EP4092371B1 - Heat pipe with improved performance under various distributions of thermal loads - Google Patents

Description

Technical field

The invention relates to heat pipes, heat transfer devices, in particular for cooling a heating element.

Context

A heat pipe generally comprises a central axial channel in which vaporous working fluid moves, and longitudinal grooves extending axially and around the central axial channel, intended to advance the liquid working fluid in a direction opposite that of the vapor.

In the case of a thermal load that is not evenly distributed around the heat pipe, the grooves work in a very differentiated manner and the most stressed grooves can dry out while the others work only weakly. This phenomenon can also be the consequence of an uneven and evolving distribution of hot and cold sources along the heat pipe, as is frequently the case in a large number of heat pipe application cases (heat pipe networks, heat spreading on radiators, temperature uniformity over a relatively large surface, etc.)

In practice, this observation leads to oversizing the heat pipe to avoid groove drying out in the case of thermal loading that is not regularly distributed, or which may even change over time.

The documents US 2007/240855 , DE 20 2005 021911 U1 And US 2020/248970 each carry heat pipes.

Inventors have sought to improve this situation.

Statement of the invention

• ledit corps profilé comprenant une pluralité de canaux longitudinaux (3) (réalisés en pratique comme des rainures longitudinales), chacun desdits canaux ayant une section délimitée par un fond (76) formé par une paroi tubulaire périphérique (75) du corps profilé, et latéralement par deux murets longitudinaux (2) qui s'étendent radialement vers l'intérieur depuis la paroi tubulaire périphérique, les canaux longitudinaux entourant un canal axial (15) (convoyant de la vapeur), les canaux longitudinaux étant ouverts en direction du canal axial,
• caractérisé en ce qu'il est prévu, à au moins une première position (P1) le long du parcours longitudinal (PX), un canal circonférentiel de transfert (6), agencé transversalement à la direction axiale locale (X), et mettant en communication fluide tout ou partie de la pluralité des canaux longitudinaux entre eux, et en ce que les murets longitudinaux sont interrompus, partiellement ou totalement, à l'endroit du canal circonférentiel.

For this purpose, a heat pipe (1) is provided, configured to be used under low or zero gravity, comprising a profiled body (10) generally obtained by extrusion, said profiled body extending along a longitudinal path (PX), said profiled body forming a hollow body closed at at least two ends by closing elements, thus forming an interior space hermetically isolated from the external environment, and filled with a predefined volume of two-phase working fluid,

• said profiled body comprising a plurality of longitudinal channels (3) (made in practice as longitudinal grooves), each of said channels having a section delimited by a bottom (76) formed by a peripheral tubular wall (75) of the profiled body, and laterally by two longitudinal walls (2) which extend radially inwards from the peripheral tubular wall, the longitudinal channels surrounding an axial channel (15) (conveying steam), the longitudinal channels being open towards the axial channel,
• characterized in that there is provided, at at least a first position (P1) along the longitudinal path (PX), a circumferential transfer channel (6), arranged transversely to the local axial direction (X), and putting all or part of the plurality of longitudinal channels into fluid communication with each other, and in that the walls longitudinal are interrupted, partially or totally, at the location of the circumferential canal.

Thanks to these arrangements, the circumferential transfer channel allows the grooves adjacent to the most stressed groove(s) to contribute to the liquid fluid supply function. Liquid passes through the circumferential transfer channel from a less stressed groove to a more stressed groove. This helps to push back the thermal load limits that could lead to partial or total drying of one or more of the most stressed grooves. The most thermally stressed parts are those where the vaporization flow/rate is greatest.

It should be noted that the longitudinal path (PX) can be straight or non-straight. If the path is not straight, the axial direction is therefore local and not an absolute direction.

It should be noted that the circumferential transfer channel (6) generally appears as an annular passage. In practice, it often appears as an annular groove.

It should be noted that the longitudinal channels are made as longitudinal grooves, generally obtained by extrusion and made in one piece with the main profiled body.

It should be noted that the circumferential transfer channel can fluidly connect all the longitudinal channels, in which the annular passage actually makes a complete turn. But it is not excluded that in particular configurations with thermal loads known in advance, the circumferential transfer channel fluidly connects the longitudinal channels over half the circumference (only half a turn) or over one or more arbitrary angular ranges.

It should be noted that the section of the longitudinal channels can have various possible shapes, the bottom not necessarily being flat, the walls not necessarily being straight. In a particular example the section of the longitudinal channels has a general concavity. In a particular example the section of the longitudinal channels can generally be in the shape of an arc of a circle or an arc of an oval. In a particular example, the section of the longitudinal channels can be trapezoidal.

In various embodiments of the invention relating to the method, one and/or the other of the following arrangements may optionally be further used, taken alone or in combination.

Alternatively, the circumferential transfer channel runs all the way around and connects all the longitudinal channels with fluid. This provides consistent and predictable behavior regardless of the load distribution around the heat pipe. Regardless of the most thermally loaded part of the circumference, the most thermally stressed groove(s) receive additional fluid from the other grooves via the circumferential transfer channel.

Alternatively, several circumferential transfer channels can be provided, arranged one after the other in the longitudinal direction. By means of this, it is possible to multiply the liquid redistribution effect and increase capillary pressure over an entire area.

Alternatively, depending on the specific groove dimensions, especially thin circumferential grooves, the cover ring discussed below can be dispensed with.

According to one option, the circumferential transfer channel can be delimited radially inwards by a cover ring, the cover ring then being interposed between the circumferential transfer channel and the axial channel. Advantageously, the presence of the cover ring makes it possible to promote the formation of liquid meniscus on its wall and the walls of adjacent low walls. The presence of the cover ring makes it possible to increase the capillary pressure at this axial position of the heat pipe. Advantageously, the design of the ring is optimized to limit local pressure losses in the longitudinal flow, on the liquid or on the vapor.

According to one option, the circumferential channel can be arranged at an intermediate position, the walls (2) being interrupted over a predefined length (L6) at this location. Thus, for a circumferential channel in an intermediate position, it can be produced as an annular passage by means of a material removal operation with a revolution tool such as a centrifugal cutter, or by electro-erosion or other general machining technique.

According to one option, at the location of the circumferential channel, the material of the walls (2) is preferably removed over a height (H6) of between 50% and 100% of the height (H2) of the walls.

According to one option, at the location of the circumferential channel, a wall base remains with a residual height (H7) of between 0% and 50% of the normal height (H2) of the walls. The preservation of a wall base makes it possible to maintain longitudinal contact lines to channel the liquid by capillarity notwithstanding the presence of the circumferential transfer channel.

According to one option, the walls may comprise a first bearing area (B1) for receiving a first longitudinal end of the cover ring (4) and a second bearing area (B2) for receiving a second longitudinal end of the cover ring. Whereby the ring is held securely in place on the bearing areas relative to the walls, on either side of the circumferential transfer channel.

According to one option, the cover ring (4) may comprise a central excess thickness (45) forming a radially external shoulder received between the walls at the location of the first and second bearing zones (B1, B2). This is a simple and robust solution, because in fact the machining of the annular groove is relatively simple to carry out and such a ring with excess thickness can be obtained by standard turning/bar turning.

Alternatively, the cover ring (4) may have a constant thickness and the first and second bearing areas are then formed as flats (14) set back from the top of the walls. By using a suitable cutter or two machining passes to form the circumferential channel, the ring is then a simple cylinder obtained by sawing a tube, a very cheap component.

Alternatively, the cover ring (4) can be made of a deformable material, either in the elastic or plastic range, so that the cover ring can be introduced from one end of the profiled body to the first and second bearing areas, so that in the target position the cover ring closes the circumferential transfer channel radially inwards. At the target position, the elastic force is released or a plastic force (deformation) is applied outwards to achieve the final positioning.

According to one option, the first position (P1) is chosen in the vicinity of an evaporation portion (71) of the heat pipe coupled to a hot source (81). This optimizes the effect of equalizing the pressures of the liquid phase in the longitudinal channels as close as possible to the zone where drying under high thermal load is to be avoided.

According to one option, the first position (P1) is an intermediate position on the longitudinal path. Said intermediate position being any on the longitudinal path, there is thus complete freedom to position the circumferential transfer channel (or circumferential channels) as close as possible to the need.

According to one option, the first position (P1) is an end position on the longitudinal path. In this configuration, it is easier to remove material from the walls to form the annular groove forming the transfer channel.

Alternatively, the circumferential channel is formed in an end cap (5) attached to one end of the profiled body. In this configuration, no reworking is performed on the extruded profiled body. The complexity of the shapes and the attachment is carried by the end cap.

According to an option, one or more other circumferential channels are provided along the path, at distinct axial positions different from the first position. The multiple positions can be advantageously determined depending on the application or be distributed regularly in the longitudinal direction, over the whole or part of the heat pipe.

According to one option, the heat pipe may comprise a combination of circumferential channels, some arranged in an intermediate longitudinal position and some arranged in an end position. In other words, there is no incompatibility in having several circumferential channels of different types coexist.

Alternatively, the heat pipe can include a combination of different types of circumferential channels. For example, annular channels (360°) can be used on the condenser side, but also partially annular channels (<360°) can be used on the evaporator side. If the thermal load is known, the circumferential channels can be adapted to optimize the thermo-hydraulic performance.

According to one option, a plurality of circumferential channels may be provided along the path, at regularly spaced axial positions (P2, P3, P4), with a predetermined pitch, for example every 300 mm. This makes it possible to equalize the pressures of the liquid phase in all the grooves at regular intervals along the heat pipe.

According to one option, one or more intersections can be provided along the heat pipe route, with two circumferential channels arranged on either side of each intersection. This minimizes the a priori harmful effect of the intersection from the point of view of hydraulic continuity between the channels.

Alternatively, the heat pipe can be presented as a three-dimensional object. It then extends through space in all three Cartesian dimensions, not just in a plane. This advantageously provides complete freedom of design and configuration to perfectly suit all possible applications.

Advantageously, in the proposed solutions, there is no porous layer, porous mass, or porous coating in the proposed heat pipes, neither punctually nor generally along the length of the heat pipe. In other words, the proposed heat pipes are devoid of capillary porous material intended to ensure capillary pumping.

Description of the figures

• La figure 1 représente schématiquement un caloduc couplé à une source chaude d'un côté et à une source froide du côté opposé.
• La figure 2 représente schématiquement un caloduc couplé à une source chaude dans une position intermédiaire d'un côté et couplé à 2 sources froides aux extrémités.
• La figure 3 représente schématiquement un caloduc couplé à une source froide continue sur la longueur, en partie supérieure du caloduc, et couplé à des sources chaudes en partie inférieure du caloduc, dans une configuration dite 'Heat Spreader'.
• La figure 4 représente une section transversale générale du corps profilé selon un mode de réalisation, selon la ligne de coupe IV illustrée à la figure 7.
• La figure 5 représente une section longitudinale du corps profilé.
• La figure 6 montre une section transversale du caloduc au voisinage du canal circonférentiel de transfert, selon la ligne de coupe VI illustrée à la figure 7.
• La figure 7 représente une section longitudinale du caloduc à l'endroit du canal circonférentiel de transfert.
• La figure 8 montre une section transversale du caloduc à l'endroit du canal circonférentiel de transfert, selon la ligne de coupe VIII illustrée à la figure 7.
• La figure 9 représente une demi-coupe longitudinale du caloduc à l'endroit du canal circonférentiel de transfert.
• La figure 10 est analogue à la figure 7 et représente pour une variante de réalisation, une section longitudinale du caloduc à l'endroit du canal circonférentiel de transfert.
• La figure 11 montre une section transversale du caloduc, selon la ligne de coupe XI illustrée à la figure 12.
• La figure 12 représente une section longitudinale du caloduc au voisinage d'une extrémité avec un bouchon rapporté, selon la ligne de coupe XII illustrée à la figure 11.
• La figure 13 déclinée selon les figures 13A,13B,13C représente diverses formes du ménisque de la phase liquide du fluide de travail à l'intérieur d'un canal longitudinal.
• La figure 14 déclinée selon les figures 14A,14B représente diverses formes du ménisque de la phase liquide du fluide de travail à l'intérieur du canal circonférentiel de transfert.
• La figure 15 représente, dans une variante de réalisation, une section longitudinale du caloduc au voisinage d'une extrémité, avec un bouchon rapporté.
• La figure 16 représente une section transversale du corps profilé selon un second mode de réalisation.
• La figure 17 illustre plus en détail un exemple de géométrie du canal longitudinal et des murets qui le bordent.
• La figure 18 illustre l'exemple de parcours général d'un caloduc dans lequel l'invention peut être mise en oeuvre.
• La figure 19 représente une demi-coupe longitudinale du caloduc au voisinage d'un raccordement à angle droit avec 2 canaux circonférentiels de transfert.
• La figure 20 représente une demi-coupe longitudinale du caloduc au voisinage d'un raccordement en croix avec 4 canaux circonférentiels de transfert.

Other aspects, aims and advantages of the invention will appear on reading the following description of an embodiment of the invention, given by way of non-limiting example. The invention will also be better understood with reference to the attached drawings in which:

• There Figure 1 schematically represents a heat pipe coupled with a hot source on one side and a cold source on the opposite side.
• There Figure 2 schematically represents a heat pipe coupled to a hot source in an intermediate position on one side and coupled to 2 cold sources at the ends.
• There Figure 3 schematically represents a heat pipe coupled to a continuous cold source along the length, in the upper part of the heat pipe, and coupled to hot sources in the lower part of the heat pipe, in a configuration called 'Heat Spreader'.
• There Figure 4 represents a general cross-section of the profiled body according to one embodiment, according to section line IV illustrated in Figure 7 .
• There Figure 5 represents a longitudinal section of the profiled body.
• There Figure 6 shows a cross-section of the heat pipe in the vicinity of the circumferential transfer channel, along section line VI shown in Figure 7 .
• There Figure 7 represents a longitudinal section of the heat pipe at the location of the circumferential transfer channel.
• There figure 8 shows a cross-section of the heat pipe at the location of the circumferential transfer channel, along section line VIII shown in Figure 7 .
• There figure 9 represents a longitudinal half-section of the heat pipe at the location of the circumferential transfer channel.
• There Figure 10 is analogous to the Figure 7 and represents, for an alternative embodiment, a longitudinal section of the heat pipe at the location of the circumferential transfer channel.
• There Figure 11 shows a cross-section of the heat pipe, along section line XI shown in Figure 12 .
• There Figure 12 represents a longitudinal section of the heat pipe in the vicinity of one end with an attached cap, along section line XII illustrated in Figure 11 .
• There Figure 13 declined according to the figures 13A, 13B, 13C represents various shapes of the meniscus of the liquid phase of the working fluid inside a longitudinal channel.
• There figure 14 declined according to the figures 14A,14B represents various shapes of the meniscus of the liquid phase of the working fluid inside the circumferential transfer channel.
• There Figure 15 represents, in an alternative embodiment, a longitudinal section of the heat pipe in the vicinity of one end, with an attached cap.
• There figure 16 represents a cross-section of the profiled body according to a second embodiment.
• There Figure 17 illustrates in more detail an example of the geometry of the longitudinal canal and the walls that border it.
• There figure 18 illustrates the example of a general route of a heat pipe in which the invention can be implemented.
• There figure 19 represents a longitudinal half-section of the heat pipe in the vicinity of a right-angle connection with 2 circumferential transfer channels.
• There figure 20 represents a longitudinal half-section of the heat pipe in the vicinity of a cross connection with 4 circumferential transfer channels.

Detailed description

In the various figures, the same references designate identical or similar elements. For reasons of clarity of the presentation, certain elements are not necessarily represented to scale.

On the Figure 1 , a heat pipe 1 is shown which takes calories from a hot source 81 and rejects them towards a cold source 82. The hot source 81 is in contact with the heat pipe at an evaporation portion 71. The cold source 82 is in contact with the heat pipe at a condensation portion 72.

The heat pipe 1 is presented as an elongated device closed at a first end 11 by a closing element 50, and at a second end 12 by a second closing element 50.

On the Figure 2 , another example is illustrated where the heat pipe receives the calories in an intermediate portion and discharges the calories in two end portions.

On the Figure 3 , another example is illustrated where the heat pipe receives the calories on one side of the heat pipe axis (from below in the illustrated example) and rejects the calories on the other side of the heat pipe axis (from above in the illustrated example). This is a configuration known in the art as a "Heat Spreader".

The heat pipe 1 generally comprises a central axial channel 15 in which working fluid in the form of vapor moves, and longitudinal grooves extending axially and around the central axial channel. As illustrated in Figures 4 and 5 , the longitudinal grooves, also called longitudinal channels 3 are intended to advance the working fluid in liquid form in a direction opposite to that of the vapor.

Heat pipe 1 is configured for use in low or zero gravity. For example, this type of heat pipe is used in spacecraft and devices. In particular, this type of heat pipe is used in communications satellites, surveillance satellites, satellites with all types of other functions. Heat pipe 1 can be used in total weightlessness or in a low gravity situation, for example on the surface of a celestial body such as the Moon or Mars. Heat pipe 1 can be used with zero or very low external pressure.

Basic profile

The heat pipe 1 comprises a profiled body 10 obtained by extrusion. Additional operations can be carried out as will be seen later. However, the extrusion operation is the main manufacturing operation. Using a press, an aluminum alloy is pushed through a die having the desired shapes to obtain the profiled body at the die outlet.

In the example illustrated in figures 4 to 11 , the profiled body forms a hollow body which delimits an interior space hermetically isolated from the external environment, and which will be used to contain working fluid.

The profiled body has a section which, after extrusion, extends identically along the longitudinal axis marked X. The profiled body can then be bent, so that the finished heat pipe is not necessarily straight.

Generally, the profiled body 10 extends along a longitudinal path PX. The longitudinal path PX can be straight or curved.

The length of the PX route can be between 0.5 meters and 10 meters.

The profiled body 10 comprises a peripheral tubular wall 75, from which two diametrically opposed feet 16, 17 extend radially outwards. These feet each end in a support plane adapted to exchange calories with the cold or hot source 82, 81.

In another configuration, there could be only one foot and one support plane for thermal coupling, a foot designed to integrate integration functions or mechanical functions, or no foot at all.

In another configuration it could have four interface planes, and in a particular case the outer boundary of the body could be substantially square or totally cylindrical.

In yet another configuration, the thermal coupling elements could be separate and added, as shown in figure 16 In this case, the profile is generally of revolution around the X axis, with inside a repetition of the pattern [groove + wall] in the circumferential direction .

The profiled body comprises a plurality of longitudinal channels 3. In practice, the longitudinal channels are made as longitudinal grooves.

Each of said longitudinal channels has a section delimited by a bottom 76 formed by a peripheral tubular wall 75 of the profiled body, and laterally by two longitudinal walls 2 which extend radially inwards from the peripheral tubular wall.

The longitudinal channels surround the central axial channel 15 conveying steam. The longitudinal channels 3 are generally open towards the axial channel,

In the example shown, we have sixteen longitudinal walls 2 and sixteen longitudinal channels 3. Generally speaking, the number of longitudinal channels is between 6 and 48.

The longitudinal channels 3 are arranged annularly around the axis. However, non-circular arrangements are also possible.

The peripheral tubular wall 75 has a primitive external diameter D0. D0 can be between 3 millimeters and 50 millimeters.

The diameter D1 represents the internal dimension of the peripheral tubular wall 75, in other words the diameter taken at the level of the bottom of the grooves.

The diameter D2 represents the internal dimension of the axial channel, in other words the diameter of the circumscribed circle passing through the top 77 of the walls.

It is noted that throughout the profiled body, the interior space is perfectly hermetically isolated from the external environment, because the profile is a single piece and made of extruded material, it surrounds the interior space with continuous material, without any orifice.

Thus, the sealing problem must be managed only at the longitudinal ends 11, 12. We will see later the case of profile-to-profile butt joints.

The working fluid may be ammonia, propylene, methanol or any other medium exhibiting a liquid-vapor equilibrium under saturation conditions at operating pressures defined by temperature. A predetermined quantity of working fluid is introduced through one of the end elements equipped with a sealable filling orifice. The pressure in the interior space of the heat pipe may range from 0.1 bar to several tens of bars.

The predetermined amount of working fluid is set to preferably have limited excess liquid on the cold/condenser side, i.e. the grooves are completely filled and, if necessary, fill the end of the axial channel, cold side.

It should be noted that the section of the longitudinal channels 3 can have any suitable shape, the bottom 76 not necessarily being flat, the walls not necessarily being straight. In a preferred embodiment, the section of the longitudinal channels has a general concavity. In a particular example, the section of the longitudinal channels can generally be in the shape of an arc of a circle or an arc of an oval, or even a drop shape open towards the axial channel 15. In the example illustrated in the figures, the section is in the shape of a trapezoidal section.

Circumferential passage/canal

Advantageously, at least one circumferential transfer channel 6 is provided, arranged transversely to the local axial direction. The circumferential transfer channel 6 is located at a first position P1 along the longitudinal path PX.

We will see below several possibilities for this position P1 along the longitudinal path PX.

The circumferential transfer channel 6 places all the longitudinal channels in fluid communication with each other. More generally, the circumferential transfer channel 6 places all or part of the plurality of longitudinal channels in communication with each other.

The circumferential transfer channel 6 generally appears as an annular passage. In practice, it often appears as an annular groove, which forms a complete ring (360°) without excluding a smaller angular opening.

Referring to the figures 7 , 10 And 17 , we notice that the longitudinal walls 2 are interrupted at the location of the circumferential channel 6. The material of the walls has been removed to a depth H6. Along the X axis, the circumferential transfer channel 6 has an axial length L6 .

The axial length L6 of the circumferential channel can be, as in the example illustrated, greater than the height H2 of the grooves.

In other configurations, the axial length L6 of the circumferential channel may be less than the height H2 of the grooves.

In the example shown, part of the wall has not been removed (this corresponds to the residual height H7 = H2 - H6).

For example, H6 can be between 50% and 100% of the height H2. For example, H6 can be between 70% and 100% of the height H2.

In other configurations, the entire height of the wall could be removed (therefore H7=0).

In practice, a wall base remains at a residual height H7 of between 0% and 50% of the height H2 of the walls. Maintaining a wall base allows longitudinal contact lines to be maintained to channel the liquid by capillarity, notwithstanding the presence of the circumferential transfer channel.

It is noted that several circumferential transfer channels can be provided, arranged one after the other in the longitudinal direction X. It could be envisaged to produce such a fairly tight succession of transverse channels of small longitudinal dimension (L6 small).

It is noted that there is no porous layer, porous mass, or porous coating in the circumferential transfer channel(s), either punctually or generally along the length of the heat pipe. The proposed heat pipes are devoid of capillary porous material intended to ensure capillary pumping and are therefore easy to manufacture.

Cover ring

According to an advantageous option, the circumferential transfer channel 6 is delimited radially inwards by a cover ring 4. The cover ring 4 is interposed between the circumferential transfer channel and the axial channel. The cover ring 4 closes the circumferential transfer channel 6 radially towards the X axis.

The cover ring 4 generally appears as a tubular body 40, otherwise called a sleeve.

The cover ring 4 has an axial length L5 . The axial length L5 of the cover ring is in practice chosen to be slightly larger than the axial length L6 of the circumferential channel.

The radial thickness E5 of the cover ring, at the level of the circumferential transfer channel, is between 0.1 millimeter and 1 millimeter.

In the position of use, the internal diameter of the ring is noted D4.

The external diameter of the ring at the circumferential channel is noted D5.

The cover ring 4 can be made of a deformable material, either in the elastic or plastic domain, so that it can be installed in position to cover and radially close the circumferential channel 6.

According to the elastic deformation option, the ring is constrained radially inwards and then inserted by threading inside the axial channel and once it has reached the correct axial position (target position), the elastic constraint is released, which leads to expansion and final positioning.

Depending on the plastic deformation option, an initial diameter of the ring is chosen slightly smaller than D2, then the ring is inserted by threading inside the axial channel and once it has reached the correct axial position (target position), a radial expansion is caused by introducing a deformable tool. Then the cover ring is pressed against the walls or the bearing surfaces/flats provided for this purpose.

To receive the cover ring in the circumferential channel area, a first bearing area B1 is provided to receive a first longitudinal end 41 of the cover ring 4 and a second bearing area B2 is provided to receive a second longitudinal end 42 of the cover ring.

According to a first solution, illustrated in figures 7 And 9 , the cover ring 4 may comprise a central excess thickness 45 forming a radially external shoulder 47. The central excess thickness 45 is received between the walls on stop fronts 44 at the location of the first and second bearing zones.

In this configuration we notice that D4 < D2 < D5.

According to a second solution, illustrated in the Figure 10 , the cover ring has a constant thickness E4 and the first and second bearing areas B1, B2 are formed as flats 14 set back from the top of the walls.

We note that in this case, the diameter D4 is larger than D2, i.e. the ring is radially set back from the tops 77 of the walls.

The flats 14 are obtained by removing material.

The cover ring forms an additional contact line which increases the capillary pressure at the circumferential channel 6. Thus the capillary pressure at the circumferential channel 6 is higher than the capillary pressure along the longitudinal channels 3. The ring allows the total recovery of the hydraulic section at the circumferential channel to ensure the continuity of the liquid flow.

Cork

In the case of a standard heat pipe end, there are closure elements 50 which simply close the profiled body. The present invention, however, provides for the clever use of the closure elements.

According to one embodiment, the circumferential channel is formed in an end cap 5 fixed to one end of the profiled body.

According to a first stopper solution, illustrated in the Figure 12 , the cap comprises an inner sleeve 51 and a closing disc 52. We come to weld/seal the disc on the end of the profiled body 10 at the level of a hermetic joint 53 for solid fixing. The closing disc 52 is thick enough to withstand the internal pressure. On the other hand, the inner sleeve 51 does not support any substantial force, and it is sufficient that the axial length L65 of the sleeve is greater than the axial length L6 of the circumferential channel, to come flush with the tops 77 of the walls 2.

The circumferential channel 6 is obtained by removing material from the walls on their end portion. This machining is relatively standard; it is sufficient to introduce a milling cutter with the prescribed diameter axially into the end portion of the body 10.

According to a second stopper solution , illustrated in the Figure 15 , the cap comprises an inner sleeve 51. The inner sleeve 51 may be separate from the closing disc 52 or else made according to a single-piece logic. When it is separate, the inner sleeve 51 is received in a circular housing 57 at the bottom of the closing disc, and is presented as an easy-to-obtain part: simple tubular sleeve.

Here too, a watertight closing seal 53 is provided which connects the outer ferrule 54 of the cap 5 to the profiled body 10.

It is noted that here too the longitudinal walls 2 are interrupted at the location of the circumferential channel. The outer limit of the circumferential channel is formed by a thickness 56 of the plug projecting radially inwards.

Operation and other particularities

In a weightless situation, the forces of gravity are negligible compared to the forces generated by the phenomenon of capillarity. Thus, the physical phenomenon of capillarity is predominant with regard to the forces and pressures applied to the different parts of liquid present in the heat pipe.

The first position P1 for the circumferential transfer channel is chosen in the vicinity of an evaporation portion 71 of the heat pipe coupled to a hot source. The circumferential transfer channel is filled with liquid and the pressure differences of the different grooves are equalized at this location.

Menisci M are formed in the longitudinal channels, they are all the more hollowed out as the pressure difference is important along the length of the groove, in particular in the longitudinal direction, between the cold sources corresponding to the lowest pressures and the hot sources corresponding to the highest pressures.

So to the Figure 13A , the meniscus is almost flat. At the Figure 13B , the meniscus is more hollow. At the Figure 13C , the meniscus is even more hollowed out.

A meniscus forms in the circumferential transfer channel, allowing fluid to move in a circumferential direction and transit from one longitudinal channel to another.

At the time of priming, as illustrated in the Figure 14A , the ring as well as the bottom of the longitudinal canal initiate a meniscus. The Figure 14B illustrates the steady state where the entire volume of the circumferential transfer channel is filled with liquid.

In other words, the meniscus forms in the circumferential channel only in transient conditions, and in steady state, it is the menisci of the longitudinal channels, deeper downstream than upstream, which generate the flow in the circumferential groove.

So the recirculation groove is designed to have higher capillary pumping than the longitudinal groove to prime with liquid properly.

In reference to the figure 16 , channel C1 is the most thermally stressed, it receives the calories by a short conductive path, it is at this point that the vaporization flow rate is the most important. The neighboring channels C2, CG also participate in the vaporization, but slightly less. The slightly more distant channels C2, CG and following participate a little less in the vaporization, depending on the intensity of the heat flow, until they no longer participate at all in the vaporization for the most distant grooves, when all the incoming flow has been vaporized. Advantageously, the presence of a circumferential transfer channel near the heat source allows liquid that has not arrived via C1 along its length to be transferred to channel C1. In other words, the neighboring channels supply liquid to the first channel C1.

Not only direct or indirect neighbors, but all other channels can participate in the supply of liquid to avoid local drying out at the most stressed point.

So in a case of top loading as illustrated in the figure 16 , channels CG, C1, C2 will be supplied by all other channels, i.e. C3, C4, C5, C6, C7, C8, C9, CA, CB, CC, CD, CE, CF.

Expressed differently, the circumferential transfer channel has a function of pooling and sharing the liquid supply. It supplies liquid to the longitudinal channel 3 with the greatest demand, from the other channels.

Various other points

The closing ring promotes the supply of liquid to the circumferential transfer channel.

But the ring also promotes the passage in a straight line in a particular longitudinal channel.

If the closing ring is slightly set back from the top of the walls, it has a favorable effect on the straight passage of the liquid in a longitudinal channel.

In addition, one or more other circumferential channels are provided on the path, at distinct axial positions (P2, P3, P4) different from the first position.

As illustrated the figure 18 , the PX route may include one or more curves 18, and where appropriate may even include one or more right angles 19.

There figure 19 represents a longitudinal half-section of the heat pipe in the vicinity of a right-angle connection with two circumferential transfer channels. In the illustrated case, two profiled bodies cut at 45° have been joined to form a right angle at this point; there is an imbalance in meniscus formation between the well-irrigated outer grooves and the rather dry inner grooves. The presence of one or two circumferential transfer channels in the vicinity of the angle makes it possible to equalize the pressures between the different longitudinal channels.

There figure 20 represents a half longitudinal section of the heat pipe in the vicinity of a cross connection with 4 circumferential transfer channels. This configuration is an extrapolation of the previous case illustrated the figure 19 , with four profiles joined at a cross intersection. The presence of the four circumferential channels near the intersection makes it possible to equalize the pressures between the different longitudinal channels.

At the intersections, external fixing sleeves are provided to ensure mechanical cohesion and sealing, generally obtained by welding.

Regarding the dimensional aspects, we can choose L6 being between 0.1 D0 and 0.5 D0. We also observe D0 > D1 > D2.
Regarding the height of the walls, a value of H2 between 0.05 D1 and 0.2 D1 can be chosen.

Claims (14)

1. A heat pipe (1) configured for being used in low or zero gravity comprising a profiled body (10) generally obtained by extrusion, where said profiled body extends along a longitudinal path (PX), and where said profiled body forms a hollow body closed at at least two ends by closing elements, thereby forming an interior space hermetically isolated from the outside environment, and filled with a predefined volume of diphasic working fluid,

   said profiled body comprising a plurality of longitudinal channels (3), where each longitudinal channel has a section delimited by a bottom (76) formed by one tubular peripheral wall (75) of the profiled body, and laterally by two longitudinal dividers (2) which extend radially inwards from the peripheral tubular wall, where the longitudinal channels surround an axial channel (15), and where the longitudinal channels are open towards the axial channel,

   characterized in that there is provided, at at least one first position (P1) along the longitudinal path, a circumferential transfer channel (6), arranged transversely to the local axial direction (X) and providing mutual fluid connection between all or part of the plurality of longitudinal channels,

   and in that the longitudinal dividers are interrupted, partially or completely, in the area of the circumferential channel.
2. The heat pipe according to claim 1, wherein the circumferential transfer channel is radially delimited on the inside by a covering ring (4), where the covering ring is interposed between the circumferential transfer channel and the axial channel (15).
3. The heat pipe according to claim 2, wherein the circumferential channel may be arranged at an intermediate position, where the dividers (2) are interrupted over a predefined length (L6) in that area, with preferably the material of the dividers (2) being removed over a height (H6) comprised between 50% and 100% of the height (H2) of the dividers.
4. The heat pipe according to claim 3, wherein the dividers comprise a first bearing zone (B1) for receiving a first longitudinal end (41) of the covering ring (4) and a second-bearing zone (B2) for receiving a second longitudinal end (42) of the covering ring.
5. The heat pipe according to claim 4, wherein the covering ring comprises a central excess thickness (45) forming a radially outward shoulder received between the dividers in the area of the first and second bearing zones (B1, B2).
6. The heat pipe according to claim 4, wherein the covering ring (4) has a constant thickness and the first and second bearing zones are formed as flat areas (14) recessed from the summit of the dividers.
7. The heat pipe according to claim 1, wherein the first position (P1) is selected near an evaporation portion (71) of the heat pipe coupled to a heat source (81).
8. The heat pipe according to claim 1, wherein the first position (P1) is an intermediate position along the longitudinal path (PX).
9. The heat pipe according to claim 1, wherein the first position is an end position (P1) on the longitudinal path.
10. The heat pipe according to claim 1, wherein the circumferential channel is formed in an end cap (5) fixed to an end of the profiled body.
11. The heat pipe according to claim 1, wherein one or more other circumferential channels are provided on the path at distinct axial positions (P2, P3, P4) different from the first position.
12. The heat pipe according to claim 1, wherein a plurality of circumferential channels are provided along the length, at uniformly spaced axial positions (P2, P3, P4), with a predetermined step, for example every 300 mm.
13. The heat pipe according to claim 1, comprising one or more intersections with two circumferential channels arranged on either side of each intersection.
14. The heat pipe according to claim 1 formed like a three-dimensional object.

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