EP2756251B1 - Capillary-pumping heat-transport device - Google Patents

Description

The present invention relates to capillary pumping heat transport devices, in particular passive biphasic fluid loop devices.

It is known from the document FR-A-2949642 and document US - 4,957,157 such devices used as cooling means for electrotechnical power converter.

However, it appeared that the starting phases were particularly delicate for large thermal powers, it can occur a drying of the capillary wick and thus a failure of startup.

In addition, if the device is subjected to accelerations, it can occur a phenomenon of cold shock in the tank which suddenly lowers the pressure and deteriorates the performance.

It has therefore appeared a need to increase the reliability of startup and operation of such loops.

• au moins un évaporateur, ayant une entrée et une sortie, et une masse microporeuse adaptée pour assurer un pompage capillaire de fluide en phase liquide
• au moins un condenseur, ayant une entrée et une sortie,
• un réservoir ayant un volume intérieur et au moins un orifice d'entrée et/ou sortie, avec une portion de phase gazeuse située au-dessus d'une portion de phase liquide,
• un premier circuit de communication, pour du fluide essentiellement en phase vapeur, reliant la sortie de l'évaporateur à l'entrée du condenseur,
• un deuxième circuit de communication, pour du fluide essentiellement en phase liquide, reliant la sortie du condenseur au réservoir et à l'entrée de l'évaporateur, caractérisé en ce que le réservoir comprend plusieurs volumes distincts de phase liquide, les dits volumes distincts restant en communication fluide,

le réservoir comprenant une pluralité de parois internes formant des compartiments adaptés pour séparer lesdits plusieurs volumes distincts de phase liquide,
lesdits plusieurs volumes distincts communiquant par des passages de faible section, de manière à créer un amortissement hydraulique entre les volumes distincts de phase liquide.For this purpose, the subject of the invention is a capillary pumping thermal transfer device adapted to extract heat from a hot source and to restore this heat to a cold source by means of a two-phase working fluid contained in a enclosed general circuit, comprising:

• at least one evaporator, having an inlet and an outlet, and a microporous mass adapted to provide capillary pumping of fluid in the liquid phase
• at least one condenser, having an inlet and an outlet,
• a reservoir having an interior volume and at least one inlet and / or outlet orifice, with a portion of gaseous phase located above a portion of liquid phase,
• a first communication circuit, for substantially vapor phase fluid, connecting the evaporator outlet to the condenser inlet,
• a second communication circuit, for fluid essentially in the liquid phase, connecting the condenser outlet to the reservoir and to the inlet of the evaporator, characterized in that the reservoir comprises several distinct volumes of liquid phase, the said distinct volumes remaining in fluid communication,

the reservoir comprising a plurality of internal walls forming compartments adapted to separate said several distinct volumes of liquid phase,
said plurality of separate volumes communicating through passages of small section, so as to create a hydraulic damping between the separate volumes of liquid phase.

Thanks to these provisions, and the hydraulic damping thus created, it avoids excessive liquid fluid movements in the tank when the device is subjected to accelerations, for example if it is on board a transport vehicle , and thus avoids a mixture in the tank that can lead to the effect of 'cold shock', namely a sudden lowering of the free surface temperature of the liquid in the tank which causes a drop in pressure and a decrease in efficiency of the loop. Similarly, the partition in several separate volumes of liquid avoids a mixture that could occur due to sudden increases in thermal power, especially the case of startup.

• la phase liquide ne dépasse pas de l'extrémité supérieure des parois; ce qui évite le mélange de liquide en cas d'accélérations subies ;
• lesdits plusieurs volumes distincts communiquent par des passages de faible section de préférence inférieure au 1/10 de la plus grande section du réservoir ; moyennant quoi le déplacement d'un volume distinct à l'autre est possible mais limité en débit;

• la pluralité de parois internes forment une structure de compartiments régulière; moyennant quoi les parois se supportent les unes par rapport aux autres ;
• le réservoir comprend une structure macroporeuse et les compartiments sont dépourvus de structure microporeuse
• la structure de compartiment prend la forme d'une structure en nid d'abeille ; de sorte que la structure de compartiment présente un coût modéré car cette structure est optimisée ;
• le dispositif est principalement soumis à la gravité terrestre et la structure de compartiment comprend des cloisons inclinées ou verticales ; de sorte que les déplacements de fluides sont limités en cas d'accélération horizontale ;
• la structure de compartiment est formée en acier inox ; moyennant quoi sa durabilité est très satisfaisante ;
• la structure de compartiment est formée en plastique compatible avec le fluide de travail en particulier le méthanol ; moyennant quoi elle est compatible avec ce fluide communément utilisé, sa durée de vie est satisfaisante et son coût est faible ;
• lesdits plusieurs volumes distincts sont formés dans une structure maillée serrée (tissu métallique) ; moyennant quoi une alternative à la structure de parois est proposée ;
• la structure de compartiment comprend un matériau à changement de phase conférant une inertie thermique ; moyennant quoi l'effet de 'cold shock' est encore amoindri ;
• le réservoir comprend un déflecteur de jet d'entrée ; moyennant quoi l'effet de jet produit par l'entrée du liquide dans le réservoir est limité à une zone restreinte ;
• le réservoir peut être adjacent à l'évaporateur ou le réservoir peut être intégré à l'évaporateur ; moyennant quoi l'intégration mécanique du réservoir peut être améliorée ;
• le dispositif comprend en outre un organe anti retour agencé entre le volume intérieur du réservoir et la masse microporeuse de l'évaporateur, et agencée pour empêcher que du liquide présent dans l'évaporateur ne se déplace vers le volume intérieur du réservoir ;
• le dispositif est principalement soumis à la gravité, et l'organe anti retour comprend un flotteur;
• le dispositif de transfert thermique est préférentiellement dépourvu de pompe mécanique ; de sorte que sa fiabilité est augmentée ;
• le dispositif comprend en outre un élément d'apport d'énergie au niveau du réservoir pour contrôler la mise en pression de la boucle lors du démarrage ; de sorte que le démarrage de la boucle peut être fiabilisé.

In various embodiments of the invention, one or more of the following provisions may also be used:

• the liquid phase does not exceed the upper end of the walls; which avoids the mixing of liquid in case of accelerations undergone;
• said several different volumes communicate through passages of small section preferably less than 1/10 of the largest section of the tank; whereby the displacement of a separate volume to another is possible but limited in flow;

• the plurality of inner walls form a regular compartment structure; whereby the walls are supported with respect to each other;
• the reservoir comprises a macroporous structure and the compartments are devoid of microporous structure
• the compartment structure takes the form of a honeycomb structure; so that the compartment structure has a moderate cost because this structure is optimized;
• the device is mainly subjected to earth gravity and the compartment structure comprises inclined or vertical partitions; so that the movements of fluids are limited in case of horizontal acceleration;
• the compartment structure is formed of stainless steel; whereby its durability is very satisfactory;
• the compartment structure is formed of plastic compatible with the working fluid, in particular methanol; whereby it is compatible with this commonly used fluid, its life is satisfactory and its cost is low;
• said plurality of distinct volumes are formed in a tight mesh structure (metal fabric); whereby an alternative to the wall structure is proposed;
• the compartment structure comprises a phase change material imparting thermal inertia; whereby the effect of cold shock is further diminished;
• the reservoir comprises an inlet jet deflector; whereby the jet effect produced by the entry of the liquid into the reservoir is limited to a restricted area;
• the tank can be adjacent to the evaporator or the tank can be integrated with the evaporator; whereby the mechanical integration of the tank can be improved;
• the device further comprises an anti-return member arranged between the internal volume of the tank and the microporous mass of the evaporator, and arranged to prevent the liquid present in the evaporator from moving towards the interior volume of the tank;
• the device is mainly subjected to gravity, and the anti-return member comprises a float;
• the heat transfer device is preferably free of mechanical pump; so that its reliability is increased;
• the device further comprises an energy supply element at the reservoir to control the pressurization of the loop during startup; so that the start of the loop can be made reliable.

• la figure 1 est une vue générale d'un dispositif selon un mode de réalisation de l'invention,
• la figure 2 est une variante du dispositif de la Figure 1,
• la figure 3 montre de façon plus détaillée le réservoir du dispositif de la figure 2,
• les figures 4a et 4b montre des structures de compartiment dans le réservoir du dispositif des figures 1 et 2,
• la figure 5 est analogue à la figure 3 et montre une variante du réservoir du dispositif de la figure 2.
• la figure 6 est une variante du dispositif de la Figure 1.

Other aspects, objects and advantages of the invention will appear on reading the following description of several embodiments of the invention, given by way of non-limiting examples, with reference to the accompanying drawings, in which:

• the figure 1 is a general view of a device according to one embodiment of the invention,
• the figure 2 is a variant of the device of the Figure 1 ,
• the figure 3 shows in more detail the reservoir of the device of the figure 2 ,
• the Figures 4a and 4b shows compartment structures in the tank of the device Figures 1 and 2 ,
• the figure 5 is analogous to the figure 3 and shows a variant of the reservoir of the device of the figure 2 .
• the figure 6 is a variant of the device of the Figure 1 .

In the different figures, the same references designate identical or similar elements.

The figure 1 shows a capillary pumping heat transport device with a two-phase fluid loop. The device comprises an evaporator 1, having an inlet 1a and an outlet 1b , and a microporous mass 10 adapted to provide capillary pumping. For this purpose, the microporous mass 10 surrounds a blind central longitudinal recess 15 in communication with the inlet 1a to receive working fluid 9 in the liquid state from a reservoir 3.

The evaporator 1 is thermally coupled to a heat source 11, such as a set comprising electronic power components or any other element that generates heat, for example by the Joule effect, or by any other process.

Under the effect of the supply of calories to the contact 16 of the microporous mass filled with liquid, fluid passes from the liquid state to the vapor state and is evacuated by the transfer chamber 17 and by a first circuit. communication 4 which conveys said vapor to a condenser 2 having an inlet 2a and an outlet 2b.

In the evaporator 1, the cavities released by the evacuated vapor are filled with liquid sucked by the microporous mass 10 from the aforementioned central recess 15; it is the phenomenon of capillary pumping well known in itself.

Inside said condenser 2, heat is transferred by the fluid in the vapor phase to a cold source 12, which causes a cooling of the vapor fluid and its phase change to the liquid phase, ie its condensation.

At the condenser 2, the fluid temperature 9 is lowered below its liquid-vapor equilibrium temperature, which is also called sub-cooling ('sub-cooling' in English) so that the fluid can not return to the vapor state without a consequent contribution heat.

The vapor pressure pushes the liquid towards the outlet 2b of the condenser 2 which opens onto a second communication circuit 5, furthermore connected to the tank 3.

The reservoir has at least one inlet and / or outlet orifice 31, here in this case on the figure 1 a separate inlet orifice 31a and outlet 31b , and the reservoir 3 has an internal volume 30, filled with the coolant 9. The working fluid 9 can be, for example, ammonia or any other suitable fluid, but it is preferable to choose methanol. The working fluid 9 is two-phase and is partly in liquid phase 9a and partly in vapor phase 9b. In an environment where gravity is exerted (vertical along Z), the gas phase portion 9b is located above the liquid phase portion 9a and a liquid-vapor interface 19 separates the two phases (free surface of the liquid in the liquid phase). tank).

It is the temperature of this separation surface 19 which determines the pressure in the loop, this pressure corresponds to the saturation pressure of the fluid at the temperature prevailing at the separation surface 19.

At the base of the reservoir 34, the temperature of the liquid is generally lower than the temperature prevailing at the separation surface 19.

For proper operation of the capillary pumping loop, it is necessary to prevent the temperature prevailing at the separation surface 19 from changing rapidly, and in particular to avoid mixing the liquid phase 9a which tends to bring cold liquid from the bottom of the tank upwards and therefore to bring down the surface temperature, and by the same pressure.

This phenomenon of sudden drop in temperature and pressure is commonly called cold shock and should be avoided.

The first and second fluid communication circuits 4,5 are preferably tubular conduits, but could be other types of fluid communication conduits or channels (rectangular, flexible conduits, etc.).

Similarly, the second fluid communication circuit 5 may be in the form of two separate independent conduits 5a, 5b (cf. Fig 1 ) or a single pipe with a 'T' connection 5c (cf. Fig 2 ).

These pipe configurations remain relevant when multiple and / or multiple condensers are connected in parallel.

In all cases, the second fluid communication circuit 5 connects the outlet of the condenser 2b to the inlet of the evaporator 1a, either indirectly via the reservoir (in the case of two independent conduits) or directly (case or a single driving with 'T').

In order to avoid mixing phenomena within the reservoir which are conducive to the phenomenon of 'cold shock', there are provided, inside the reservoir, several distinct volumes of liquid separated from each other but said distinct volumes remaining in fluid communication. In particular, and more specifically, in the reservoir can be arranged a plurality of internal walls 7 adapted to separate said several separate volumes.

However, according to one alternative, said several distinct volumes may be formed in a tight mesh structure (not shown in the figures), such as for example an iron straw type structure, or a sponge-type structure or a macroporous structure, or still a stack of hollow spheres pierced with small orifices.

In addition, advantageously according to the invention, the reservoir comprises an inlet jet deflector 8 in the vicinity of the inlet orifice 31a or the inlet / outlet orifice 31 according to the configuration of the second conduit.

This inlet jet deflector prevents a rapid arrival of liquid in the tank creates a bubbling or a current promoting the mixing of the liquid. It may be in the form of a downward U-shaped profile, or a bell or other shape creating a sufficient deflection of the path of the inlet jet.

The figure 3 shows a compartment structure 71, with vertical walls 7, that is to say oriented in the direction of gravity. It should be noted, however, that the walls may just as well be slightly or substantially inclined, as illustrated for example on the Figure 1 . Preferably, the compartment structure is regular, i.e. a certain geometric pattern is repeated several times. It should be noted that the reservoir may have any shape, and in particular parallelepipedal or cylindrical. In addition, the compartment structure can be formed of stainless steel to give it good durability. In addition, the compartment structure may be formed of compatible plastic of the working fluid and in particular methanol; whereby it is compatible with this fluid commonly used for terrestrial applications, its life is satisfactory and its cost is low.

According to one aspect of the present invention, said several distinct volumes communicate through passages of small section, preferably less than 1/10 of the largest section of the tank. For example as illustrated on the figure 3 , the inner walls 7 have orifices 70 whose passage section is small, in order to create a hydraulic damping between the separate volumes of liquid.

The passages between the separate volumes can also be located at the base of the compartments, without orifice on the height of the compartments. In this case, a grid 28 pierced with a plurality of small section holes allows the fluid to move between the compartments through a transfer chamber 29 located in the base zone 34 of the reservoir. This grid 28 also known as diffusion can advantageously serve as a support for the compartment structure 71.

The height of the walls may be between 30% and 90% of the height of the tank, and will be chosen in particular so that the upper surface 19 of the liquid does not exceed the upper end of the walls 7.

Advantageously, it is possible to choose a honeycomb structure of hexagonal mesh or a square mesh structure, as illustrated respectively in FIGS. Figures 4a and 4b . Hexagonal compartments 77, (respectively square 78 ) communicate between their lower opening 76 (respectively 79 ).

In addition, the plurality of walls may comprise walls oriented differently from each other. In particular, there may be some walls parallel to the XZ plane, others parallel to the XY plane and others parallel to the YZ plane: thus one can limit the movements in all directions in space, which is particularly advantageous if the device is on board an aircraft.

In addition, the size of the cells must not be too thin (less than one millimeter), otherwise the structure traps the liquid by capillarity and requires overfilling. to avoid drying the loop when starting in cold conditions or drops in power. The compartments are thus devoid of microporous structure, although the reservoir can form a macroporous structure.

According to another advantageous aspect of the invention, the compartment structure comprises a phase change material imparting a thermal inertia to said structure which contributes to limiting the sudden variations in temperature.

The figure 5 is analogous to the figure 3 and shows a variant of the reservoir of the device with a liquid inlet at the bottom and on the side 35, which can simplify the inlet jet baffle 8. The inlet jet baffle 8 can then be reduced to a plate extending horizontally or at an extension pierced with a multitude of holes in the tube 5.

In addition, as illustrated in figure 6 (similar to figure 1 ), the device may furthermore incidentally comprise a non-return member 6, arranged between the internal volume 30 of the reservoir and the microporous mass 10 of the evaporator, to prevent the liquid present in the evaporator from moving towards the volume inside the tank. This non-return member 6 makes it possible to prevent a liquid movement from the evaporator towards the reservoir when the boiling is triggered during the start-up phases of the system.

Preferably, this non-return member 6 may comprise a float (not shown in detail) whose density is slightly less than the fluid density in the liquid phase.

Furthermore, the device may further comprise a power supply element 36, for example a heating element or pressurizing, located at the reservoir to control the pressurization of the loop during startup. A control system 'Ctrl' driver 38, in the case of a heating element, the supply of calories to this heating element 36, as a function of temperature information and / or pressure information delivered by sensors (not shown), in order to ensure the start of the two-phase loop.

The heating element can be located both in the liquid phase and / or the vapor phase. Preferably, this element is located in the liquid phase and generates steam towards the upper part of the reservoir. The regulation with the heating element will be facilitated by the presence of a cold source in contact with the latter (ambient air, or other). In addition, this control system 'Ctrl' can also prepare the two-phase loop for an imminent and important arrival of calories on the evaporator, which makes it possible to anticipate the reaction of the two-phase loop with respect to the need for heat dissipation. The design of the loop can be optimized for large quantities of heat to be evacuated.

Advantageously according to the invention, the device is devoid of any mechanical pump although the invention does not exclude the presence of a mechanical booster pump.

Claims (14)

1. Capillary-driven heat transfer device under the influence of gravity, adapted to extract heat from a heat source (11) and to release this heat to a cold source (12) by means of a two-phase working fluid contained in a closed general circuit, comprising:

   - at least one evaporator (1), having an inlet and an outlet, and a microporous mass (10) adapted to perform capillary pumping of fluid in the liquid phase

   - at least one condenser (2), having an inlet and an outlet,

   - a reservoir (3) having an inner chamber (30), and at least one inlet and/or outlet port (31;31a,31b), with a vapor phase portion located on top of a liquid phase portion,

   - a first communication circuit (4), for fluid mainly in the vapor phase, connecting the outlet of the evaporator to the inlet of the condenser,

   - a second communication circuit (5), for fluid mainly in the liquid phase, connecting the outlet of the condenser to the reservoir and to the inlet of the evaporator,

   characterized in that the reservoir (3) includes multiple separate volumes of the liquid phase, said separate volumes remaining in fluid communication, the reservoir including a plurality of inner partitions (7) forming compartments adapted to separate said multiple separate volumes of the liquid phase,
   said multiple separate volumes communicating through small cross-sectional passages, in order to create hydraulic damping between the separate volumes of the liquid phase.
2. Device according to claim 1, wherein the liquid phase does not go over the upper edge of the partitions (7).
3. Device according to one of claims 1 to 2, wherein the plurality of inner partitions form a regular compartment structure.
4. Device according to one of claims 1 to 3, wherein the reservoir includes a macroporous structure and the compartments are deprived of a microporous structure.
5. Device according to claim 4, mainly under the influence of the Earth's gravity, wherein the partitions form inclined or vertical separating walls.
6. Device according to one of claims 4 to 5, wherein the compartment structure takes the form of a honeycomb structure.
7. Device according to one of claims 4 to 6, wherein the compartment structure consists of a phase change material providing thermal inertia.
8. Device according to one of claims 1 to 7, wherein the reservoir includes an input stream deflector (8) near the inlet port.
9. Device according to one of claims 1 to 8, wherein the reservoir can be located next to the evaporator, or the reservoir can be integrated into the evaporator.
10. Device according to one of claims 1 to 9, including a non-return device (6) arranged between the inner chamber (30) of the reservoir and the microporous mass (10) of the evaporator, and arranged to prevent the liquid present in the evaporator from moving into the inner chamber of the reservoir.
11. Device according to claim 10, mainly under the influence of the Earth's gravity, wherein the non-return device includes a float (60).
12. A heat transfer device according to one of the preceding claims, characterized in that it is deprived of a mechanical pump.
13. A device according to one of the preceding claims, additionally including an energy-providing element at the reservoir to control the pressurisation of the loop during startup.
14. A device according to one of the preceding claims, wherein the cross-section of the small cross-sectional passages is preferably less than 1/10 of the largest cross-section of the reservoir.

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