Heat pipe of the capillary pumped type with reentrance ducts for enhanced thermal conductivity

Abstract

The invention essentially consists of a heat pipe with re-entrant grooves, having thicker walls between liquid channels in the evaporator and, advantageously, in the condenser, unlike in the heat pipes of the prior art which have the same internal cross-section along the entire length of the pipe.

Description

Technical field

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

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

[0003] 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. This establishes an equilibrium between the liquid and vapor phases.

[0004] Under the effect of a heat source applied in an area at one of the longitudinal ends, called the evaporator, the liquid vaporizes, inducing a slight overpressure which causes the vapor to move towards an area at the other longitudinal end, called the condenser. At the condenser, the vapor condenses and returns to the liquid phase. The condensed fluid circulates in the capillary network and returns to the evaporator 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.

[0005] 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 through which the liquid circulates. Due to a change 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 change in capillary pressure. The smaller the groove width, the greater the capillary pumping effect.

[0006] Furthermore, deep grooves provide a large passage section for the liquid return, thus minimizing pressure loss.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] These heat pipes are made mainly by extrusion. With this technique, the depth to width ratio of rectangular grooves is of the order of 1.

[0011] 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.

[0012] 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.

[0013] Another technique uses chemical etching. But it also does not allow for a high depth-to-width ratio.

[0014] 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. A heat pipe according to the preamble of claim 1 is known from document FR3080172A1.

[0015] In the case of grooved heat pipes, the research axes identified by the inventors, to improve the thermal conductivity, focus on the characteristics of the working fluid, in particular by the use of nano-fluids with only water as the working fluid: [2] or by the use of so-called rewetting fluids, i.e. fluids whose surface tension increases with temperature: [3] or self-rewetting [4]. The authors of the publication [5] showed that the main effect of nanofluids was in reality the modification of the surface state at the evaporator of the heat pipe.

[0016] There is a need to further improve grooved heat pipes, particularly reentrant grooved heat pipes, in order to optimize their operation, improve their performance and extend their operating ranges, particularly to increase their thermal conductivity.

[0017] The general aim of the invention is then to respond at least in part to this need. Statement of the invention

[0018] To do this, the invention firstly relates to a 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 heat source to form, within the enclosure, an evaporator and a second longitudinal end intended to be cooled by a cold source to form, within the enclosure, a condenser, the sealed enclosure delimiting an adiabatic zone between the evaporator and the condenser, the enclosure comprising a stack of plates in a second direction (Z) orthogonal to the first direction (X), the stack comprising two closing plates, at least a number of n modules on top of each other with n being an integer > 1, each module comprising at least one intermediate plate between the closing 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 (Z) directions, at least one structure whose edges partly delimit a liquid channel in the evaporator and the condenser, at least the first intermediate plate delimiting a connecting channel connecting the vapor channel and the liquid channel at least in the evaporator and the condenser.,

[0019] According to the invention, the structures and intermediate plates of the n modules define a single vapor channel and on at least one lateral side of the vapor channel, n liquid channels, the walls between liquid channels are of progressively increased thickness in the evaporator, from the adiabatic zone.

[0020] According to an advantageous embodiment, the walls between liquid channels are of progressively increased thickness in the condenser, from the adiabatic zone.

[0021] Advantageously, the length, along the third direction Y, of the liquid-vapor connection channels is progressively increased in the evaporator, from the adiabatic zone.

[0022] Advantageously, the length, along the third direction Y, of the liquid-vapor connection channels is progressively increased in the condenser, from the adiabatic zone.

[0023] According to an advantageous embodiment variant, the structures are only on one lateral side of the window delimiting the steam channel.

[0024] Alternatively, the structures can be on each of the two lateral sides of the window, facing each other.

[0025] Advantageously, the cross-section in a YZ plane of the steam channel, preferably rectangular, is constant over the entire length X of the heat pipe.

[0026] 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 from the hot source (SC) onto the evaporator, and the heat extraction at the condenser towards the cold source (SF) being on at least one lateral face of the enclosure facing the liquid channels, or on a lateral face perpendicular to them.

[0027] Thus, the invention essentially consists of proposing a heat pipe with reentrant grooves, which unlike heat pipes according to the state of the art with an identical internal cross-section over the entire length of the heat pipe, has walls between liquid channels which are thickened in the evaporator, and advantageously in the condenser.

[0028] Even if this thickening degrades the capillary limit a little, it has the advantage of pushing back the boiling limit and improving the conductance of the heat pipe at the evaporator, and therefore the total conductance, by improving the thermal path between the hot source and the fluid.

[0029] To improve the thermal conductivity of a heat pipe, the inventors of the present invention started from thermal modeling.

[0030] In fact, 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 1 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 [6] 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 1: 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] The inventors of the present invention analyzed that with the realization of the heat pipes with reentrant grooves according to the patent application EP3553445, which consists of stacking and then assembling together punched or machined metal plates to define the different heat pipe channels, they could advantageously thicken the walls between channels at the evaporator and at the condenser to increase the thermal conductivity of a heat pipe. Due to the embodiment of the heat pipe according to the invention, it is possible to limit the thickening of the inter-channel walls to only the zones of the evaporator and the condenser, which are of limited length, and in which the fluid flow rate is not at its maximum, which makes it possible to reduce the negative impact on the capillary limit.

[0040] The invention provides numerous advantages, among which we can cite those compared to patent application EP3553445, as follows: increase in heat pipe thermal conductance, increase in heat pipe boiling limit.

[0041] Since the three zones of a heat pipe according to the invention (evaporator, adiabatic zone, condenser) do not have the same internal cross-section, different heat pipes will have to be produced for two applications where the lengths of the three zones differ, which is not favorable from a production cost point of view. But, in the case of embedded systems, more particularly in the space domain, this disadvantage is compensated by better performance.

[0042] The invention applies to many fields in which a system, particularly an electronic system, must be thermally managed, but in particular for on-board systems in the space sector to be thermalized.

[0043] 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

[0044] [ Fig 1 ] there Figure 1 is a symbolic representation of a network of thermal resistances that are established for a heat pipe. Fig 2 ] there Figure 2 is a schematic side view of an example of a heat pipe with reentrant grooves according to the invention. Fig 2A] and [Fig 2B ] THE Figures 2A and 2B are perspective and cross-sectional views respectively along AA and BB, of the evaporator of a heat pipe with reentrant grooves according to the Figure 2 . [ Fig 2C ] there Figure 2C is a perspective and cross-sectional view along CC of the adiabatic zone of a heat pipe with reentrant grooves along the Figure 2 . [ Fig 2D ] there 2D figureis a perspective and cross-sectional view along DD of the condenser of a heat pipe with reentrant grooves according to the Figure 2 . [ Fig 2E ] there Figure 2E is a perspective and cross-sectional view along EE of the condenser of a heat pipe with reentrant grooves according to the Figure 2 . [ Fig 3A] and [Fig 3B ] THE Figures 3A and 3B are perspective and cross-sectional views of the evaporator of a reentrant grooved heat pipe according to the invention, these figures showing the reduction in the width of the walls separating the liquid channels from the end of the heat pipe towards the adiabatic zone, and also the reduction in the length of the connecting channel as well as the increase in the length along the Y axis of the liquid channels. Fig 4 ] there Figure 4 illustrates in the form of curves the capillary limits obtained for a heat pipe with reentrant grooves respectively according to the invention and according to the state of the art. Fig 5 ] there Figure 5illustrates, in perspective view and in cross-section, another embodiment of a heat pipe with reentrant grooves according to the invention, each of the two lateral sides of which comprises six liquid channels in the condenser and evaporator. Fig 6], [Fig 6A], [Fig 6B ], [ Fig 7], [Fig 7A], [Fig 7B ], [ Fig 8], [Fig 8A], [Fig 8B ], [ Fig 9], [Fig 9A], [Fig 9B ], [ Fig 10], [Fig 10A], [Fig 10B ], [ Fig 11], [Fig 11A], [Fig 11B ] THE Figures 6 to 11B illustrate different possibilities for arranging the liquid channels of the evaporator and the condenser of a heat pipe according to the invention, relative to the hot and cold sources. Detailed description

[0045] There Figure 1 has already been commented on in the preamble. It will therefore not be detailed below.

[0046] On the Figures 2 to 2E , we can see an example of a heat pipe 1 with capillary pumping with reentrant grooves according to the invention.

[0047] On the Figure 2 , the example of capillary pumped heat pipe 1 extending along a longitudinal axis X is seen from the outside.

[0048] 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 heat 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.

[0049] The sealed enclosure 2 internally delimits an adiabatic zone ZA between the evaporator and the condenser.

[0050] 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.

[0051] The sealed enclosure 2 is produced by stacking and assembling end plates and intermediate plate modules 10 arranged between the end plates, according to a method described in patent application EP3553445.

[0052] A module comprises at least two intermediate plates, the plates of the different intermediate plate modules 10 comprising windows or other structures, being stacked so as to delimit channels 20, 21, 22 as detailed below. A module can also comprise a single plate machined on its two main faces.

[0053] The production, stacking and assembly of the plates is not detailed here; reference may be made to the aforementioned application EP3553445. Nevertheless, the plates 10 are preferably made of aluminum alloy and assembled by vacuum brazing.

[0054] A preferred embodiment consists of machining plates 10 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.

[0055] For assembly, different processes are possible: salt bath brazing, inert gas brazing, ultrasonic welding, friction stir welding, gluing, etc.

[0056] 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.

[0057] Large machines are also required for cutting and machining sheet metal. In addition, the mechanical stability of sheet metal with narrow and long cuts must be taken into account.

[0058] For example, windows are made by punching, cutting, for example by laser or water jet.

[0059] In the example illustrated, all the plates 10 have the same external dimensions, the stack defining the sealed enclosure 2 is then of rectangular parallelepiped shape with four longitudinal faces 11, 12, 13, 14, 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.

[0060] According to the invention, the stack of plates 10 with their windows or their structures internally delimits a channel called vapor channel 20, and as detailed below liquid channels 21.1 to 21.6 and connecting channels 22.

[0061] More precisely, the steam channel 20 of constant rectangular cross-section extends along the longitudinal axis X. The steam channel 20 is used for the circulation of the vapor phase from the evaporator ZE to the condenser Zc via the adiabatic zone ZA.

[0062] A liquid channel 21, 21.1 to 21.6 is connected to the vapor channel 20 by a connecting channel 22 with a section in the XZ plane smaller than that of the liquid channel. Each liquid channel is intended for the circulation of the liquid from the condenser Zc to the evaporator ZE.

[0063] A connecting channel 22 is therefore an exchange zone between the vapor and the liquid.

[0064] More precisely, according to the invention, the liquid channels 21, 21.1 to 21.6 have internal cross-sections differentiated according to the different zones of the heat pipe (evaporator ZE, adiabatic zone ZA, condenser ZC).

[0065] This differentiation is clearly visible in relation to the Figures 2A to 2E .

[0066] These Figures 2A to 2E show a heat pipe according to the invention comprising liquid channels only on one longitudinal side of the sealed enclosure 2.

[0067] THE Figures 2A and 2B show the evaporator of the heat pipe: it comprises a number of six liquid channels 21.1, 21.2, 21.3, 21.4, 21.5, 21.6 of cross-section identical to each other at a given dimension along the X axis, but which evolves progressively from the first longitudinal end 3 to the adiabatic zone ZA.

[0068] More specifically, each of the six liquid channels 21.1 to 21.6 has a cross-section in the YZ plane which increases from the first longitudinal end 3 ( Figure 2A ) up to its limit with the adiabatic zone ( Figure 2B ). In other words, the thickness of the walls separating the six liquid channels 21.1 to 21.6 decreases from the first longitudinal end 3 ( Figure 2A ) up to its limit with the adiabatic zone ( Figure 2B ).

[0069] There Figure 2C shows the adiabatic zone of the heat pipe: the liquid channels 21.1 to 21.6 have a cross-section in the YZ plane and a thickness between channels, which is constant over the entire length X of the adiabatic zone.

[0070] THE Figures 2D and 2Eshow the condenser of the heat pipe: it comprises a number of six liquid channels 21.1, 21.2, 21.3, 21.4, 21.5 21.6 of identical cross-section to each other at a given dimension along the X axis, but which can evolve progressively from the adiabatic zone ZA to the second longitudinal end 4.

[0071] The thickening of the walls between liquid channels 21.1 to 21.6 in the evaporator ZE, is illustrated in detail in Figures 3A and 3B .

[0072] THE Figures 3A and 3B further illustrate the variation in the length of the liquid-vapor connection channel, which allows on the one hand better management of the liquid (greater length to accommodate the recoil of the meniscus at the evaporator, and greater volume to accommodate variations in liquid volume depending on the operating temperature), and on the other hand to push back the boiling limit, and to a lesser extent to improve the thermal resistance.

[0073] It improves the conductance of the heat pipe at the evaporator and therefore the total conductance, by improving the thermal path between the heat source and the fluid. This helps delay the onset of the boiling point.

[0074] Thickening also has the effect of reducing the liquid flow section in the evaporator (from L2 to L1 in the illustrated example), and therefore increasing its speed, which increases pressure losses (negative effect on the capillary limit), but has the advantage of delaying the appearance of bubbles (positive effect on the boiling limit). Several authors have in fact observed that in boiling configurations, increasing the flow speed makes it possible to delay the start of nucleation: see for example [7] and [8].

[0075] This thickening can be identical over the entire length, or be progressive. The advantage of progressive thickening is that it adjusts the section of the liquid flow to the liquid flow rate, the latter increasing from the first longitudinal end 3 of the heat pipe to the end of the evaporator ZE.

[0076] As shown on the curves of the Figure 4 , for a heat pipe of 1m effective length, including 20cm of evaporator and 20cm of condenser, the capillary limit drop is 1% to 3% over the temperature range of the heat pipe, which is negligible. It is specified that the calculation was made from the reduction in the section of the liquid channel. The assumption is that the section of the liquid channel at the end of the evaporator, and at the end of the condenser, is 50% of that in the adiabatic zone, and that this reduction in section is progressive. This reduction can be a combination of thickening of the walls and lengthening of the connection zone.

[0077] As illustrated in the previous figures, it is advantageous to place liquid channels only on one longitudinal face, for example face 11 of a heat pipe.

[0078] This makes it possible, for a constant heat pipe section, to enlarge the liquid channels 21, and thus to reduce the pressure losses in them.

[0079] There Figure 5 shows an example variant of a heat pipe according to the invention, according to which the liquid channels 21.1, 21.2, 21.3, 21.4, 21.5 21.6 are arranged on two opposite longitudinal faces 11, 13 of the heat pipe, i.e. facing each other.

[0080] Different position configurations of the liquid channels in the heat pipe and relative to the cold SF and hot SC sources can be envisaged within the framework of the invention: THE Figures 6, 6A and 6Bshow an arrangement of liquid channels on two opposite longitudinal faces 11, 13 with the heat source flows coming directly into contact with these at the evaporator and the extraction by the cold source also in contact with these at the condenser; Figures 7, 7A and 7B show an arrangement of liquid channels on two opposite longitudinal faces 12, 14 with the heat source flows arriving on the faces 11, 13 orthogonal to these at the evaporator and the extraction by the cold source also by the faces 11, 13 orthogonal to these at the condenser; Figures 8, 8A and 8B show an arrangement of liquid channels on a single longitudinal face 14 with the heat source flow arriving on a single face 11 orthogonal to these at the evaporator and the extraction by the cold source also by a single face 12 opposite this at the condenser; Figures 9, 9A and 9Bshow an arrangement of liquid channels on a single longitudinal face 11 with the heat source flow arriving directly on this face 11 at the evaporator and the extraction by the cold source also by a single face 12 orthogonal to this at the condenser; Figures 10, 10A and 10B show an arrangement of liquid channels on two opposite longitudinal faces 11, 13 with the heat source flow coming directly into contact with only one of these faces 11 at the evaporator and the extraction by the cold source also by a single face 12 orthogonal to the condenser; Figures 11, 11A and 11B show an arrangement of liquid channels on two opposite longitudinal faces 12, 14 with the heat source flow arriving on a single face 11 orthogonal to these at the evaporator and the extraction by the cold source by one of the two faces 11, 13 orthogonal to these at the condenser.

[0081] Other advantages and improvements may be made without departing from the scope of the invention.

[0082] For example, a heat pipe according to the invention may comprise a greater or lesser number of liquid channels than six per longitudinal face.

[0083] The invention is not limited to the examples which have just been described; in particular, it is possible to combine characteristics of the examples illustrated within non-illustrated variants.

[0084] 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.

[0085] For example, for a heat pipe made of aluminum alloy assembled by eutectic brazing, ammonia, acetone, methanol, n-heptane, R134a or other fluorinated refrigerants can be used as fluids. List of cited references

[0086] [1]: Christine Hoa :«Thermique des caloducs à rainures axiales : études et réalisations pour des applications spatiales». Université de Poitiers, 2004. [2]: R.K. Bumataria, N.K. Chavda and H.Panchal, «Current research aspects in mono and hybrid nanofluid based heat pipe technologies», Heliyon 5 : e01627 (2019). [3]: N.K. Gupta, A.K. Tiwari, S.K. Ghosh, «Heat transfer mechanisms in heat pipes using nanofluids» - A review, Exp. Therm. Fluid Sci. 90 : 84-100 (2018). [4]: Y. Hu, K. Huang and J. Huang: "A review of boiling heat transfer and heat pipes behavior with self-rewetting fluids", Int. J. Heat Mass Transfer 121 : 107-118 (2018). [5]: Do et Jang : "Effect of nanofluids on the thermal performance of a flat micro heat pipe with a rectangular grooved wick. " Int. J. Heat Mass Transfer 53 : 2183-2192 (2010). [6]: S. W. Chi, "Heat Pipe Theory and Practice," McGraw-Hill, NY, U.S.A., 1976. [7]: M.C. Vlachou, J.S. Lioumbas, K. David, D. Chasapis, T.D.Karapantsios, "Effect of channel height and mass flux on highly subcooled horizontal flow boiling ", Exp. Therm. Fluid Sci. 83 : 157-168 (2017). [8]: K.R. Balasubramanian, R.A. Krishnan, S. Suresh, "Spatial orientation effects on flow boiling performances in open microchannels heat sink configuration under a wide range of mass fluxes", Exp. Therm. Fluid Sci. 99 : 392-406 (2018).

Claims

1. 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 enclosure comprising a stack of plates (10) in a second direction (Z), orthogonal to the first direction (X), the stack comprising two closing plates, 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 between the closing plates, the intermediate plate or plates comprising at least one first intermediate plate (10) including at least one window, the edges of which partially delimit a vapour channel (20) 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 with edges that partially delimit a liquid channel (21.1 to 21.6) in the evaporator and the condenser, at least the first intermediate plate delimiting a connecting channel (22) connecting the vapour channel and the liquid channel at least in the evaporator and the condenser, the structures and intermediate plates of the n modules defining a single vapour channel (20) and n liquid channels (21.1 to 21.6) on the at least one lateral side of the vapour channel, characterized in that the thickness of the walls between liquid channels increases gradually in the evaporator, from the adiabatic zone.

2. Heat pipe with re-entrant grooves according to Claim 1, wherein the thickness of the walls between liquid channels increases gradually in the condenser, from the adiabatic zone.

3. Heat pipe with re-entrant grooves according to Claim 1 or 2, wherein the length of the liquid-vapour connecting channels in the third direction Y increases gradually in the evaporator, from the adiabatic zone.

4. Heat pipe with re-entrant grooves according to one of the preceding claims, wherein the length of the liquid-vapour connecting channels in the third direction Y increases gradually in the condenser, from the adiabatic zone.

5. Heat pipe with re-entrant grooves according to one of the preceding claims, wherein the structures are only on one lateral side of the window delimiting the vapour channel.

6. Heat pipe with re-entrant grooves according to either of Claims 1 and 2, wherein the structures are on each of two lateral sides of the window, facing each other.

7. Heat pipe with re-entrant grooves according to one of the preceding claims, wherein the cross section in a plane YZ of the vapour channel, which is preferably rectangular, is constant over the entire length X of the heat pipe.

8. System comprising: - a cold source (SF); - a hot source (SC); and - at least one heat pipe with re-entrant grooves according to one of the preceding claims, wherein the heat pipe is arranged so that the heat flow from the hot source (SC) to the evaporator, and the extraction of heat at the condenser to the cold source (SF) occur on at least one lateral face of the enclosure facing the liquid channels, or on a lateral face perpendicular thereto.

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