US20110209864A1

US20110209864A1 - Thermal control device with network of interconnected capillary heat pipes

Info

Publication number: US20110209864A1
Application number: US13/128,192
Authority: US
Inventors: Christophe Figus; Laurent Ounougha
Original assignee: Astrium SAS
Current assignee: Airbus Defence and Space SAS
Priority date: 2008-11-12
Filing date: 2009-11-09
Publication date: 2011-09-01
Also published as: CN102245995A; EP2344827B1; WO2010055253A1; FR2938323B1; ES2404083T3; FR2938323A1; CN102245995B; EP2344827A1

Abstract

The thermal control device comprises at least one network of capillary heat pipes, in which each heat pipe comprises a tube enclosing an essentially annular longitudinal capillary structure, for the circulation of a two-phase heat-transfer fluid in the liquid phase, and surrounding a central channel for the circulation of said two-phase fluid in the vapor phase. The tubes of at least two heat pipes of the network intersect and are interconnected in such a way that at each intersection of heat pipes forming a node of the network, an exchange of fluid in the liquid phase can take place by capillary action between the capillary structures of said two or more heat pipes, and such that, simultaneously, an exchange of fluid in the vapor phase can take place by free circulation between the central channels of said two or more heat pipes.

Description

This invention relates to a thermal control device based on capillary heat pipes providing heat transfer by fluid circulation, used to respectively cool heat sources or heat cold sources and interconnected into at least one network.
While a capillary tube is a simple hollow tube with a smooth inner wall, a capillary heat pipe for transferring heat 1, in the most common and economical variant of the prior art as represented schematically in longitudinal and transverse cross-sections in FIGS. 1 a and 1 b, is in the form of a hollow tube 2 having longitudinal inner grooves 3 extruded from its inner surface and surrounding a central channel 4.
In other variants, as schematically represented in the transverse cross-section in FIG. 1 c, the central channel 4 is surrounded by a substantially annular structure of a porous material, such as porous copper or any other porous structure 5, covering the inner wall of the tube 2. These particular structures (grooves 3, porous structure or material 5) will be referred to below as “capillary structures”, and are generally placed on the inner surface of the tube 2 of the capillary heat pipe 1 to retain the liquid phase of a heat transfer fluid and separate it from the vapor phase circulating in the central channel 4. The heat pipe 1 thus has two different capillary dimensions, for example the diameter of the central channel 4 and the thickness or radial dimension of the capillary structure 3, 5, which allow separate flows (co-current or counter-current) of the liquid phase and the vapor phase of the fluid used to transport the heat.
A prior art capillary heat pipe 1 generally comprises a tube 2 that is straight, or comprises at least one section, closed at both ends, and filled with a two-phase heat transfer fluid at an appropriate pressure, to enable the transport of heat by vaporization, vapor flow, then fluid condensation.
The capillary heat pipe 1 is generally in the shape of a rod, possibly bent at an angle at certain points, of dimensions adapted to requirements. The transverse cross-section of the tube 2 may, for example, be circular or quadrangular in shape. The tube 2 may be in direct thermal contact with at least one heat source such as 6 in FIG. 1 a and at least one cold source such as 7 in FIG. 1 a, or in thermal contact with at least one plate which in turn is in thermal contact with at least one heat source or at least one cold source.
The capillary heat pipe 1 connects one or more heat sources 6 (for example heat dissipating electronic equipment or heaters) in an evaporation zone 8, to one or more cold sources 7 (for example coolers, or equipment or structures to be heated) in a condensation zone 9. The liquid phase of the fluid circulates from the condensation zone 9, in a heat exchange relationship with the cold source(s) 7, to the evaporation zone 8, in a heat exchange relationship with the heat source(s) 6, through the capillary structure 3, 5 covering the wall of the tube 2. In the evaporation zone 8, in contact with the heat source(s) 6, the liquid vaporizes and the vapor that forms is carried away through the central channel 4 of the tube 2 to the condensation zone 9, where the vapor condenses into its liquid phase and releases heat to the cold source(s) 7.
In contrast to the capillary heat pipe 1 described above with reference to FIGS. 1 a to 1 c, there are also “pulsating” heat pipes, consisting of simple capillary tubes (hollow tubes of small internal diameter, for example 2 to 5 mm) interconnected at their ends to form one or more loops. This closed capillary line, in which the opposing ends of the loop(s) are in a heat exchange relationship with an evaporator on one side and a condenser on the other, is filled with a heat transfer fluid present in its two phases (liquid and vapor). The flow of the phases is exclusively co-current: segments or “slugs” of liquid are pushed by bubbles (“plugs”) of vapor formed by heat absorption in the evaporation zone thermally coupled to one or more heat sources. Thus the closed capillary line, partially filled with liquid brought by the evaporation zone into thermal contact with the heat source(s), promotes the successive expansion of vapor plugs which can be up to several millimeters in length (typically 5 to 10 mm). The expansion of these vapor plugs pushes the liquid slugs at their ends as well as the vapor plugs between successive liquid slugs, such that the displacement of these slugs and plugs brings the liquid and vapor into thermal contact with one or more cold sources, by means of the condensation zone, which condenses the vapor into liquid. Thus the flow of the liquid in this closed circuit encourages the return of the liquid to the evaporation zone and the generation of a new plug in said zone. As a result, in general the liquid slugs and gas plugs alternately move towards the evaporation zone and towards the condensation zone.
Pulsating heat pipes of this type are described for example in U.S. Pat. No. 4,921,041 and U.S. Pat. No. 5,219,020. These patents can be referred to for more details.
The operation of a capillary heat pipe therefore differs from, and is much more efficient than, a simple capillary tube used in pulsating heat pipes or in co-current heat pipes such as in U.S. Pat. No. 6,269,865 and as described below with reference to FIG. 2 (which corresponds to FIG. 3 in U.S. Pat. No. 6,269,865). A capillary tube, which has a smooth inner wall, is limited in pumping power to a value inversely proportional to the diameter of the tube, that is less than 100 Pa. A capillary heat pipe, because of the small capillary dimensions of the porous structure or grooves in the inner wall, can reach pumping powers of more than 500 Pa. Unlike a capillary tube, a capillary heat pipe achieves a homogeneous temperature along the length of the heat pipe tube, as the liquid and vapor phases of the fluid can flow independently of each other in both directions in the tube as a function of the different hot and cold points along the heat pipe.
As represented in FIG. 2, U.S. Pat. No. 6,269,865 describes a network 11 of heat pipes that are simple capillary tubes 12 interconnected to form substantially square or rectangular closed loops 13, connected to each other and to two capillary tubes (the inlet 12 a and outlet 12 b), which close off the opposite ends of a heat exchanger. This exchanger can operate as an evaporator 18, if it is placed in thermal contact with at least one heat source 16 and if the network 11 is operating as a heat dissipation unit, in thermal contact with at least one cold source or heat sink. This exchanger can also operate as a condenser 19, if it is placed in thermal contact with at least one cold source and if the network 11 is operating as a heat transfer unit, in thermal contact with at least one heat source.
In the network 11, one can clearly see the succession of liquid slugs 14 and vapor bubbles (plugs) 15. This type of network 11 is used to dissipate the heat produced in a heat source such as 16. The performance limitations of such a system compared to capillary heat pipes have been explained above. In addition, this network 11 only functions if it is connected to a heat absorption unit 18, in a heat exchange relationship with at least one heat source 16. This heat absorbing unit 18 is separate from the network 11 used for the heat dissipation, and must vaporize the fluid at the inlet 12 a into the network 11 of capillary tubes. The vapor 15 thus created is condensed in the network 11 by contact with at least one cold source, progressively forming liquid slugs 14 pushed along by vapor bubbles 15. The fluid in the liquid state 14 is carried away at the outlet 12 b from the network 11 and sent to the heat absorbing unit 18. In this type of network 11, the liquid 14 and the vapor 15 must circulate in the same direction (co-current flows). The liquid 14 and the vapor 15 cannot be independent of each other within the network 11, which prevents establishing a two-phase state throughout the network 11. The liquid 14, which is increasingly present as the fluid condenses, offers a much smaller heat resorption capacity than that created by the condensation of vapor 15. The accumulation of liquid 14 at certain points in the network 11, particularly in the nodes 20 of the network 11, which are at the interconnections of at least two loops 13 of the network 11, slows the circulation of the vapor 15. In general, the heat flux absorbable by the network 11 is limited, and the thermal load cannot be effectively distributed within the network 11.
U.S. Pat. No. 5,506,032, U.S. Pat. No. 5,806,803, and U.S. Pat. No. 6,776,220 describe networks of capillary heat pipes that cross one another and are not interconnected (particularly at their intersections). These are used to regulate heat in walls (panels) for mounting equipment. This type of two-dimensional network, as schematically represented in the attached FIG. 3, is formed of crisscrossing capillary heat pipes 21 (each represented here as a tube 22 having a capillary structure consisting of internal grooves 23 around a central channel), extending in at least two different and coplanar directions, and in general substantially perpendicular, but without any interconnection between the heat pipes 21, meaning that the fluid contained in the heat pipes 21 cannot circulate from any one heat pipe to at least one other heat pipe. At the point where two heat pipes 21 intersect, the heat exchanges between the two heat pipes 21 can therefore only occur by conductive exchanges, either by direct contact between the tubes 22 of the two heat pipes 21, or possibly by having at least one intermediate part of a material that is a good heat conductor, covering the two heat pipes 21 at their intersection and sometimes referred to as a plate, forming a thermal interface or a thermal bridge between these two heat pipes 21.
Thus a significant limitation of this type of passive thermal control device with its network of crisscrossing capillary pipes comes from the inevitable heat transfer losses at the points where they cross. This is a limitation in terms of transported power, as well as a limitation related to the maximum density of the heat flux that a heat pipe 21 can support at a crossing point. An amount of heat collected by one of the heat pipes 21 of the network flows efficiently along this heat pipe 21, but cannot flow efficiently in the other direction in the network, along the heat pipes 21 it crosses over and which extend in said other direction, advantageously such as towards a cold source located in said other direction.
If a heat source is placed at an intersection of two heat pipes 21, only these two heat pipes 21 can efficiently transport the heat in their respective directions, and cold sources must be placed in at least one of these directions. Thus, in order to efficiently collect and carry away heat using such a network, there either must be a sufficient number of cold sources located in all directions of the network, which imposes layout constraints, or the heat conductivity must be increased at the points where the heat pipes 21 cross, which substantially increases the mass of the device. In addition, such a tangle of pipes 21 increases the overall dimensions of the device and does not allow the creation of thin networks. Lastly, the low modularity of this type of network does not allow simple and efficient heat removal in structural forms with complex surfaces or volumes. In particular, there is no known generalization of this type of network to three dimensions. Such a generalization would lead to even greater complexity, inefficiency in the heat exchange within the network, and a need for numerous cold sources in thermal contact with the heat pipes of the network.
The aim of the invention is to propose a thermal control device with a network of capillary heat pipes which remedies all the above prior art limitations and provides other advantages which are presented in the following description.
An object of the invention is a thermal control device, comprising at least one network of capillary heat pipes in which each heat pipe comprises a tube enclosing a substantially annular longitudinal capillary structure, for the circulation of a two-phase heat transfer fluid in the liquid phase, and surrounding a central channel for the circulation of said two-phase fluid in the vapor phase, and which is characterized in that the tubes of at least two heat pipes of the network intersect and are interconnected in such a way that at each intersection of heat pipes forming a node of the network, an exchange of fluid in the liquid phase can take place by capillary action between the capillary structures of said at least two heat pipes, and such that, simultaneously, an exchange of fluid in the vapor phase can take place by free circulation between the central channels of said at least two heat pipes.
In a first variant embodiment, there may be heat pipe ends not connected to network nodes. These ends are then closed, for example by welding, in order to retain the fluid in the network. In another variant, each end of each heat pipe is connected to a node of the network, except at one or more network inlets/outlets, which in particular can connect the network to at least one extension from this network of heat pipes and/or to at least one other network of heat pipes in said device.
In these variants, one or more heat pipes of the network can be extended to distances of up to several meters away from the network, in order to establish thermal contact with heat sources or cold sources that are at a distance from said network.
Advantageously, a tank of fluid is connected to the network, for example at a network inlet or outlet, in order to adjust the amount of fluid present in the network to the network's temperature variations, particularly in order to accommodate fluid expansion and the condensed fluid level.
If in the following description, the portion of heat pipe arriving at a node of the network is referred to as a branch, then in order to allow efficient heat transfer across the entire network, the device of the invention is advantageously such that at each node of the network, the capillary structures of all the heat pipe branches ending at said node ensure capillary continuity for the fluid in the liquid phase, such that the fluid in the liquid phase arriving at said node in any heat pipe branch ending at said node can flow by capillary action into all the other heat pipe branches ending at said node. Therefore there is capillary continuity for the liquid in all directions between the different branches ending at the nodes and across the nodes.
Also with the same aim of enabling the most efficient heat transfer possible across the entire network, the device is advantageously arranged such that at each node of the network, the central channels of all heat pipe branches ending at said node ensure, simultaneously with the flow continuity of the fluid in the liquid phase, the flow continuity of the fluid in the vapor phase, such that the fluid in the vapor phase which reaches said node by any heat pipe branch ending at said node can flow into all the other heat pipe branches ending at said node. There is therefore flow continuity in all directions for vapor in the line, between the various branches ending at the nodes and across the nodes.
The capillary continuity at the different nodes must allow fluid in the liquid phase to flow by capillary action, in a zone where the effects of surface tension predominate over the effects of gravity or inertia. It is not necessary to have perfect continuity in said capillary structures, but there must at least be no discontinuity in the capillary effect. Advantageously, at each node in the network, the capillary structures of the heat pipe branches ending at said node have no discontinuity between them of a size greater than the typical dimensions of a pore or a groove in the capillary structure of the heat pipes, depending on whether said structure respectively consists of porous material or of internal grooves in the corresponding tube.
Similarly, the continuity in the flow line for the fluid in the vapor phase, at the various nodes of the network, must allow the vapor to flow by inertial flow. It is therefore unnecessary to have perfect continuity in the geometry of said conduit, but there must at least be no significant load loss. Advantageously, at each node in the network, the flow continuity of fluid in the vapor phase is assured between the central channels of the heat pipe branches ending at said node, by a flow conduit having a flow area or at least one typical dimension that is substantially equal to the flow area or to at least one typical dimension of the central channels of said heat pipe branches ending at said node.
However, in order to support higher heat flux densities, or for example to allow integration into specific volumes or geometries because of network dimensions, the presence of bends in certain heat pipes, or having to work against gravity, at least one heat pipe in the network may have at least one branch which differs from the branches of at least one other heat pipe in the network, in its capillary structure and/or in at least one typical dimension of said heat pipe branch.
Advantageously in the device of the invention, said at least one network of heat pipes of the device is a two-dimensional network comprising two pluralities of heat pipes such that the heat pipes of each plurality are substantially oriented, along at least a portion of their length, in one of two respective directions sloped relative to one another and preferably perpendicular to each other, such that the heat pipes of the two pluralities intersect and are interconnected at their intersection according to the characteristics described above.
The device of the invention can be generalized such that at least one network of heat pipes of the device is a three-dimensional network comprising, in at least one node of the network, at least three heat pipe branches oriented for at least a portion of their length in one of three respective directions, each pair sloped relative to one another and preferably perpendicular to each other, with said at least three heat pipe branches intersecting with each other and being interconnected according to the characteristics described above.
In a first embodiment of the device, in at least one node of the network, the at least two heat pipes which intersect and are interconnected at said node have cutouts of complementary shapes cut into their respective tube and capillary structure such that the heat pipes fit together at the cutouts and reestablish the continuity of the tube walls (the heat pipes being integrally attached all along the cutouts), the capillary continuity in the capillary structures, and the flow continuity along the channels of said heat pipes. This embodiment is particularly appropriate for heat pipes that have a quadrangular (rectangular or square) or circular cross-section forming a two-dimensional network. One can see that to avoid leakage of fluid from a node formed in this manner, there must be continuity in the tube walls of the two heat pipes where they intersect, for example by externally welding these tubes along the length of the cutouts. Similarly, the continuity between the capillary structures inside the two tubes is more easily assured if this capillary structure consists of a porous structure (of a porous material) rather than grooves.
One can see that it is more difficult to apply this embodiment to grooved heat pipes and/or three dimensional networks, and that this embodiment is more appropriate for two-dimensional networks and/or heat pipes lined with porous materials.
Due to these limitations, in a second particularly advantageous embodiment of the device of the invention, the interconnection of the heat pipes at the at least one node, and preferably at all the nodes where at least two heat pipe branches connect to each other, is achieved in a modular manner by means of a hollow connecting piece, which is cross-shaped in a two-dimensional network node where four heat pipe branches interconnect, and which is more generally referred to below as a cross-piece.
More specifically, in this second embodiment, at least one node of the network of the device comprises a hollow connecting piece, referred to as the cross-piece, interconnecting all the heat pipe branches ending at said node. This connecting piece consists of tubular connecting arms of an equal number as the heat pipe branches which interconnect at said node, each with an internal and substantially annular capillary structure surrounding a central channel. Each connecting arm connects to the other connecting arms by a longitudinal end, referred to as the inside end, and to a respective heat pipe branch by its longitudinally opposite end, referred to as the outside end, such that the capillary structure of each connecting arm has capillary continuity at its outside end with the capillary structure of said corresponding heat pipe branch, and has capillary continuity at its inside end with the capillary structure of each of the other connecting arms, and such that its central channel communicates at its outside end with the central channel of the corresponding heat pipe branch, and at its inside end with the central channel of each of the other connecting arms.
In this case and when the capillary structure of the heat pipes is formed by grooves, it is advantageous for this capillary structure of the heat pipes to have capillary continuity with the capillary structure of the connecting arms of the cross-pieces, which consists of a porous structure or porous material, having a high permeability, with a pore diameter of the porous structure or material no greater than twice the aperture of said grooves, in order to facilitate the flow of liquid. This value may change as a function of the fluid's wettability properties in the various materials used.
Similarly, in heat pipes in which the capillary structure consists of a porous structure or a porous material, it is advantageous for this capillary structure of the heat pipes to have capillary continuity with the capillary structure of the connecting arms of the cross-pieces, which also consists of a porous structure or porous material, having a high permeability with a pore diameter no greater than the pore diameter of the porous structure or porous material of the heat pipes. This value may also change as a function of the fluid's wettability properties in the various materials used
A significant advantage of this embodiment of the device with cross-pieces is that the heat pipes of the network can be the standard heat pipe tubes already commercially available, whether grooved or having a porous capillary structure.
In a standard embodiment, the tubes of the heat pipes in the network are simply welded to the tubes of the cross-piece(s).
Another advantage is that any cross-piece can be arranged to connect any number of heat pipe branches, generally from 2 to 8 heat pipe branches, in a two- or three-dimensional network.
One of the advantages obtained in any embodiment of the device of the invention, when one or more heat sources is/are in thermal contact with the network, is that heat exchange can occur between each heat source and one or more network elements (branches or nodes of the network). The network then allows efficiently collecting all the heat produced by the heat source(s) and having a homogeneous temperature throughout.
In examples of the device of the invention, the network of heat pipes collects the heat generated by at least one heat source in thermal contact with at least a part of the network, and draws off said heat through at least one cold source in thermal contact with at least one other part of the network.
The heat sources may be “localized”, such as a heat dissipating element or heater, or generalized, such as a structure heated by at least one external source. Similarly, the cold sources may be localized, such as a cold finger cooling element, or generalized, such as a radiator structure cooled by at least one external source.
Thus, through heat exchanges due to state changes in the two-phase fluid, the device efficiently collects the heat released by one or more heat sources due to fluid evaporation, and transfers it through the network to one or more cold sources where the fluid condenses to return via capillary action to the heat source(s).
Such a device can be used to cool one or more heat sources, and/or to heat one or more cold sources. The fluid used will be adapted to the operating temperatures of the system. For example, ammonia can be used for operating temperatures of between −40° C. and +100° C.
Advantageously, said at least one network of heat pipes of the device can be at least partially integrated into a structure having a temperature that is to be controlled.
In another advantageous embodiment of the device, a portion of said at least one network of heat pipes is in thermal contact with at least one heat or cold source, and another portion of said network is in thermal contact with at least one respective cold or heat source.
In a preferred embodiment, the device, in any form of the above embodiments, additionally comprises at least one fluid loop that is preferably two-phase and capillary pumped, for transporting heat from said at least one network of heat pipes to at least one distant cold source, the evaporation zone of the fluid loop being in thermal contact with at least a portion of the network of heat pipes. In this case, at least one condensation zone of said fluid loop is in thermal contact with said at least one cold source.
In the reverse form of the embodiment, the device comprises at least one fluid loop, preferably two-phase and capillary pumped, for transporting heat from at least one distant heat source to said at least one network of heat pipes, the condensation zone of the fluid loop being in thermal contact with at least a portion of said network of heat pipes. In this case, at least one evaporation zone of said loop is in thermal contact with said at least one heat source.
These two embodiments benefit from the performance of the fluid loops which are presumed to be much more efficient than heat pipes, at equal mass, when transporting a significant heat flux from one point to another.
Also in the device of the invention, said at least one network of heat pipes is an integral part of a supporting structure onto which at least one heat source and/or at least one cold source is mounted.
In this case, said supporting structure may advantageously be comprised of said at least one network of heat pipes, suitable for supporting heat dissipating equipment, which limits the mass of the ensemble. The network of heat pipes then serves a dual function: thermal, for the heat transport and establishing heat homogeneity, and mechanical, for supporting/maintaining the heat dissipating equipment.
The device of the invention can be applied to a thermal control system which controls the temperature of said at least one network, or at least one element in thermal contact with said network. This is done by arranging the device so that it additionally comprises at least one temperature sensor placed on said at least one network of heat pipes or in the vicinity of at least one element in thermal contact with said at least one network, and at least one heating or cooling means in thermal contact with said at least one network, such that the temperature of said at least one network or said at least one element is controlled by applying a thermal power setpoint for the heating or cooling to be produced by said at least one respective heating or cooling means, based on the observed differences between the temperate measurements provided by said at least one temperature sensor and a temperature setpoint.
The element(s) in thermal contact with the network may be one or more localized sources such as equipment, or an equipment-supporting structure into which the network is integrated, or a mechanical component into which the network is integrated. In all these applications, the advantage of the network of heat pipes of the invention is that it efficiently establishes a homogeneous temperature although the heating or cooling means act locally in the network; the distribution of heat in all elements, the supporting structure or the mechanical component occurs very efficiently by means of the network.
To anticipate the consequences of a failure in said at least one network of interconnected heat pipes, such as a leak in the network, there can be redundancy in the network by superimposing at least two possibly identical networks, or subdividing the network into several non-interconnected sub-networks while advantageously maintaining a thermal contact between said sub-networks.
The device of the invention may be the object of numerous advantageous applications. A first such application concerns the cooling of an active antenna comprising radiofrequency (RF) tiles, having similar dimensional characteristics and possibility different power dissipation characteristics, and which are arranged, preferably at regular intervals, on a supporting structure in the form of a grid, characterized in that at least one network of heat pipes of said device is integrated into said supporting structure of the active antenna, and the heat collected by said network is drawn off to at least one radiator by at least one extension from said network of heat pipes and/or at least one other network of heat pipes and/or at least one fluid loop of said device.
A second advantageous application concerns the cooling of a supporting wall for mounting electronic equipment, characterized in that at least one network of heat pipes of said device is attached to at least one thermally conductive facesheet of the wall, and preferably between two thermally conductive facesheets of said wall, and the heat collected by said at least one network of heat pipes is drawn off to at least one cold source, such as a radiator, by at least one extension from said network of heat pipes and/or at least one other network of heat pipes and/or at least one fluid loop of said device.
A third particularly advantageous application concerns the thermal control of a mechanical component, and is characterized in that at least one network of heat pipes of said device is in a heat exchange relationship with said mechanical component or is integrated with said component having a temperature to be controlled, at least one heating element and at least one heat sink connected to at least one cooling element being placed in thermal contact with said network of heat pipes to contribute or remove heat in said network, and at least one temperature sensor measures a variable physical quantity, representative of the temperature of said component, the measurement being compared to at least one reference value in order to control a variation in the amount of heat to be contributed to or removed from said component, so as to reduce the difference resulting from said comparison.
The use of a two- or three-dimensional network of heat pipes will more be advantageous depending on the shape and dimensions of the mechanical component. The two-dimensional network may be completely planar, or may have bends and curves at certain locations in order to better follow the shape of the component.
This last application can advantageously be used to ensure thermal control of a large focal plane in an optical instrument.

Other features and advantages of the invention will become apparent from reading the following non-limiting description of some embodiments described with reference to the attached drawings, in which:

FIG. 1 a is a longitudinal or diametric cross-sectional view of a prior art capillary heat pipe with grooves,

FIG. 1 b is a transverse cross-sectional view of the capillary heat pipe of FIG. 1 a,

FIG. 1 c is a transverse cross-sectional view, analogous to FIG. 1 b, of a prior art capillary heat pipe with a porous structure or porous material,

FIG. 2 is a schematic cross-sectional view in a median plane of a co-current heat pipe in a network of simple interconnected capillary tubes and closed loops, according to the prior art in U.S. Pat. No. 6,269,865,

FIG. 3 is a partial perspective view of a prior art two-dimensional network of intersecting capillary heat pipes with grooves,

these FIGS. 1 a to 3 having already been described above,

FIG. 4 a is a schematic view of a two-dimensional network of intersecting and interconnected capillary heat pipes according to the invention, in a cross-sectional view in the axial plane of the heat pipes,

FIG. 4 b is a larger scale cross-sectional view in the axial plane of the heat pipes, showing a node of the network in FIG. 4 a to which four heat pipe branches are connected,

FIG. 5 is an exploded partial perspective view of two segments of capillary heat pipes with complementary cutouts fitted into each other to form a first variant of a node of a two-dimensional network analogous to the one in FIG. 4 a ,

FIG. 6 a is a schematic cross-sectional view in an axial plane of the heat pipes, showing a second variant of a node of a two-dimensional network such as the one in FIG. 4 a, with a connecting piece arranged as a cross-piece with four arms, for connecting four heat pipe branches together,

FIG. 6 b is a perspective view of the four-armed cross-piece of the node in FIG. 6 a ,

FIG. 6 c is a perspective view of a six-armed cross-piece forming the connecting piece in a node of a three-dimensional network, for connecting 6 heat pipe branches in this network,

FIG. 7 is a schematic perspective view of an application of a device of the invention, in which a network of interconnected capillary heat pipes cooperates with a capillary-pumped two-phase fluid loop to transfer heat from heat sources to a radiator, and

FIG. 8 is a partial schematic cross-sectional view of another application of a device of the invention, in which a network of heat pipes is used in a structure supporting an active antenna that comprises radiofrequency (RF) tiles to be cooled.

The network 30 in FIG. 4 a, which is two-dimensional and generally flat, comprises two groups of capillary heat pipes that are rectilinear, parallel, regularly spaced apart, and each group oriented in one of two directions perpendicular to each other. More specifically in this example, the first group comprises four heat pipes 31 a, 31 b, 31 c and 31 d, referred to below as the “horizontal” ones in FIG. 4 a, intersecting with the five heat pipes 31 e, 31 f, 31 g, 31 h and 31 i, referred to below as the “vertical” ones in the second group, such that the heat pipes of each group are interconnected with the heat pipes of the other group at all points where they intersect or connect, inside and at the edges of a rectangle delimited by the upper 31 a and lower 31 d horizontal heat pipes of the first group, and the vertical and lateral heat pipes 31 e and 31 i of the second group.
There are as many connecting points in the network 30 as there are nodes. The number of heat pipe branches connecting to a node in the network may vary. For example, the network 30 considered here comprises nodes with four heat pipe branches such as the node 36 represented in the enlarged view in FIG. 4 b, where two successive branches 31 b 1 and 31 b 2 of a horizontal heat pipe such as 31 b and two successive branches 31 f 1 and 31 f 2 of a vertical heat pipe such as 31 f are connected.
The network 30 also comprises nodes with 3 branches such as the node 37, to which an ending branch (the first or the last) is connected, such as 31 b 1 of a horizontal heat pipe such as 31 b or a vertical one, inside the rectangle of the network 30, and two successive branches such as 31 e 1 and 31 e 2 of a vertical or horizontal heat pipe forming an edge of the network, such as 31 e.
The network also comprises nodes with two branches such as the node 38 situated at a “corner” of the rectangular network 30, to which an end branch such as 31 a 1 of a heat pipe on a horizontal edge such as 31 a is connected with an end branch such as 31 e 1 on a vertical edge such as 31 e in the network.
The heat pipes and/or branches of capillary heat pipes are of a type known in the prior art, as described above with reference to FIGS. 1 a to 1 c, meaning they comprise a tube 32 enveloping a capillary structure for the circulation of two-phase heat transfer fluid in the liquid phase, which surrounds a central channel 34 for the circulation of this fluid in the vapor phase, with the capillary structure consisting of longitudinal grooves in the inner surface of the wall of the tube 32 or of a porous annular structure 35, possibly of a porous material, as represented in FIG. 4 a and on a larger scale in the node with four branches 36 in FIG. 4 b.
At each of the nodes 36, 37 and 38 of the network 30, all the branches which interconnect at this node are connected to each other in a manner that ensures flow continuity from the central channel 34 of any of these branches to the channel 34 of each of the other branches of this node, such that the fluid in the vapor phase flowing towards the node via the channel 34 of any heat pipe branch ending at this node can flow into the central channels 34 of all the other heat pipe branches connected to this node, as indicated by the six two-headed arrows F in FIG. 4 b.
For heat transfer to occur successfully through free circulation of the two-phase heat transfer fluid in the vapor phase, between the central channels 34 of all the heat pipe branches connecting to the same node, these central channels 34 have a flow area, or at least one typical dimension of the channel 34 such as its diameter, which remains substantially constant and equal from one channel 34 to another, and, if applicable, in any flow conduit connecting the channels 34 of all heat pipe branches at the same node. The continuity of flow in all directions between the different heat pipe branches ending at the same node and across that node thus allows the vapor to travel by inertial flow, without requiring perfect continuity between the central channels 34 but ensuring the absence of significant pressure loss at each node.
Simultaneously, capillary continuity for the fluid in the liquid phase is ensured between the capillary structures, such as 35, for all heat pipe branches connected to the same node 36 or 37 or 38, so that an exchange of fluid in the liquid phase can occur by capillary action between these capillary structures 35, in a manner such that the fluid in the liquid phase flowing towards a node in the capillary structure 35 of any of the heat pipe branches connected to this node can flow by capillary action in the capillary structures 35 of all other heat pipe branches connected to this node. For this purpose, the capillary structure 35 of each heat pipe branch ending at a node rests, to the extent possible, at its inside end (pointing towards the center of the node), against the inside ends of the capillary structures 35 of the adjacent heat pipe branches connected to the same node. If these capillary structures are porous structures or of porous material such as 35 in FIG. 4 b, satisfactory capillary continuity is achieved if there is no discontinuity between the porous structures 35 which exceeds the typical dimension of a pore of this structure 35 or of the constituent porous material. If the capillary structure of the heat pipe branches consists of grooves, as described above, the discontinuity between the capillary structures of the heat pipe branches ending at the same node should not exceed the typical dimension of a groove of these structures, at the center of the node, where the inside ends of these structures are in as much contact as possible with each other, and such that the grooves of one capillary structure are at least partially in communication with grooves of the capillary structures of the adjacent heat pipe branches at this node.
Thus, for any of these types (grooves or porous structure or porous material) of capillary structure in the heat pipe branches, the fluid in the liquid phase can flow by capillary action in the zone at the center of the node, which has a geometry such that the effects of surface tension predominate over the effects of gravity or inertia. Capillary continuity for the fluid in the liquid phase is thus ensured in all directions between the different heat pipe branches ending at the nodes and through the nodes 36, 37 and 38.
In order to accommodate fluid expansion and contraction by adapting the amount of fluid present in the network 30 in the liquid phase to the temperature variations in the network 30, a tank 39 of fluid is connected to the network 30. In FIG. 4 a, the tank 39 is connected to the network 30 by a branch 31 g 4 of the heat pipe 31 g, which prolongs the latter heat pipe to extend outside of the network 30. The inside surface of this tank 39 is lined with a capillary coating 40, which has capillary continuity with the capillary structure of the branch 31 g 4 connecting the tank 39 to the network 30. This capillary continuity between the internal capillary lining 40 of the tank 39 and the capillary structure of the branch 31 g 4 is ensured in the same manner as described above for the nodes of the network, and therefore also between the capillary structure of the connecting branch 31 g 4 and the branches of the heat pipes 31 d and 31 g to which the connecting branch 31 g 4 is connected at a node of the network 30, as shown in FIG. 4 a. Thus, fluid in the liquid phase can circulate in both directions between the tank 39 and the network 30, flowing by capillary action in the capillary lining 40 of the tank 39 and the capillary structures 35 of the branch 31 g 4 and of the other heat pipe branches in the network 30, and, simultaneously, fluid in the vapor phase can also circulate in both directions between the central volume of the tank 39 and the central channels 34 of the branch 31 g 4 and of the other heat pipe branches in the network 30. In this example, the diameter or the flow area of the central channel 34 of the connecting branch 31 g 4 is less than the diameter or the flow area of the central channels 34 of the other heat pipe branches in the network 30, and/or the radial thickness of the capillary structure 35 of the connecting branch 31 g 4 is less than the thickness of the capillary structure 35 of the other heat pipe branches in the network 30.
Preferably, the grooved (parallel to the longitudinal axis of the branch 31 g 4) or porous nature of the internal capillary lining 40 of the tank 39 is the same as that of the capillary structure of the connecting branch 31 g 4, which itself is of the same nature as that of the capillary structures of the other heat pipe branches in the network 30, but this is not an absolute requirement. Advantageously, this capillary lining 40 is in the form of a porous structure or a porous material.
If needed, in order to support flux densities that are more or less high, or to integrate the network 30 or portions or extensions of it into specific volumes and/or volumes having specific geometries, particularly in their overall dimensions, or when at least a portion of the network must operate under specific conditions, such as against gravity, one or more heat pipes 31 of the network 30 may each comprise one or more branches which differ from the other branches of the heat pipes 31 of the network 30 in the dimensions of the central channel 34 and/or the capillary structure 35, and/or in the type of capillary structure 35, for example a porous structure constituted of different porous materials in different heat pipe branches of the network.
FIG. 5 represents an embodiment of a node with 4 branches, created by interconnecting, at their intersection, two capillary heat pipes in a network (not represented) that have a rectangular transverse cross-section. The two heat pipes 41 are identical to each other and each consists of a tube 42 of metal or plastic lined with a tubular capillary structure 43 on its inner wall, in this example a porous structure or porous material of a substantially constant thickness, surrounding a central channel 44. The tube 42, the capillary structure 43, and the channel 44 have a rectangular transverse cross-section.
To form a node interconnecting the two heat pipes 41, a cutout 45 is made in each one, forming a hollow area 46 where they intersect and interconnect. This cutout 45 extends into the tube 42 and the capillary structure 43 for an axial length (along the axis of the heat pipe 41) equal to the width of the large sides of the heat pipes 41, between two cross-sections of the heat pipe 41 (perpendicular to the axis of the heat pipe 41) into each of which the cutout 45 extends for half the perimeter of the heat pipe 41, through one large side (for example the horizontal upper large side) of the heat pipe 41, and for half the height of the two vertical sides of the heat pipe 41.
Then a heat pipe 41 a, belonging to a first group (not represented) of parallel heat pipes spaced apart from each other, is turned over so that its hollow area 46 faces downwards and fits inside the hollow area 46 of the other heat pipe 41 b, and said other heat pipe 41 b belongs to a second group (also not represented) of parallel heat pipes spaced apart from each other, and the longitudinal axis of said other heat pipe 41 b is oriented to be perpendicular to that of the heat pipe 41 a.
Thus the central channels 44 of the two heat pipes 41 a and 41 b are reestablished by this interconnection, as are the capillary structures 43, which reestablish capillary continuity by their contact at the cutouts 45. The two tubes 42 fitting inside one another at their complementary-shaped cutouts 45 are then welded together at the cutouts 45 to reestablish the fluid-tightness of the tubes 42 and to solidly attach them to each other along the cutouts 45. This simultaneously assures flow continuity for the fluid in the vapor phase along the central channels 44 and capillary flow continuity for the fluid in the liquid phase along the capillary structures 43 of the heat pipes 41.
The same type of intersection and interconnection can be achieved with heat pipes in which the tube, capillary structure, and central channel are cylindrical with a circular cross-section, or a square cross-section, in the two-dimensional network. The tubes of two heat pipes are attached at their intersection and interconnection in a manner such that fluid cannot escape at that point, which is why the two tubes must be solidly attached to each other in a fluid-tight manner along the cutouts, which can be achieved not only by welding as described above, but also by other means such as adhesive bond for example. One can also see that the capillary continuity which must be ensured between the capillary structures of two interconnected heat pipes can be more easily obtained if this capillary structure is a porous structure, for example formed of a porous material, rather than formed of grooves.
It is clear that the embodiment of a network node shown in FIG. 5 lends itself with difficulty to the use of a heat pipe with a grooved capillary structure and/or to incorporation in a three-dimensional network.
A second embodiment of a node with four heat pipe branches will now be described with reference to FIG. 6 a, in an application which creates a two-dimensional network analogous to the one in FIG. 4 a.
This second embodiment is much more advantageous than the one described above with reference to FIG. 5, because it overcomes the limitations described for the latter, and therefore allows easily creating not only two-dimensional networks but also three-dimensional ones, and/or using prior art heat pipes having a capillary structure that can be grooved or porous. In addition, the cross-sections of the heat pipes used are not necessarily limited to circular, rectangular, or square shapes.
In this second embodiment, the interconnection of all the different branches of the heat pipes 51 ending at the same node of the network is done in a modular manner, by means of a connecting piece 55 or joint, also called a cross-piece in the example in FIG. 6 a showing a node where four heat pipe branches 51 connect. Two of them, shown as horizontal in FIG. 6 a, belong to a first group of heat pipes, and the two others, shown as vertical in FIG. 6 a and perpendicular to the first two, belong to a second group of heat pipes that intersect and interconnect with the heat pipes of the first group in a network analogous to the one in FIG. 4 a, and not further described or represented.
The connecting piece 55 is hollow and has as many tubular connecting arms 56 as there are heat pipe branches 51 connected to each other by this connecting piece 55 at the corresponding node in the network.
Each connecting arm 56 has the same general structure as the heat pipe branches 51, each of them comprising, in a known manner, an external rigid tube 52 enveloping an annular capillary structure 53 (for the circulation of fluid in the liquid phase by means of capillary action) preferably consisting of longitudinal grooves arranged in the inner surface of the tube 52 in the example in FIG. 6 a, but which also may be of a porous structure or a porous material covering the internal wall of the tube 52, with this capillary structure 53 itself surrounding a central channel 54 (for the inertial circulation of the fluid essentially in the liquid phase).
More specifically, each connecting arm 56 comprises a rigid external tube 57, by which this arm 56 is integrally attached to the other arms 56 and forming a single part with them: the connecting piece 55. The inner wall of this tube 57 is covered by an annular capillary structure 58 (for the circulation of the fluid in the liquid phase by means of capillary action), advantageously in the form of a porous structure or a porous material, and itself surrounding a central channel 59 (for the circulation of the fluid essentially in the vapor phase).
As represented in FIG. 6 a, each of the heat pipe branches 51 connected to each other at the corresponding node is held, by its end facing the connecting piece or cross-piece 55, against the outside end, so called because it is facing away from the center of the cross-piece 55, of a corresponding connecting arm 56, such that the two branches 51 and 56 are maintained end to end and in alignment, while the central channel 59 of each connecting arm 56 is in communication at the inside end of this connecting arm 56, meaning its end facing the center of the cross-piece 55, with the central channels 59 of all the other connecting arms 56 of the cross-piece 55. In addition, similarly to the communication at the outside end of each connecting arm 56 of the cross-piece 55, the central channel 59 of this connecting arm 56 is in communication with the central channel 54 of the corresponding heat pipe branch 51, and the flow continuity of the fluid essentially in the vapor phase is assured in all directions of the heat pipe branches 51 and across the node by placing the central channels 59 of the connecting arms 56 in continuous communication with each other and with the central channels 54 of the heat pipe branches 51. Simultaneously, the cross-piece 55 provides capillary continuity between the capillary structure 58 of each connecting arm 56, at the outside end of said arm, and the capillary structure 53 of the corresponding heat pipe branch 51, while at the inside end of said connecting arm 56, its capillary structure 58 has capillary continuity with the analogous capillary structure 58 of each of the other connecting arms 56 of the cross-piece 55.
The arms 56 of the cross-piece 55 are dimensionally and geometrically adapted to the heat pipe branches 51 to which they are connected, particularly the branches 51 and 56 having substantially the same cross-sectional area and shape, and in particular substantially the same outside diameters, thickness of the capillary structures 53 and 58, and diameter of the central channels 54 and 59.
In practice, the tubes 57 of the cross-piece 55 can be of the same material as the tubes 52 of the heat pipe branches 51. These latter can be welded to the arms 56 of the cross-piece 55, possibly after fitting the ends of the heat pipe branches 51 into sleeves formed by outward extensions from the tubes 57 of the arms 56 of the cross-piece 55.
In the example in FIG. 6 a, as the capillary structure 53 of the heat pipe branches 51 consists of grooves, while the capillary structure 58 of the connecting arms 56 of the cross-piece 55 is a porous structure or of porous material giving the capillary structure 58 a high permeability, the porous structure or the porous material comprising it preferably has a pore diameter less than or equal to about twice the aperture of the grooves in the capillary structure 53, to facilitate the flow of the fluid in the liquid phase. However, this value may be adapted, depending on the wettability characteristics of the heat transfer fluid used in the different materials used.
On the other hand, in heat pipe branches 51 in which the capillary structure consists of a porous structure or porous material, it is advantageous for the capillary structure 58 of the arms 56 of the cross-piece 55 to have high permeability with a pore diameter that is less than or substantially equal to the pore diameter of the porous structure or porous material forming the capillary structure of the heat pipe branches 51. This value also may be adapted, depending on the wettability characteristics of the fluid in the different materials used.
Using a porous structure or porous material to create the capillary structure 58 of the arms 56 of the cross-piece 55 is advantageous because of the complex form of the cross-piece 55, although for simplicity, the capillary structure 53 of the heat pipe branches 51 is often achieved by internal grooves extruded in the same process as the tubes 52. To create this type of cross-piece 55, several methods can be applied, including methods based on basic sintering, laser sintering, or stereolithography.
The creation of heat pipes 51 compatible with connecting pieces such as cross-pieces 55, or T-shaped or L-shaped connectors in which the respective three or two attaching arms have the same structure and cooperate with each other and with the heat pipe branches 51 in the same manner as the arms 56 of the cross-piece 55, when the respective three or two branches of the heat pipes 51 are connected to the same node, there is no particular problem because the heat pipes 51 of the network can consist of standard heat pipes already commercially available, in which the capillary structure is either grooved or porous.
FIG. 6 b shows a perspective view of the cross-piece 55 of FIG. 6 a, in an embodiment where the connecting arms 56 and their tube 57, capillary structure 58, and central channel 59, are cylindrical with a circular cross-section.
FIG. 6 c represents an exploded perspective view of a node with six branches in a three-dimensional network, created using the same principles of heat pipe intersection and interconnection for three groups of rectilinear, parallel heat pipes spaced apart from each other, where each group is oriented in one of three respective directions each perpendicular to the other, the interconnection being achieved at each node by a hollow connecting piece with tubular connecting arms which, in FIG. 6 c, is a cross-piece 65 with six connecting arms 66. Compared to the cross-piece 55 in FIG. 6 a, the cross-piece 65 in FIG. 6 c has two additional connecting arms 66, mutually symmetrical relative to the center of the cross-piece 65, and coaxial to an axis perpendicular to the plane of the two axes perpendicular to each other and to which two of the four other connecting arms 66 are coaxial.
Similarly to the example in FIGS. 6 a and 6 b, each connecting arm 66 is cylindrically tubular with a circular cross-section and consists of an external tube 67 with an internal wall covered by a porous capillary structure 68 which surrounds a central channel 69, and the ends next to the six heat pipe branches 61 connecting to the cross-piece 65 also consist, as in the example in FIGS. 6 a and 6 b, of an external rigid tube 62 having an axially grooved internal wall to form its capillary structure 63 around a central channel 64.
Another advantage of this type of device is that a cross-piece can be adapted to connect any number of heat pipe branches, typically from two to eight, in two- or three-dimensional networks.
As represented in the left part of FIG. 7, in a thermal control device of the invention, a two- or three-dimensional network as described above, for example the two-dimensional network 70 of interconnected heat pipes 71 in FIG. 7, analogous to the network 30 in FIG. 4 a, can be placed in a direct heat exchange relationship with one or more heat sources such as 72 a, 72 b and 72 c, such that a heat exchange is established between each heat source 72 a, 72 b, 72 c, and one or more elements of the network 70, such as branches of heat pipes 71, nodes, or even grid cells in the network 70, each grid cell consisting of four branches of heat pipes 71 connected in pairs by four nodes to form a closed loop in the network 70 (in FIG. 7, each heat source 72 a to 72 c is schematically represented as covering a respective grid cell in the network 70, and therefore is in thermal contact with the four branches of heat pipes 71 and the four nodes in this grid cell). The network 70 can thus efficiently collect the heat produced by one, several, or all the heat sources 72 a to 72 c and establish a homogeneous temperature for the whole assembly.
One or more heat sources 72 a to 72 c may be localized in nature, particularly heat dissipating elements such as electronic circuits, equipment, or components attached directly to the network of heat pipes or possibly mounted on a supporting wall, each of the heat sources being in thermal contact with a portion of the network 70 at different points in this network, either directly or by means of an intermediate part providing heat conduction between the network and the heat sources.
As a variant, one or more heat sources 72 a to 72 c can be of a so-called “continuous” nature, consisting for example of structure(s) which themselves are heated by external sources and are in thermal contact with a part of the network 70.
In another variant, in the two above cases and assuming that only the sources 72 a and 72 b are heat sources, another part of the network 70 is in a direct heat exchange relationship with a cold source, such as 72 c, which itself can be a localized source such as a cold finger cooling element for example, or “continuous” such as a radiator cooled by an external source, to which the radiator transmits the heat it receives from the network 70.
In general, this other variant consists of placing the entire network 70 of heat pipes 71 in thermal contact with one or more heat (or cold) sources, except for at least one branch of the heat pipes 71 and/or at least one node of the network, which is or are in thermal contact with at least one respective cold (or heat) source.
Thus the device efficiently collects, through liquid/vapor and vapor/liquid phase changes in the two-phase heat transfer fluid circulating in the network 70, the heat diffused by one or more heat source(s) such as 72 a and 72 b, by fluid evaporation, and transfers it across the network 70 to one or more cold source(s), such as 72 c, where the fluid condenses to return by capillary action to the heat source(s).
Such a thermal control device can therefore be used, passively and with equal ease, to cool one or more heat sources (such as 72 a and 72 b) and/or to reheat one or more cold source(s) (such as 72 c), the heat transfer fluid used being adapted to the operating temperatures of the device, for example ammonia for operating temperatures of between −40° C. and +100° C.
However, in a preferred embodiment, the device additionally comprises at least one fluid loop, for example a capillary-pumped loop for a two-phase heat transfer fluid, which is advantageously the same as that of the network 70 of heat pipes 71, for transporting the heat from the network 71 to at least one cold source, or, conversely, from at least one heat source to the network 70, because such fluid loops are known to be much more efficient than heat pipes (at equal mass) for transporting significant heat flux from one point to another.
As represented in the entire diagram in FIG. 7, when cooling at least one of the heat sources 72 a, 72 b and 72 c placed in contact with the network 70 of heat pipes 71, the evaporation zone 74 of a fluid loop 73 is placed in thermal contact with the network 70, in this example at a node where three branches of heat pipes 71 interconnect at an edge of the network 70, and the condensation zone 75 of the fluid loop 73 is placed in thermal contact with at least one cold source 76, in this example an external radiator, with the heat sources possibly heat dissipating equipment, possibly mounted on a supporting wall, and the cold source 76 (the radiator) possibly being at a distance from the network 70 and the heat sources 72 a to 72 c. Thus the heat transmitted by the heat sources 72 a to 72 c to the network 70 is transferred in the evaporation zone 74 to the fluid of the fluid loop 73, which is vaporized at that point and flows in the vapor phase to the condensation zone 75, where this heat is transferred by condensation of the fluid in the loop 73 to the radiator 76 which releases it to the heat sink of the surrounding space.
One can use such a device in a reverse mode, to heat at least one cold source 72 a to 72 c that is in thermal contact with the network 70. In this case, the evaporation zone 75 of the fluid loop 73 is placed in thermal contact with a heat source 76, external to the network 70, and the condensation zone 74 of the fluid loop 73 is placed in thermal contact with the network 70.
When applying the thermal control device of FIG. 7, with or without at least one fluid loop 73, to cooling electronic equipment on a wall supporting such equipment, as described above, the network 70 of heat pipes 71 of the device can be attached to a thermally conductive facesheet (not represented), for example of metal or a composite material, and preferably between two facesheets of this type. The heat collected by the network 70 is drawn off by an extension outward from the network 70, or via at least one fluid loop such as 73, to one or more cold source(s) such as one or more radiator(s) 76.
In other applications of the thermal control device of the invention, at least a portion of a two- or three-dimensional network of heat pipes, depending on the application, can advantageously be integrated into the mass of a structure for which the temperature may need to be actively controlled. This structure can be a supporting structure to which at least one heat source and/or at least one cold source is/are attached.
Such an application is now described, with reference to FIG. 8, for cooling an active antenna with radiofrequency tiles. In this FIG. 8, the network 80 of heat pipes 81 is only represented by two parallel heat pipes 81 oriented in one of the two directions of this two-dimensional network. Each heat pipe 81 comprises a flat plate, of a good heat conducting material, forming a single piece with a central semicylindrical portion traversed by the tube 82 of the heat pipe 81, of which the internal wall has grooves in its capillary structure 83 around the corresponding central channel 84. By the sides of this plate, each heat pipe 81 is suspended in a trough 86 inside a rib 87, oriented in the same direction as the heat pipes 81, of a grid-like supporting structure 88 which has ribs analogous to but perpendicular to the ribs 87 and similarly equipped with troughs like 86, for accommodating the heat pipes of the network 80 which are perpendicular to the heat pipes 81. The supporting structure 88 supports radiofrequency (RF) tiles 85 that have thinner edges for resting atop ribs such as 87, placed next to each other to define a surface of the active antenna. These RF tiles 85 have similar dimensional characteristics and are arranged in a matrix, but the thermal dissipation possibly differs from one to another. The tiles 85 regularly arranged in this manner on the supporting structure 88 transmit heat to the plates of the heat pipes 81 on which the tiles 85 rest, and this heat is then transmitted from the heat pipes 81 of the network 80 to an evaporator 89, integrated into the base of at least one rib 87 and therefore into the supporting structure 88, and part of a fluid loop in which the condenser is in thermal contact with at least one cold source such as an external radiator distanced from the active antenna.
In a variant, the heat collected by the network 80 of heat pipes 81 integrated into the supporting structure 88 is efficiently drawn away towards one or more radiator(s), by an extension outward from this network 80.
In certain applications, the supporting structure for at least one heat source and/or at least one cold source may advantageously consist of a network of heat pipes of the device. This reduces the mass of the device assembly, in which said network of heat pipes serves a dual function: a thermal function of transporting/homogenizing the heat and a mechanical function of supporting/maintaining the dissipating equipment constituting the heat or cold source(s).
The thermal control device of the invention may also be applied in the creation of a temperature control device for at least one network of heat pipes of the device and/or at least one heat source and/or at least one cold source and/or at least one part and/or at least one assembly with which at least one network of heat pipes of the device is in a heat exchange relationship, or even into which said at least one network of heat pipes of the device is at least partially integrated. In this case, at least one temperature sensor and/or at least one cooling element and/or at least one heating element are in a heat exchange relationship with said network, at different locations in the network, and at least one setpoint for the thermal power to be transferred by said at least one cooling element and/or said at least one heating element is applied to this or these heating or cooling element(s) as a function of at least one temperature differential observed between at least one temperature setpoint and at least one temperature measurement obtained by said at least one temperature sensor. An example of such an application is the thermal control of a mechanical component for which the temperature is to be monitored, and with which a two- or three-dimensional network of heat pipes of a device of the invention is in close thermal contact or of which said network of heat pipes is a part. Because of this, the thermal properties of the network of heat pipes allow the network to rapidly establish a uniform temperature within the mechanical component. In addition, at least one heating element and/or at least one heat sink connected to at least one cooling element, and placed in thermal contact with said network, may respectively provide or remove heat in said network, while respectively increasing or decreasing the temperature of the mechanical component. In addition, at least one temperature sensor is implanted in the device in order to measure a variable that is representative of the component's temperature, and can therefore be used to actively control the temperature of this mechanical component, by comparing the measurement of said at least one temperature sensor to at least one reference value and causing the amount of heat passed on to the part or removed from the part to vary as a function of the difference resulting from the comparison between said measurement and said reference value in order to reduce said difference.
In an example application of the invention, this type of thermal regulation and temperature control device for a mechanical component may advantageously be used to control the temperature of a large focal plane in an optical system.
In the various embodiments and applications of the device of the invention, the harmful effects of a failure in a network of interconnected heat pipes, for example a heat transfer fluid leakage from said network, can be limited or even completely compensated for if the device is arranged so that it is redundant, for example by having at least two non-interconnected networks, preferably but not necessarily identical, or by subdividing the network into multiple non-interconnected sub-networks, while advantageously maintaining said at least two networks or said sub-networks in a heat exchange relationship with each other.

Claims

1. A thermal control device, comprising at least one network of capillary heat pipes, in which each heat pipe comprises a tube enclosing a longitudinal and substantially annular capillary structure, for circulating a two-phase heat transfer fluid in liquid phase, and surrounding a central channel for circulating said two-phase fluid in vapor phase, and wherein said tubes of at least two heat pipes of said network intersect and are interconnected in such a way that at each intersection of heat pipes forming a node of said network, an exchange of fluid in liquid phase can take place by capillary action between said capillary structures of said at least two heat pipes, and such that, simultaneously, an exchange of fluid in vapor phase can take place by free circulation between said central channels of said at least two heat pipes.

2. The device according to claim 1, wherein at each node of said network all heat pipes interconnected at said each node have branches respectively ending at said node and having respective capillary structures providing capillary continuity for said fluid in liquid phase, such that said fluid in liquid phase arriving at said node in any heat pipe branch ending at said node can flow by capillary action into all other heat pipe branches ending at said node.

3. The device according to claim 2, wherein at each said node of said network, said capillary structures of said heat pipe branches ending at said node have no discontinuity between them of a size greater than a typical dimension of a pore or groove of said capillary structure of said heat pipes, depending on whether said capillary structure respectively consists of porous material or of internal grooves in the corresponding tube.

4. The device according to claim 1, wherein at each node of the said network, all heat pipes interconnected at said each node have branches respectively ending at said node and having respective central channels assuring flow continuity for said fluid in vapor phase, such that said fluid arriving at said node in vapor phase via any heat pipe branch ending at said node can flow into all other heat pipe branches ending at said node.

5. The device according to claim 4, wherein at each said node of said network, flow continuity of said fluid in vapor phase is assured between said central channels of said heat pipe branches ending at said node, by a flow conduit having a flow area or at least one typical dimension that is substantially equal to said flow area or to said at least one typical dimension of said central channels of said heat pipe branches ending at said node.

6. The device according to claim 1, wherein at least one heat pipe of said network comprises at least one branch ending at a node and which differs from at least one branch of at least one other heat pipe ending at said node of said network, in a capillary structure and/or in at least one typical dimension of said heat pipe branch.

7. The device according to claim 1, wherein said at least one network of heat pipes is a two-dimensional network, comprising two pluralities of heat pipes such that the heat pipes of each plurality are substantially oriented, along at least a portion of their length, in one of two respective directions sloped relative to one another such that the heat pipes of said two pluralities intersect and are interconnected at their intersection.

8. The device according to claim 1, wherein said at least one network of heat pipes is a three-dimensional network, comprising, in at least one node of said network, at least three heat pipe branches ending at said node and oriented for at least a portion of the length of said branches in one of three respective directions, each direction branch sloped relative to any one the other two of said branches, with said at least three heat pipe branches intersecting with each other and being interconnected to each other.

9. The device according to claim 1, wherein, in at least one node of said network, said at least two heat pipes which intersect and are interconnected at said node have cutouts of complementary shapes cut into their respective tube and capillary structure such that said heat pipes fit together at said cutouts and reestablish the continuity of tube walls, integrally attached all along said cutouts, the capillary continuity in said capillary structures, and the flow continuity along said central channels of said heat pipes.

10. The device according to claim 1, wherein each of said heat pipes of said network has at least one branch ending at a node of said network, at least one node of said network comprises a hollow connecting piece, referred to as a cross-piece, interconnecting all the heat pipe branches ending at said one node, said cross-piece comprising tubular connecting arms of an equal number as said heat pipe branches which interconnect at said one node, each connecting arm with an internal and substantially annular capillary structure surrounding a central channel of said connecting arm, each connecting arm connecting to the other connecting arms by a longitudinal end, referred to as the inside end, and to a respective heat pipe branch by a longitudinally opposite end, referred to as the outside end, of said connecting arm such that said capillary structure of each connecting arm has capillary continuity at said outside end of said connecting arm with a capillary structure of said corresponding heat pipe branch, and has capillary continuity at said inside end of said connecting arm with said capillary structure of each of the other connecting arms, and such that said central channel of said connecting arm communicates at said outside end of said connecting arm with a central channel of said corresponding heat pipe branch, and at said inside end of said connecting arm with said central channel of each of said other connecting arms.

11. The device according to claim 10, wherein said capillary structure of said heat pipes is formed by grooves and has capillary continuity with said capillary structure of said connecting arms of said cross-pieces, which capillary structure of said connecting arms consists of a porous structure or porous material, having a high permeability, with a pore diameter of said porous structure or material no greater than twice an aperture of said grooves.

12. The device according to claim 10, wherein said capillary structure of said heat pipes comprises a porous structure or a porous material and has capillary continuity with said capillary structure of said connecting arms of said cross-piece, also comprising a porous structure or a porous material, having a high permeability with a pore diameter no greater than a pore diameter of said porous structure or porous material of said heat pipes.

13. The device according to claim 10, wherein at least a cross-piece is arranged to connect from two to eight heat pipe branches, in a two- or three-dimensional network.

14. The device according to claim 1, wherein said at least one network of heat pipes is at least partially integrated into a structure having a temperature that is to be controlled.

15. The device according to claim 1, wherein a portion of said at least one network of heat pipes is in thermal contact with at least one heat source or cold source, and another portion of said network is in thermal contact with at least one respective cold source or heat source.

16. The device according to claim 1, additionally comprising at least one fluid loop for transporting heat from said at least one network of heat pipes to at least one distant cold source, an evaporation zone of said fluid loop being in thermal contact with at least a portion of said network of heat pipes.

17. The device according to claim 1, additionally comprising at least one fluid loop for transporting heat from at least one distant heat source to said at least one network of heat pipes, a condensation zone of said fluid loop being in thermal contact with at least a portion of said network of heat pipes.

18. The device according to claim 1, wherein said at least one network of heat pipes is an integral part of a supporting structure onto which at least one heat source and/or at least one cold source is mounted.

19. The device according to claim 18, wherein said supporting structure is comprised of said at least one network of heat pipes, suitable for supporting heat dissipating equipment.

20. The device according to claim 1, additionally comprising at least one temperature sensor placed on said at least one network of heat pipes or in the vicinity of at least one element in thermal contact with said at least one network, and at least one heating or cooling means in thermal contact with said at least one network, such that the temperature of said at least one network or said at least one element is controlled by applying a heat power setpoint for the heating or cooling to be produced by said at least one respective heating or cooling means, based on observed differences between temperature measurements obtained by said at least one temperature sensor and a temperature setpoint.

21. A method for cooling an active antenna comprising radiofrequency tiles, having similar dimensional characteristics and which are arranged at regular intervals, on a supporting structure in the form of a grid with the help of a thermal control device, comprising at least one network of capillary heat pipes, in which each heat pipe comprises a tube enclosing a longitudinal and substantially annular capillary structure, for circulating a two-phase heat transfer fluid in liquid phase, and surrounding a central channel for circulating said two-phase fluid in vapor phase, and wherein said tubes of at least two heat pipes of said network intersect and are interconnected in such a way that at each intersection of heat pipes forming a node of said network, an exchange of fluid in liquid phase can take place by capillary action between said capillary structures of said at least two heat pipes, and such that, simultaneously, an exchange of fluid in vapor phase can take place by free circulation between said central channels of said at least two heat pipes, wherein at least one network of heat pipes of said device is integrated into said supporting structure of said active antenna, and the heat collected by said network is drawn off to at least one radiator by at least one of an extension from said network of heat pipes and at least one other network of heat pipes of said device and at least one fluid loop of said device.

22. A method of cooling a supporting wall for mounting electronic equipment with the help of a thermal control device, comprising at least one network of capillary heat pipes, in which each heat pipe comprises a tube enclosing a longitudinal and substantially annular capillary structure, for circulating a two-phase heat transfer fluid in liquid phase, and surrounding a central channel for circulating said two-phase fluid in vapor phase, and wherein said tubes of at least two heat pipes of said network intersect and are interconnected in such a way that at each intersection of heat pipes forming a node of said network, an exchange of fluid in liquid phase can take place by capillary action between said capillary structures of said at least two heat pipes, and such that, simultaneously, an exchange of fluid in vapor phase can take place by free circulation between said central channels of said at least two heat pipes, wherein at least one network of heat pipes of said device is attached to at least one thermally conductive facesheet of the wall, and the heat collected by said at least one network of heat pipes is drawn off to at least one cold source, by at least one of an extension from said network of heat pipes and at least one other network of heat pipes of said device and at least one fluid loop of said device.