CAPILLARY PUMP HEAT PIPE WITH GROOVES RUNNING TRANSVERSE TO THE LONGITUDINAL AXIS OF THE HEAT PIPE

Description

Technical field

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

[0002] The present invention aims to improve the boiling limit of such a heat pipe. Prior art

[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 condensates) 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 regime, 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 capillary network in which the liquid phase circulates. Due to a change in curvature of the liquid-vapor interface between the condenser and evaporator zones, a pressure gradient appears in the liquid, which leads to a change 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. These heat pipes are used mainly in the space sector, for example for thermal regulation in satellites and / or spacecraft.

[0012] Known production techniques for 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 made mainly by extrusion. With this technique, the depth to width ratio of rectangular grooves is around 1.

[0014] 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.

[0015] 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.

[0016] Another technique uses chemical etching. But it also does not allow for a high depth-to-width ratio.

[0017] 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 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.

[0018] Patent US7051793 describes a heat pipe comprising one or more zones for circulation of the fluid in vapor form and on either side of these zones porous zones for circulation of the liquid, these capillary zones extending over the entire heat pipe. The heat pipe is also made by stacking plates. The capillary zones are obtained by stacking plates comprising windows, the windows having orthogonal directions from one plate to the other. The capillary pumping effect is not optimal. In addition, a significant pressure drop exists. This heat pipe spreads the heat flow over the width of the heat pipe and is not optimized for transporting the heat flow over its length.

[0019] Over the operating temperature range of a heat pipe, various physical limits can limit its performance. The operating curve of the heat pipe, which allows its maximum transport capacity to be determined, is obtained by combining the curves corresponding to the various physical operating limits which ultimately define the operating range of the heat pipe in terms of the maximum power it can transfer.

[0020] 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.

[0021] 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 increase with the mass flow rate of the working fluid (and with the length of the heat pipe): the capillary limit is reached when the capillary driving pressure is equal to the sum of the pressure losses. In other words, a heat pipe only operates if the capillary driving pressure is higher, in microgravity conditions, than the pressure losses, and therefore below the capillary limit.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Furthermore, when the meniscus of the liquid / vapor interface evaporates in the groove that 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.

[0029] It is therefore advantageous to have a large volume of liquid in a connecting channel, in order to minimize this phenomenon.

[0030] The overall thermal resistance of a heat pipe can be assessed by making a network analogy of independent thermal resistances.

[0031] 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.

[0032] 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 1 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.

[0033] On this path, the limiting thermal resistance is that of the liquid channels (capillary network), respectively to the evaporator and the condenser (R3, R7).

[0034] 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.

[0035] 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

[0036] 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.

[0037] 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.

[0038] 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.

[0039] Finally, the film resistance depends in particular on the length of the triple contact lines between liquid, vapor and solid.

[0040] 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.

[0041] Therefore, in state-of-the-art reentrant groove heat pipes, the connecting channels between the liquid-filled reentrant grooves (channels) and the vapor channel are made along the entire length along the longitudinal axis of the heat pipe, which leads to the following disadvantages: limitation of the thermal resistance to the evaporator by limited thermal conduction in the walls between channels; limitation of the thermal resistance to the evaporator by limiting the lengths of triple contact lines between liquid, vapor and solid, the preferred location for evaporation of the liquid; limitation of the heat flux that can be transported by the heat pipe, by limited volume of the connecting channels leading to a risk of the meniscus moving back in the re-entering liquid channels and thereby a loss of priming of the heat pipe. An increase in the length of the connecting channels would make it possible to avoid this risk, but at the expense of the volume and mass of the heat pipe; brazing, bonding or welding of the stacked plates, between them only in the peripheral longitudinal walls of the heat pipe.

[0042] Therefore, there is a need to further improve reentrant groove heat pipes to overcome the above-mentioned drawbacks.

[0043] The general aim of the invention is then to respond at least in part to this need. Statement of the invention

[0044] 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 partly delimit a 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 partly 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 and the liquid channel(s).,

[0045] According to the invention, each exchange zone comprises a plurality of connecting channels, opening out which extend transversely to the first direction (X), preferably along the third direction (Y), two adjacent connecting channels being separated by a structuring thickness.

[0046] The width of the connecting channels is preferably between 0.1 mm and 0.5 mm, and optimally 0.2 mm.

[0047] A structuring thickness is preferably between 0.3 mm and 3 mm and optimally equal to 1 mm.

[0048] The greater the number of connecting channels, the greater the number of triple liquid-vapor interface lines, which allows for better local conductance at the evaporator, crossed with estimated manufacturability limits (by machining or additive manufacturing).

[0049] 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 and the liquid channel(s), each exchange zone comprising at least one connecting channel, opening which extends transversely to the first direction (X), preferably in the third direction (Y).

[0050] Advantageously, the cross-section in the XZ plane of each connecting channel opening into the condenser is greater than that in the evaporator. Indeed, the connecting channels can be wider in the condenser because there is no need for capillary pressure unlike in the evaporator.

[0051] Advantageously, the adiabatic zone of the heat pipe is free from an exchange zone between the vapor channel and the liquid channel(s).

[0052] 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.

[0053] 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 XZ 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 XZ 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.

[0054] According to an advantageous embodiment variant, each connecting channel is made opening onto the entire thickness in the YZ plane of a structure of an intermediate plate.

[0055] This variant brings several advantages: it facilitates the machining of the connecting channels because they are made in a single operation on each plate, it allows the re-entering channels to partially communicate with each other (from one liquid channel to another), which can make it possible to balance the flows in them, in particular if there is a two-phase flow, it makes it possible to increase the liquid share in a connecting channel, as well as the length of the triple lines, which further improves the thermal resistance to the evaporator.

[0056] According to another advantageous embodiment variant, the connecting channels are made in such a way as to be arranged in a staggered pattern in an XZ plane.

[0057] According to an advantageous embodiment, the structures comprise longitudinal, non-opening grooves, which extend in the first direction (X), on the side of the vapor channel, crossing the connecting channels. These longitudinal, non-opening grooves make it possible to increase the contact surface between liquid and vapor, and the length of the triple lines, thus making it possible to reduce the thermal resistance in the evaporation zone.

[0058] According to this mode, the width in the YZ plane of the longitudinal grooves is preferably substantially equal to the width in the XZ plane of the connecting channels.

[0059] The width in the YZ plane of the longitudinal grooves is preferably substantially equal to their depth in the third direction (Y).

[0060] According to an advantageous embodiment, at least one intermediate plate comprises longitudinal grooves which extend in the first direction, at the interface with an adjacent intermediate plate or a closing plate, crossing the connecting channels. In order to avoid blocking the connecting channels with solder during a soldering operation for assembly between the different plates of the stack, these longitudinal grooves on the soldering surfaces in this area make it possible to trap the excess solder.

[0061] These grooves can be placed on one of the longitudinal sides, or on both sides of an intermediate plate.

[0062] The width of these grooves is advantageously substantially equal to or slightly smaller than that of the connecting channels in order to promote, by capillary pumping, the preferential trapping of excess solder in these areas.

[0063] 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.

[0064] 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.

[0065] 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).

[0066] Thus, the invention essentially consists of proposing a heat pipe of which at least the evaporator comprises connecting channels between the vapor channel and the liquid channel(s) which are not produced along the length of the heat pipe as according to the state of the art, but transversely to this length.

[0067] The production of such a heat pipe is implemented using a method as in 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.

[0068] The invention provides numerous advantages, among which we can cite those compared to solutions according to the state of the art, in particular a heat pipe according to EP3553445: an increase in the pressure resistance of the heat pipe due to an additional assembly area by the structures between the channels of the connections. This makes it possible to reduce the peripheral thicknesses in the section of the heat pipe, and therefore to reduce the mass and volume of the heat pipe, an improvement in the thermal resistance of the heat pipe at the evaporator level thanks to a greater length of the triple lines, without disturbing the thermal flow lines which connect the area where the flow to be thermalized is applied to these triple lines.In addition, the thermal conduction resistance at a connecting channel is improved, an increase in the liquid / vapor interface meniscus surface area, while maintaining the smallest possible connecting channel opening, which ensures the driving pressure ensuring capillary pumping in the heat pipe, an increase in the volume of liquid in a connecting channel between the liquid channel and the vapor channel, which allows a meniscus recoil which is less, at equivalent heat flux. This implies a necessary length of connecting zone (connecting channels) which is less and therefore a gain in volume and additional mass. This gain can also be used, by keeping the same connecting channel length, to obtain a wider operating temperature range at a given filling rate. Alternatively, by keeping the same connecting channel length, a wider operating temperature range can be obtained at a given filling rate of the heat pipe.

[0069] 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. Brief description of the drawings

[0070] [ 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 side view of a heat pipe with reentrant grooves, according to the state of the art. Fig 4 ] there figure 4 is a perspective and cross-sectional view of the figure 3 , at the level of the evaporator of the reentrant grooved heat pipe according to patent application EP3553445. [ Fig 5 ] there Figure 5 is a detailed and cross-sectional view of the figure 4 . [ Fig 6 ] there figure 6is a partial perspective 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 the invention. Fig 7 ] there figure 7 is a is a detailed and cross-sectional view of the figure 6 . [ Fig 7A ] there Figure 7A is a detailed and longitudinal sectional view of the figure 7 . [ Fig 8 ] there figure 8 is a perspective view of part of a state-of-the-art evaporator, as illustrated in figure 4 . [ Fig 9 ] there figure 9 is a perspective view of a portion of an evaporator according to the invention, as illustrated in figure 6 . [ Fig 10 ] there figure 10 is a graphical representation of mechanical calculations carried out using finite element simulation software of the state-of-the-art part illustrated in figure 8 . [ Fig 11 ] there figure 11is a graphical representation of mechanical calculations carried out using finite element simulation software of the part according to the invention illustrated in figure 9 . [ Fig 12 ] there figure 12 illustrates in the form of curves the gains respectively on the liquid-vapor interface volume and the length of triple lines, obtained at the level of the evaporator of a heat pipe thanks to the transverse connection channels in accordance with the invention. Fig 13 ] there figure 13 is a partial perspective and cross-sectional view of a heat pipe with reentrant grooves according to the invention according to a variant of supplying the heat flow from a hot source. Fig 14 ] there figure 14 is a partial perspective and cross-sectional view of a heat pipe with reentrant grooves according to the invention according to another variant of supplying the heat flow from a hot source. Fig 15 ] there figure 15is a partial perspective and cross-sectional view of a heat pipe with reentrant grooves according to the invention according to an alternative embodiment where only one longitudinal face of the intermediate plates of the stack is machined. Fig 16 ] there figure 16 is a partial perspective and cross-sectional view of a heat pipe with reentrant grooves according to an alternative embodiment where the transverse connecting channels according to the invention are produced over the entire thickness of the intermediate plates of the stack. Fig 17 ] there figure 17 illustrates in the form of curves the gains respectively on the liquid-vapor interface volume and the length of triple lines, obtained at the level of the evaporator of a heat pipe thanks to the transverse connection channels conforming to the variant of the figure 16 . [ Fig 18 ] there figure 18is a partial perspective and cross-sectional view of a heat pipe with reentrant grooves according to an alternative embodiment where the transverse connecting channels according to the invention are arranged in a staggered pattern in a longitudinal plane XZ of the heat pipe. Fig 19 ] there figure 19 is a partial perspective and cross-sectional view of a heat pipe with re-entrant grooves according to an alternative embodiment where non-opening longitudinal grooves are made on the steam channel side by crossing the transverse connecting channels according to the invention. Fig 20 ] there figure 20 is a partial perspective and cross-sectional view of a heat pipe with re-entrant grooves according to an alternative embodiment where non-opening longitudinal grooves are made at the interface between plates of the stack by crossing the transverse connecting channels according to the invention. Detailed description

[0071] THE Figures 1 and 2have already been commented on in the preamble. They are not detailed below.

[0072] For the sake of clarity, the same element according to the prior art and the invention is designated by the same numerical reference.

[0073] 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 thermal flux emitted by the hot source directly on the lateral face of a heat pipe enclosure.

[0074] On the figures 3 to 5 , we can see an example of a heat pipe 1 with capillary pumping with reentrant grooves produced according to patent application EP3553445.

[0075] This example of a capillary pumped heat pipe 1 extending along a longitudinal axis X is seen from the outside on the figure 3 .

[0076] 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.

[0077] The sealed enclosure 2 internally delimits an adiabatic zone ZA between the evaporator and the condenser.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] A preferred embodiment consists of machining plates 20 cladded 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 cladded plates.

[0083] For assembly, different processes are possible: salt bath brazing, inert gas brazing, ultrasonic welding, friction stir welding, gluing, etc.

[0084] 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.

[0085] 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.

[0086] For example, windows are made by punching, cutting, for example by laser or water jet.

[0087] 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).

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] Thus, in the state of the art, as illustrated in figures 4And 5 , the connecting channels 12 extend along the longitudinal direction X of the heat pipe. As symbolized in the Figure 5 , 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.

[0093] According to the invention, as illustrated in Figures 6 to 7A , each connecting channel 12 is produced by machining opening transversely to the X direction. Thus, each connecting channel 12 extends in the Y direction. As symbolized on the Figures 7 and 7A , with such transverse connecting channels 12, the brazing zones B between intermediate plates 20 and with the end plates 22 are physically present on both longitudinal sides of the liquid channels 11.

[0094] 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.

[0095] The end plates 22 have a thickness of between 1 mm and 3 mm, preferably equal to 2 mm.

[0096] The width in the XZ plane of a connecting channel 12 is between 0.1 and 1 mm, preferably of the order of 0.2 mm.

[0097] The structuring thickness 14 in the XZ plane delimiting the space between two adjacent connecting channels is between 0.2 and 2 mm, preferably of the order of 0.4 mm.

[0098] 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.

[0099] The external dimensions of the heat pipes according to the invention are between a few centimeters and a few meters. The maximum size of the heat pipes is generally limited by the available tools. Indeed, the assembly of sheets by vacuum brazing requires large vacuum furnaces, a few meters long. For cutting and machining the sheets, large machines are also required. In addition, the mechanical strength of sheets with narrow and long cuts must be taken into account. For example, windows are made by punching, cutting, for example by laser or water jet.

[0100] The fact of producing connecting channels 12 transversely to the longitudinal axis of the heat pipe makes it possible to increase the brazing zones B between plates 20, 22, since they are now present on either side of each liquid channel 11. This increases the pressure resistance of the heat pipe and thereby makes it possible to reduce the peripheral thicknesses in the section of the heat pipe, and therefore a gain in mass and volume is achieved for a heat pipe 1 according to the invention.

[0101] To highlight these gains in volume and mass of a heat pipe 1 produced with transverse connecting channels 12, i.e. in the Y direction, compared to a heat pipe according to the state of the art with longitudinal connecting channels, i.e. in the X direction, the inventors of the present invention carried out mechanical calculations by finite elements.

[0102] These comparative configurations are illustrated respectively in figures 8 And 10for a heat pipe 1 according to the state of the art and to figures 9 And 10 for a heat pipe 1 according to the invention.

[0103] Mechanical calculations thus show that by applying an internal pressure of 130 bars, in order not to exceed the elastic limit of the aluminium alloy, closing plates 22 of 2.1 mm thickness would be required for heat pipe 1 according to the figures 8 And 10 , while a thickness of 1.4 mm is sufficient for a heat pipe 1 according to the invention. Consequently, this represents a mass gain of 24%, and a volume gain of 11% at equal capillary limit.

[0104] Other thermo-hydraulic calculations also make it possible to establish gains for a heat pipe 1 according to the invention compared to a heat pipe 1 according to the state of the art.

[0105] There figure 12illustrates respectively the gains on the volume of the liquid-vapor interface meniscus and on the length of the triple lines as a function of the space between two adjacent transverse connecting channels 12. It is specified here that for the comparative example according to the state of the art and the example according to the invention, the width of the connecting channels 12 is the same and equal to 0.2 mm.

[0106] From these curves of the figure 12 , it appears that: for a space between two transverse channels 12, equal to 8 mm, the volume of the meniscus is equivalent to that of a heat pipe 1 according to the state of the art. On the other hand, the gain is 40% over the length of the triple lines, for a space between two transverse channels 12, equal to 4 mm, the gain in volume of the meniscus is 60% compared to that of a heat pipe 1 according to the state of the art. The gain is 140% over the length of the triple lines.

[0107] This therefore implies a gain in thermal resistance to the evaporator ZE and to the condenser ZC which must depend on the length of the triple lines.

[0108] Furthermore, the volume of the meniscus is larger, which makes it possible to reduce the length of a connection channel 12 (to obtain an equivalent meniscus volume), or to have greater safety in the event of the meniscus moving back to avoid the heat pipe from being defused.

[0109] This also makes it possible to accommodate a greater variation in the volume of liquid in the heat pipe and therefore potentially to widen, at a given filling rate, the operating temperature range.

[0110] THE figures 13 And 14 respectively illustrate the possibility of having the heat flow (ϕ E ) from the hot source (SC) on a lateral face 21 of the enclosure 2 opposite the liquid channels 11 or opposite the vapor channel 13.

[0111] In the example illustrated previously, the transverse connecting channels 12 are machined on each longitudinal side at the level of a structure 14 of an intermediate plate 20. Alternatively, it is possible to machine them only on one longitudinal side, as illustrated in the figure 15 .

[0112] There figure 16 illustrates an advantageous embodiment variant where the transverse connecting channels 12 according to the invention are produced over the entire thickness of the intermediate plates of the stack. In other words, these channels 12 are extended by grooved extensions 15.

[0113] This variant of the figure 16firstly facilitates the machining of the connecting channels 12 because they are produced in a single operation on each intermediate plate 20. Then these emerging extensions 15 make it possible to partially communicate the re-entering channels with each other (from one liquid channel 11 to another), which can make it possible to balance the flows in them, in particular if there is a two-phase flow.

[0114] Finally, machining these connecting channels 12 with extensions 15 over the entire height of the plates 20 makes it possible to increase the liquid portion in each connecting channel 12, as well as the length of the triple lines, which further improves the thermal resistance to the evaporator. This last advantage is illustrated in the form of curves in figure 17 depending on the space between two adjacent transverse connecting channels 12.

[0115] From these curves of the figure 17 , it appears that: for a space between two transverse channels 12 with extensions 15 over the entire height of the plates 20, equal to 8 mm, the gains in volume of the meniscus and over the length of the triple lines are respectively 70% and 90% compared to that of a heat pipe 1 according to the state of the art; for a space between two transverse channels 12, equal to 4 mm, the gain in volume of the meniscus is 180% compared to that of a heat pipe 1 according to the state of the art. The gain is 210% over the length of the triple lines.

[0116] The transverse connecting channels 12 may be aligned from one plate 20 to the other or arranged in a staggered manner in the XZ plane as illustrated in the figure 18 .

[0117] There figure 19illustrates an advantageous variant according to which several non-emerging longitudinal grooves 16 are made on the side of the vapor channel 13 in each intermediate plate 20. These grooves 16 make it possible to increase the contact surface between liquid and vapor, and the length of the triple lines, and thereby to reduce the thermal resistance in the evaporation zone. The width of these additional grooves 16 is preferably equal to that of the transverse connecting channels 12 and their depth advantageously equal to their width. In the figure 19 , the non-opening grooves 16 intersect transverse connecting channels 12 made over the entire height and aligned from one plate to the other. It is of course possible to produce a configuration with transverse connecting channels 12 over part of the height of the plates 20 and / or arranged in a staggered pattern.

[0118] There figure 20illustrates an advantageous variant according to which several longitudinal grooves 17 are produced on the structure 14 of each intermediate plate 20 in the stacking interface zone with an adjacent intermediate plate 20 or closing plate 22. These grooves 17 are intended to avoid blocking the connecting channels 12 with solder during the soldering operation between plates 20, 22. Indeed, in the event of excess solder, it will be able to lodge in these grooves 17 and therefore not come to lodge in the transverse connecting channels 12. The width of these soldering grooves 17 is preferably equal to or slightly smaller than that of the connecting channels 12 in order to promote, by capillary pumping, the preferential trapping of the excess solder in these zones. In the figure 19, the non-opening brazing grooves 17 are produced on a single longitudinal side of structures 14 of an intermediate plate 20. These grooves 17 can of course be produced on both longitudinal sides of the structures 14 of each plate 20.

[0119] Other advantages and improvements may be made without departing from the scope of the invention.

[0120] 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.

[0121] 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 17 at the interface between plates 20 or 20, 22.

[0122] 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.

[0123] 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.

[0124] For example, for a heat pipe according to the invention made of an aluminum alloy, nickel, copper, titanium or an alloy based on a combination of them, assembled by eutectic brazing, ammonia, water, acetone, methanol, etc. can be used as fluid.

[0125] 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

[0126] [1]: Christine Hoa: "Thermal properties of axially grooved heat pipes: studies and developments for space applications." University of Poitiers, 2004. [2]: SW Chi, "Heat Pipe Theory and Practice," McGraw-Hill, NY, USA, 1976.

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 > 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 including at least one window, the edges of which partially delimit a 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) with edges that 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 defining a liquid-vapour interface that is delimited between the at least one intermediate plate and at least one other intermediate plate or a closing plate, connecting the vapour channel and the liquid channel(s), the heat pipe (1) being characterized in that each exchange zone comprises a plurality of connecting through-channels (12) which extend transversely to the first direction (X), preferably in the third direction (Y), two adjacent connecting channels being separated by a structure thickness.

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 defining a liquid-vapour interface that is delimited between the at least one intermediate plate and at least one other intermediate plate or a closing plate, connecting the vapour channel and the liquid channel(s), each exchange zone comprising at least one connecting through-channel (12) which extends transversely to the first direction (X), preferably in the third direction (Y).

3. Capillary-pumped heat pipe (1) with re-entrant grooves according to Claim 2, the cross section in the plane XZ of each connecting through-channel (12) in the condenser being greater than the cross section in the evaporator.

4. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the adiabatic zone of the heat pipe having no exchange zone between the vapour channel and the liquid channel(s).

5. 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.

6. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the intermediate plates (20) having a thickness of between 0.5 mm and 6 mm, preferably of the order of 2 mm.

7. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the closing plates (22) having a thickness of between 1 mm and 3 mm, preferably of the order of 2 mm.

8. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the width in the plane XZ of a connecting channel (12) being between 0.1 mm and 1 mm, preferably of the order of 0.2 mm.

9. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the structure (14) thickness in the plane XZ delimiting the space between two adjacent connecting channels (12) being between 0.2 mm and 2 mm, preferably of the order of 0.4 mm.

10. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the width in the plane YZ of a liquid channel (11) being between 0.5 mm and 4 mm, preferably of the order of 3 mm.

11. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, each connecting channel (12, 15) being designed to pass through the entire thickness in the plane YZ of a structure (14) of an intermediate plate (20).

12. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the connecting channels (12) being formed in such a way as to be arranged in a staggered pattern in a plane XZ.

13. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the structures (14) comprising longitudinal grooves (16), which are not through-grooves and which extend in the first direction (X) on the side facing the vapour channel (13), crossing the connecting channels (12).

14. Capillary-pumped heat pipe (1) with re-entrant grooves according to Claim 13, the width in the plane YZ of the longitudinal grooves (16) being substantially equal to the width in the plane XZ of the connecting channels (12).

15. Capillary-pumped heat pipe (1) with re-entrant grooves according to Claim 13 or 14, the width in the plane YZ of the longitudinal grooves (16) being substantially equal to the depth thereof in the third direction (Y).

16. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, at least one intermediate plate comprising longitudinal grooves (17) which extend in the first direction (X) at the interface with an adjacent intermediate plate or a closing plate (22), crossing the connecting channels (12).

17. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, including 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.

18. Capillary-pumped heat pipe (1) with re-entrant grooves according to one of the preceding claims, the cross section in the plane YZ of the vapour channel and of the preferably rectangular liquid channel(s) being constant over the entire length of the heat pipe.

19. System comprising: - 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.