange relation with the evaporator 22, this heat discharged from the hot source 27 being transferred by the condenser 28 to the cold source 30, when the fluid loop is in operation, under the same conditions as described above for the example
• the microporous element 40 ' comprises the annular mass 38, similar to one of the two annular masses 38 of FIG. 3 and occupying the radial space between the end 33 and the outer tube 21, and extended towards the closed end of the outer tube 21 by a thin axial microporous tube 39 'and a thin microporous radial disk 41 against the bottom closing this end of the tube 21, the tube 39' and the microporous disk 41 constituting a capillary drain which facilitates the supply of the mass 38 in condensed liquid including the condenser 20 inside the element 40 ', and thus guided by capillary pumping in the outer pipe 31.
• the tubes 21 and 31 are rectilinear, but they can be bent, in their central parts between the evaporator 22 and the condenser 28, to adapt the ??
• FIGS. 7 and 8 show an alternative embodiment of the device according to FIGS. 3 to 5, in which the outer sleeves of one evaporator 22 and of the condenser 28 are removed and each replaced by a respective section of outer tube 21 of external diameters and constant internal throughout its length. Similarly, the outer and inner diameters of the inner tubes 31 are constant over their entire length, the internal diameters of the inner tubes 31 and the central duct 25 of the microporous mass 23 being equal.
• the arrangement of the evaporator 22 and the condenser 28 is essentially the same as in FIGS. 3 and 4, so that the same references designate the same elements.
• capillary drains 42 in the form of grooves are hollowed out in the outer face of each inner tube 31 at least at the end portion 32 of the inner tube 31 which engages in the microporous mass 23, so as to bring liquid deep into said mass 23.
• a large number of grooves 42 may be formed throughout the outer periphery of each inner tube 31, to optimize the pumping rate of the fluid (see Figure 8).
• capillary drains 42 in the form of grooves which tighten at their opening in the outer face of the inner tube 31, thus of favorable section capillary pumping of the liquid used in the loop, can extend over the entire length of the inner tube 31 corresponding up to the level of the condenser 28, in the end 33 of the tube 31, as shown in the upper half-sections of Figures 7 and 8.
• these grooves do not sink deeper than the half of the thickness of the wall of the inner tube 31, in order to maintain good thermal insulation between the vapor and liquid phases of the fluid.
• each inner tube 31 enters the microporous mass 23 over an axial distance of one to several times the diameter of the outer tube 21, so that the grooves defining the capillary drains 42 guide the liquid deep inside the mass 23 by capillarity.
• the grooves of the drains 42 which may be parallel to the axis of the tube 31 or helical, are filled with a microporous material, whose pores have dimensions greater than those of the pores of the microporous mass 23, and substantially equal to or greater than those of the pores of the microporous mass 40.
• the groove-shaped capillary drains 42 may be replaced, at least at the level of the evaporator 22, but preferably along the entire length of each inner tube. 31, by another annular microporous mass 43 surrounding the inner tube 31, this other microporous mass 43 may have a constitution different from the main microporous mass 23 used for the evaporation of the fluid, for example have pores with a mean diameter significantly more importantly, typically by a factor of 2 to 10, than the average pore diameter of the main microporous mass 23 and substantially equal to or slightly greater than that of the pores of the microporous mass 40. Microporous capillary drains 43 are thus produced.
• Figures 9 and 10 respectively show in longitudinal sections at one evaporator 22 and transverse between the latter and the condenser 28, two other embodiments of the device according to the invention.
• the outer wall of each inner tube 31 is in contact with the inner wall of the outer tube 21, from the longitudinal ends of the microporous mass 23 of the evaporator 22 to condenser 28, except at the narrow openings of many external conduits 34 ', each of which is of small cross section, in this example in the form of a drop, and formed in the outer surface of the inner tubes 31 which is hollowed out a plurality of grooves 42 'on the entire periphery of each tube 31.
• These longitudinal grooves 42' or helical, or other, which each define an outer pipe 34 ', are hollowed only in substantially the outer radial half of the thickness of the wall of each inner tube 31, so that the liquid phase flowing in these grooves 42 '- external conduits 34' remains well thermally insulated from the vapor phase flowing in the internal conduits 35 inside the tubes 31.
• the external conduits 34 ' with a microporous material with pores of average size greater than those of the pores of the mass 23, at least in the end portions 32 and, optionally 33, of the tubes 31. at the level of the evaporator and the condenser, even over the entire length of the tubes 31.
• the outer conduits 34 'forming capillary drains may be replaced by another annular microporous mass 43', surrounding the ends 32 and / or 33, or all of each tube 31, whose radial thickness is reduced to substantially its inner radial half, the average pore size of the annular mass 43 'being greater than that of the pores of the mass 23, and substantially equal to or slightly greater than that of the microporous mass of the condenser.
• External conduits arranged in capillary drains 43 ' are thus produced. It is also possible to produce a single loop device with a single inner tube 31 according to FIG.
• the filling tube opens "radially" or perpendicularly into a portion of the outer tube 21 situated between the condenser and the evaporator 22.
• such a device finds an advantageous application to the transfer of thermal energy from a hot source 27 with a high thermal power density but of small dimension, such as a component or electronic circuit, placed in heat exchange relationship with the evaporator of the device of the invention, a cold source 30 placed in heat exchange relationship with the condenser of said device.

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