EP4323711B1 - Two-phase heat-transfer device with liquid overflow tank - Google Patents

Description

Technical area

The present disclosure relates to the field of two-phase heat transfer devices, containing a saturated two-phase fluid in circulation between a cold source and a hot source, and thus making it possible to evacuate heat generated by the hot source. It finds a particular application in the space field, in particular for the thermal control of equipment of a spacecraft, such as for example a satellite.

Prior art

A two-phase heat transfer device conventionally comprises a closed cavity containing a two-phase fluid at saturation, a portion of which is in the liquid phase and another in the gas phase. The heat transfer device is in a heat exchange relationship on the one hand with a so-called hot source, and on the other hand with a so-called cold source, relatively colder than the heat source.

In a two-phase heat transfer device, the volume of liquid phase fluid present in the cavity varies depending on the operating temperature. Thus, a surplus of liquid can disrupt the operation of the two-phase heat transfer device. The patent application WO2016/058966 entitled flat heat pipe with reservoir function teaches a liquid reservoir arranged at one end of the condensation channels and under a capillary structure. The document US 6,695,040 B1 describes a device according to the preamble of claim 1.

This type of solution, however, imposes constraints on the design and use of the heat pipe. Part of the surface of the cold plate is used in particular to make thermal contact with the liquid reservoir, which therefore reduces the useful surface area available for the condenser and therefore the performance of the heat pipe. Furthermore, the fact of placing the tank in thermal contact with the cold plate also represents an additional design constraint from which we wish to overcome.

Summary

The present invention thus aims to propose a two-phase structure, also designated in English as “two phase heat transport equipment” or TPHTE, more efficient and simpler in design.

• la cavité fermée contenant un fluide diphasique à l'état d'équilibre liquide-vapeur et comprenant au moins un canal de circulation du fluide diphasique en phase vapeur et au moins une structure capillaire principale adaptée pour permettre la circulation du fluide diphasique en phase liquide entre ladite source froide et ladite source chaude,
• le dispositif diphasique étant caractérisé en ce qu'il comprend en outre au moins un milieu capillaire additionnel permettant un stockage et une restitution d'un excédent de liquide par rapport à une capacité maximale de liquide contenu dans la structure capillaire principale, ledit milieu capillaire additionnel et ladite structure capillaire principale étant connectés de façon à assurer une continuité capillaire pour le fluide diphasique en phase liquide.

It is thus proposed according to claim 1 a two-phase heat transfer device, comprising a closed cavity comprising at least one evaporation zone in a heat exchange situation with at least one hot source and at least one condensation zone in a heat exchange situation. heat exchange with at least one cold source,

• the closed cavity containing a two-phase fluid in the state of liquid-vapor equilibrium and comprising at least one circulation channel for the two-phase fluid in the vapor phase and at least one main capillary structure adapted to allow the circulation of the two-phase fluid in the liquid phase between said cold source and said hot source,
• the two-phase device being characterized in that it further comprises at least one additional capillary medium allowing storage and restitution of an excess of liquid relative to a maximum capacity of liquid contained in the main capillary structure, said additional capillary medium and said main capillary structure being connected so as to ensure capillary continuity for the two-phase fluid in the liquid phase.

In embodiments, said additional medium forming at least one capillary reservoir zone, while the main capillary structure comprises at least one capillary condensation zone and at least one capillary flow zone connected on the one hand to the capillary zone of condensation and on the other hand to the evaporator.

In embodiments, the reservoir capillary zone has a characteristic capillary dimension less than a characteristic capillary dimension of the condensation capillary zone but greater than or equal to a characteristic capillary dimension of the flow capillary zone to which the reservoir capillary zone is connected.

In embodiments, the reservoir capillary zone has a characteristic capillary dimension less than a characteristic capillary dimension of the circulation channel of the two-phase fluid in the vapor phase but greater than a characteristic capillary dimension of the condensation capillary zone.

In embodiments said reservoir capillary zone is connected directly to the flow zone or respectively to the evaporation zone and has a characteristic capillary dimension greater than a characteristic capillary dimension of the flow zone or respectively of the zone d 'evaporation.

In embodiments, the main capillary structure has a characteristic capillary dimension decreasing from the condensation zone to the evaporation zone.

In embodiments, the additional capillary medium has a minimum characteristic capillary dimension at the connection with the main capillary structure for the circulation of the two-phase fluid in the liquid phase.

In embodiments, the additional capillary medium is dimensioned so as to have a filling rate of strictly between 0 and 100%, preferably strictly between 5 and 95%, when the two-phase heat transfer device is in operation.

In embodiments, the volume available for the liquid in the additional capillary medium is between 10 and 40% of the volume available for the liquid in the main capillary structure of the cavity.

In embodiments, the additional capillary medium is a mesh and/or is formed of a porous material.

The heat transfer device advantageously comprises a liquid reservoir having a capillary structure and which is connected to the main capillary structure for the circulation of liquid between the condenser and the evaporator, the liquid reservoir being connected to the main capillary structure of way to ensure capillary continuity between them making it possible to maintain liquid continuity. This avoids having a surplus of liquid which would disrupt or even prevent the operation of the heat transfer device, for example if it was located in a place preventing the circulation of steam to the cold source, or if it came partially or completely mask a heat exchange surface with the cold source.

Advantageously, an excess volume of liquid is housed in the additional capillary medium, thus avoiding a useless and inactive excess volume, which would move according to local pressure variations induced by capillary forces, temperature gradients and forces. hydrodynamics and which would disrupt the operation of the heat transfer device. For this, the additional capillary medium does not need to be located in thermal contact with the cold source. More generally, constraints on design and use are reduced. The device is suitable for use in space but use on Earth, in the presence of gravity, is also possible. The thermal performance of the heat transfer device relating to its transport capacity or its heat exchange coefficient is advantageously optimized.

Advantageously again, thanks to capillary continuity, in particular by controlling a hierarchy of capillary dimensions between the liquid reservoir and the main capillary structure, it is possible to ensure storage and restitution of two-phase fluid in liquid phase so as to maintain an optimum volume of two-phase fluid in liquid phase in the main capillary structure.

Brief description of the drawings

• Fig. 1a
  [Fig. 1a] représente un schéma de principe d'un dispositif diphasique de transfert thermique.
• Fig. 1b
  [Fig. 1b] représente une vue en coupe d'un évaporateur d'un dispositif de la figure 1a.
• Fig. 2
  [Fig. 2] est une vue en perspective partielle et schématique d'un dispositif diphasique de transfert thermique selon un mode de réalisation.
• Fig. 3
  [Fig. 3] est une vue en coupe en perspective du dispositif de la figure 2.
• Fig. 4
  [Fig. 4] est une vue en coupe de face d'un condenseur d'un dispositif diphasique de transfert thermique selon un mode de réalisation.
• Fig. 5
  [Fig. 5] représente schématiquement la circulation du fluide diphasique dans un dispositif de transfert thermique selon un mode de réalisation.
• Fig. 6
  [Fig. 6] représente un exemple de structure capillaire pouvant former le réservoir de surplus de liquide.
• Fig. 7
  [Fig.7] représente schématiquement un autre exemple de dispositif diphasique dans lequel le milieu capillaire additionnel se situe dans le prolongement du condenseur.
• Fig. 8a
  [Fig. 8a] représente un exemple de hiérarchie des dimensions capillaires caractéristiques d'un dispositif lorsque notamment le dispositif est dépourvu de zone adiabatique et comprend un milieu capillaire additionnel formant une section supplémentaire du dispositif, adjacente au condenseur.
• Fig. 8b
  [Fig. 8b] représente un exemple de hiérarchie des dimensions capillaires caractéristiques d'un dispositif lorsque notamment le dispositif comprend une zone adiabatique et un milieu capillaire additionnel formant une section supplémentaire du dispositif, adjacente au condenseur.
• Fig. 8c
  [Fig. 8c] représente un exemple de hiérarchie des dimensions capillaires caractéristiques d'un dispositif lorsque notamment le dispositif comprend une zone adiabatique et un milieu capillaire additionnel relié au condenseur et à la zone adiabatique.
• Fig. 8d
  [Fig. 8d] représente un exemple de hiérarchie des dimensions capillaires caractéristiques d'un dispositif lorsque notamment le dispositif ne comprend pas de zone adiabatique et comprend un milieu capillaire additionnel relié au condenseur et à l'évaporateur.

Other features, details and advantages will become apparent from reading the detailed description below, and from analyzing the attached drawings, in which:

• Fig. 1a
  [ Fig. 1a ] represents a schematic diagram of a two-phase heat transfer device.
• Fig. 1b
  [ Fig. 1b ] represents a sectional view of an evaporator of a device of the Figure 1a .
• Fig. 2
  [ Fig. 2 ] is a partial and schematic perspective view of a two-phase heat transfer device according to one embodiment.
• Fig. 3
  [ Fig. 3 ] is a perspective sectional view of the device of the figure 2 .
• Fig. 4
  [ Fig. 4 ] is a front sectional view of a condenser of a two-phase heat transfer device according to one embodiment.
• Fig. 5
  [ Fig. 5 ] schematically represents the circulation of the two-phase fluid in a heat transfer device according to one embodiment.
• Fig. 6
  [ Fig. 6 ] represents an example of a capillary structure that can form the reservoir of excess liquid.
• Fig. 7
  [ Fig.7 ] schematically represents another example of a two-phase device in which the additional capillary medium is located in the extension of the condenser.
• Fig. 8a
  [ Fig. 8a ] represents an example of a hierarchy of capillary dimensions characteristic of a device when in particular the device is devoid of an adiabatic zone and comprises an additional capillary medium forming an additional section of the device, adjacent to the condenser.
• Fig. 8b
  [ Fig. 8b ] represents an example of a hierarchy of characteristic capillary dimensions of a device when in particular the device comprises an adiabatic zone and an additional capillary medium forming an additional section of the device, adjacent to the condenser.
• Fig. 8c
  [ Fig. 8c ] represents an example of a hierarchy of capillary dimensions characteristic of a device when in particular the device comprises an adiabatic zone and an additional capillary medium connected to the condenser and to the adiabatic zone.
• Fig. 8d
  [ Fig. 8d ] represents an example of a hierarchy of capillary dimensions characteristic of a device when in particular the device does not include an adiabatic zone and includes an additional capillary medium connected to the condenser and the evaporator.

Description of embodiments

With reference to figures 1a to 5 , two examples of a two-phase heat transfer device 1 have been shown. On the figures 1a and 1b , the device has a substantially cylindrical shape. In the example shown on the figures 2 to 4 , the device has a substantially parallelepiped shape. The shape of the device is however not restrictive and can be adapted according to the constraints of use, in particular according to the relative positions of the hot and cold sources between which the heat transfer must be implemented.

The two-phase heat transfer device 1 comprises a closed cavity 10 in a sealed manner and delimited by an envelope 11, in which circulates a saturated two-phase fluid comprising a vapor phase and a liquid phase. The liquid part of the two-phase fluid evaporates in the vicinity of the heat source, and the vapor obtained moves towards the cold source where it liquefies, thus returning the thermal energy, stored near the hot source, to the cold source. . To allow the circulation of the liquid phase within the cavity, the two-phase heat transfer devices include for example a particular structure which is shaped to allow liquid flow by capillary action. These structures can take variable shapes, such as for example a set of grooves, a porous structure or a lattice. The circulation of the vapor phase is allowed by one or more channels allowing a dissociated flow of the vapor and the liquid.

As schematically shown in the Figure 1a , the cavity 10 of the two-phase heat transfer device comprises at least one evaporation zone or evaporator 20, this zone being in a heat exchange situation, typically in thermal contact, with a hot source 2, such as for example equipment to be cooled. At the evaporator 20, the liquid phase of the fluid contained in the cavity evaporates by absorbing the heat provided by the hot source.

The evaporation zone includes in particular a capillary evaporation zone, for example in the form of a capillary structure. The evaporation zone notably comprises at least one capillary structure for the liquid and at least one vapor channel for the vapor.

In embodiments, the heat transfer device 1 can be used in a space environment, to cool one or more pieces of equipment of a spacecraft such as a satellite. This equipment may include optical equipment, such as for example a focal plane, telecommunications equipment or other equipment such as for example electrical actuator control equipment.

The heat transfer device 1 also comprises at least one condensation zone or condenser 30, this zone being in a heat exchange situation, typically in thermal contact, with a cold source 3. At the level of the condenser, the vapor phase of the fluid content in the cavity condenses, thus returning, to the cold source, the calories absorbed from the hot source. The condenser zone notably comprises a capillary condensation zone, for example in the form of a capillary structure. The condenser zone notably comprises at least one capillary structure for the liquid and at least one vapor channel for the vapor.

In the case where the heat transfer device is used in a spatial context, the cold source may for example comprise a radiator adapted to evacuate heat to space.

The heat transfer fluid contained in the cavity can for example be in the form of water, ammonia, methane, ethane, propylene, methanol or ethanol, in the state of liquid-gas equilibrium. .

In order to allow thermal exchanges between the two-phase fluid and the hot source on the one hand, and between the two-phase fluid and the cold source on the other hand, the envelope 11 is advantageously produced, at least at the level of each evaporator and each condenser, made of a thermally conductive material, such as for example a metal, or a metal alloy, for example based on aluminum.

In embodiments, and as shown for example on the figure 1a , the heat transfer device 1 can also include an adiabatic zone 12 located between an evaporator 20 and a condenser 30, that is to say a zone where heat transfers between the two-phase fluid present in the cavity and the environment of the heat transfer device are limited. Such a zone can for example be provided in the case where the cold source 3 and the hot source 2 are relatively far from each other and it is then desired to circulate the two-phase fluid between the two while limiting the transfers. heat with the environment. In this regard, a thermally insulating material can be used to ensure thermal insulation between the two-phase fluid and the environment of the heat transfer device 1, for example directly during the constitution of the envelope of the cavity, at the level of said adiabatic zone or by adding an additional insulating envelope around the adiabatic zone. The adiabatic zone notably comprises a capillary flow zone, for example in the form of a capillary structure. The adiabatic zone notably comprises at least one capillary structure for the liquid and at least one vapor channel for the steam.

The closed cavity 10 is shaped to allow the circulation of the two-phase fluid between the evaporator 20 and the condenser 30. In this regard, the closed cavity comprises at least one channel 13 for circulation of the two-phase fluid in the vapor phase which allows, as represented by the FV arrows on the figure 1a , to circulate the vapor obtained at the evaporator towards the condenser. The steam circulation channel(s) 13, or a network formed by these channels, therefore extend over the entire length of the cavity, going from the evaporator to the condenser. In addition, the closed cavity also comprises a main capillary structure 14 adapted to allow the circulation of the liquid phase of the two-phase fluid, and in particular to allow the liquid condensed at the level of the condenser to reach the evaporator, as represented by the FL arrows on the figure 1a . The main capillary structure 14 also extends over the entire length of the cavity, going from the evaporator to the condenser, to allow this circulation of liquid.

A capillary structure is a structure whose geometry is such that it generates surface tension effects, thus making it possible to retain and circulate the liquid by capillary action. The effects of surface tension can in particular be predominant over the effects of gravity or inertia. Hair structure can be done in different ways. For example, and as visible on the figure 1b , the capillary structure can be formed from a set of grooves 140 of small diameter, for example between 1 and 3 mm. In the example of the figure 2 , the capillary structure comprises a plurality of grooves which are distributed around a steam circulation channel 13, extending parallel to it. The grooves 140 each have a lateral opening 141 extending in the main direction of the groove, the lateral opening opening into the steam circulation channel 13 to allow steam contained in a groove 140 to join the channel. On the figure 1b , the profile of the grooves has a rounded open profile in Ω. This type of profile particularly favors the appearance of capillary pressure.

Alternatively, we could have an open teardrop or ω profile with its wide curvatures arranged opposite the cold surface, opposite the opening. Such a profile closes for example slightly at a ratio less than 2 (that is to say that the width of the opening is greater than half of the greatest width) so as to avoid the formation of a bridge and avoid trapping steam in the grooves. Advantageously with a teardrop or ω profile, we avoid retaining steam because of a liquid bridge which would form at the end, particularly in micro-gravity, which could make the two-phase structure unstable or even non-operational. Advantageously, a teardrop or ω profile promotes drainage of the cold surface.

The choice of profile will, for example, be made to best adapt to the use case.

In another example, shown in Figure 4 , the heat transfer device 1 may have a generally parallelepiped shape, and comprise at least one steam circulation channel 13 extending in the main direction of the heat transfer device 1. Grooves 140 for the circulation of the liquid phase can also extend parallel in the main direction of the heat transfer device, and comprise a lateral opening 141 extending in the main direction of each groove and opening into the channel 13 of steam circulation. Alternatively, as shown in the Figure 6 , the main capillary structure 14 can be formed of a lattice, comprising a set of small diameter capillary fibers, for example between 0.5 and 1 mm, interconnected to each other. According to yet another variant, the capillary structure can be a porous medium, for example by being formed of a material consisting of a porous micro-structure making said material permeable to the fluid in question.

On the figure 1b the circulation of the two-phase fluid at the level of an evaporator 20 has been schematically represented. The liquid contained in the capillary structure and conveyed from the condenser 30 vaporizes under the effect of the heat transmitted by the hot source 2. The vapor obtained joins the steam circulation channel 13 and as visible on the figure 1a , progresses in the cavity 10 until reaching the condenser 30, where it condenses and the condensed liquid joins the main capillary structure 14.

The heat transfer device 1 further comprises a reservoir 15 for storing excess liquid of the two-phase fluid, this reservoir being formed by an additional capillary medium. The additional capillary medium 15 which carries out storage and restitution of the fluid in the liquid phase is connected to the main capillary structure 14 so as to ensure capillary continuity for the fluid in the liquid phase. The additional medium includes a capillary reservoir zone and may also include a vapor channel. Such a vapor channel can for example be useful in cases, as shown in figures 8a and 8b , where the liquid filling rate in the tank varies between 0% and 100% or even between 5% and 95%, steam then also being present in this tank zone. Thus the presence of a steam channel nearby will allow the steam to be evacuated more easily when the liquid enters the tank.

In embodiments, the additional capillary medium has no structural function for the heat transfer device 1, that is to say it does not contribute to its mechanical strength, unlike the cavity 10 and in particular to its envelope 11.

The steam channels are, for example, all connected to each other. The interconnected steam channels thus form a single continuous space. In embodiments, if the additional capillary medium 15 is adjacent to the vapor channel 13 of the cavity 10, it does not completely obstruct the section of this vapor channel.

By “capillary continuity for the fluid in the liquid phase” or by “liquid capillary continuity” is meant the fact that an exchange of fluid in the liquid phase can take place by capillarity, in one direction or the other, at the level of each place where capillary continuity is formed for the fluid in the liquid phase, in particular between the additional capillary medium and the main capillary structure. The additional capillary medium is thus attached to the main capillary structure.

The fluid in the liquid phase can thus move towards the additional capillary medium or towards the capillary structure. In this regard, the main capillary structure 14 and the additional capillary medium 15 are preferably shaped so that there is no discontinuity between these two capillary media. By discontinuity we mean one or more cavities whose dimension would exceed the largest characteristic capillary dimension of the two media.

Thus when the device 1 heats up, the volume of two-phase fluid in liquid form will tend to increase and the additional capillary storage medium will fill passively and thus prevent the formation of a liquid plug. Conversely, when the device 1 cools, the volume of two-phase fluid in liquid form will tend to decrease and the additional capillary storage medium will empty passively and thus prevent the main capillary structure from drying out.

In this way, the additional capillary medium 15 can store excess liquid which could not be contained in the main capillary structure 14 which is already full and which would disrupt the operation of the heat transfer device by being placed in the vapor channels. This storage makes it possible to make the heat transfer device operational, with optimized performance, whatever the position or configuration of the heat transfer device.

• lorsque le volume de liquide est minimal, la structure capillaire principale 14 est toujours pleine de liquide, et le milieu capillaire additionnel est faiblement rempli, de l'ordre de 0 à 5% de taux de remplissage, et
• lorsque le volume de liquide est maximal, la structure capillaire principale 14 est pleine de liquide et le milieu capillaire additionnel est complètement rempli, sans atteindre toutefois la saturation pour éviter une perturbation du fonctionnement du dispositif, c'est -à-dire avec un taux de remplissage de l'ordre de 95% à 100%.

In embodiments, the additional capillary medium is dimensioned, depending on the dimensioning of the heat transfer device 1 and the quantity of two-phase fluid, to present a filling rate of strictly between 0 and 100%, preferably strictly understood between 5 and 95% when the heat transfer device is in operation. The filling rate corresponds to the ratio between the volume of liquid contained in the additional capillary medium, constituting the reservoir(s), and the total volume that can be contained in this medium. In other words, the quantity of two-phase fluid in the cavity being constant but with a volume of liquid which can vary between a minimum volume and a maximum volume, the additional capillary medium can be advantageously sized, as illustrated in figures 8a and 8b , so that :

• when the volume of liquid is minimal, the main capillary structure 14 is always full of liquid, and the additional capillary medium is weakly filled, of the order of 0 to 5% filling rate, and
• when the volume of liquid is maximum, the main capillary structure 14 is full of liquid and the additional capillary medium is completely filled, without however, reach saturation to avoid a disruption in the operation of the device, that is to say with a filling rate of the order of 95% to 100%.

The volume of liquid in the cavity can vary between Volume_min and Volume_max, so that at any instant the total volume of liquid is equal to Volume_t = Volume_min + Delta_Volume_t

Furthermore, Volume_max = Volume_min + Delta_Volume_max.

The main capillary structure has, for example, a reception volume equal to Volume_min and all of the excess liquid, i.e. Delta_Volume_t, will be housed in the additional structure forming a reservoir. The additional structure forming a reservoir must then be able to contain a volume corresponding to Delta_Volume_max.

We can thus provide a volume of the additional capillary structure forming a reservoir greater than or equal to Delta_Volume_max.

Thus for a minimum total volume, only the main structure 14 will be filled, while for a maximum total volume, the main structure 14 and the additional structure forming a reservoir 15 are full.

• pour un volume minimum, la structure principale 14 pleine et la structure additionnelle formant réservoir 15 remplie à 5 % et
• pour un volume maximum, la structure principale 14 pleine et la structure additionnelle formant réservoir 15 remplie à 95%.

In practice we can provide an operating safety margin with, for example:

• for a minimum volume, the main structure 14 full and the additional structure forming a reservoir 15 filled to 5% and
• for maximum volume, the main structure 14 full and the additional structure forming a reservoir 15 filled to 95%.

In the cases of figures 8a and 8b , the reservoir 15 is for example filled to a filling rate varying between 0% and 100% or even between 5% and 95%, while the rest of the capillary structure is always 100% full.

In the cases of figures 8c and 8d , condenser 143, which has the largest capillary structure, will fill last, while all other capillary structures receiving liquid are always 100% filled. The filling rate of the condenser varies for example between 0% and 100% or even between 5% and 95%. The capillary structure of the condenser (which is part of the main structure 14) is preferably not 100% full since the additional capillary structure 15 has a smaller dimension than that of the condenser. The additional capillary structure 15 will therefore have a tendency to suck the liquid from the condenser. We therefore have the evaporator structure which is full and the adiabatic structure which is full, while the capillary structure of the condenser is partially filled and varies for example between 5 and 95%.

The additional liquid storage volume represented by the additional capillary medium is for example less than the volume of the main capillary structure 14 and preferably less than 50% of the volume of the main capillary structure.

In embodiments, the storage volume available for the liquid in the additional capillary medium is between 10 and 40% of the volume available for the liquid in the main capillary structure. The volume of the additional storage medium depends on the two-phase fluid considered as well as the operational temperature range.

With reference to figures 8a to 8d , we will now describe embodiments of the dimensioning of the different capillary structures.

In the following, we call “characteristic capillary dimension” the average dimension of the capillary cavities of the capillary structure considered. In the case where the capillary structure is porous, the characteristic capillary dimension can correspond to the average diameter of the pores. In the case where the capillary structure is formed of a latticework of solid fibers ( fig 6 ), the characteristic capillary dimension can correspond to the diameter of the largest spherical particle that could pass through. In the case where the capillary structure is formed of grooves, the characteristic capillary dimension can correspond to the hydraulic diameter of the opening 141 connecting a groove 140 to the steam circulation channel 13.

The smaller the characteristic capillary dimension, the more significant the capillarity phenomenon. Consequently, the different capillary structures of the device 1 advantageously present a hierarchy of characteristic capillary dimensions making it possible to ensure the flow of the liquid to the evaporator.

Thus, the main capillary structure 14 can have different characteristic capillary dimensions along the cavity. For example, the capillary structure 14 may comprise at least one capillary condensation zone 143 in the condenser 30, a capillary evaporation zone 142 in the evaporator 20 and optionally a capillary flow zone 144 connected on the one hand to the capillary condensation zone and on the other hand to the evaporator, and the different zones of the capillary structure 14 can have different characteristic capillary dimensions.

In an embodiment shown schematically in figure 8a , the capillary structure 14 has a characteristic capillary dimension εc that is greater at the level of the condenser 30, that is to say in the capillary condensation zone 143, than at the level of the evaporator 20 (εev).

In a variant represented in figure 8b , the cavity 10 further comprises an adiabatic zone 12 and the main capillary structure 14 comprises a capillary evaporation zone 142 having a characteristic capillary dimension εev less than the characteristic dimension of the adiabatic zone εa, which is itself less than the characteristic capillary dimension εc of the capillary condensation zone 143.

In embodiments, the additional capillary medium 15 may have a characteristic capillary dimension εr greater than or equal to the maximum characteristic capillary dimension of the main capillary structure 14. Thus, when the quantity of liquid decreases and the excess liquid stored in the reservoir must be recovered to contribute to the operation of the device, this hierarchy of capillary dimensions ensures that the liquid returns to the main capillary structure and does not remain stored in the reservoir. This is the case represented schematically in the figures 8a and 8b .

As a variant shown schematically on the figures 8c and 8d , which represent a device respectively with and without an adiabatic zone, in the case where the main capillary structure 14 has zones of variable characteristic capillary dimensions, the additional capillary medium 15 can have a characteristic capillary dimension εr less than a characteristic capillary dimension εc of the capillary condensation zone 143, but greater than or equal to a characteristic capillary dimension εa of the capillary flow zone 144 and/or that εev of the capillary evaporation zone 142.

The additional capillary storage medium 15 may also have a variable characteristic capillary dimension and in this case, the minimum characteristic capillary dimension of the additional capillary storage medium is located at the level of the connection with the main capillary structure.

This minimum characteristic capillary dimension of the storage medium may for example be greater than or equal to the maximum characteristic capillary dimension of the main capillary structure.

As indicated previously, the cavity 10 may comprise one or more steam circulation channels 13. These channels 13 may also have different sections, the channels of minimum section being located at the level of the evaporation zone.

In embodiments, the maximum characteristic capillary dimension of the additional capillary storage medium 15 is less than or equal to the minimum characteristic dimension of the steam circulation channels 14, which corresponds typically to their hydraulic diameter. The channels of the evaporation zone 20 only may have a diameter less than a capillary dimension characteristic of the additional capillary medium.

In embodiments, the additional capillary storage medium 15 can be connected to the main capillary structure 14 at the level of the condensation zone 30.

In embodiments, the additional capillary storage medium can also be connected to the capillary structure at an adiabatic zone 12, or even at the level of the evaporation zone 20. However, the condensation zone 30 being the colder and furthest from the heat source, it is advantageous to have at least one connection between the main capillary structure 14 and an additional capillary storage medium 15 at this condensation zone 30.

One or more additional capillary media can be provided, each connected by a single connection with the main capillary medium, the main capillary medium ensuring circulation of the liquid between the cold source and the hot source.

We represented on the Figure 5 the circulation of the two-phase fluid between the evaporator 20 and the condenser 30, the dotted arrows representing the possible connections between an additional capillary storage medium and the main capillary structure, the main capillary medium ensuring circulation of the liquid between the cold source and the hot spring. Evaporation at the evaporator is represented by the arrow L→V and condensation at the condenser 30 is represented by the arrow V→L.

In embodiments, the additional capillary storage medium 15 is manufactured by additive manufacturing (3D printing), also referred to as ALM, to enable precise capillary structuring of this medium.

Alternatively, the additional capillary storage medium can also be produced by extrusion or machining.

The additional capillary storage medium is for example made of metal, for example aluminum, titanium or invar.

With reference to figures 2 to 4 , we have shown an example of configuration of an additional capillary medium for the storage of excess liquid. On the figures 2 And 3 , the envelope 11 of the device is not shown, unlike the figure 4 .

On these figures 2 to 4 , the heat transfer device has a substantially extended parallelepiped shape of which the condensation zone 30 occupies an end section.

The heat transfer device may comprise an adiabatic zone 12, corresponding to another section of the device, this adiabatic zone, as shown in figure 2 , can be arranged in the extension of the condensation zone 30.

The example of a heat transfer device according to figure 2 also includes an evaporation section. This evaporation section, not shown in the figure 2 , is connected to the adiabatic section.

The heat transfer device may comprise a steam circulation channel 13 of parallelepiped section extending in the main direction of the heat transfer device 1. The steam circulation channel 13 can be delimited, in the condenser, on one side, by the capillary structure of the condenser 30 and on other sides by the additional capillary medium 15. As shown in Figure 4 , the capillary structure of the condenser 30 comprises a set of grooves 140 extending parallel to the steam circulation channel. The grooves 140 include a lateral opening 141 extending in the main direction of the grooves and opening into the steam circulation channel. The additional capillary medium 15 is here shaped in a U to surround the steam circulation channel 13, and to be connected, by the two free ends of the U, to the capillary structure of the condenser 30. The additional capillary medium 15 can thus delimit, on three sides, the steam circulation channel 13.

As shown on the figure 2 , the vapor channel can extend into the adiabatic zone by passing through the center of an adiabatic capillary structure extending around the periphery of the adiabatic zone.

The capillary continuity between the capillary structure of the condenser 30 on the one hand and the additional capillary medium and possibly the capillary structure of the adiabatic zone on the other hand is achieved, for example, at the ends of the grooves 140 of the capillary structure. of the condenser 30.

Capillary continuity can also be achieved on one face of the U, between the additional capillary medium 15 and the capillary structure of the adiabatic zone.

The additional capillary medium 15 can be formed, for example, of a lattice or of a porous structure. An example of a trellis is shown in Figure 6 .

In a variant embodiment, represented schematically in Figure 7 , the additional capillary medium 15 can form an additional section at one end of a two-phase device 1 successively comprising an evaporation zone 142, optionally an adiabatic zone 144 and a condensation zone 143. The additional section corresponding to the additional capillary medium 15 is preferably adjacent to the condensation zone 143 so that the additional capillary medium 15 is connected in liquid capillary continuity with the capillary condensation structure.

List of reference signs

• 1: heat transfer device or heat pipe
• 2: hot spring
• 3: cold source
• 10: cavity
• 11: envelope
• 12: adiabatic zone
• 13: steam circulation channel
• 14: main hair structure
• 140: groove
• 141: lateral opening of a groove
• 142: evaporation zone of the main hair structure
• 143: condensation zone of the main capillary structure
• 144: flow zone of the main capillary structure
• 15: additional capillary storage medium
• 150: section of additional capillary medium
• 20: evaporation zone / evaporator
• 30: condensation zone / condenser
• FV: steam circulation arrow
• FL: liquid circulation arrow
• εev: characteristic capillary dimension of the evaporation zone of the main capillary structure
• εc: characteristic capillary dimension of the condensation zone of the main capillary structure
• εa: characteristic capillary dimension of the flow zone of the main capillary structure
• εr: characteristic capillary dimension of the additional capillary medium.

Claims (11)

1. A two-phase heat transfer device (1), comprising a closed cavity (10) comprising at least one evaporation area (20) in a situation of heat exchange with at least one hot source (2) and at least one condensation area (30) in a situation of heat exchange with at least one cold source (3), the closed cavity (10) containing a two-phase fluid in a state of liquid-vapour equilibrium and comprising at least one channel (13) for circulation of the two-phase fluid in the vapour phase and at least one main capillary structure (14) adapted to allow the circulation of the two-phase fluid in the liquid phase between said cold source and said hot source,
   the two-phase device (1) being characterised in that it further comprises at least one additional capillary medium (15) allowing storage and restitution of an excess of liquid in relation to a maximum capacity of liquid contained in the main capillary structure (14), said additional capillary medium (15) and said main capillary structure (14) being connected so as to ensure capillary continuity for the two-phase fluid in the liquid phase, said additional medium (15) comprising at least one capillary reservoir area, the main capillary structure (14) comprising at least one capillary condensation area (143) and a capillary evaporation area (142), characterised in that the evaporation (142) and condensation (143) areas of the main capillary structure, taken in order, have increasing characteristic capillary dimensions, said capillary dimensions being less than the diameter of the vapour circulation channel, and the additional capillary medium (15) has a characteristic capillary dimension greater than that of the evaporation area and less than the diameter of the vapour circulation channel.
2. The two-phase device (1) according to claim 1, wherein the capillary reservoir area is directly connected to the capillary condensation area and has a characteristic capillary dimension (εr) greater than a characteristic capillary dimension (εc) of the capillary condensation area (143).
3. The two-phase device (1) according to one of claims 1 or 2, wherein the main capillary structure (14) further comprises a capillary flow area connected on the one hand to the capillary condensation area (143) and on the other hand to the capillary evaporation area (142), the areas, taken in order, of evaporation, flow, and condensation having increasing characteristic capillary dimensions, said characteristic capillary dimensions being less than the diameter of the vapour circulation channel.
4. The two-phase device (1) according to claim 3, wherein said capillary reservoir area is directly connected to the flow area and has a characteristic capillary dimension greater than a characteristic capillary dimension of the flow area.
5. The two-phase device (1) according to one of the preceding claims, wherein the additional capillary medium (15) is in contact, on the one hand, with the vapour circulation channel (13), and on the other hand, with the main capillary structure (14).
6. The two-phase device (1) according to the preceding claim, wherein the additional capillary medium (15) comprises the capillary reservoir area and a vapour circulation channel.
7. The two-phase device (1) according to one of the preceding claims, the volume of the two-phase fluid in liquid phase in the cavity is variable between a minimum volume Vmin and a maximum volume Vmax, the volume of the additional capillary medium (15) is greater or equal to the volume difference between the maximum volume and the minimum volume, and less than 50% of the volume of the main capillary structure (14).
8. The two-phase device (1) according to one of the preceding claims, wherein the additional capillary medium (15) has a minimum characteristic capillary dimension at the connection with the main capillary structure (14) for the circulation of the two-phase fluid in liquid phase.
9. The two-phase device (1) according to one of the preceding claims, wherein the additional capillary medium (15) is dimensioned so as to have a filling rate strictly comprised between 0 and 100%, preferably strictly comprised between 5 and 95 %, when the two-phase heat transfer device (1) is in operation.
10. The two-phase device (1) according to one of the preceding claims, wherein the volume available for the liquid in the additional capillary medium (15) is comprised between 10 and 40% of the volume available for the liquid in the main capillary structure (14) of the cavity (10).
11. The two-phase device (1) according to one of the preceding claims, wherein the additional capillary medium (15) is a lattice and/or is formed of a porous material.

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