EP4325155A1 - Wärmerohr mit nichtzylindrischem querschnitt mit einem verdampfer mit verbesserter dampf-flüssigkeits-grenzflächenstruktur zur erhöhung der kochgrenze - Google Patents

Wärmerohr mit nichtzylindrischem querschnitt mit einem verdampfer mit verbesserter dampf-flüssigkeits-grenzflächenstruktur zur erhöhung der kochgrenze Download PDF

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Publication number
EP4325155A1
EP4325155A1 EP23190790.8A EP23190790A EP4325155A1 EP 4325155 A1 EP4325155 A1 EP 4325155A1 EP 23190790 A EP23190790 A EP 23190790A EP 4325155 A1 EP4325155 A1 EP 4325155A1
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EP
European Patent Office
Prior art keywords
channel
evaporator
heat pipe
liquid
vapor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23190790.8A
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English (en)
French (fr)
Inventor
Mathieu Mariotto
Bénédicte CHAMPEL
Jean-Antoine Gruss
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Original Assignee
Commissariat a lEnergie Atomique CEA
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Publication of EP4325155A1 publication Critical patent/EP4325155A1/de
Pending legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
    • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
    • F28D15/0233—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes the conduits having a particular shape, e.g. non-circular cross-section, annular
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
    • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
    • F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
    • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
    • F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
    • F28D15/046—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure characterised by the material or the construction of the capillary structure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F1/00—Tubular elements; Assemblies of tubular elements
    • F28F1/10—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses
    • F28F1/12—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only outside the tubular element
    • F28F1/14—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only outside the tubular element and extending longitudinally
    • F28F1/16—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only outside the tubular element and extending longitudinally the means being integral with the element, e.g. formed by extrusion

Definitions

  • 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.
  • 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.
  • 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.
  • the condenser 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.
  • 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 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.
  • 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.
  • 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.
  • 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.
  • FIG. 1 illustrates the curve delimiting the operating range for an example of a capillary pumped heat pipe.
  • the curve portions Q viscous , Q sonic , Q entrainment , Q capillary , Q boiling define respectively the viscous, sonic, entrainment, capillary and boiling limits.
  • 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.
  • 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.
  • 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.
  • 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).
  • SC hot source
  • 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.
  • ⁇ T overheated ⁇ L T v ⁇ v h lv 1 R b ⁇ 1 R in which ⁇ 1 designates the surface tension of the fluid (N/m), Tv the temperature of the vapor ⁇ 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.
  • axial groove heat pipes 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.
  • 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 ⁇ 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 ⁇ 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.
  • 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.
  • the liquid phase at the evaporator Z E is not directly subjected to the heat flow ⁇ 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the general aim of the invention is then to respond at least in part to this need.
  • 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.
  • X first longitudinal direction
  • 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.
  • each thermal conduction pillar has at least one rectilinear shape over the entire height of the steam channel, in the second direction (Y).
  • 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.
  • 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.
  • the pillars include one or more branches forming one or more ramifications, this decrease in cross section balances the thermal paths of each branch.
  • the cross section is oblong, with the length of the section in the first direction (X).
  • the liquid channel is connected to the vapor channel by at least one connecting channel forming a reentrant groove defining the liquid-vapor interface.
  • 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 reent
  • 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 .
  • 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.
  • 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.
  • the size of the pores of the porous media is between 100 and 200 ⁇ m.
  • 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.
  • the thermal conduction pillars are nested at least partly in the porous media.
  • 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 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.
  • 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.
  • 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.
  • the width of an through slot is substantially equal to that of a connecting channel.
  • 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.
  • ZA adiabatic zone
  • Y second direction
  • the structures are only on one lateral side of the window delimiting the steam channel.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 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.
  • machining can be carried out on a single main face of the clad plates.
  • salt bath brazing for assembly, different processes are possible: salt bath brazing, inert gas brazing, ultrasonic welding, friction stir welding, bonding, etc.
  • 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.
  • windows are made by punching, cutting, for example by laser or water jet.
  • 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 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.
  • a liquid channel 11 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.
  • a connection channel 12 defines at least one liquid-vapor interface.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • FIG. 8 A relative arrangement between thermal conduction pillars 15 and stiffening pillars 17 within the same intermediate plate 20 is illustrated in figure 8 .
  • FIG. 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.
  • 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).
  • 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.
  • 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.
  • FIG. 14 illustrates an advantageous characteristic to be implemented at the level of the intersections between connecting channels 12 and through-out slots 18.
  • 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.
  • 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 .
  • 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.
  • through slots 18 and branching pillars 19 an increase of more than 40% in length of the triple lines can be envisaged.
  • 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.
  • FIG. 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 200 ⁇ m.
  • 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.
  • 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.
  • solder is deposited at the start of the stacking of plates 20, 22.
  • solder is deposited at the interface between the end of a pillar 15 and the porous media 5.
  • 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 ⁇ m, so that the migration of the solder into the porous media 5 is minimal.
  • this thickness of cord B is between 10 and 100 ⁇ m 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.
  • FIG. 19A and 19B 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.
  • 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.
  • 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.
  • 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.
  • FIG. 25A 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.
  • the evaporator of enclosure 2 integrates, as thermal conduction pillars 15, branched three-dimensional shaped profiles 19 and a U-shaped porous media 5.
  • 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.
  • 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 ⁇ m and 100 ⁇ m, and the particles of the powder material have a diameter of, for example, between 10 ⁇ m and 50 ⁇ m. A minimum wall thickness of around 0.4 mm can be achieved by this process.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • this minimum interval is equal to 0.3mm.
  • 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.
  • 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.
  • 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

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  • Physics & Mathematics (AREA)
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  • Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
EP23190790.8A 2022-08-17 2023-08-10 Wärmerohr mit nichtzylindrischem querschnitt mit einem verdampfer mit verbesserter dampf-flüssigkeits-grenzflächenstruktur zur erhöhung der kochgrenze Pending EP4325155A1 (de)

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Application Number Priority Date Filing Date Title
FR2208350A FR3138943A1 (fr) 2022-08-17 2022-08-17 Caloduc à section transversale non cylindrique, comprenant un évaporateur à structure d’interface vapeur/liquide améliorée afin d’augmenter la limite d’ébullition.

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