EP4325155A1 - Heat pipe with non-cylindrical cross section, comprising evaporator with improved vapor-liquid interface structure to increase boiling limit - Google Patents

Abstract

The invention relates to a heat pipe (1) extending along a first longitudinal direction (X), comprising a sealed enclosure (2) extending between a first longitudinal end (3), intended to be heated by a source hot SC to form, within the enclosure, an evaporator (ZE) and a second longitudinal end (4) intended to be cooled by a cold source SF to form a condenser (ZC), the sealed enclosure delimiting an adiabatic zone (ZA) between the evaporator and the condenser, the evaporator comprising a vapor channel (13), at least one liquid channel (11) connected to the vapor channel by defining at least one liquid-vapor interface (I), and a plurality of uprights (15) forming thermal conduction pillars which extend at least in the steam channel in a second direction (Y) orthogonal to (X), from a side face (21) of the enclosure from which the flow from the hot source is applied, up to the liquid-vapor interface.

Description

Technical area

The present invention relates to a heat pipe, in particular with capillary pumping with reentrant grooves.

The present invention aims to improve the boiling limit of such a heat pipe.

Prior art

A heat pipe is a thermal device allowing a quantity of energy to be transferred from a hot source to a cold source, a certain length apart.

A heat pipe comprises 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 closed and subjected to a hot source, an equilibrium is established between the liquid phase and the vapor phase.

Under the effect of a hot source applied in a zone at one of the longitudinal ends, designated the evaporator, part of the liquid phase vaporizes and absorbs the heat flow in latent form by inducing a slight overpressure which causes the movement of the steam towards an area at the other longitudinal end, designated the condenser where the cold source is applied. At the condenser, the vapor condenses and returns to the liquid phase. The condensed fluid (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.

Indeed, in the absence of gravity, the engine of the heat pipe is the capillary pumping of the fluid which takes place at the level of the liquid-vapor interface zones specifically configured so that a meniscus forms, resulting from the angle of contact between the fluid and the metal constituting the heat pipe (itself depending on the surface tension of the fluid, and the solid/liquid and solid/vapor interfacial tensions). The greater the capillary pumping forces greater in relation 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. The heat pipes affected by this absence of gravity are for example those used in space operating conditions, such as for the thermalization of satellite telecommunications systems.

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

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

Furthermore, deep grooves make it possible to obtain a large passage section for the liquid return, and therefore to minimize pressure loss.

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

Reentrant groove heat pipes are particular examples of groove heat pipes, in which the grooves have a narrow connection channel relative to the rest of the groove, which allows the capillary pumping effect to be increased while limiting heat losses. charge in the liquid phase. These heat pipes are used mainly in the space sector, for example for thermal regulation in satellites and/or spacecraft.

Over the operating temperature range of a heat pipe, different physical limits can limit its performance. 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 maximum power that it can to transfer.

There figure 1 illustrates the curve delimiting the operating range for an example of a capillary pumped heat pipe. On this figure 1 , we recall that the curve portions Q _viscous , Q _sonic , Q _entrainment , Q _capillary , Q _boiling , define respectively the viscous, sonic, entrainment, capillary and boiling limits.

In the context of the invention, the inventors were more specifically interested in the boiling limit.

This operating limit is defined as the maximum flux (or flux density), for which bubbles created at the wall of the liquid channel at the evaporator can migrate without being blocked in the connecting channels up to the interface meniscus. liquid-vapor.

The boiling limit thus originates from the birth of vapor bubbles within the capillary network, when the heat flux density radial to the evaporator becomes too high.

Thus if the radial flow density is too great, the circulation of the liquid in the capillary structure can be affected by the appearance of trapped bubbles or by a congestion of a large number of bubbles which migrate towards the liquid channel. This disrupts the hydrodynamics of the heat pipe, degrades its performance and ultimately its operation, or even stops it, and causes the wall to dry out, which means that there is overheating at the source to be thermalized.

Conservatively, we consider that the boiling limit is the flux or flux density for which the first bubbles appear at the wall of the evaporator of a heat pipe.

We have schematically illustrated in Figures 3A to 3C this phenomenon of the appearance of bubbles which can occur in the evaporator of a heat pipe with reentrant grooves with a cross section in the general shape of Omega, such as that illustrated in figure 2 .

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 cross section in the general shape of Omega, regularly distributed angularly and opening via a connecting channel 12 on a central cylindrical hollow 13 in which the vapor phase circulates. The peripheral wall 10 is in contact with a hot source (SC).

On the Figure 3A , under the effect of the incoming heat flow φ _E , coming from the heat source SC, the boiling has, at the interface I between liquid and vapor, the shape of a film F, no bubble is created. Operation is nominal.

On the Figure 3B , there is nucleate boiling, but the size of the bubbles B created is small enough for them to escape through the connecting channel 12 via the meniscus M at the interface to the vapor phase 13. However, if the density bubbles B is too large, the positioning of the meniscus M may be altered and very degraded, which impairs capillary pumping.

On the Figure 3C , there is also boiling with too large a bubble size B or too high a number of bubbles which does not allow them to escape through the connecting channel 12 via the meniscus M towards the vapor phase. The bubbles B then rise into the liquid channel 11. There is also a risk of local drying of the wall.

The boiling limit is associated with a radial thermal power density which is generally expressed in W/m ² : it is proportional to the surface area of the heat pipe evaporator, that is to say that for the same design (same cross section over the entire length of the evaporator), the boiling limit, expressed in W, of a heat pipe whose evaporator length is 10 centimeters is half that of a heat pipe whose evaporator length is 10 centimeters evaporator length is 20 centimeters.

avec Geq qui est la conductance équivalente au niveau de l'évaporateur (en W/K), et ΔTsurchauffe, le gradient de température entre la paroi et la température vapeur nécessaire à l'apparition d'une bulle (en K).The maximum thermal power before the boiling limit appears is given by the following equation: $$Q_{\mathrm{e}\mathit{boiling}}=G_{\mathit{eq}}\mathrm{\Delta }{T}_{\mathit{overheated}}|$$

with Geq which is the equivalent conductance at the evaporator (in W/K), and ΔTsuperheat, the temperature gradient between the wall and the vapor temperature necessary for the appearance of a bubble (in K).

dans laquelle σ1 désigne la tension superficielle du fluide (N/m), Tv la température de la vapeur ρ_v la densité de la vapeur, h_1v l'enthalpie de vaporisation du fluide, R_b le rayon des bulles et R le rayon du ménisque.Using the Clausius-Clapeyron relation, we can connect ΔTsuperheat to the radius of the bubbles: $$\mathrm{\Delta }{T}_{\mathit{overheated}}=\frac{{\sigma }_L{T}_v}{{\rho }_v{h}_{\mathit{lv}}}\left(\frac{1}{R_b}-\frac{1}{R}\right)$$

in which σ1 designates the surface tension of the fluid (N/m), Tv the temperature of the vapor ρ _v the density of the vapor, h _1v the enthalpy of vaporization of the fluid, R _b the radius of the bubbles and R the radius of the meniscus.

To push back the boiling limit, we can therefore increase the conductance at the evaporator (Geq), or increase the superheat, in particular by modifying the surface state of the liquid channels, in order to reduce the bubble radius. To do this, the roughness of the channels can be reduced, which can for example be done by carrying out electrolytic polishing of the sheets before or after machining.

We can also increase the radius of the meniscus of the liquid-vapor interface but this is counterproductive for the capillary pumping forces.

In addition to Omega cross-section heat pipes, axial groove heat pipes have a cylindrical cross section and the liquid return path from the condenser to the evaporator is located at the periphery of this cylindrical section: [1]. Heat pipes with other sections, rectangular or square, or even triangular, generally have this same characteristic.

Artery heat pipes are favorable for pushing the boiling limit. A heat pipe 1 with artery is shown in figures 4, 4A And 4B : like 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 Z _E 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 Z _A between the evaporator and the condenser.

Such an artery heat pipe 1 integrates a liquid channel 11 forming an artery which brings the liquid from the condenser Zc to the evaporator Z _E , which is dissociated from the vapor channel 13. In such a heat pipe, there is no liquid-vapor interface except for the evaporator Z _E 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 Z _E is not directly subjected to the heat flow Φ _E from the hot source, and this plays a role in moving away from the boiling limit.

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 steam channel 13, as illustrated in the Figure 5 . 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 loss of reduced liquid pressure that it induces, the porous medium 14 ensures a very good boiling limit at the level of the evaporator by a multiplication of lines and triple points P, that is to say solid-liquid-vapor contact points, which are very favorable to evaporation.

Capillary-pumped two-phase loops are also another type of favorable device for pushing the boiling limit. We can refer to the publication [2] which gives a definition and precisely describes this type of two-phase thermal control system. A two-phase capillary pump loop, like a heat pipe, aims to transfer a flow of thermal energy from a hot source (evaporator) to a cold source (condenser) using a fluid in liquid-vapor equilibrium and its changes phase. In a two-phase capillary pumped loop, the evaporator and the condenser are connected by independent pipes and as the authors of the publication [2] themselves define: unlike heat pipes, the liquid and vapor phases are separated and circulate in the same meaning in different behaviors. We can also refer to the Figure 3 to understand the structure of such a two-phase loop, in which the evaporator provides capillary pumping, in order to drive the liquid phase coming from the condenser towards the evaporator. The diagrams of figures 3 to 5 proposed by the authors of the publication [2] show that the heat flow to the evaporator is not directly applied to the liquid phase, but at the level of the porous medium which constitutes an interface between the two phases, liquid and vapor, by also allowing a reduction in the lines and triple points, favorable to evaporation without creating potential blockages of bubbles or destruction of the menisci, or even reflux of bubbles in the liquid channel.

Returning to axial groove heat pipe technology, to date, no specific arrangement is put in place to move away from the boiling limit. The liquid channels are directly configured under the zone where the heat flow from the hot source arrives, and therefore, are subject to the limitations described above. Indeed, over a high temperature range, mainly due to the variation in physical properties, the boiling limit is reached and conditions the operation of the heat pipe.

It is always possible to apply the heat flow to be evacuated at the level of the evaporator from a side opposite the liquid channels when these are not distributed over the entire periphery of the heat pipe, without any particular arrangement. But this is not favorable to the local thermal resistance at the evaporator and deteriorates the thermal chain and the conductance of the heat pipe. Reducing the flow at the level of the liquid channels has the advantage of avoiding the problem of the appearance of bubbles in the liquid, which deteriorates the hydrodynamics of the heat pipe. To do this, it is necessary to ensure that the heat flow is properly transmitted to the solid parts of the heat pipe in the transition zone, where the liquid-vapor interfacial menisci are configured. At the same time, this arrangement must not hinder the development and migration of the vapor phase towards the condenser (cold point).

Many solutions to the general problems of liquid-vapor interface and boiling limit are known in the scientific literature.

Thus, the authors of the publication [3] investigate a new artery evaporator structure and highlight the interest of applying the heat flow indirectly to the liquid-vapor interface and at the same time providing clearances for the evacuation of the vapor phase generated.

The authors of the publication [4] studied a two-phase capillary pumped loop evaporator configuration, where the heat flow is applied at the liquid vapor interface of a porous material which provides the driving force of the fluid in the loop. Indeed, these two functions are uncorrelated, the flow applies according to the authors to a sheet of liquid coming from the porous medium containing the liquid phase. Still according to the authors, when evaporation occurs via this liquid layer and, indirectly, also via the liquid-vapor interface configured on the surface of the porous medium, the heat flow is brought by the vapor phase (fluid already evaporated ). This does not resolve the critical flow problem of boiling (drying). However, the bubbles potentially created in the fluid layer (post porous medium) do not interfere with the hydrodynamics of the loop (capillary pumping).

The authors of the publication [5] studied a porous evaporator medium of a two-phase capillary pumped loop in which a porosity gradient is produced with a fractal shape. The authors considered their results promising, including very good aptitude when starting the heat pipe.

The article [6] shows a heat pipe configuration with axial grooves in the adiabatic zone associated with a peripheral porous media (sintered metal powder or a wick screen) in the evaporator. It highlights the impact of the porous media on the capacity of the heat pipe to support high heat flow densities, which are on the other hand applied directly to a wall in contact with the porous media.

1. A/ dissocier l'application de la source chaude d'un évaporateur au niveau de canaux liquides et/ou de milieu poreux contenant la phase liquide;
2. B/ configurer des dégagements pour l'évacuation de la vapeur créée, simultanément à A/;
3. C/ mettre en avant des gradients de porosité sous la forme d'une fractale dans les milieux poreux contenant une phase liquide et servant d'interface liquide vapeur pour générer la force de pompage capillaire dans un dispositif de transfert thermique;
4. D/ agencer un média poreux à l'évaporateur d'un caloduc pour éloigner la limite d'ébullition. La littérature brevets divulgue également la mise en oeuvre de milieux poreux dans les caloducs.

From this literature, the inventors of the present invention have concluded that the following points are known:

1. A/ dissociate the application of the hot source from an evaporator at the level of liquid channels and/or porous medium containing the liquid phase;
2. B/ configure clearances for the evacuation of the steam created, simultaneously with A/;
3. C/ highlight porosity gradients in the form of a fractal in porous media containing a liquid phase and serving as a liquid vapor interface to generate the capillary pumping force in a heat transfer device;
4. D/ arrange a porous media at the evaporator of a heat pipe to move away from the boiling limit. The patent literature also discloses the use of porous media in heat pipes.

US2002/0050341A1 thus proposes a flat heat pipe comprising two plates, one constituting the evaporator and the other the condenser, connected together by a thermally conductive structural element and a porous media applied to them.

CN210165803U discloses an artery heat pipe for a cell phone, comprising a peripheral porous media allowing the return of the liquid phase to the evaporator, which allows the boiling limit to be moved away.

US8100170B2 discloses several original loop heat pipe evaporator configurations, with plates connected by an insert and integrating porous media, allowing to arrange liquid circulation channels in the plates. The channels are connected to a liquid inlet and a steam outlet.

US6330907B 1 discloses a heat pipe with a cylindrical cross section for which the heat flow applied to the evaporator is disconnected from the liquid phase and applied in a zone where the evaporated flow circulates. The heat flow is transmitted to the liquid-vapor interface configured in a porous media or superpositions of porous media, between the liquid inlet zone and the vapor phase evacuation zone, by conduction pillars.

EP3628956A1 discloses a capillary-pumped two-phase loop, integrating liquid channels with peripheral porous surfaces to assist the migration of the liquid flow by capillary effect. The porous surfaces are implemented by superimposing machined plates (chemical etching) and assembled together by diffusion welding.

Thus, whether for the field of flat heat pipes, arteries, two-phase loop evaporators with capillary pumping, several geometric arrangements as according to the aforementioned patent documents make it possible not to directly apply the thermal flow to be evacuated at the level of the liquid channels. These arrangements also take into account the possible transmission of the heat flow via a porous medium interfacing the liquid phase and the vapor phase, with further means of evacuating the vapor phase from the liquid vapor interface. This is mainly described for two-phase capillary pumped loop evaporators, and necessarily assumes fluidic connections specific to it, such as the liquid inlet and the vapor outlet.

Furthermore, the applicant proposed in the patent application EP3553444A1 an artery heat pipe, made by stacking machined or shaped clad aluminum plates, structurally different, joined together with sealing, which can be assembled by different welding techniques, vacuum brazing or bonding. Such an assembly offers a much higher degree of configurations than those of the state of the art. In particular, in this heat pipe with a stack of plates, thermal links are made between the liquid arteries and the flow application zone, via the vapor channel. The production of such a heat pipe is however not fully satisfactory insofar as it is necessary to machine two different plates, and where the opening of the connecting channel depends only on the thickness of one of the plates and remains subjected to control of solder drips during an assembly process by vacuum brazing. This mastery is very difficult to achieve so as not to block the connecting channels. Furthermore, in this patent application, there is no provision for the integration of porous media at the liquid-vapor transition zone.

Consequently, there is a need to further improve grooved heat pipes, more particularly reentrant groove heat pipes, in order to optimize their operation, improve their performance and extend their operating ranges, more particularly increase the boiling limit without this being to the detriment of other characteristics, in particular the capillary pumping limit.

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

Presentation of the invention

To do this, the invention firstly relates to a heat pipe 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 a zone adiabatic between the evaporator and the condenser, the evaporator comprising a vapor channel, at least one liquid channel connected to the vapor channel by defining at least one liquid-vapor interface, and a plurality of uprights forming thermal conduction pillars which extend at least in the steam channel in a second direction (Y) orthogonal to the first direction (X), from a side face of the enclosure from which the flow coming from the hot source is applied, to the liquid-vapor interface.

Preferably, the flow coming from the hot source is intended to be applied exclusively to the side face of the enclosure facing the steam channel in which the thermal conduction pillars extend.

According to an advantageous characteristic, each thermal conduction pillar has at least one rectilinear shape over the entire height of the steam channel, in the second direction (Y).

According to an advantageous variant, each thermal conduction pillar comprises one or more branches forming one or more ramifications which extend(s) obliquely from a central portion of the rectilinear shape to the liquid-interface. steam. These ramifications can constitute stiffening pillars. Depending on their size and configuration, they can eliminate any stiffener in the liquid channel. These branches improve the supply of the heat flow coming from the hot source over the entire liquid-vapor interface without greatly increasing the pressure loss of the vapor phase compared to a higher number of pillars without branching.

According to another advantageous variant, the rectilinear shape of each thermal conduction pillar has a cross section in the second direction (Y), which decreases from the side face of the enclosure to the liquid-vapor interface. This decrease in cross section forms clearances reducing the pressure loss for the evacuation of the vapor phase. When the pillars include one or more branches forming one or more ramifications, this decrease in cross section balances the thermal paths of each branch.

Advantageously, the cross section is oblong, with the length of the section in the first direction (X).

According to a first embodiment, the liquid channel is connected to the vapor channel by at least one connecting channel forming a reentrant groove defining the liquid-vapor interface.

According to this first mode, from a process of stacking plates and assembling them together, the sealed enclosure comprises a stack of plates in a third direction (Z), orthogonal to the first (X) and second (Y ) directions, including two closing 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 closing plates, the plate(s) spacers comprising at least a first spacer 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 the second direction (Y), at least one structure whose edges partly delimit a liquid channel in the evaporator and the condenser, at least one intermediate plate comprising at least one window the edges of which partly delimit the vapor channel, at least the first intermediate plate delimiting a connecting channel forming the reentrant groove connecting the vapor channel and the liquid channel at least in the evaporator, the structures and intermediate plates of the n modules defining a single vapor channel in which the thermal conduction pillars extend in the evaporator up to the connecting channel and on at least one lateral side of the vapor channel, a single liquid channel at least in the evaporator.

According to this first mode, and an advantageous alternative embodiment, the heat pipe comprises amounts which extend in the second direction (Y) over the entire height of the single liquid channel at least in the evaporator, so as to constitute stiffening pillars .

According to this first mode, and an alternative production method, the sealed enclosure, the thermal conduction pillars, the structures delimiting the reentrant grooves are constituted by a one-piece part produced by metal additive manufacturing, in particular by selective laser sintering.

According to a second advantageous mode, the evaporator integrates a porous media, the liquid channel being connected to the vapor channel by at least part of the pores of the porous media defining the liquid-vapor interface.

Preferably the size of the pores of the porous media is between 100 and 200 μm.

According to an advantageous alternative embodiment, the porous media has a cross section in the first longitudinal direction (X), in particular U, E, comb-shaped, such that its lateral edges at least partially cover the lateral edges of the liquid channel, in contact with the side walls of the sealed enclosure, the material constituting the porous media being the same as that of the sealed enclosure, preferably chosen from aluminum, copper, nickel, or an alloy based on at least two of these.

According to an advantageous characteristic, the thermal conduction pillars are nested at least partly in the porous media.

According to this second mode, from a process of stacking plates and assembling them together, the sealed enclosure comprising a stack of plates in a third direction (Z), orthogonal to the first (X) and second (Y ) directions, including two closing 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 closing plates, the plate(s) spacers comprising at least a first spacer plate comprising at least one window whose edges partially delimit a vapor channel extending along the first direction (X) between the evaporator and the condenser, in which the steam is intended to circulate, and on at least one lateral side of the window in the second direction (Y), at least one structure whose edges partly delimit a liquid channel in the evaporator and the condenser, at least one intermediate plate comprising at least one window whose edges partially delimit the vapor channel, at least the first intermediate plate integrating the porous media whose part of the pores defining the liquid-vapor interface connecting the vapor channel and the liquid channel at least in the evaporator, the structures and intermediate plates of the n modules defining a single vapor channel in which the thermal conduction pillars extend in the evaporator to the porous media and on at least one lateral side of the channel vapor, a single liquid channel at least in the evaporator.

According to this second mode, and an alternative production method, the sealed enclosure, the thermal conduction pillars, the porous media are constituted by a single piece made by metal additive manufacturing, in particular by selective laser sintering.

Advantageously, the thermal conduction pillars are arranged staggered in a plane YZ of the steam channel. Such an arrangement makes it possible to limit pressure losses in the vapor phase, i.e. in the vapor channel.

According to an advantageous variant, at least part of the intermediate plates comprises, in the evaporator, one or more through slots which extend transversely to the connecting channel, preferably in the third direction (Z). These through slots further increase the triple lines at the level of the menisci, in order to maximize the latter.

Advantageously, the width of an through slot is substantially equal to that of a connecting channel.

According to a preferred configuration, the structures and intermediate plates of the n modules define a single vapor channel and a single liquid channel also in the condenser and in the adiabatic zone (ZA) between evaporator and condenser, the condenser and the adiabatic zone further comprising uprights which extend in the second direction (Y) over the entire height of the single liquid channel, so as to constitute stiffening pillars.

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

• une source froide (SF) ;
• une source chaude (SC) et
• au moins un caloduc à rainures réentrantes tel que décrit précédemment, le caloduc étant agencé de sorte que le flux de chaleur de la source chaude (SC) sur l'évaporateur étant sur au moins une face latérale de l'enceinte en regard du canal vapeur dans lequel les piliers de conduction thermique s'étendent, tandis que l'extraction de chaleur au condenseur vers la source froide (SF) est sur au moins une face latérale de l'enceinte en regard du(des) canal(ux) liquide(s), ou sur une face latérale perpendiculaire à celui-ci (ceux-ci).

Advantageously, the cross section in a plane YZ of the vapor channel and the liquid channel, preferably rectangular, is constant over the entire length of the heat pipe, the third direction (Z) being orthogonal to the first (X) and second (Y) directions. The invention also relates to a system comprising:

• a cold source (SF);
• a hot spring (SC) and
• at least one heat pipe with reentrant grooves as described above, the heat pipe being arranged so that the heat flow from the hot source (SC) to the evaporator is on at least one side face of the enclosure facing the steam channel in which the thermal conduction pillars extend, while the heat extraction from the condenser towards the cold source (SF) is on at least one side face of the enclosure facing the liquid channel(s) ( s), or on a side face perpendicular to it (these).

Preferably, the hot source is arranged so that the heat flow on the evaporator is applied exclusively to the side face of the enclosure facing the steam channel.

Thus, the invention essentially consists of proposing a heat pipe whose evaporator is designed to transmit directly by conduction the heat emitted by the hot source by means of thermal conduction pillars in the steam channel which supplies the lines/points as close as possible. evaporation configured at the liquid-vapor interfaces (menisci), and without hindering the circulation of the vapor flow.

By thus directly supplying the evaporation points with the thermal flow, the boiling limit at the evaporator is increased.

Two alternatives for implementing the liquid-vapor interfaces are considered, namely either by reentrant grooves, or by a porous media integrated directly into the evaporator. Two manufacturing methods are each applicable for the two alternatives,

A first embodiment, which can be implemented as according to the 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 media can be inserted into the stack before the actual assembly step. When it is carried out by brazing, a preliminary and local addition of solder between the end of a thermal conduction pillar and the porous media is preferably carried out in order to allow optimization of the transmission of the thermal flow.

A second manufacturing method consists of producing the various walls and structures, in particular the thermal conduction pillars, and where appropriate the porous media by 3D metal additive manufacturing, in particular by selective laser sintering. Metal additive manufacturing makes it possible to obtain heat pipe sections having technical particularities to meet the functional constraints of the final heat pipe (mechanical pressure withstand constraints and functional constraints for the fluid continuity of the liquid and vapor channels) and also allowing improved operation in terms of limits (viscous, sonic, entrainment, capillary and boiling). Publication [7] indicates in particular an additive manufacturing of aluminum with a porous media whose pore sizes are from 50 microns to several hundred microns, which allows the realization of the designs proposed in the context of the invention.

The invention provides numerous advantages among which we can cite those compared to solutions according to the state of the art, an increase in the boiling limit, without this harming the capillary pumping limit or the thermal conductance of the heat pipe.

Other advantages and characteristics will become clearer on reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures.

Brief description of the drawings

• [ Figure 1 ] there figure 1 illustrates the curve delimiting the operating range for an example of a capillary pumped heat pipe.
• [ Figure 2 ] there figure 2 is a photographic reproduction of an example of a heat pipe with reentrant grooves with an Omega cross section according to the state of the art.
• [ Fig 3A], [Fig 3B], [Fig 3C ] THE Figures 3A, 3B, 3C are schematic views in cross section and in detail showing different boiling situations which take place in an evaporator of a heat pipe according to the figure 2 .
• [ Figure 4 ] there Figure 4 is a schematic view of an artery heat pipe according to the state of the art.
• [ Figure 4A ], [ Fig 4B ] THE figures 4A And 4B are cross-sectional views of the Figure 4 , respectively at the level of the evaporator and the condenser of the artery heat pipe according to the state of the art.
• [ Figure 5 ] there Figure 5 is a cross-sectional view of a variant of the arterial heat pipe according to the state of the art.
• [ Figure 6 ] there Figure 6 is a schematic side view of a heat pipe with reentrant grooves, according to a first mode of the invention.
• [ Fig 6A ] there Figure 6A is a cross-sectional view of the Figure 6 , carried out at the heat pipe evaporator.
• [ Figure 7 ] there Figure 7 is a side view of an intermediate metal plate for producing, by stacking and assembling plates, a heat pipe with reentrant grooves according to the first mode of the invention.
• [ Figure 8 ] there figure 8 is a perspective view of part of the intermediate plate of the Figure 7 , at the evaporator level.
• [ Figure 9 ] there Figure 9 is a partial perspective view of a stack of metal plates assembled to produce a heat pipe with reentrant grooves according to the first mode of the invention.
• [ Figure 10 ] there Figure 10 illustrates, in partial view in longitudinal section and from above, a variant arrangement of thermal conduction pillars within a heat pipe with reentrant grooves according to the first mode of the invention.
• [ Figure 11 ] there Figure 11 illustrates, in partial perspective view, a heat pipe with reentrant grooves with the thermal conduction pillars according to the variant of the Figure 10 .
• [ Figure 12 ] there Figure 12 illustrates, in partial perspective view, a part of an intermediate plate according to a variant with through slots, at the level of the evaporator.
• [ Figure 13 ] there Figure 13 is a partial perspective view of a stack of metal plates assembled to produce a heat pipe with reentrant grooves according to the variant of the Figure 12 .
• [ Figure 14 ] there Figure 14 is a detail and top view which shows the crossing of through-out slots according to the figures 12 and 13 with the reentrant grooves within the evaporator.
• [ Figure 15 ] there Figure 15 illustrates, in partial perspective view, a part of an intermediate plate according to a variant of thermal conduction pillars with branches forming ramifications, at the level of the evaporator.
• [ Figure 16 ] there Figure 16 is a partial perspective view, a stack of metal plates assembled for the production of a heat pipe with reentrant grooves according to the variant of the Figure 15 .
• [ Figure 17 ] there Figure 17 is a cross-sectional view, taken at the level of the evaporator of the porous media heat pipe, according to a second mode of the invention.
• [ Figure 18 ] there Figure 18 is a partial perspective view of a stack of metal plates assembled to produce a heat pipe with porous media according to the second mode of the invention.
• [ Fig 18A ] there Figure 18A is a detailed view of the Figure 18 showing local brazing zones for the junction between porous media and the thermal conduction pillars, according to a first alternative embodiment.
• [ Fig 19A], [Fig 19B ] THE Figures 19A, 19B are detailed views of a porous media, respectively machined with its imprints and afterwards, with metal discs to produce local solders with thermal conduction pillars, according to a second alternative embodiment.
• [ Figure 20 ] there Figure 20 is a cross-sectional view, produced at the level of the evaporator of the heat pipe with porous media, according to the second mode of the invention and according to a variant where the media has lateral edges configured to match those of the sealed enclosure of the heat pipe .
• [ Figure 21 ] there Figure 21 is a perspective view of the porous media according to the Figure 20 .
• [ Figure 22 ] there Figure 22 illustrates, in partial perspective view, a part of an intermediate plate implemented with the porous media according to the Figure 21 .
• [ Figure 23 ], [ Figure 24 ] THE figures 23 And 24 are partial perspective views of a stack of metal plates assembled for the production of a heat pipe with porous media according to the variant of figures 21 And 22 .
• [ Fig 25A ], [ Fig 25B], [Fig 25C ] THE figures 25A , 25B, 25C are cross-sectional views, taken at the level of the evaporator of the porous media heat pipe, illustrating variant shapes of the media.
• [ Figure 26 ] there Figure 26 is a perspective and cross-sectional view, produced at the level of the evaporator of a heat pipe with porous media, according to the second mode of the invention, produced by metal additive manufacturing.
• [ Fig 26A ] there figure 26A is a perspective view and longitudinal section of the Figure 26 .
• [ Figure 27 ] there Figure 27 is a perspective view of an example of a thermal conduction pillar according to the invention produced by metal additive manufacturing.

detailed description

THE figures 1 to 5 have already been commented on in the preamble. They are not detailed below.

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

It is specified here that the reference SC used in the figures designates the hot source or, by extension, the zone of application of the heat flux emitted by the hot source directly on the side face of a heat pipe enclosure.

On the figures 6 And 6A , we can see an example of a heat pipe 1 with capillary pumping with reentrant grooves according to the invention.

On the Figure 6 , the example of heat pipe 1 with capillary pumping extending along a longitudinal axis X is seen from the outside.

The heat pipe 1 comprises a sealed enclosure 2 extending along the longitudinal axis within the enclosure an evaporator Z _E. The second longitudinal end 4 is intended to be cooled by a cold source SF to form a condenser Zc within the enclosure.

The sealed enclosure 2 internally delimits an adiabatic zone Z _A between the evaporator and the condenser.

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

According to a first mode of the invention, the sealed enclosure 2 is produced by stacking and assembling end plates and intermediate plate modules 20 arranged between the end plates 22, according to a method described in the patent application EP3553445 .

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 include a single plate machined on its two main faces.

The production, stacking and assembly of the plates are not detailed here, we can refer to the aforementioned request EP3553445 . However, the plates 20 are preferably made of aluminum alloy and assembled by vacuum brazing.

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

For assembly, different processes are possible: salt bath brazing, inert gas brazing, ultrasonic welding, friction stir welding, bonding, etc.

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 tooling available. Indeed, the assembly of sheets by vacuum brazing requires large vacuum furnaces, several meters long.

For sheet metal cutting and machining, large machines are also required. In addition, the mechanical strength of sheets with small width and long length cuts must be taken into account.

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

In the example illustrated, 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 the XZ plane, each having a large surface area promoting heat exchange with the hot source SC and the cold source SF.

The stack of plates 20 with their windows or their structures 12, 15, 16, internally delimits, in the evaporator Z _E , a liquid channel 11, a vapor channel 13 connected to the liquid channel 11 by connecting channels 12.

More _precisely , the vapor channel 13 of constant rectangular cross section extends along the longitudinal axis adiabatic Z _A .

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

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

According to this first mode, in the evaporator, a plurality of uprights 15 forming thermal conduction pillars extend in the vapor channel 13 in the second direction (Y), from a side face 21 of the enclosure from which the flow from the hot source SC is applied, up to the liquid-vapor interface. In fact, these thermal conduction pillars 15 regularly spaced from each other provide, in addition to their function of conducting the heat flow coming from the hot source SC from the side face 21 of the enclosure, a function of stiffening each intermediate plate 20 and therefore the mechanical strength of enclosure 2.

In other words, the liquid-vapor interface is provided according to this first mode by the reentrant grooves 12. These reentrant grooves 12 are each delimited by structures 16 of two adjacent plates 20, to which the thermal conduction pillars 15 are connected.

As illustrated in Figure 6A , the thermal conduction pillars 15 each supply thermal flow along the lines L directly to the menisci constituting the interfaces liquid-vapor while allowing the vapor flow which has just been evaporated at the level of the triple lines/points P to escape into the vapor channel 13.

The enclosure 2 can also integrate uprights or pillars 17 which extend in the second direction (Y) over the entire height of the single liquid channel 11, so as to constitute stiffening pillars 17. These pillars 17 thus also participate in the mechanical maintenance of the monobloc enclosure 2.

As shown in Figure 7 , these stiffening pillars 17 can not only be installed in the evaporator Z _E but also in the adiabatic zone ZA or in the condenser Zc of the heat pipe 1, that is to say over the entire length of the enclosure 2. As shown also on this Figure 7 , these pillars 17 are positioned as offset as possible relative to two thermal conduction pillars 15, so as to prevent part of the heat flow from being drained precisely by these pillars 17 towards the liquid channel. Preferably, as illustrated, these stiffening pillars 17 are also fewer in number than the thermal conduction pillars 15.

A relative arrangement between thermal conduction pillars 15 and stiffening pillars 17 within the same intermediate plate 20 is illustrated in figure 8 .

On this figure 8 , we also see the offset e/2 of the structures 16 relative to the longitudinal edge of a plate 20, according to the stacking direction Z of the plates 20. This offset e/2 makes it possible to calibrate the opening of a channel of connection 12, therefore equal to e, that is to say twice the offset of two plates stacked one on top of the other. Control, if necessary by machining, of this e/2 value makes it possible to control the capillary limit of heat pipe 1, which is the most restrictive limit over a majority of the operating temperature range, with a direct impact on the transportable power. in Wm through the heat pipe.

There Figure 9 illustrates the interior of an enclosure 2 of heat pipe 1 (a closing plate 22 being omitted), once the stacking of intermediate plates 20 has been made and their assembly with two closing plates 22. The density and shape of the pillars of thermal conduction 15 in the evaporator Z _E can be adjusted depending on the compromise to be achieved, loss of capillary limit (more pressure loss on the side of the vapor channel 13) and gain on the boiling limit, which is sometimes predominant in operating conditions with respect to other limits.

In the example illustrated in figures 7 to 13 , each thermal conduction pillar 15 has a rectilinear shape over the entire height of the steam channel 13 and a cross section at the second direction (Y), which decreases from the side face 21 of the enclosure to the liquid-vapor interface. This cross section is oblong with the length of the section in the first direction (X). We can of course consider other types of cross section and shape, taking into account the production constraints, in particular machining. For example, we can consider rectilinear shapes with a square cross section, which are a priori more easily machinable, but more likely to generate pressure loss.

THE figures 10 and 11 show an advantageous arrangement of the thermal conduction pillars 15, according to which they are staggered in a plane YZ of the vapor channel 13 of the evaporator Z _E of the enclosure 2. To achieve this staggered arrangement, intermediate plates can be stacked 20 alternating with offsets between the pillars 15 from one plate to another adjacent one. This arrangement is advantageous for limiting pressure losses in the vapor phase.

THE figures 12 and 13 illustrate an advantageous variant where through slots 18 extend transversely to the connecting channel 12 in the third direction (Z). The width of a through slot 18 is substantially equal to that of a connecting channel 12. These through slots make it possible to maximize the triple lines at the level of the menisci at the vapor-liquid interface. Typically, with the through slots 18 as illustrated, an increase of more than 20% in length of the triple lines can be envisaged.

There Figure 14 illustrates an advantageous characteristic to be implemented at the level of the intersections between connecting channels 12 and through-out slots 18. In fact, the maximum opening dimension d of a connecting channel 12, which is therefore the value of the diagonal at level of an intersection, conditions the capillary performance of the heat pipe. To maintain this dimension d at an equal value in the rest of the evaporator, it is necessary to produce additional thicknesses of the structures 16, which are symbolized by the portions of material beyond the dotted lines on the Figure 14 .

As illustrated in figures 15 And 16 , the thermal conduction pillars 15 can have a rectilinear shape with branches 19 forming ramifications which extend obliquely from a central portion of the rectilinear shape to the liquid-vapor interface. This variant ensures more homogeneous flow transmission at the liquid-vapor interface where the triple lines are located at the level of the menisci, facing a configuration with iso number of pillars 15 of rectilinear shape as illustrated according to the figures 8 to 13 .

It is possible, depending on the sizing constraints of the heat pipe and its evaporator Z _E , to determine an optimum between the homogeneity of the heat flow transmitted to the liquid-vapor interfaces and the pressure losses in the vapor channel 13 generated by the pillars 15 and their ramifications 19.

The variants with through slots 18 and ramification pillars 19 can be combined with each other with the presence of reentrant grooves, which makes it possible to further increase the lengths of the triple line. Typically, with through slots 18 and branching pillars 19, an increase of more than 40% in length of the triple lines can be envisaged.

As also shown in figures 15 And 16 , providing branches 19 which can serve as stiffeners as such can make it possible to overcome the presence of stiffening pillars 17 in the liquid channel 11.

Like what is illustrated in figures 10 and 11 with thermal conduction pillars 15 of rectilinear shape, it is also possible to arrange pillars 15 with ramifications 19 in a staggered manner in a plane YZ of the vapor channel 13 of the evaporator Z _E of enclosure 2. To achieve this staggered arrangement, we can stack intermediate plates 20 alternately with offsets between the pillars 15 with ramifications 19 from one plate to another adjacent one. This arrangement is also advantageous for limiting pressure losses in the vapor phase.

There Figure 17 illustrates the implementation of the liquid-vapor interface by a porous media 5 in place of reentrant grooves 12. The pores of the porous media 5 have a size substantially equal to the width of a reentrant groove 12. It can be between several tens of microns to a few hundred microns, preferably between 100 and 200µm.

The main advantage of installing a porous media 5 in place of reentrant grooves to ensure the liquid-vapor interface is to multiply the triple lines while maintaining a strong capillary pumping potential. This increase in triple lines improves the evaporation process and reduces the local thermal resistance to evaporation.

Furthermore, by integrating a porous medium 5 of a certain thickness, we increase the capacity to accommodate variations in liquid volume, which are a function of variations in the thermal powers involved and the operating temperature of the heat pipe, while avoiding defusing the heat pipe. It is specified here that defusing is the consequence of variations in the operating conditions of the heat pipe, that is to say variations in temperature and power. Indeed, depending on the initial mass of fluid, and a density of the working fluid (liquid and vapor phases) changing as a function of temperature, the volume of the fluid also changes. In addition, the shape of the meniscus and its position in the connecting channel evolve along the longitudinal direction meniscus deepens and recedes the most. If this volume of working fluid becomes too low, potentially, if the connecting channel 12 and/or the porous media 5 are too short or too thin, the meniscus may become detached from the connecting channel or the porous media. This disconnection is a defusing.

Compared to a configuration previously described with connecting channels 12 forming the reentrant grooves, the volume involved in a porous media 5 is much greater.

The use of such a porous media 5 must be done so as to ensure very good thermal contact between the thermal conduction pillars 15 and the material of the media at their contact zones.

To do this, it is necessary to make a local addition of solder between the end of a thermal conduction pillar 15 and the porous media 5. This local addition of solder can be made, before putting the assembly of plates 20 , 22 stacked in a vacuum brazing furnace.

Two variants can be considered for this local addition of solder.

The first variant consists of depositing solder, in the same eutectic metal as that of the plates 20 in the form of a bead around the end of each pillar 15. As a result, the porous media 5 is positioned at the start of the stacking of plates 20, 22. On each stacked plate 20, solder is deposited at the interface between the end of a pillar 15 and the porous media 5. During brazing, the solder, due to the porous medium of media 5 will spread locally and ensure good mechanical and thermal contact between porous media 5 and pillar 15.

THE figures 18 and 18A illustrate the local deposition of the solders B in the form of a bead and the overall maintenance of the porous media 5 in the evaporator Z _E. The thickness of solder metal B deposited locally on one end of a pillar 15 is advantageously less than 100 μm, so that the migration of the solder into the porous media 5 is minimal. Preferably, this thickness of cord B is between 10 and 100 μm depending on the properties of the porous media 5, in particular depending on the average size of its pores and its void ratio. Solder B can initially be in the form of a metal strip identical to that of the clad plates 20, 22.

A second variant is illustrated in Figures 19A and 19B . The porous media 5 is machined in such a way as to produce impressions 50, preferably in the form of discs, thermal conduction pillars, where contact with the porous media 5 is required. The depth of an imprint 50 is preferably equal to the thickness of a metal sheet, typically from one to several hundred microns. A metal disc 51 is forcefully introduced into each cavity 50 before the plates 20, 22 are stacked and assembled in a vacuum brazing furnace.

As illustrated in figures 20 and 21 , the porous media 5 is a machined part whose cross section in the YZ plane is a U shape.

The machining allows the flow of liquid to easily migrate into the liquid channel 11 and to impregnate the porous media 5 effectively.

In addition, the lateral branches 52 of the U of the machined porous media 5 make it possible, in addition to ensuring a mechanical holding function, to recover the thermal flow lines L of losses through the sides of the enclosure 2. Thus, the branches 52 make it possible to transmit these loss lines L directly to the liquid phase contained in the last channel 11, which also contributes to improving the evaporation function and moving away the boiling limit of the heat pipe 1.

THE figures 22 to 24 illustrate an example respectively of an intermediate plate 20 which is suitable for integrating such a U-shaped porous media 5, and of an assembly of plates 20 obtained with this media 5.

Other cross sections than the U shown in figure 25A can be considered for the porous media 5: it can be a general E shape ( Figure 25B ) or comb ( Figure 25C , always with the side branches 52 which are in contact and cover the edges side of the closing plates 22 to recover the heat flow lines coming from the face 21 subjected to the heat source and bring them directly into the liquid channel 11.

THE figures 26 to 27 illustrate a heat pipe 1 according to the invention, produced not by stacking and assembling plates 20, 22 as described previously but by 3D metal additive manufacturing. Here, the evaporator of enclosure 2 integrates, as thermal conduction pillars 15, branched three-dimensional shaped profiles 19 and a U-shaped porous media 5. Enclosure 2, the pillars 15 with their three-dimensional ramifications 19 and the porous media 5 are constituted by a single, single-piece part resulting from additive manufacturing or 3D manufacturing.

For example, the part may be manufactured by the powder bed fusion process in which an area of a layer of powdered material is melted in a given area using a laser beam or electron beam . Then a new layer of powdered material is deposited, which will then be melted in a given area. These steps are repeated until the piece is complete. The layers have a thickness of, for example, between 20 µm and 100 µm, and the particles of the powder material have a diameter of, for example, between 10 µm and 50 µm. A minimum wall thickness of around 0.4 mm can be achieved by this process.

Alternatively, the part can be manufactured by material deposition and fusion or DED (“ Direct Energy Deposition” in Anglo-Saxon terminology). A material is provided in the form of powder or wire, this is melted by a high energy source. The material is selectively deposited layer by layer on a substrate, for example guided by a multi-axis robotic arm and then finished with CNC machining to melt the material. Thermal energy is generated either by laser, by an electron beam, or by an ionized gas. The material is directly projected into the heated zone where it melts.

Alternatively, the module can be manufactured by the so-called Binder Jetting process in which binders are selectively projected onto the powder bed, binding these areas together to form a solid part, one layer at a time. Heat post-treatment, such as sintering, then takes place to remove the binder and create an all-metal part.

Alternatively, the part can be manufactured by metal extrusion, in which a filament or rod made of a polymer and heavily loaded with metal powder is extruded through a nozzle (as in the FDM process) to form the "green" part. » which is post-processed, for example by carrying out a deburring step and a sintering step, to create an entirely metallic part.

As a further variant, the part can be produced by ultrasonic additive manufacturing. To do this, metal sheets are glued layer by layer using ultrasonic welding, then formed to the desired shape using numerically controlled machining. The part is modeled by CAD, this modeling is then used in the additive manufacturing machine to direct the laser beam.

As recommended by the authors of the publication [7], the production by additive manufacturing of the different elements and in particular of the pillars 15 and the channels 11, 13 requires a minimum interval between two adjacent elements, in order to avoid the fusion of facing surfaces -notice. Typically, this minimum interval is equal to 0.3mm.

The shapes that it is possible to obtain with additive manufacturing for a heat pipe 1 according to the invention, as illustrated in figures 26 to 27 allow a very good compromise in terms of homogeneity of the heat flow at the liquid-vapor interfaces, weight and pressure losses on the side of the vapor channel 13.

• des rainures réentrantes 12 où se développent les lignes triples et le cas échéant dans des fentes traversantes 18 ;
• un media poreux 5 avec des ramifications 19 de piliers 15 qui peuvent s'imbriquer à l'intérieur même du média, ce qui apporte une plus-value considérable pour l'homogénéité du flux dans ledit média poreux 5.

This applies to liquid-vapor interfaces which are ensured by:

• reentrant grooves 12 where the triple lines develop and where appropriate in through slots 18;
• a porous media 5 with ramifications 19 of pillars 15 which can nest within the media itself, which provides considerable added value for the homogeneity of the flow in said porous media 5.

Other advantages and improvements could be made without departing from the scope of the invention.

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.

A heat pipe is filled with a two-phase fluid, it 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, depending on the constraints due to pressure, flammability, toxicity of the fluid and chemical compatibility between the fluid and the material. forming the heat pipe.

In addition, certain 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 the heat pipes.

By way of example, for a heat pipe according to the invention made of nickel aluminum alloy, copper, titanium or an alloy based on a combination of them, which is either assembled by eutectic brazing, or made by metal additive manufacturing, ammonia, water, acetone, methanol, etc. can be used as fluid.

Due to the limits of use, between the working fluids and the metals mentioned, the couples envisaged 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

• [1]: Christine Hoa: “Thermal of heat pipes with axial grooves: studies and achievements for space applications”. University of Poitiers, 2004 .
• [2]: Jocelyn Bonjour, et al.: “Two-phase thermal control systems - Capillary and gravity loops”. Engineer's Techniques BE9546 v1 (2011 ).
• [3]: Lizhan Bi, Lanpei et al.: “Pool boiling with high heat flux enabled vapors artery structure” Appl. Phys. Lett. 108.23901 (2016); https://doi.org/10.1063/1.495374 .
• [4]: Kai Zhu et al.: “Operation characteristics of a new-type loop heat pipe (LHP) with wick separated from heating surface in the evaporator”. Applied Thermal Engineering 123 (2017) 034-1041 .
• [5]: Eric A.Silk et al.: “Fractal Loop Heat Pipe performance testing with a compressed carbon”. Applied Thermal Engineering 59 (2013) 290e297 .
• [6]: https:/www. 1-actom/case-wtudies/high-heat-flux-50-w-cm2-hybrid-constant-conductance-heat-pipes/
• [7]: M. Ameli et al. : “A novel method for manufacturing sintered aluminum heat pipes”, Applied Thermal Engineering 52 (2013) 498e504 .

Claims (15)

Heat pipe (1) extending along 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 (Z _E ) and a second longitudinal end (4) intended to be cooled by a cold source SF to form, within the enclosure, a condenser (Z _C ), the enclosure sealed delimiting an adiabatic zone (Z _A ) between the evaporator and the condenser, the evaporator comprising a vapor channel (13), at least one liquid channel (11) connected to the vapor channel by defining at least one liquid-vapor interface ( I), and a plurality of uprights (15) forming thermal conduction pillars which extend at least in the steam channel in a second direction (Y) orthogonal to the first direction (X), from a side face (21) from the enclosure from which the flow coming from the hot source is applied, to the liquid-vapor interface, each thermal conduction pillar having at least a rectilinear shape over the entire height of the vapor channel, according to the second direction (Y), the rectilinear shape of each thermal conduction pillar having a cross section in the second direction (Y), which decreases from the side face of the enclosure to the liquid-vapor interface. Heat pipe (1) according to claim 1, each thermal conduction pillar comprising one or more branches (19) forming one or more branch(s) which extend(s) obliquely from a central portion of the rectilinear shape to 'at the liquid-vapor interface. Heat pipe (1) according to claim 1 or 2, the cross section being oblong with the length of the section in the first direction (X). Heat pipe (1) according to one of the preceding claims, the liquid channel being connected to the vapor channel by at least one connecting channel forming a reentrant groove defining the liquid-vapor interface. Heat pipe (1) with reentrant grooves according to claim 4, the sealed enclosure comprising a stack of plates (20, 22) in a third direction (Z), orthogonal to the first (X) and second (Y) directions, including two plates closure (22) and at least a number of n modules one on top of the other with n being an integer greater than or equal to 1, each module comprising at least one interposed plate between the closure plates (22), the plate(s) spacers comprising at least one first spacer plate (20) comprising at least one window whose edges partly delimit a steam channel (13) extending along the first direction (X) between the evaporator and the condenser, in which the steam is intended to circulate, and on at least one lateral side of the window in the second direction (Y), at least one structure (16) whose edges partly delimit a liquid channel in the evaporator and the condenser, at least one intermediate plate comprising at least one window whose edges partly delimit the vapor channel (13), at least the first intermediate plate delimiting a connecting channel forming the reentrant groove connecting the vapor channel and the liquid channel at least in the evaporator, the structures and intermediate plates of the n modules defining a single vapor channel in which the thermal conduction pillars extend in the evaporator up to the connecting channel and on at least one lateral side of the vapor channel, a single liquid channel at least in the evaporator , the heat pipe preferably comprising uprights (17) which extend in the second direction (Y) over the entire height of the single liquid channel at least in the evaporator, so as to constitute stiffening pillars. Heat pipe (1) with reentrant grooves according to claim 4, the sealed enclosure, the thermal conduction pillars, the structures delimiting the reentrant grooves being constituted by a single piece made by metal additive manufacturing, in particular by selective laser sintering. Heat pipe (1) according to one of claims 1 to 3, the evaporator integrating a porous media (5), the liquid channel being connected to the vapor channel by at least part of the pores of the porous media defining the liquid-vapor interface , preferably the size of the pores of the porous media being between 100 and 200µm, preferably the porous media having a cross section in the first longitudinal direction (X), in particular U, E, comb-shaped, such that its lateral edges cover at least partially the lateral edges of the liquid channel, in contact with the side walls of the sealed enclosure, preferably the thermal conduction pillars being nested at least partly in the porous media, preferably the material constituting the porous media being in the same as that of the sealed enclosure, preferably chosen from aluminum, copper, nickel, or an alloy based on at least two of these. Heat pipe (1) with porous media according to claim 7, the sealed enclosure comprising a stack of plates in a third direction (Z), orthogonal to the first (X) and second (Y) directions, including two closing 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 closing plates (22 ), the intermediate plate(s) comprising at least one first intermediate plate (20) comprising at least one window whose edges partially delimit a vapor channel (13) extending along the first direction (X) between the evaporator and the condenser, in which the steam is intended to circulate, and on at least one lateral side of the window in the second direction (Y), at least one structure (16) whose edges partly delimit a liquid channel in the evaporator and the condenser, at least one intermediate plate comprising at least one window whose edges partially delimit the vapor channel (13), at least the first intermediate plate integrating the porous media whose part of the pores define the liquid-vapor interface connecting the vapor channel and the liquid channel at least in the evaporator, the structures and intermediate plates of the n modules defining a single vapor channel in which the thermal conduction pillars extend in the evaporator up to the porous media and on, the at least one lateral side of the vapor channel, a single liquid channel at least in the evaporator. Heat pipe (1) with porous media according to claim 7, the sealed enclosure, the thermal conduction pillars, the porous media being constituted by a single piece made by metal additive manufacturing, in particular by selective laser sintering. Heat pipe (1) according to one of claims 5 and 8, the thermal conduction pillars being arranged staggered in a plane YZ of the steam channel. Heat pipe (1) according to claim 5, at least part of the intermediate plates comprising, in the evaporator, one or more through slots (18) which extend transversely to the connecting channel, preferably in the third direction (Z), preferably the width of an through slot being substantially equal to that of a connecting channel. Heat pipe according to one of claims 5 and 8, the structures and intermediate plates of the n modules defining a single vapor channel and a single liquid channel also in the condenser and in the adiabatic zone (ZA) between evaporator and condenser, the condenser and the adiabatic zone further comprising uprights (17) which extend in the second direction (Y) over the entire height of the single liquid channel, so as to constitute stiffening pillars. Heat pipe (1) according to one of claims 5 and 8, the structures being only on one lateral side of the window delimiting the steam channel. Heat pipe according to one of the preceding claims, the cross section in a plane YZ of the vapor channel and the liquid channel, preferably rectangular, being constant over the entire length of the heat pipe, the third direction (Z) being orthogonal to the first (X) and second (Y) directions. System comprising: - a cold source (SF); - a hot spring (SC) and - at least one heat pipe (1) according to one of the preceding claims, the heat pipe being arranged so that the heat flow from the hot source (SC) on the evaporator being on at least one side face (21) of the the enclosure (2) facing the steam channel in which the thermal conduction pillars extend, while the heat extraction from the condenser towards the cold source (SF) being on at least one side face of the facing enclosure of the liquid channel(s), or on a lateral face perpendicular to it (these).

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