CAPILLARY DEVICE FOR USE IN HEAT PIPE AND METHOD OF MANUFACTURING SUCH CAPILLARY DEVICE

Abstract

A capillary device (102) for use in a heat pipe in which heat is transferred from at least one evaporation region to at least one condensation region by means of evaporated working fluid is disclosed. The capillary device comprises a body portion defining chambers (108) containing powdered material (110) therein, wherein at least part of the periphery of at least one said chamber is porous to allow flow of condensed working fluid, by means of capillary action, through said powdered material in said chamber when flowing from a condensation region to an evaporation region.

Claims

1. A heat transfer pipe in which heat is transferred from an evaporation region to a condensation region by means of working fluid, the heat transfer pipe comprising: a body portion defining a central channel, the central channel extending between and in fluid communication with the evaporation region and the condensation region; and a capillary structure within the body portion and surrounding the central channel, wherein the capillary structure comprises a plurality of spaced-apart porous protrusions extending radially into the central channel with each protrusion separated from an adjacent protrusion by a gap therebetween; wherein the heat transfer pipe includes successive layers of metal powder that are located over a donor material and have been melted by an energetic beam, wherein the successive layers at least partially define the plurality of porous protrusions.

2. A heat transfer pipe according to claim 1, wherein each porous protrusion of the plurality of porous protrusions includes a hollow interior and contains unfused metal powder within the hollow interior.

3. A heat transfer pipe according to claim 2, wherein the successive, melted layers of metal powder at least partially define the hollow interiors.

4. A heat transfer pipe according to claim 2, wherein the unfused metal powder is aluminum.

5. A heat transfer pipe according to claim 1, wherein the body portion is formed from aluminum.

7. A heat transfer pipe according to claim 1, wherein each of the gaps extends in a longitudinal direction parallel to the central channel.

8. A heat transfer pipe according to claim 1, further comprising lattice capillary structures positioned in the gaps between the porous protrusions, wherein each of the capillary lattice structures extends longitudinally along a length of the heat transfer pipe between the evaporation region and the condensation region.

9. A heat transfer pipe according to claim 8, wherein the lattice capillary structures do not extend to the evaporation region.

10. A heat transfer pipe according to claim 8, wherein the lattice capillary structures are formed from a plurality of pores which increase in size along lengths of the lattice capillary structures from the condensation region to the evaporation region.

11. A heat transfer pipe according to claim 1, wherein the successive layers at least partially define the body portion.

12. A heat transfer pipe in which heat is transferred from an evaporation region to a condensation region by means of working fluid, the heat transfer pipe comprising: a solid outer body portion; a porous capillary structure within the outer body portion extending between and in fluid communication with the evaporation region and the condensation region; and a plurality of vapor flow channels embedded in the capillary structure and extending between and in fluid communication with the evaporation region and the condensation region.

13. A heat transfer pipe according to claim 12, wherein the plurality of vapor flow channels is spaced circumferentially around an interior region of the porous structure.

14. A heat transfer pipe according to claim 12, wherein the heat transfer pipe includes successive layers of metal powder that are located over a donor material and have been melted by an energetic beam, wherein the successive layers at least partially define the porous capillary portion and the vapor flow channels.

15. A heat transfer pipe according to claim 12, further comprising a fluid flow passage formed in the center of the porous capillary structure and extending between and in fluid communication with the evaporation region and the condensation region.

16. A heat transfer pipe according to claim 15, further comprising a region of powder metal between the porous capillary structure and the fluid flow passage.

17. A heat transfer pipe in which heat is transferred from an inlet chamber to an outlet chamber by means of working fluid, the heat pipe comprising: an outer body portion; and a porous capillary structure positioned within the outer body portion between and in fluid communication with the inlet chamber and the outlet chamber, wherein the porous capillary structure has a porous rigid outer wall and contains unfused powder material.

18. A heat transfer pipe according to claim 17, wherein the inlet chamber and the outlet chamber are divided by the porous capillary structure.

19. A heat transfer apparatus comprising: an evaporation chamber; and a condensation chamber in fluid communication with the evaporation chamber, wherein heat is transferred from the evaporation chamber to the condensation region by means of working fluid, wherein the evaporation chamber includes an outer cylindrical body that defines an interior volume, a porous capillary structure positioned within the interior volume adjacent an interior surface of the outer cylindrical body, wherein the porous capillary structure defines an interior annular chamber enclosing a layer of unfused metal powder, an elongate escape channel positioned between the interior surface of the outer cylindrical body and the interior annular chamber, wherein the elongate escape channel extends from an interior of the porous capillary structure to a first opening in the porous capillary structure, wherein the first opening is in fluid communication with the interior volume and is formed at an end face of the porous capillary structure, a plurality of spaced-apart circumferential vapor channels interconnected by the elongate escape channel, and a central bore surrounded by the interior annular chamber, wherein the central bore extends between the end face and a second opening of the porous capillary structure to the interior volume, wherein the second opening is in fluid communication with the interior volume and positioned opposite the end face.

20. A heat transfer apparatus according to claim 19, wherein the evaporation chamber and the condensation chamber are in the form of a loop heat pipe.

21. A heat transfer pipe comprising: an evaporation region; a condensation region; a body portion extending between and in fluid communication with the evaporation region and the condensation region; and a capillary structure configured to direct working fluid between the evaporation region and the condensation region; wherein the capillary structure includes successive layers of metal powder that have each been melted by an energetic beam to be secured to one or more other layers of the successive layers.

22. The heat transfer pipe of claim 21, wherein the condensation region includes a condenser plate, wherein the condenser plate defines a donor material, wherein the successive layers of metal powder include a first, melted layer of metal powder disposed on the donor material and a second, melted layer of metal powder disposed on the first layer of metal powder.

23. The heat transfer pipe of claim 22, wherein the first, melted layer of metal powder and the second, melted layer of metal powder define a rigid, porous structure that defines a portion of the capillary structure.

24. The heat transfer pipe of claim 23, wherein the capillary structure extends along an interior surface of the body portion.

25. The heat transfer pipe of claim 22, wherein the condenser plate is an aluminum plate, wherein the first, melted layer of metal powder is aluminum powder, and wherein the second, melted layer of metal powder is aluminum powder.

26. The heat transfer pipe of claim 21, wherein the evaporation region includes an evaporator plate, wherein the evaporator plate defines a donor material, wherein the successive layers of metal powder include a first, melted layer of metal powder disposed on the donor material and a second, melted layer of metal powder disposed on the first layer of metal powder.

27. The heat transfer pipe of claim 26, wherein the first, melted layer of metal powder and the second, melted layer of metal powder define a portion of the body portion.

28. The heat transfer pipe of claim 27, wherein the successive layers of metal powder further include additional layers of melted, metal powder that define the capillary structure, wherein the capillary structure is disposed within the body portion.

29. The heat transfer pipe of claim 28, wherein the capillary structure includes rigid, porous protrusions.

30. The heat transfer pipe of claim 21, wherein the body portion also includes successive layers of metal powder that have each been melted by an energetic beam to be secured to one or more other layers of the successive layers of the body portion.

Description

[0035] FIG. 1 is a schematic diagram of a conventional loop heat pipe;

[0036] FIG. 2 is a cross sectional view of a conventional axially grooved heat pipe;

[0037] FIG. 3 is a perspective view of a flat heat pipe of a first embodiment of the present invention with an upper evaporator plate thereof removed;

[0038] FIG. 4 is a schematic view of a process for forming the heat pipe of FIG. 3;

[0039] FIG. 5 is a detailed view of region C of the heat pipe of FIG. 4;

[0040] FIG. 6 is a detailed view of part of a heat pipe of a second embodiment of the present invention;

[0041] FIG. 7 is a side cross sectional view of a capillary device of an axially grooved heat pipe of a third embodiment of the present invention;

[0042] FIG. 8 is a side cross sectional view, corresponding to FIG. 7, of a capillary device of an axially grooved heat pipe of a fourth embodiment of the present invention;

[0043] FIG. 9 is a side cross sectional view, corresponding to FIG. 8, of a capillary device of a fifth embodiment of the present invention;

[0044] FIG. 10 is a side cross sectional view, corresponding to FIG. 9, of a capillary device of a sixth embodiment of the present invention;

[0045] FIG. 11 is a side cross sectional view, corresponding to FIG. 10, of a capillary device of a heat pipe of a seventh embodiment of the present invention;

[0046] FIG. 12 is a schematic view of a heat transfer apparatus of an eighth embodiment of the present invention;

[0047] FIG. 13 is a perspective view of a heat transfer apparatus of a ninth embodiment of the present invention;

[0048] FIG. 14 is a side cross sectional view of an evaporation apparatus of the heat transfer apparatus of FIG. 13;

[0049] FIG. 15 is a perspective view of a heat transfer apparatus of a tenth embodiment of the present invention;

[0050] FIG. 16 is a view of an evaporation apparatus and a condenser apparatus of the heat transfer apparatus of FIG. 15 with an adiabatic section of the heat transfer apparatus removed; and

[0051] FIG. 17 is a schematic view of a heat transfer apparatus of an eleventh embodiment of the present invention.

[0052] Referring to FIG. 3, a flat heat pipe 102 of a first embodiment of the present invention is formed from aluminium and has an upper evaporator plate 124 (FIG. 4), a lower condenser plate 104 and solid side walls 106. Porous chambers 108 formed from aluminium are arranged between the upper evaporator plate 124 and the lower condenser plate 104, and unmelted aluminium powder 110 is provided inside the chambers 108. The regions 112 between the chambers 108 form a vapour space 109 covered by a layer 122 on the underside of upper evaporator plate 124 such that working fluid such as water is caused by the upper evaporator plate 124 to evaporate and transfer heat via the vapour space 109 to the lower condenser plate 104, and condensed working fluid passes by capillary action through the walls of the chambers 108 and the powdered aluminium 110 in the chambers 108 back to the upper evaporator plate 124. The powdered aluminium 110 enhances fluid flow due to capillary action, but thermal conduction through the powdered aluminium 110 is limited, as a result of which the parasitic heating effect on condensed working fluid passing through the aluminium powder 110 is minimised. This in turn maximises the amount of heat removed from the upper evaporator plate 124 by evaporation of the working fluid.

[0053] The formation of the heat pipe 202 of FIG. 3 is shown in detail with reference to FIGS. 4(a) to 4(h). Initially, as shown in FIG. 4(a), a solid sheet of aluminium is provided, to form lower condenser plate 104 and a layer 114 of powdered aluminium is placed on the donor material, as shown in FIG. 4(b). A high intensity energy beam (not shown) such as a laser beam is then directed onto the layer 114 of powdered material and the path of the beam controlled to selectively melt the layer of powder in the selected regions to form rigid porous regions 116 forming the base of the vapour space 109, separated by regions 118 of unfused powder material which forms the powdered aluminium 110 in the chambers 108. Further layers of powdered aluminium are added and selectively melted in FIGS. 4(c) to 4(e) to form porous side walls 120 of the chambers 108. Similarly, porous upper walls 122 of the vapour space 109 can be formed on the lower surface of solid upper evaporator plate 124 as shown in FIGS. 4(f) to 4(h).

[0054] As shown in greater detail in FIG. 5, each of the chambers 108 encapsulates unmelted powdered material 110, and the vapour space 109 encloses a volume of working fluid at reduced pressure. In use, heat is removed from the upper evaporator plate 124 by evaporation of the working fluid enclosed in chambers 108 and transferred to the lower condenser plate 104 by condensation of the working fluid. The condensed working fluid can pass through the porous walls 120 of chambers 108 into the unfused powder material 110 and returned to the upper evaporator plate 124 through the powder material 110 by means of capillary action.

[0055] Referring to FIG. 6, in which parts common to the embodiment of FIGS. 3 to 5 are denoted by like reference numerals but increased by 100, a heat pipe of a second embodiment of the present invention differs from the arrangement shown in FIGS. 4 and 5 in that one or more support struts 228a, 228b, 228c extend through the interior of one or more of the chambers 208 to assist in capillary transfer of condensed working fluid between the condenser 204 and evaporator 224 plates and to enhance the mechanical strength of the heat pipe. The struts may be a single solid strut 228a, a 3D CAD generated micro capillary strut 228b, or a combination strut 228c consisting of a 3D micro capillary core 230 having a sintered structure 232 mounted on its outer walls. The struts 228b, 228c provide the advantage that by tailoring the 3D CAD geometry and the sintering and/or selective laser melting treatment, the capillary structure can be formed with a graded porosity and permeability, which allows customisation of the mass flow rate of the condensed working fluid around the device. In an alternative arrangement, the sintered structure can be provided on the inside of the strut 228c and the 3D CAD capillary structure on the external surface of the strut.

[0056] Referring to FIG. 7, a capillary device 240 for use in an axially grooved heat pipe of a third embodiment of the present invention is shown. The capillary device 240 is built up by means of selected laser melting of aluminium powder to build up successive layers on a solid donor plate 242 for placing in contact with a heat source, a solid aluminium housing 244, and a capillary structure 246 comprising circumferentially separated porous aluminium protrusions 248 protruding into a central elongate channel 250. By use of the selective laser melting technique used to form the capillary structure 246, the porous protrusions 248 can be separated by smaller channel widths than in the case of the known arrangement shown in FIG. 2, as a result of which the protrusions 248 and gaps 252 therebetween generate significantly enhanced capillary action compared with the arrangement shown in FIG. 2, thereby enabling the heat pipe to operate under the influence of gravity and have improved heat transfer performance.

[0057] In operation, one end of the capillary device 240 is placed in contact with a heat source, and the other end is placed in contact with cooling means to form a condenser. The heat source causes the working fluid to evaporate, and evaporated working fluid travels along the central channel 250 to the condenser. Condensed working fluid travels along the axial gaps 252 between protrusions 248, and is drawn through the porous protrusions 248 by capillary action at the hot end of the heat pipe to maintain the flow of condensed working fluid to the evaporator. The porous protrusions 248 and gaps 252 cooperate to enhance the capillary action to the extent that the capillary action can overcome the effects of gravity.

[0058] Referring to FIG. 8, in which parts common to the embodiment of FIG. 7 are denoted by like reference numerals but increased by 100, a capillary device 340 of a heat pipe of a fourth embodiment of the present invention differs from the arrangement shown in FIG. 7 in that porous protrusions 348 are hollow and contain unfused aluminium powder to enhance the capillary action of flow of condensed working fluid through the porous walls of the protrusions 348 and the powder contained in the protrusions 348.

[0059] FIG. 9 shows a capillary device 440 of a heat pipe of a fifth embodiment of the present invention, in which parts common to the embodiment of FIG. 8 are denoted by like reference numerals but increased by 100. The capillary device 440 of FIG. 9 differs from the arrangement shown in FIG. 8 in that a lattice capillary structure 454 is formed in longitudinal gaps 452 between porous protrusions 448 by means of a selective laser melting or sintering process to form capillary pores having characteristic dimensions below 50 microns at the condenser end of the heat pipe to draw condensed working fluid into the capillary structure. At the condenser, there is also a transition from sintered capillary to lattice within the channel, and as the lattice moves towards the evaporator region, the minimum characteristic dimension is graded to produce open channels with minimum characteristic dimension that are suitable to allow passage of evaporated working fluid. At the evaporator, the lattice may be removed completely to remove any restriction to flow of evaporated working fluid into the vapour channel along the centre of the heat pipe. By grading the pore size along the length of the heat pipe, the means in which it interacts with the working fluid can be manipulated. At the condenser end of the heat pipe, the capillary structure 454 is tailored to draw in and become flooded with condensed working fluid, and the adiabatic region of the heat pipe is tailored to provide a high mass flow rate of fluid from the condenser to the evaporator regions. At the evaporator region, the capillary structure 454 is tailored to allow much larger surface heat fluxes to be input over this region. Through the thickness of the evaporator capillary structure, its properties are graded to allow the vapour to easily pass from the capillary structure 454 into the vapour space and also to provide a flow of liquid fluid to the vapour generation sites.

[0060] Referring to FIG. 10, a selective laser melting process is used to build up a capillary device 540 as a single solid component having vapour flow channels 556 for passage of evaporated working fluid. To improve heat transfer, the vapour flow channels 556 are entirely embedded within a porous capillary structure 558, in order to increase the evaporation heat transfer surface area around the walls of the vapour flow channels 556. Since it is no longer necessary to machine the vapour flow channels 558, the shape and flow path into the device is unlimited.

[0061] Referring to FIG. 11, in which parts common to the embodiment of FIG. 10 are denoted by like reference numerals, a capillary device 640 differs from the arrangement shown in FIG. 10 in that the porous capillary structure 658 in which the vapour flow channels are formed encapsulates aluminium powder material 660 and has a radial inner wall 662 surrounding a central fluid flow passage 664.

[0062] A heat transfer apparatus 700 of a further embodiment of the present invention is shown in FIG. 12. The apparatus 700 has a main body 704 divided by a porous capillary structure 702, having porous rigid walls and containing unmelted powdered material, into an inlet chamber 706 and an outlet chamber 708. Liquid working fluid introduced through an inlet 710 enters the capillary structure 702 via the inlet chamber 706 and is heated by heat passing through the side wall of the main body 704. The heated working fluid then passes in heated liquid or vapour form via the outlet chamber 708 and through an outlet 712.

[0063] Referring to FIGS. 13 and 14, a heat transfer apparatus 800 of a ninth embodiment of the present invention is in the form of a flanged loop heat pipe comprising an evaporation chamber 802 cooperating with a condensation loop 804 and a cylindrical compensation chamber 806. As shown in more detail in FIG. 14, the evaporation chamber 802 has an outer cylindrical body 808 in which a porous capillary structure 810 defines a complex 3D vapour flow network 812 comprising a series of circumferential vapour channels 814 interconnected by an elongate escape channel 816. The capillary structure 810 also defines an annular chamber 818 enclosing unmelted metallic powder material 820. The chamber 818 surrounds a central bore 822 which is closed by an end face 824 of the capillary structure 810 and a solid wall 826. By manufacturing the capillary structure 810 by means of selective melting of metallic powder to form successive layers, complex 3D capillary structures having a wider range of dimensions and properties can be provided.

[0064] In operation, the evaporation device 802 cooperates with the compensation chamber 806 such that the central bore 822 of the evaporation device 802 is filled with condensed working fluid which passes into the capillary structure 810 and unmelted metallic powder 820 within the chamber 818 by means of capillary action. When the evaporation chamber 802 is brought into contact with a source of heat (not shown), working fluid evaporates from the radially outer parts of the capillary structure 810 and passes into the vapour flow network 812 and out of the fluid vapour escape hole 816 into condensation loop 804 where it is condensed by means of cooling at a location separated from the heat source. Condensed working fluid then passes into the end of the compensation chamber 806 remote from the evaporation chamber 802.

[0065] FIGS. 15 and 16 show a heat pipe 900 in which an evaporation section 902, manufactured in successive layers by means of selective melting of metallic powder, is connected, by means of a curved adiabatic section 904, to a much longer extruded condenser section 906 having a flow channel design 910 which matches that of the evaporation section 902. The evaporation section 902 has a grooved capillary structure 908, which may contain unmelted metallic powder, having enhanced performance which therefore enables larger amounts of heat to be input into the evaporator section 902, thereby enabling the device 900 to cool smaller, high power devices. Evaporated working fluid passes along a central channel (not shown) of the curved adiabatic section 904 to the longer condenser section 906, while condensed working fluid passes along a capillary structure (not shown) contained in the curved adiabatic section 904 to the capillary structure 908 of the evaporation section 902.

[0066] FIG. 17 shows a heat transfer apparatus 1000 of an eleventh embodiment of the present invention in which a single central evaporator section 1002 having a capillary structure (not shown), manufactured in successive layers by means of selective melting of powdered metallic material using an energetic beam, is connected to multiple, larger condensation sections 1004, each of which is manufactured by means of conventional extrusion methods.

[0067] It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, as an alternative to a selective laser melting process, electron beam melting may be used. In addition, as an alternative to selective melting of a layer of powdered material, a stream of powdered material may be directed by means of inert gas to the location at which the powdered material is melted by the energy beam. This enables a wider range of applications of the process to be used. Furthermore, in addition to aluminium, other powdered materials such as metals, metal alloys or polymer materials may be used.