CAPILLAR PUMP HEAT TUBE WITH DEFENDANT GRILLES THAT INTEGRATES AT LEAST A POROUS SUBSTRATE INTO THE EVAPORATOR

Description

Domaine technique

[0001] The present invention relates to a capillary pumping type heat pipe with reentrant grooves.

[0002] The present invention aims to improve capillary pumping, while ensuring a high surface heat flux of such a heat pipe. Technique antérieure

[0003] A heat pipe is a thermal device used to transfer a quantity of energy from a hot source to a cold source, a certain distance apart.

[0004] A heat pipe consists of a hermetically sealed enclosure, a working fluid, and a capillary network. During manufacturing, all the air present in the heat pipe tube is evacuated and a quantity of pure liquid is introduced to saturate the capillary network. Once the enclosure is sealed and subjected to a heat source, an equilibrium is established between the liquid phase and the vapor phase.

[0005] Under the effect of a heat source applied in an area at one of the longitudinal ends, called the evaporator, part of the liquid phase vaporizes and absorbs the heat flux in latent form by inducing a slight overpressure which causes the movement of the vapor towards an area at the other longitudinal end, called the condenser where the cold source is applied. At the condenser, the vapor condenses and returns to the liquid phase. The condensed fluid (the condensate) circulates in the capillary network and returns to the evaporator to repeat a cycle, under the effect of capillary forces, when the heat pipe is not subject to gravity. The return of the liquid fluid from the condenser to the evaporator is obtained by capillary pumping.

[0006] Indeed, in the absence of gravity, the engine of the heat pipe is the capillary pumping of the fluid which takes place at the liquid-vapor interface zones specifically configured so that a meniscus is formed, resulting from the contact angle between the fluid and the metal constituting the heat pipe (itself dependent on the surface tension of the fluid, and the solid / liquid and solid / vapor interfacial tensions). The greater the capillary pumping forces compared to the various friction forces of the phases of the fluid with the walls and between them, the more efficient the heat pipe is and can transport a large quantity of energy. Heat pipes concerned by this absence of gravity are, for example, those implemented in space operating conditions, such as for the thermalization of satellite telecommunications systems.

[0007] In terrestrial conditions, with gravity, the problem of liquid phase return is completely different, and other liquid-vapor / wall interface configurations are implemented.

[0008] Grooved heat pipes operate on the principle of capillary pumping. They consist of a tube, in which the inner surface has axial / longitudinal grooves [1] or slightly spiral-shaped grooves. Grooved heat pipes consist of a vapor core and a peripheral capillary network in which the liquid phase circulates. Due to a variation in the curvature of the liquid-vapor interface between the condenser and evaporator zones, a pressure gradient appears in the liquid, which leads to a variation in capillary pressure. The smaller the groove width, the greater the capillary pumping effect.

[0009] Furthermore, deep grooves provide a large passage section for the liquid return, thus minimizing pressure loss.

[0010] The maximum power that grooved heat pipes can carry is generally set by the capillary limit, the driving term of which is the capillary pressure, and the limiting term essentially the loss of liquid pressure in the grooves and, to a lesser extent, the pressure losses of the steam flow.

[0011] Reentrant grooved heat pipes are special examples of grooved heat pipes, in which the grooves have a narrow connecting channel compared to the rest of the groove, which increases the capillary pumping effect while limiting pressure losses in the liquid phase. These heat pipes are used mainly in the space sector, for example for thermal regulation in satellites and / or spacecraft.

[0012] Known techniques for producing grooved heat pipes, and in particular reentrant grooved heat pipes, do not allow grooves to be obtained with a depth significantly greater than their width.

[0013] These heat pipes are produced mainly by extrusion with or without a floating mandrel including the groove pattern. This process makes it possible to produce, generally in relatively soft metals (aluminum or copper), generally cylindrical tubes provided with longitudinal or slightly spiral internal grooves inside the tube.

[0014] These tubes are also used in evaporators and condensers, but can also be used to make heat pipes.

[0015] The grooves are generally rectangular or trapezoidal and have an aspect ratio limited by the extrusion process. The depth of the grooves can generally be up to 0.2 mm with a depth / width aspect ratio of around 1 maximum.

[0016] In the case of reentrant grooves, the manufacturing constraints are even more draconian, limiting the width, the length of the narrowing and the section of the reentrant part.

[0017] Another technique uses mechanical machining, with this technique also the depth to width ratio is not significantly greater than 1. In addition, this technique has a relatively high cost price and is not suitable for medium and large series manufacturing.

[0018] Another technique uses chemical etching. But it also does not allow for a high depth-to-width ratio.

[0019] To overcome these drawbacks, the applicant proposed in patent application EP3553445A1 a heat pipe made by stacking plates secured to each other with sealing, the end plates of which form closing plates and the intermediate plates of which are structured so that their stacking delimits re-entrant grooves extending over the entire length of the heat pipe. The plates can be assembled by different welding, brazing or bonding techniques.

[0020] Over the operating temperature range of a heat pipe, various physical limits can constrain its performance.

[0021] The operating curve of the heat pipe, which allows us to know its maximum transport capacity, is obtained by combining the curves corresponding to the different physical operating limits which ultimately define the operating range of the heat pipe in terms of the maximum power it can transfer.

[0022] There figure 1 illustrates the curve delimiting the operating domain for an example of a capillary pumped heat pipe. In this figure 1 , we recall that the portions of the curve Q viscous , Q sonic , Q entrainment , Q capillary , Q boiling , respectively define the viscous, sonic, entrainment, capillary and boiling limits.

[0023] Regarding the boiling limit, in a capillary pumped heat pipe, the capillary driving pressure must compensate for the static pressure losses related to the volume and dynamic forces generated by the flow of the working fluid in the heat pipe (friction between the flows and the walls). This capillary driving pressure, which corresponds to the capillary pressure difference between the evaporator and the condenser, is a function of the structure of the heat pipe, and the dynamic pressure losses which increase with the mass flow rate of the working fluid (and with the length of the heat pipe), itself a function of the thermal power imposed on the evaporator: the capillary limit is reached when the capillary driving pressure is equal to the sum of the pressure losses (liquid phase and vapor phase).In other words, a heat pipe only works if the capillary driving pressure is higher, in microgravity conditions, than the pressure losses, and therefore below the capillary limit.

[0024] This limit is generally expressed in Wm: it is inversely proportional to the effective length of the heat pipe, that is to say that for the same design (same cross-section over the entire length), the capillary limit, expressed in W, of a 2-meter heat pipe is half that of a 1-meter heat pipe.

[0025] Frictional pressure losses in a flow are expressed by the Darcy-Weisbach equation as follows: dP dz = f 1 D h ρ v 2 2 in which: f is the pressure drop coefficient (dependent on the fluid flow regime, and which can be determined via the Reynolds number from correlations), v the speed of the working fluid (proportional to the thermal power to be transported), ρ the density of the working fluid and Dh the hydraulic diameter.

[0026] The hydraulic diameter is itself defined by the following equation: D h = 4 S P m with S the fluid section and Pm the wetted perimeter.

[0027] It is therefore understood that to maximize the capillary limit, it is necessary to favor liquid and vapor channels with a high cross-section, in order to minimize the fluid speeds in these channels without reducing the flow rate, which is proportional to the thermal power transferred in the heat pipe.

[0028] It is also necessary to have a narrow groove width at the interface, in order to have a high capillary pressure. But this groove width cannot be too narrow to be technologically achievable by a brazing operation according to the method of application EP3553445A1. Indeed, too narrow a width would induce a risk of clogging by the brazing.

[0029] Furthermore, the ratio of the sections between the channel and the groove must not be too high, in order to facilitate the evacuation of steam bubbles which may appear in the channels.

[0030] Furthermore, when evaporation occurs at the level of the meniscus of the liquid / vapor interface in the groove which delimits a connection channel, the meniscus moves back into the latter, especially as the heat flux is high. If the meniscus moves back too much, it can reach the reentrant channel. In this case, the capillary radius at the interface increases and therefore the capillary pressure, the driving force of the heat pipe, decreases; there is then a risk of the heat pipe losing its priming.

[0031] It is therefore advantageous to have a large volume of liquid in a connecting channel, in order to minimize this phenomenon.

[0032] The overall thermal resistance of a heat pipe can be assessed by making a network analogy of independent thermal resistances.

[0033] Such a network is schematized in figure 2 in which a heat flux Q emitted by a hot source SC must be evacuated by a heat pipe to a cold source SF.

[0034] From a thermal point of view, the heat pipe can be considered as a set of a number of eleven thermal resistors R1 to R11 in series and / or in parallel as shown in this figure 2 The axial resistances of the outer wall R10 and the capillary network R11 along the length of the heat pipe are immense. Therefore, the preferred heat flow path is through the steam circulation section. This path consists of five different resistances, as follows: the resistance between the external source and the wall R1, R9 respectively to the evaporator and to the condenser; the resistance of the external wall R2, R8 respectively to the evaporator and to the condenser; the resistance of the liquid channels (capillary network) R3, R7 respectively to the evaporator and to the condenser; the resistance of the interface between liquid and vapor R4, R6 respectively to the evaporator and to the condenser and the resistance of the vapor flow R5.

[0035] On this path, the limiting thermal resistance is that of the liquid channels (capillary network), respectively to the evaporator and the condenser (R3, R7).

[0036] For the evaporator, the author of the publication [2] proposed a thermal resistance model with a path through the liquid in the groove in parallel with a conductive path in the tooth and then in the evaporation film.

[0037] In this very conservative model, the equivalent conductivity of the film is given by an empirical formula according to equation 3: λ film = λ l 0.185 ∗ c

[0038] In an aluminum-walled heat pipe filled with ammonia as the working fluid, given the thermal conductivity difference between liquid ammonia (0.4 W / m / K) and aluminum (150 W / m / K), the preferred path of heat flow between the hot source and the steam will pass through the metal walls between the liquid channels.

[0039] The same pattern occurs in the condenser, where the preferred path of heat flow between the steam and the cold source will pass through the walls between channels.

[0040] It therefore appears that, to increase the thermal conductance in the evaporator and condenser, it is advantageous for the walls between liquid channels to have the largest possible cross-section.

[0041] Finally, the film resistance depends in particular on the length of the triple contact lines between liquid, vapor and solid.

[0042] The mechanical strength of a heat pipe with reentrant grooves can also impact its performance. In particular, in patent application EP3553445A1, a connecting channel between a liquid channel and a vapor channel is completely open along its entire length along the longitudinal axis of the heat pipe, the brazed, glued or welded assembly of the stacked plates can therefore only be carried out on the peripheral walls thereof, which results in significant wall thicknesses to withstand the internal pressure of the heat pipe.

[0043] We also know another type of heat pipe, called an artery type, as disclosed in patent US4422501A, which is a heat pipe whose liquid return of the condensates is physically separated from the channel where the steam circulates after evaporation.

[0044] The main advantage of an arterial heat pipe is to eliminate the maximum flow of liquid particle entrainment by the steam by eliminating the liquid / steam interfaces in the adiabatic zone of the heat pipe.

[0045] Furthermore, the construction of an artery heat pipe is much less expensive and simpler to install than a heat pipe with a sintered capillary peripheral network. With a small diameter artery, depending on the fluid and materials selected, if the capillary forces are sufficiently high, operation against gravity can be expected with good performance.

[0046] Such an artery heat pipe 1 is shown in figures 3, 3A And 3B: just like the other rectilinear heat pipes, it comprises a sealed enclosure delimited by a wall 10 and extends between a first longitudinal end, intended to be heated by a thermal flow Φ E emitted by a hot source, to form, within the enclosure, an evaporator ZE and a second longitudinal end intended to output a thermal flow Φ S towards a cold source to form, within the enclosure, a condenser Zc where the vapor V condenses, the sealed enclosure delimiting an adiabatic zone ZA between the evaporator and the condenser.

[0047] Such an artery heat pipe 1 incorporates a liquid channel 11 forming an artery which brings the liquid back from the condenser Zc to the evaporator ZE, which is dissociated from the vapor channel 13. In such a heat pipe, there is no liquid-vapor interface except at the evaporator ZE and the condenser Zc. This also makes it possible to reduce the friction forces of the liquid phase. In addition, the liquid phase at the evaporator ZE is not directly subjected to the heat flux Φ E from the hot source, and this plays a role in moving away from the boiling limit.

[0048] A very interesting configuration for a terrestrial application, that is to say where gravity applies, consists of integrating one or more of the arteries 11 in a porous medium 14, peripheral to the vapor channel 13, as illustrated in figure 4 . This porous medium 14, also called wick, can have pores with an average size of a few hundred microns per millimeter. In addition to the reduced liquid pressure loss that it induces, the porous medium 14 ensures a very good boiling limit at the evaporator level by a multiplication of lines and triple points P, that is to say solid-liquid-vapor contact points, which are very favorable to evaporation.

[0049] Grooved heat pipes, particularly those with reentrant grooves, have the major disadvantage of having a high thermal resistance to the evaporator, and a radial heat flux that can be transmitted into the evaporator that is also limited by boiling phenomena in the grooves. Typically, this flux is limited to approximately 15 W / cm 2 for an ammonia heat pipe.

[0050] Heat pipes with a porous capillary structure, such as sintered powder, achieve higher performance than grooved heat pipes. In particular, these heat pipes with porous capillary structure can accommodate much higher surface heat flows to the evaporator, and have a lower thermal resistance to the evaporator. However, they have two major disadvantages: for a structure made from sintered powder, it is necessary to sinter it inside the heat pipe, which is difficult to achieve over lengths of several meters, typically encountered in space applications (satellites); the size of the pores of the porous capillary structure being a few microns, the pressure losses of the liquid return in said structure quickly become prohibitive over lengths of several meters, which limits the transportable thermal power.

[0051] Patent US9618275B1 describes a heat pipe with a hybrid structure, i.e. with grooves extending longitudinally in the adiabatic part and the condenser and with a cylindrical porous insert in the evaporator. This heat pipe with a hybrid structure partially addresses the problem mentioned above of grooved heat pipes. However, it has several drawbacks. First of all, the return of the liquid (in the evaporator zone) is longitudinally in the thickness of the cylindrical porous insert, which induces a high loss of liquid pressure. Indeed, the size of the pores of the porous insert is intrinsically small so as to obtain a high capillary pressure, but with the counterpart of necessarily inducing a low permeability. The embodiment of the figure 6 of this patent provides a solution to this problem of low permeability: it provides for an enlargement of the diameter of the porous insert in the evaporator. However, such an enlargement necessarily induces an increase in the thermal resistance in this area of ​​the heat pipe (evaporator). Furthermore, the disclosed cylindrical porous insert must ensure fluid continuity with the grooves of the adiabatic zone, otherwise the capillary pumping risks being defused. However, in practice, this fluid continuity seems difficult to guarantee, and requires expensive and complex solutions (machining of fingers in the porous insert penetrating into the grooves), and random.

[0052] Therefore, there is a need to further improve grooved heat pipes, in particular reentrant heat pipes, in order to overcome the aforementioned drawbacks, in particular the high thermal resistance at the evaporator and the limitation of the radial heat flux at the evaporator, typically of the order of 15 W / cm 2< for a heat pipe filled with ammonia.

[0053] The general aim of the invention is then to respond at least in part to this need. Exposé de l'invention

[0054] To do this, the invention firstly relates to a capillary pumping heat pipe with reentrant grooves, extending along a first longitudinal direction (X), comprising a sealed enclosure extending between a first longitudinal end, intended to be heated by a hot source SC to form, within the enclosure, an evaporator and a second longitudinal end intended to be cooled by a cold source SF to form, within the enclosure, a condenser, the sealed enclosure delimiting an adiabatic zone between the evaporator and the condenser, the sealed enclosure comprising a stack of plates in a second direction, orthogonal to the first direction, including two closure plates and at least a number of n modules on top of each other with n being an integer greater than or equal to 1, each module comprising at least one interposed plate between the closure plates,the intermediate plate(s) comprising at least one first intermediate plate comprising at least one window whose edges partially delimit at least one vapor channel extending along the first direction (X) between the evaporator and the condenser, in which the vapor is intended to circulate, and on at least one lateral side of the window in a third direction (Y) orthogonal to the first (X) and second direction (Z), at least one structuring whose edges partially delimit at least one liquid channel in the evaporator and the condenser, the heat pipe comprising, at least in the evaporator, at least one exchange zone defining a liquid-vapor interface and delimited between the at least one intermediate plate and at least one other intermediate plate or a closing plate, connecting the vapor channel(s) and the liquid channel(s), each exchange zone comprising at least one connecting channel opening out.,

[0055] According to the invention, at least a portion of the connecting channels emerging from the evaporator each housing an insert made of porous material which extends at least partly into the liquid channel(s) and into the vapor channel(s), the porous insert being adapted to bring the liquid by capillarity from the liquid channel(s) to the vapor channel(s) in which it evaporates.

[0056] According to an advantageous configuration, the condenser of the heat pipe also comprises at least one exchange zone defining a liquid-vapor interface and delimited between the at least one intermediate plate and at least one other intermediate plate or a closing plate, connecting the vapor channel(s) and the liquid channel(s), each exchange zone comprising at least one opening connecting channel, at least a portion of the opening connecting channels of the condenser each housing an insert made of porous material which extends at least partly into the liquid channel(s) and into the vapor channel(s), the porous insert being adapted to condense the vapor in the vapor channel(s) and to bring the condensed liquid by capillarity towards the liquid channel.

[0057] The porous inserts in the evaporator can be made of the same constituent material, have the same shape and / or the same dimensions as the porous inserts in the condenser.

[0058] According to another advantageous configuration, the adiabatic zone of the heat pipe comprises at least one exchange zone between the vapor channel(s) and the liquid channel(s), defining a liquid-vapor interface and delimited between the at least one intermediate plate and at least one other intermediate plate or a closing plate, each exchange zone comprising at least one connecting channel emerging without an insert.

[0059] These two configurations can be combined and thus have porous inserts in the evaporator and in the condenser of the heat pipe while having an adiabatic zone free of porous inserts. Preferably, the liquid channels are present in all zones of the heat pipe (evaporator, adiabatic zone, condenser), in order to minimize the pressure loss of the liquid return.

[0060] Advantageously, the porous insert of the evaporator and, where appropriate, of the condenser extend(s) over the entire width of the steam channel in the third direction (Y).

[0061] Advantageously, the porous insert of the evaporator and, where appropriate, of the condenser extends over the entire width of the liquid channel in the third direction (Y).

[0062] According to an advantageous embodiment variant, the porous insert has the shape of a flat sheet. According to an advantageous embodiment, at least a portion of the intermediate plates comprises, in the evaporator and where appropriate in the condenser, at least one longitudinal notch extending in the first direction (X) forming a surface for supporting and holding the porous flat sheet.

[0063] Preferably, the material constituting a porous insert is based on graphite, preferably not wettable by a brazing filler metal. Such a material has the advantage of having high porosity and thermal conductivity, a low density and is slightly compressible. In addition, it is not wettable by the eutectic aluminum alloy during a process of assembling the plates of the stack by eutectic brazing. Conversely, it is perfectly wettable with ammonia, which is a reference fluid for filling the heat pipe enclosure. Examples include graphite sheets marketed under the name SIGRACET ®< or that under the name AvCarb ®<.

[0064] Preferably, the width of a porous insert is between 0.1 and 1 mm, preferably of the order of 0.6 mm. This width determines its thickness and is advantageously slightly greater than or equal to the width of the connecting channels, so as to ensure continuity of the flow of the liquid, and simplify the production of the intermediate plates.

[0065] Generally, the porous insert is compressible and slightly thicker than the width of the connecting channels in the YZ plane so as to ensure good wedging in the interlayer plates. Good wedging allows good thermal contact with the plates and thus efficient heat conduction between the heat flow inlet on the plates and the evaporation zone on the faces of the porous insert in the vapor channel.

[0066] In the configuration where the condenser also houses one or more porous inserts, the heat flow is applied between the faces of each porous insert in the steam channel, and the extraction of the heat flow is done by the external faces of the heat pipe.

[0067] More preferably, the average pore size of a porous insert is between 1 and 100 µm, preferably of the order of 50 µm.

[0068] The material constituting the plates forming the sealed enclosure is preferably chosen from aluminum, copper, nickel, or an alloy based on at least two of these. The material(s) used for the manufacture of the heat pipe are chosen according to the constraints of mass, assembly, required robustness, compatibility with the fluid, etc.

[0069] The technique of joining the sheets depends on the material.

[0070] For example, in the case of aluminum alloy plates, vacuum brazing with cladding sheets, salt bath brazing, inert gas brazing, ultrasonic welding, laser welding, friction stir welding, bonding, etc. can be used.

[0071] In the case of copper, stainless steel or superalloy plates, diffusion welding, laser welding, diffusion brazing, bonding, etc. can be used.

[0072] In the case of stainless steel plates, super alloys, diffusion welding, laser welding, diffusion brazing, bonding, etc. can be used.

[0073] For example, the assembly of aluminum alloy plates is obtained by eutectic brazing. Aluminum alloy plates are used in a known manner, one or both faces of which is or are coated with an aluminum alloy with a lower melting point.

[0074] For example, a sheet of AA3xxxx series alloy is used at the core, with a coating of a eutectic alloy of the AA4xxxx series comprising lower melting silicon. The coating is typically done by a roll-bond technique. The total thickness of the plates is typically 0.05 mm to 5 mm, with a coating typically of 5% to 10% of the total thickness on one or both sides. By hot pressing two aluminum plates thus coated at a temperature above the melting temperature of the eutectic, but below the temperature of the core alloy, the eutectic alloy on the surface melts and forms a sealed joining braze alloy between the two plates. Brazing is preferably carried out under pressure using a mechanical holding system, which maintains pressure on the stack during brazing in a vacuum furnace.Cutting and / or bending are required in the manufacturing process to lighten and / or shape the structure. These are preferably performed after assembly. It should be noted that the cutting of windows in the plates, for example the central windows, is performed before assembly.

[0075] The method for producing a heat pipe according to the invention can advantageously consist of the following steps: Etape a / : Plates made of a given material are cut according to the desired external shape for the heat pipe. The porous inserts are also cut, advantageously in the form of flat sheets. Etape b / : The interlayer plates are structured, for example by punching, machining, laser cutting, water jet cutting or through chemical etching... in order to create the specific windows in the different plates, so that once assembled a heat pipe with reentrant grooves is formed. Etape c / : The plates are then stacked in a given order, alternating between two intermediate plates a porous insert for the evaporator and, if necessary, for the condenser. Then two closing plates are arranged at the ends of the stack to close the channel(s). The stack is made so that a porous insert is sandwiched between two intermediate plates or between an intermediate plate and a closing plate, preferably by being compressed. Optionally, cooling channels are provided on one or both sides of the stack. Etape d / : The plates are then assembled together using an assembly technique chosen according to the material(s) of the plates, for example welding, brazing, gluing, etc. The final assembly of the plates is watertight. The material(s) of the plates is(are) chosen according to the working fluid, which is itself chosen according to the thermalization specifications of the system to be produced. Etape e / : The heat pipe is then filled. In order to fill the heat pipe with the working fluid, a filler pipe inserted on the edge of the enclosure can be used. Alternatively, a pipe fixed to an orifice made through one or other of the closure plates, and perpendicular to it. The fluid is chosen according to the operating conditions of the heat pipe (operating temperature, etc.) and compatibility with the material(s) of the heat pipe.

[0076] According to one or more advantageous characteristics which can be combined with each other: the intermediate plates have a thickness of between 0.5 and 6 mm, preferably of the order of 2 mm, the closing plates have a thickness of between 1 and 3 mm, preferably of the order of 2 mm, the width in the YZ plane of a connecting channel is between 0.1 and 1 mm, preferably of the order of 0.2 mm, the structuring thickness in the YZ plane delimiting the space between two adjacent connecting channels is between 0.2 and 2 mm, preferably of the order of 0.4 mm, the width in the YZ plane of a liquid channel is between 0.5 and 4 mm, preferably of the order of 3 mm.

[0077] According to an advantageous configuration, the heat pipe comprises n modules one on top of the other, n being an integer greater than or equal to 1, defining a single vapor channel and n liquid channels on at least one lateral side, in particular on each lateral side of the vapor channel. Preferably, the heat pipe comprises a single central vapor channel arranged between n liquid channels distributed laterally on either side of the vapor channel.

[0078] According to an advantageous embodiment, at least one of the end plates has a surface area greater than that of the intermediate plates in a direction transverse to that (Z) of the stack so as to form thermal diffusers. With such thermal diffusers, the heat flow entering and leaving the heat pipe is spread over a larger surface area and locally reduces the maximum flux density which would be achieved without a diffuser.

[0079] According to another advantageous embodiment variant, the cross-section in the XY plane of the evaporator incorporating the porous insert and / or that of the condenser, preferably rectangular, is greater than that of the adiabatic zone of the heat pipe. In the case of a heat flow perpendicular to the main plane of the plates, this variant makes it possible to increase the exchange surface area of ​​the evaporator and / or the condenser and therefore minimize the external thermal resistances, while limiting the increase in mass of the heat pipe.

[0080] In the case of heat flow parallel to the plane of the plates, the size of the liquid and / or vapor channels in the YZ plane can be increased, allowing the capillary limit of the heat pipe to be increased.

[0081] If there are no liquid channels under a porous insert, but only a capillary return of the liquid into the porous insert, it is preferable to increase the width of a porous insert in the liquid zone, in order to limit pressure losses in it.

[0082] According to yet another advantageous embodiment variant, the structures of the evaporator and, where appropriate, of the condenser comprise a plurality of pads distributed, preferably uniformly, along the first direction (X). These pads make it possible to minimize the pressure loss in a porous insert, while ensuring mechanical support of the latter. This variant with pads can be produced for configurations with liquid channels on the sides of the heat pipe enclosure or in the central part thereof.

[0083] According to an advantageous embodiment, the heat pipe comprises heat exchange means at the first end and / or second end, the heat exchange means at the second end advantageously comprising one or more fins in thermal contact with at least one of the closure plates.

[0084] According to this embodiment, the heat exchange means may comprise a fluid circuit in thermal contact with at least one of the closing plates, said circuit being formed by a plate structured so as to delimit channels, said channels being closed by said closing plate and an additional closing plate, the heat exchange means also comprising means for supplying said fluid circuit with heat transfer fluid.

[0085] Generally speaking, a fluid circuit forming the hot and / or cold source can be integrated within the heat pipe at the evaporator and / or condenser. This circuit will take the form of a pleated or perforated closing sheet to form an integral air radiator. Alternatively, it can take the form of a liquid or two-phase circuit forming the hot and / or cold source.

[0086] Advantageously, the cross-section in the YZ plane of the vapor channel and the liquid channel(s), preferably rectangular, is constant over the entire length of the heat pipe.

[0087] According to an alternative embodiment, cuts of the narrow connecting channels can be made straight, or with a corrugated or sawtooth shape over all or part of the length of the channels. Such a shape makes it possible to obtain walls not wetted by the condensation film, in the condenser of the heat pipe, at the peaks of the corrugations or sawtooths. This also makes it possible to increase the condensation exchange coefficient by minimizing the interface resistance of the condensation film.

[0088] The invention also relates to a system comprising: a cold source (SF); a hot source (SC) and at least one heat pipe with reentrant grooves as described previously, the heat pipe being arranged so that the heat flow (φ E ) from the hot source (SC) to the evaporator is on at least one lateral face of the enclosure facing the vapor channel or on at least one lateral face facing the liquid channel(s), while the heat extraction at the condenser towards the cold source (SF) is on at least one lateral face of the enclosure facing the liquid channel(s), or on a lateral face perpendicular to the latter (these).

[0089] The same heat pipe according to the invention can be used to achieve thermal control, heat transfer, component cooling, etc. The heat source can therefore be, for example, an electrical or electronic component, heat storage, an exothermic chemical reactor, heat sinks of fins in forced convection, cold plates in single- or two-phase flow, cold storage, an endothermic chemical reaction, etc.

[0090] The cold source can consist of a radiator with natural or forced convection.

[0091] Different radiator technologies can be considered: pleated fins, extruded fins, skived fins, spiked fins, molded fins, fins fixed by knurling, fins produced by 3D printing, or any other fin obtained by a surface extension technique known to those skilled in the art.

[0092] One or more finned radiators as described above may be implemented in a heat pipe according to the invention, single-channel or multi-channel straight or having any other shape. Thus, the invention essentially consists of proposing a heat pipe of which at least the evaporator integrates within it a porous insert which extends in a connecting channel between the vapor channel and the liquid channel(s).

[0093] The production of such a heat pipe is implemented with a method as according to patent application EP3553445, which consists of stacking and then assembling together by gluing, welding, preferably by vacuum brazing, punched or machined metal plates to define the different heat pipe channels. The porous inserts according to the invention do not modify the assembly process, since they are inserted directly alternately with the plates in the stack which is assembled.

[0094] The invention finds particular application in the space sector.

[0095] For a heat pipe configured for an application in the space domain, the constraints encountered are of several types which can be listed as follows: In the evaporator, which is generally short, high radial flows are required because of the electronic components that need to be cooled, whose power densities are constantly increasing. In addition, low thermal resistance is required and, in order to ensure driving pressure in the heat pipe, high capillary pressure is required, provided by a small capillary radius at the liquid / vapor interface; in the adiabatic zone, which is generally long, pressure losses in the vapor channel and in the liquid channels must be limited, in order to have a high axial capillary heat transport limit. In the condenser, which can also be long, pressure losses must also be limited, but also efficient condensation must be ensured to minimize thermal resistance in this zone.

[0096] The invention described here makes it possible to meet these constraints, by allowing different configurations in each heat pipe zone in order to optimize it as best as possible according to the desired performance criteria.

[0097] More particularly, the porous inserts inserted longitudinally into the evaporator of the heat pipe will allow the liquid to be transported by capillarity between the liquid channel(s) and the vapor channel. The evaporation of the liquid at the surface of a porous insert allows a high capillary pressure to be obtained, while ensuring a higher surface heat flux than a heat pipe with reentrant grooves or sintered capillary, according to the state of the art. For example, the practical limit of surface heat flux with an ammonia-filled heat pipe, with reentrant grooves according to the state of the art is of the order of 15 W / cm 2< . With a heat pipe according to the invention, this practical limit can rise to more than 50 W / cm 2< .

[0098] Thermal resistance is also improved in the evaporator due to a larger liquid evaporation surface.

[0099] In the evaporator and possibly condenser zones, there are liquid channels, the circulation of liquid in the porous material taking place only over the small distances between the liquid channel and the vapor channel, making it possible to limit pressure losses in the porous material.

[0100] In the adiabatic zone, there are no pores, longitudinal grooves defining the connecting channels allow to minimize the loss of pressure of the liquid, even over large distances.

[0101] Also arranging porous inserts longitudinally in the condenser allows to reduce the thermal resistance in this area, even if this can be at the expense of an increased liquid pressure loss in this area.

[0102] Furthermore, a heat pipe according to the invention has high capillary pressure thanks to the small pore size of a porous insert. And therefore, it is likely to operate without gravity, or even against gravity. This makes the heat pipe according to the invention particularly suitable for space missions near celestial objects where there may be non-zero gravity (moon, Mars, asteroids, etc.).

[0103] Other advantages and characteristics will become more apparent upon reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures. Brève description des dessins

[0104] [ Fig 1 ] there figure 1 illustrates the curve delimiting the operating domain for an example of a capillary pumped heat pipe. Fig 2 ] there figure 2 is a symbolic representation of a network of thermal resistances that are established for a heat pipe. Fig 3 ] there figure 3 is a schematic view of a state-of-the-art arterial heat pipe (Example 1). [ Fig 3A ], [ Fig 3B ] THE figures 3A And 3B are cross-sectional views of the figure 3 , respectively at the level of the evaporator and the condenser of the arterial heat pipe according to the state of the art (Example 1). [ Fig 4 ] there figure 4 is a cross-sectional view of a variant of a heat pipe with arteries according to the state of the art. Fig 5 ] there figure 5 is a photographic reproduction of an example of a state-of-the-art Omega-shaped cross-section reentrant groove heat pipe (Example 1). Fig 6 ] there figure 6 is a schematic side view of a heat pipe with reentrant grooves, according to the state of the art (Example 2). [ Fig 7 ] there figure 7 is a perspective and cross-sectional view of the figure 6 , at the level of the evaporator of the reentrant grooved heat pipe according to patent application EP3553445 (Example 2). [ Fig 8 ] there figure 8 is a detailed and cross-sectional view of the figure 7 . [ Fig 9 ] there figure 9 is an exploded view of a reentrant grooved heat pipe with transverse connecting channels made by stacking assembled metal plates, with porous inserts at the evaporator, according to a third example of the invention with a square heat pipe aspect ratio. Fig 10 ] there figure 10 is a detailed and cross-sectional view of the figure 9 , at the level of the evaporator, according to the third example of the invention. [ Fig 11 ] there figure 11 is a detailed and cross-sectional view according to a third example of the invention, at the level of the condenser and the adiabatic zone of the heat pipe. Fig 12 ] there figure 12 is a detailed and cross-sectional view, at the level of the evaporator, of a heat pipe with reentrant grooves with transverse connecting channels produced by stacking metal plates assembled according to a fourth example of the invention, with an aspect ratio of the flat rectangular heat pipe. Fig 13 ] there figure 13 is an exploded view of a heat pipe with reentrant grooves with transverse connecting channels produced by stacking metal plates assembled according to a fifth example of the invention. Fig 14 ] there figure 14 is a detailed and cross-sectional view of the figure 13 , at the level of the evaporator according to the fifth example of the invention. [ Fig 15 ] there figure 15 is a detailed and cross-sectional view, at the level of the condenser and the adiabatic zone of the heat pipe according to the fifth example of the invention. Fig 16 ] there figure 16 is a detailed and cross-sectional view, at the level of the evaporator, of a heat pipe with reentrant grooves with transverse connecting channels produced by stacking metal plates assembled according to a sixth example of the invention. Fig 17 ] there figure 17 illustrates in the form of curves the capillary limits of the different examples of heat pipes according to the state of the art and according to the invention. Fig 18 ] there figure 18 is an exploded view of a heat pipe with reentrant grooves with transverse connecting channels produced by stacking metal plates assembled according to another embodiment of the invention. Fig 19 ] there figure 19 is a detailed and cross-sectional view of the figure 18 , at the evaporator level. [ Fig 20 ] there figure 20 is a detailed and cross-sectional view of the figure 18 , at the level of the adiabatic zone of the heat pipe. [ Fig 21 ] there figure 21 is a perspective and detailed view of an alternative embodiment of the evaporator of a heat pipe according to the invention, comprising heat diffusers integrated at the level of the evaporator. Fig 22 ] there figure 22 is a perspective and exploded view of detail of another variant embodiment of the evaporator of a heat pipe according to the invention. Fig 23 ] there figure 23 is a perspective and exploded view of detail of another variant embodiment of the evaporator of a heat pipe according to the invention. Fig 24], [Fig 25 ] THE figures 24 et 25 are perspective views of other examples of embodiments of the connecting channels at the central window with intermediate plates of a heat pipe according to the invention. Fig 26 ] there figure 26 is a perspective view of another exemplary embodiment of a heat pipe according to the invention arranged in several planes. Fig 27A ], [ Fig 27B], [Fig 27C], [Fig 27D ], [ Fig 27E], [Fig 27F], [Fig 27G ], [ Fig 27H ] THE figures 27A à 27H are perspective views of examples of fins applicable to a heat pipe according to the invention. Fig 28 ] there figure 28 is an exploded view of a heat pipe according to an exemplary embodiment comprising a heat exchanger at the condenser. Description détaillée

[0105] THE figures 1 à 4 have already been commented on in the preamble. They are not detailed below.

[0106] For the sake of clarity, the same element according to the prior art and the invention is designated by the same numerical reference.

[0107] It is specified here that the reference SC used in the figures designates the hot source or, by extension, the area of ​​application of the heat flux emitted by the hot source directly on the lateral face of a heat pipe enclosure. Φ E designates the heat flux emitted by the hot source towards a heat pipe, and Φ S designates the heat flux emitted by a heat pipe towards a cold source.

[0108] Various examples of heat pipes with reentrant grooves according to the state of the art and according to the invention are described below in order to be able to compare their performances, as detailed below.

[0109] It should be noted that for all these examples, the liquid channels are present in both the evaporator and the condenser.

[0110] All heat pipes according to these examples have the same total length, the same evaporator length, the same adiabatic zone length, and the same condenser length.

[0111] The external cross-section defining the lateral dimensions of each heat pipe according to these examples is equal to 13.2mm x 13.2mm.

[0112] Exemple 1 (selon l'état de l'art) : the reentrant groove heat pipe 1 is obtained by extrusion according to the state of the art with reentrant grooves, as shown in the figure 5 .

[0113] The evaporator of such a heat pipe 1, axisymmetric of generally cylindrical shape, comprises a peripheral wall 10 in which are made a plurality of channels 11 with a generally Omega-shaped cross-section, regularly distributed angularly and opening via a connecting channel 12 onto a central cylindrical hollow 13 in which the vapor phase circulates. The peripheral wall 10 is in contact with a heat source (SC).

[0114] Exemple 2 (selon l'état de l'art) : On the figures 6 à 8 , we can see an example of a heat pipe 1 with capillary pumping with reentrant grooves produced according to patent application EP3553445.

[0115] This example of a capillary pumped heat pipe 1 extending along a longitudinal axis X is seen from the outside on the figure 6 .

[0116] The heat pipe 1 comprises a sealed enclosure 2 extending along the longitudinal axis X between a first longitudinal end 3 and a second longitudinal end 4. The first end 3 is for example intended to be heated by a hot source SC to form an evaporator ZE within the enclosure. The second longitudinal end 4 is intended to be cooled by a cold source SF to form a condenser Zc within the enclosure.

[0117] The sealed enclosure 2 internally delimits an adiabatic zone ZA between the evaporator and the condenser.

[0118] The heat source is, for example, an electrical or electronic component, a heat storage system, an exothermic chemical reactor. The cold source is, for example, a radiating surface, fins in forced convection, cold plates in single- or two-phase flow, a cold storage system, an endothermic chemical reaction, etc.

[0119] The sealed enclosure 2 is produced by stacking and assembling end plates 22 also called closing plates and intermediate plate modules 20 arranged between the end plates 22, according to a method described in patent application EP3553445.

[0120] A module comprises at least two intermediate plates, the plates of the different intermediate plate modules 20 comprising windows or other structures, being stacked so as to delimit channels 11, 12, 13 as detailed below. A module can also comprise a single plate machined on its two main faces.

[0121] The production, stacking and assembly of the plates is not detailed here; reference may be made to the aforementioned application EP3553445. However, the plates 20, 22 are preferably made of aluminum alloy and assembled by vacuum brazing. The aluminum alloy plates may preferably be coated with a eutectic cladding.

[0122] A preferred embodiment consists of machining plates 20 cladding on their two main faces, then assembling these sheets by eutectic vacuum brazing. As a variant, machining can be carried out on only one main face of the cladding plates.

[0123] For assembly, different processes are possible: salt bath brazing, inert gas brazing, ultrasonic welding, friction stir welding, gluing, etc.

[0124] The external dimensions of heat pipes range from a few centimeters to a few meters. The maximum size of heat pipes is generally limited by the available tooling. Indeed, joining sheets by vacuum brazing requires large vacuum furnaces, a few meters long.

[0125] Large machines are also required for cutting and machining sheet metal. In addition, the mechanical strength of sheets with narrow and long cuts must be taken into account.

[0126] For example, windows are made by punching, cutting, for example by laser or water jet.

[0127] In the illustrated example, all the plates 20 have the same external dimensions, the stack defining the sealed enclosure 2 is then of rectangular parallelepiped shape with four longitudinal faces parallel to the XY plane or to the XZ plane, each having a large surface area promoting heat exchanges with the hot source SC and the cold source SF. In the illustrated example, the longitudinal face 21 parallel to the XY plane is the one which receives the heat flow (φ E ) from the hot source (SC).

[0128] The stack of plates 20 with their windows or their structures 14, internally delimits, in the evaporator ZE, liquid channels 11, a vapor channel 13 connected to the liquid channels 11 by connecting channels 12.

[0129] More precisely, the steam channel 13 of constant rectangular cross-section extends along the longitudinal axis X. The steam channel 13 serves for the circulation of the vapor phase from the evaporator ZE to the condenser Zc via the adiabatic zone ZA.

[0130] A liquid channel 11 may or may not be connected to the vapor channel 13 depending on the area of ​​the heat pipe. When it is connected to the vapor channel 13, as in the evaporator ZE, a liquid channel 11 is connected by a connecting channel 12 with a section in the XZ plane smaller than that of the liquid channel. Each liquid channel 11 is intended for the circulation of the liquid from the condenser Zc to the evaporator ZE.

[0131] A connecting channel 12 forms a reentrant groove by defining an exchange zone between the vapor and the liquid. In other words, a connecting channel 12 by defining at least one liquid-vapor interface.

[0132] Thus, in the state of the art, as illustrated in figures 7 et 8 , the connecting channels 12 extend along the longitudinal direction X of the heat pipe. As symbolized in the figure 8 , this production of the channels 12 has the particular disadvantage that the brazing zones B between intermediate plates 20 within the stack and with the end plates 22 can only be physically present on one longitudinal side of the liquid channels 11.

[0133] For example, in particular for an aluminum alloy heat pipe using ammonia as the working fluid, the intermediate plates 20 have a thickness of between 0.5 mm and 6 mm, preferably equal to 2 mm.

[0134] The end plates 22 have a thickness of between 1 mm and 3 mm, preferably equal to 2 mm.

[0135] The width in the YZ plane of a connecting channel 12 is between 0.1 and 1 mm, preferably of the order of 0.2 mm.

[0136] The width in the YZ plane of a liquid channel 11 is between 0.5 and 4 mm, preferably of the order of 3 mm.

[0137] Exemple 3 (selon l'invention) : In this example illustrated in figures 9 à 11 , the evaporator comprises a plurality of porous graphite inserts 15, each preferably in the form of a flat sheet.

[0138] A porous insert 15 rests inside a longitudinal notch 16 provided for this purpose in an intermediate plate 20.

[0139] The stacking of the intermediate plates 20 is carried out by alternating between two intermediate plates a porous insert 15 to the evaporator ZE. Then, the two closing plates 22 are arranged at the ends of the stack to close the channel(s) 11, 12, 13. The stacking is carried out so that a porous insert 15 is sandwiched between two intermediate plates 20 or between an intermediate plate 20 and a closing plate 22 while being compressed.

[0140] In this example 3, the porous insert 15 extends across the entire width in the Y direction of both the liquid 11, connecting 12 and vapor 13 channels. The porous insert 15 allows, by capillarity, the liquid to be brought from each liquid channel 11 towards the vapor channel 13 where it evaporates on the surface.

[0141] The adiabatic zone ZA and the condenser Zc are free of inserts.

[0142] The heat flow Φ E coming from the hot source reaches the lateral face 23 of the enclosure 2 of the heat pipe, that is to say being parallel to the plane of the plates 20, 22 and the liquid channels 11 are therefore opposite the face 23.

[0143] In this example 3, having several channels 11 in parallel makes it possible to increase the transmitted heat flow and / or the exchange surface. In this example 3, the return of the liquid is therefore done on the side opposite to that 23 by which the heat flow ΦE is supplied, which delays the appearance of bubbles in the liquid channels 11 (boiling limit).

[0144] At the condenser Zc, the heat flow Φ S is extracted by the lateral face 24, that is to say that on the side of the liquid channels 11. It is also possible to envisage heat extraction on the face 23 on the vapor channel side, or even on the other sides of the heat pipe.

[0145] Exemple 4 (selon l'invention) : This example illustrated in the figure 12 is identical to example 3 except that the aspect ratio between the width and height of the heat pipe is different so as to have a flatter heat pipe.

[0146] Example 5 (according to the invention) : In this example illustrated in figures 13 to 15, the evaporator also comprises a plurality of porous graphite inserts 15, each preferably in the form of a flat sheet.

[0147] A porous insert 15 rests inside a longitudinal notch 16 provided for this purpose in an intermediate plate 20.

[0148] The stacking of the intermediate plates 20 is carried out by alternating between two intermediate plates a porous insert 15 to the evaporator ZE. Then, the two closing plates 22 are arranged at the ends of the stack to close the channel(s) 11, 12, 13. The stacking is carried out so that a porous insert 15 is sandwiched between two intermediate plates 20 or between an intermediate plate 20 and a closing plate 22 while being compressed.

[0149] In this example 5, the porous insert 15 extends across the entire width in the Y direction of both the liquid 11, connecting 12 and vapor 13 channels. To hold the porous insert 15 even better, a longitudinal notch may be envisaged provided for this purpose on the outer edge of the liquid channels 11.

[0150] Here, each lateral end of a porous insert 15 along the Y direction is above a liquid channel 11. In other words, two liquid channels 11 are arranged symmetrically on either side of the vapor channel 13 inside which the porous inserts 15 extend while being parallel to each other.

[0151] The adiabatic zone ZA and the condenser Zc are free of inserts and are therefore identical to those of example 2 according to the state of the art.

[0152] The heat flow Φ E coming from the hot source reaches the lateral face 21 of the enclosure 2 of the heat pipe while being perpendicular to the plane of the plates 20, 22.

[0153] At condenser Zc, the heat flow Φ S is extracted by the side faces 23 or 24. Extraction by the side face 21 or the opposite face can also be considered.

[0154] Example 6 (according to the invention) : In this example illustrated in the figure 16 , the evaporator also comprises a plurality of porous graphite inserts 15, each preferably in the form of a flat sheet.

[0155] A porous insert 15 rests inside a longitudinal notch 16 provided for this purpose in an intermediate plate 20.

[0156] The stacking of the intermediate plates 20 is carried out by alternating between two intermediate plates a porous insert 15 to the evaporator ZE. Then, the two closing plates 22 are arranged at the ends of the stack to close the channel(s) 11, 12, 13. The stacking is carried out so that a porous insert 15 is sandwiched between two intermediate plates 20 or between an intermediate plate 20 and a closing plate 22 while being compressed.

[0157] In this example 6, the porous insert 15 extends across the entire width in the Y direction of both the liquid 11, connecting 12 and vapor 13 channels.

[0158] Here, the central part of a porous insert 15 in the Y direction is above a single liquid channel 11 which is central and which is connected to two vapor channels 13 on either side via a connecting channel 12.

[0159] The porous insert 15 allows, by capillarity, the liquid to be brought from the central channel 11 to the two vapor channels 13 where it evaporates on the surface.

[0160] The adiabatic zone ZA and the condenser Zc are free of inserts.

[0161] The heat flow Φ E coming from the hot source reaches the two lateral faces 23, 24 of the enclosure 2 of the heat pipe while being parallel to the plane of the plates 20, 22. The central liquid channels 11 are therefore distant from the faces 23, 24 where the heat flows arrive and therefore have a reduced risk of boiling within them.

[0162] At the condenser Zc, the heat flux Φ S can be extracted by any side face 21, 23, 24 of the enclosure 2 of the heat pipe.

[0163] The performances of examples 1 and 2 according to the state of the art are compared with those of examples 3 to 6 according to the invention.

[0164] The comparison criteria chosen are respectively the capillary limit, the boiling limit, the thermal resistance to the evaporator, as stated in the publication [3].

[0165] The capillary limit can be defined as the limiting power determined by the difference between the driving pressure at the liquid / vapor interface at the evaporator and the pressure losses of the liquid and vapor phases migrating inversely in the heat pipe. This limit is calculated using thermohydraulic models, and calculated in absolute value and relative to the heat pipe of example 1 according to the state of the art (cylindrical heat pipe with reentrant grooves).

[0166] The boiling limit can be defined as the flow beyond which bubbles can appear in the grooves and impair the movement of the liquid in them. This limit can be evaluated by calculating the maximum superheat in the grooves using a finite element model, and is expressed relative to the superheat in the heat pipe of example 1 according to the state of the art (cylindrical heat pipe with reentrant grooves).

[0167] Finally, the thermal resistance to the evaporator R can be evaluated by the following formula: R = tsemelle − tvapeur / flux

[0168] In which sole: average temperature of the wall on which the heat flow is applied (°C) steam: temperature of the heat pipe steam (°C) flux: heat flux on the sole (W / m 2< ).

[0169] This value will also be given in relation to example 1 according to the state of the art (cylindrical heat pipe with reentrant grooves).

[0170] There figure 17 illustrates in the form of capillary limit curves the different examples as a function of the heat pipe temperature.

[0171] Table 1 below summarizes the gains in terms of capillary limit, boiling limit and thermal resistance to the evaporator of the different examples of heat pipes compared to the heat pipe of example 1 according to the state of the art (cylindrical heat pipe with reentrant grooves) whose reference values ​​are equal to 1. It should be noted that the values ​​indicated were calculated for an adiabatic temperature of 60°C. [Table 1] Examples 1 (State of the art) 2 (State of the art) 3 (Invention) 4 (Invention) 5 (Invention) 6 (Invention) Earnings capillary limit 1 3,9 3,4 4,7 4,0 3,1 boiling point limit 1 1,3 4,8 4,3 2,3 6,9 thermal resistance to the evaporator 1 1 ,3 2,7 2,7 2,0 3,1

[0172] From this table, it appears that whatever the example according to the invention, all the parameters measuring the performance are significantly increased compared to examples 1 and 2 according to the state of the art. Example 6 according to the invention presents the best performances.

[0173] Another embodiment of the invention is illustrated in figures 18 to 20 .

[0174] In this other embodiment, the ZE evaporator comprises a plurality of porous graphite inserts 15, each preferably in the form of a flat sheet.

[0175] A porous insert 15 rests inside a longitudinal notch 16 provided for this purpose in an intermediate plate 20.

[0176] The Zc condenser also comprises a plurality of porous graphite inserts 17, each preferably in the form of a planar sheet, as shown in the figure 18 The material constituting the porous inserts 17 may be the same as that of the porous inserts 15.

[0177] The stacking of the intermediate plates 20 is carried out by alternating between two intermediate plates a porous insert 15 at the evaporator ZE, and a porous insert 17 at the condenser Zc. Then, the two closing plates 22 are arranged at the ends of the stack to close the channel(s) 11, 12, 13. The stacking is carried out so that a porous insert 15 and a porous insert 17 are sandwiched between two intermediate plates 20 or between an intermediate plate 20 and a closing plate 22 while being compressed.

[0178] In this other mode, the porous insert 15 and the porous insert 17 extend across the entire width in the Y direction of both the liquid 11, connecting 12 and vapor 13 channels.

[0179] Here, the central part of a porous insert 15 or a porous insert 17 in the Y direction is above a single liquid channel 11 which is central and which is connected to two vapor channels 13 on either side via a connecting channel 12.

[0180] The porous insert 15 allows, by capillarity, the liquid to be brought from the central channel 11 to the two vapor channels 13 where it evaporates on the surface.

[0181] The adiabatic zone ZA is free of inserts.

[0182] This other mode is advantageous compared to examples 3 to 6 above because even if the capillary limit is reduced, it makes it possible to improve the thermal resistance to the condenser Zc.

[0183] There figure 21illustrates an advantageous variant according to which the closing plates 22 of a stack defining a heat pipe enclosure according to the invention have a larger surface area in the XY plane, in order to use them as thermal diffusers to spread the heat flow over a wider area, at the level of the evaporator and / or the condenser.

[0184] Within the framework of the invention, a heat pipe can be produced that is more or less wide depending on the evaporator, adiabatic and condenser zones, which makes it possible to optimize the mass of the heat pipe.

[0185] In the case of a flow perpendicular to the plates 20, 22, this makes it possible to increase the exchange surface at the evaporator, and / or at the condenser and therefore minimize the external thermal resistances.

[0186] In the case of a heat flow parallel to the plane of the plates 20, 22, the size of the liquid and / or vapor channels is increased, making it possible to increase the capillary limit of the heat pipe.

[0187] In the absence of liquid channels 11 under a porous insert 15 or 17, and therefore with a capillary return of the liquid only in said insert 15 or 17, it is preferable to increase the width of the porous insert 15 where the liquid channels 11 are located, in order to limit the pressure losses therein, as illustrated in figure 22 .

[0188] There figure 23 illustrates an advantageous variant in which the structures 14 of the evaporator and, where appropriate, of the condenser comprise a plurality of pads 18 distributed uniformly in the connecting channels 12 along the direction (X). These pads 18 make it possible to ensure mechanical support of the porous insert. The presence of these pads 18 can be achieved for the examples with liquid channels on the sides or central ones as in this figure 23 .

[0189] The cutouts of the connecting channels 12 can be made straight, or with a wavy shape ( figure 24) or sawtooth ( figure 25 ) over all or part of the length of the canals.

[0190] This shape made with the ZC condenser makes it possible to obtain walls not wetted by the condensation film at the peaks of either the corrugations or the saw teeth. This also makes it possible to increase the condensation exchange coefficient by minimizing the interface resistance of the condensation film.

[0191] A heat pipe according to the invention may be rectilinear or arranged in different planes. It is possible to make one or more changes of direction by the shape of the plates 20, 22 and / or bends on the enclosure 2 in order to conform to the application for which the heat pipe is intended. The bends may be made in one or more planes as required, at any bending angle.

[0192] A limitation to bending would come from a bending radius that is too small compared to the thickness of the heat pipe, which could lead to crushing of the channels during bending, and delamination of the plates assembled together.

[0193] It is also not possible to bend the heat pipe in the evaporator area, due to the fragility of the porous inserts 15.

[0194] There figure 26 illustrates such a variant with a heat pipe comprising a rectilinear part 25 integrating the condenser ZC of the heat pipe and another rectilinear part 26, bent at 90° to the rectilinear part 25, which integrates over part of its length the evaporator ZE. The adiabatic zone therefore extends in the two rectilinear parts 25, 26 at 90° to each other.

[0195] This figure 26 also shows the presence of fins 27 forming a radiator to the condenser ZC.

[0196] Finally, it shows the presence of a filling pipe 28 which allows the heat pipe to be filled with the working fluid. The filling pipe can be fixed to an orifice provided on the closing plates 22, and perpendicular to it.

[0197] THE Figures 27A to 27H illustrate different fin shapes that can be used as a radiator, namely extruded straight fins, skived fins, pleated fins: straight rectangular section, triangular section, corrugated, OSF type, perforated straight, louvered.

[0198] A liquid or two-phase circuit can be integrated directly into a heat pipe as a hot and / or cold source.

[0199] There figure 28illustrates such an integration: a cooling circuit 30 in which a heat transfer fluid is intended to circulate is directly in contact with the condenser. In the example shown, the cooling circuit 30 is formed by an additional plate 31, in which grooves 32 are made defining the side walls of the circuit, and the closing plate 22 and an additional closing plate 22 form the end walls of the cooling circuit. The closing plate 22 has two orifices 29 each opening at one end of the circuit and allowing the circulation of the heat transfer fluid.

[0200] Other advantages and improvements may be made without departing from the scope of the invention.

[0201] The invention is not limited to the examples which have just been described; in particular, it is possible to combine characteristics of the illustrated examples within non-illustrated variants.

[0202] All the variants can be combined or not with each other: for example, it is possible to have non-opening longitudinal grooves 16 combined with transverse connecting channels 12 over the entire height of the intermediate plates 20, for example in a staggered pattern, and where appropriate with longitudinal brazing grooves at the interface between plates 20 or 20, 22.

[0203] A heat pipe is filled with a two-phase fluid, which may be a fluid well known to those skilled in the art. This is chosen, for example, according to the operating and storage temperature range of the device, according to the constraints due to pressure, flammability, toxicity of the fluid and the chemical compatibility between the fluid and the material forming the heat pipe.

[0204] In addition, some fluids are not compatible with certain materials, oxy-reduction reactions can lead to corrosive phenomena involving reaction products, for example non-condensable gases, degrading the hydrodynamic operation of heat pipes.

[0205] For example, for a heat pipe according to the invention made of an aluminum alloy, nickel, copper or an alloy based on a combination of them, assembled by eutectic brazing, ammonia, water, acetone, methane, etc. can be used as fluid. The preferred filling fluid is ammonia (NH3).

[0206] Due to the limitations of use, between the working fluids and the metals mentioned, the couples considered can be as follows: Working fluid Heat pipe metal(s) Ammonia Aluminum, steel, stainless steel, nickel Methanol Copper, stainless steel Acetone Aluminum, stainless steel Water Copper, nickel, titanium List of cited references

[0207] [1]: Christine Hoa: " Thermal properties of axially grooved heat pipes: studies and implementations for space applications.University of Poitiers, 2004. [2]: SW Chi, "Heat Pipe Theory and Practice," McGraw-Hill, NY, USA, 1976. [3]: Jocelyn BONJOUR et al. "Two-phase thermal control systems - Thermosiphons and heat pipes" Engineering Technique, BE9545, 2015.

Claims

1. Capillary-pumped heat pipe (1) with re-entrant grooves, extending in a first longitudinal direction (X), comprising a sealed enclosure (2) extending between a first longitudinal end (3), intended to be heated by a hot source SC to form, within the enclosure, an evaporator, and a second longitudinal end (4) intended to be cooled by a cold source SF to form, within the enclosure, a condenser, the sealed enclosure delimiting an adiabatic zone between the evaporator and the condenser, the sealed enclosure comprising a stack of plates (20, 22) in a second direction (Z), orthogonal to the first direction (X), including two closing plates (22) and at least a number n of modules on top of each other, where n is an integer greater than or equal to 1, each module comprising at least one intermediate plate (20) between the closing plates, the intermediate plate or plates comprising at least one first intermediate plate having at least one window, the edges of which partially delimit at least one vapour channel (13) extending in the first direction (X) between the evaporator and the condenser, in which the vapour is intended to flow, and, on at least one lateral side of the window in a third direction (Y) orthogonal to the first direction (X) and the second direction (Z), at least one structure (14), the edges of which partially delimit at least one liquid channel (11) in the evaporator and the condenser, the heat pipe comprising, at least in the evaporator, at least one exchange zone that defines a liquid-vapour interface and is delimited between the at least one intermediate plate and at least one other intermediate plate or a closing plate, connecting the vapour channel(s) and the liquid channel(s), each exchange zone comprising at least one open connecting channel (12), characterized in that each of at least some of the open connecting channels (12) of the evaporator accommodate an insert made of porous material (15) which extends at least partially into the liquid channel(s) and into the vapour channel(s), the porous insert being designed to bring, by capillary action, the liquid from the liquid channel(s) to the vapour channel(s), in which the liquid evaporates.

2. Capillary-pumped heat pipe (1) with re-entrant grooves according to Claim 1, the condenser of the heat pipe also comprising at least one exchange zone that defines a liquid-vapour interface and is delimited between the at least one intermediate plate and at least one other intermediate plate or a closing plate, connecting the vapour channel(s) and the liquid channel(s), each exchange zone comprising at least one open connecting channel (12), at least some of the open connecting channels (12) of the condenser each accommodating an insert made of porous material (17) which extends at least partially into the liquid channel(s) and into the vapour channel(s), the porous insert being designed to condense the vapour in the vapour channel and to bring the condensed liquid to the liquid channel by capillary action.

3. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the adiabatic zone of the heat pipe comprising at least one exchange zone between the vapour channel(s) and the liquid channel(s) that defines a liquid-vapour interface and is delimited between the at least one intermediate plate and at least one other intermediate plate or a closing plate, each exchange zone comprising at least one open connecting channel (12) with no inserts.

4. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the porous insert of the evaporator and, where applicable, of the condenser extending over the entire width of the vapour channel in the third direction (Y).

5. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the porous insert being in the form of a flat sheet, preferably at least some of the intermediate plates comprising, in the evaporator and where applicable in the condenser, at least one longitudinal notch (16) extending in the first direction (X) forming a bearing-and-holding surface for the porous flat sheet.

6. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the constituent material of a porous insert (15, 17) being graphite-based, preferably non-wettable by a filler metal for brazing.

7. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the width of a porous insert being between 0.1 mm and 1 mm, preferably of the order of 0.6 mm.

8. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the average size of the pores of a porous insert being between 1 um and 100 µm, preferably of the order of 50 µm.

9. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the constituent material of the plates forming the sealed enclosure being chosen from aluminium, copper, nickel, or an alloy based on at least two of these.

10. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims having n modules on top of each other, n being an integer greater than or equal to 1, defining a single vapour channel and n liquid channels on at least one lateral side, notably on each lateral side of the vapour channel, preferably comprising a single central vapour channel arranged between n liquid channels distributed laterally on both sides of the vapour channel.

11. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, at least one of the end plates having a surface area larger than the surface area of the intermediate plates in a direction transverse to the direction (Z) of the stack so as to form heat spreaders.

12. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the cross section in the XY plane of the evaporator incorporating the porous insert and / or the cross section of the condenser, preferably rectangular, being larger than the cross section of the adiabatic zone of the heat pipe.

13. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the structures of the evaporator and, where applicable, of the condenser comprising a plurality of studs distributed, preferably uniformly, in the first direction (X) .

14. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, comprising heat exchange means at the first end and / or second end, the heat exchange means at the second end advantageously including one or more fins in thermal contact with at least one of the closing plates, the heat exchange means preferably comprising a fluidic circuit (32) in thermal contact with at least one of the closing plates (12), said circuit being formed by a plate (36) structured so as to delimit channels (38), said channels (38) being closed by said closing plate (12) and an additional closing plate (40), the heat exchange means also including means for supplying said fluidic circuit with heat-transfer fluid.

15. System including: - a cold source (SF); - a hot source (SC); and - at least one heat pipe (1) according to one of the preceding claims, the heat pipe being arranged in such a way that the heat flow (ΦE) from the hot source (SC) on the evaporator is on at least one lateral face (21) of the enclosure facing the vapour channel or on at least one lateral face facing the liquid channel(s), while the heat extraction in the condenser to the cold source (SF) is on at least one lateral face of the enclosure facing the liquid channel(s), or on a lateral face perpendicular thereto.