WO1997008483A2

WO1997008483A2 - Heat pipe

Info

Publication number: WO1997008483A2
Application number: PCT/IL1996/000093
Authority: WO
Inventors: Alexander Levin
Original assignee: Refmed Cryo-Medical Products Ltd.
Priority date: 1995-08-30
Filing date: 1996-08-30
Publication date: 1997-03-06
Also published as: IL115109A0; WO1997008483A3

Abstract

An improved heat pipe construction includes an evaporator for evaporating a low-temperature boiling fluid so as to generate vapors thereof, and a condenser for condensing the vapors so as to provide a condensate; wherein a predetermined one of the evaporator and the condenser includes a first heat transfer arrangement and the other one of the evaporator and the condenser comprises a second heat transfer arrangement, and wherein the first heat transfer arrangement includes a generally tubular housing; a plurality of substantially flat heat transfer portions having heat transfer surfaces operative to exchange thermal energy with the fluid in contact therewith, thereby to convert the fluid from a first fluid form to a second fluid form, wherein the heat transfer portions also have fluid flow ports provided therein for permitting fluid circulation transversely through the plurality of heat transfer portions between the first and second heat transfer arrangements, and the heat transfer portions are arranged within the housing so as to be in thermally conductive touching contact with the wall surfaces and such that the heat transfer surfaces are oriented transversely with respect to the wall surfaces; apparatus for causing capillary wetting of either the inner housing surface or the heat transfer surfaces of the heat transfer portions; and apparatus for thermally coupling the housing with an external mass having a temperature in a known range, wherein the other one of the evaporator and the condenser is the second heat transfer arrangement which includes tubular apparatus having an inward-facing surface for receiving the fluid in the second fluid form from the first heat transfer arrangement and for thermally coupling the fluid with an external mass having a temperature in a known range, thereby to convert the fluid back to the first fluid form.

Description

HEAT PIPE

FIELD OF THE INVENTION The present invention relates generally to heat transfer devices and, more particularly, to heat pipes.

BACKGROUND OF THE INVENTION

The cooling of various electronic and electrical components and units is known to be problematic. This is due, at least in part, to the fact that the component or unit to be cooled is small relative to the size of conventional radiators required for their effective cooling,. This is especially true when ambient air is used for cooling the radiators.

In addition, cold transfer from the relatively small cold side of a thermoelectric element, either to a space to be cooled, or to electronic components or units having a large area, leads to significant cold losses, and thus inefficient cooling. This is due to the above-mentioned large area ofthe cooling radiators relative to that ofthe thermoelectric element.

Different shapes of heat pipes have been proposed for efficient cooling of small electric or electronic components and units .

The use of heat pipes, generally, is known to provide a satisfactory technical solution of the problem described above, as it enables:

1) mutual separation ofa heat source and sink; and

2) a possibility of achieving a large ratio between the area of a heat (or cold) sink and the area ofa heat (or cold) source.

Use of heat pipes further facilitate provision of a very small difference of the temperatures between a cold or heat source and a surface to be cooled or heated.

Several constructions of heat pipes are described in Chapter 7 ofthe publication by P.D.

Dunn and D.AReay, entitled HEAT PIPES, published by the Pergamon Press, 1994. A further approach to the construction of heat pipes is described in an article by J.H Ambrose, AR.Field, and H.R.Holmes , entitled A Pumped Heat Pipe Cold Plate For High- Flux Applications, published in the journal EXPERIMENTAL THERMAL AND FLUID SCIENCE 1995; Volume 10: pages 156 - 162.

Among disadvantages of the various constructions described in the two above publications are that they are accompanied by high manufacturing costs, and the fact that they are inefficient in as far as they do not provide a small temperature drop between a heat source and a heat sink, for large heat fluxes .

A further indication of the state of the art may be gained by referring to the following publications: US Patent No. 5,275,232 to Adkins et al; US Patent No. 5,297,619 to Faghri;

US Patent No. 5,309,457 to Minch; US Patent No. 5,310,166 to Mast et al; US Patent No.

5,320,866 to Leonard; US Patent No. 5,325,913 to Altoz; US Patent No. 5,329,993 to

Ettehadieh; US Patent No. 5,335,720 to Ogushi et al; US Patent No. 5,339,214 to Nelson; and US Patent No. 5, 12,535 to Chao et al.

Also known is US Patent No. 3,603,382 describes a radial heat flux transformer which is adapted "to be employed in the transfer of thermal energy" and is "particularly suited for use in delivering energy radially." The described structure has "two concentric cylinders interconnected by a network of groups of radially extended capillary channels having vapor spaces defined therebetween" for delivering "vapor as well as its condensate in opposite radial directions between the concentric cylinders." The channels and vapor spaces are provided by a plurality of inner and outer rings which are connected by bridging portions for capillary motion of liquid, and between which are defined vapor spaces, these permitting radial movement of vapors between the inner and outer rings. Accordingly, it is thus seen that a complete thermal cycle occurs at every portion of the transformer which includes a radial segment thereof, including portions of an inner and an outer ring, together with a bridging portion and vapor space therebetween, and together with tube portions juxtaposed to the inner and outer ring portions. SUMMARY OF THE INVENTION The present invention seeks to provide a novel heat pipe construction that is significantly more efficient than known heat pipe constructions, and which is relatively inexpensive to manufacture.

More particularly, the present heat pipe construction is characterized by provision of an evaporation area that, while contained within a relatively small volume, is significantly larger than the area to be cooled, and which may be manufactured so to provide substantially any preferred ratio ofthe evaporation areas to the area to be cooled.

There is thus provided, in accordance with a preferred embodiment ofthe invention, an improved heat pipe construction which includes an evaporator for evaporating a low- temperature boiling fluid so as to generate vapors thereof, and a condenser for condensing the vapors so as to provide a condensate; wherein a predetermined one of the evaporator and the condenser includes a first heat transfer arrangement and the other one ofthe evaporator and the condenser comprises a second heat transfer arrangement, and wherein the first heat transfer arrangement includes: a generally tubular housing; a plurality of substantially flat heat transfer portions having heat transfer surfaces operative to exchange thermal energy with the fluid in contact therewith, thereby to convert the fluid from a first fluid form to a second fluid form, wherein the heat transfer portions also have fluid flow ports provided therein for permitting fluid circulation transversely through the plurality of heat transfer portions between the first and second heat transfer arrangements, and the heat transfer portions are arranged within the housing so as to be in thermally conductive touching contact with the wall surfaces and such that the heat transfer surfaces are oriented transversely with respect to the wall surfaces; apparatus for causing capillary wetting of either the inner housing surface or the heat transfer surfaces ofthe heat transfer portions; and apparatus for thermally coupling the housing with an external mass having a temperature in a known range, wherein the other one ofthe evaporator and the condenser is the second heat transfer arrangement which includes tubular apparatus having an inward-facing surface for receiving the fluid in the second fluid form from the first heat transfer arrangement and for thermally coupling the fluid with an external mass having a temperature in a known range, thereby to convert the fluid back to the first fluid form.

Further in accordance with a preferred embodiment of the invention, the capillary wetting apparatus is either or both of a porous coating or microgrooves formed on either the inner housing surface or the heat transfer surfaces.

Additionally in accordance with a preferred embodiment of the invention, the plurality of heat transfer portions is a stack of heat-conductive disk-shaped members.

Further in accordance with a preferred embodiment of the invention, the tubular housing has a longitudinal axis and the stack includes a plurality of disk-shaped members; and apparatus for mounting the plurality of disk-shaped members transverse to the longitudinal axis.

In accordance with one embodiment ofthe invention, the first heat transfer apparatus is the evaporator, and the second heat transfer apparatus is the condenser.

In accordance with an alternative embodiment of the invention, the first heat transfer apparatus is the condenser, and the second heat transfer apparatus is the evaporator.

In accordance with yet a further embodiment of the invention, the tubular housing and the apparatus for thermally coupling are formed as an integral unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings, in which:

Fig. IA is a schematic side view of an improved horizontal heat pipe used for heat dissipation, constructed in accordance with an embodiment ofthe present invention;

Fig. IB is an enlarged, side-sectional view ofthe evaporation portion ofthe heat pipe of Fig. IA, taken along line B-B therein;

Fig. IC is an enlarged cross-sectional view ofthe heat pipe of Fig. IA, taken along line C-C therein, at right angles to the view of Fig. IB;

Fig. 2A is a perspective view of a single heat transfer disk used in the evaporation stack ofthe heat pipe of Figs. 1A-1C;

Fig. 2B is an enlarged cross-sectional view of the heat transfer disk illustrated in Fig. 2A, taken along line B-B therein;

Figs. 3 A and 3B are respective end and side views of an alternative, unitary evaporation stack, useful in the heat pipe of Fig. IA and constructed in accordance with an alternative embodiment ofthe present invention;

Fig. 4A is a partially cut-away pictorial view of a heat transfer disk constructed in accordance with an alternative embodiment ofthe invention;

Fig. 4B is an enlarged, side-sectional view ofthe evaporation portion ofthe heat pipe of Fig. IA, taken along line B-B therein, and employing a stack of disks as per the disk construction seen in Fig. 4A;

Fig. 5 is a broken-away schematic side view of the heat pipe of Fig. IA, illustrating operation ofthe heat pipe;

Fig. 6 is a cross-sectional illustration of the evaporation section of a heat pipe used for heat dissipation, and employing a wick for condensate return in accordance with a further alternative embodiment ofthe present invention; Fig. 7A is a schematic view of a heat pipe used for heat dissipation, of which the condensation portion has a tubular, zigzag, helical configuration;

Fig. 7B shows a construction similar to that of Fig. 7A, but wherein the condensation is formed of generally horizontal portions, thus requiring the use of a wick for drainage of condensate into the evaporation portion;

Figs. 8A and 8B are respective front and side views of a heat pipe used for heat dissipation, wherein removal and condensation of condensed vapors is performed via a manifold construction;

Fig. 9 is a schematic side view of a vertical heat pipe used for heat dissipation, constructed in accordance with yet a further embodiment ofthe invention;

Fig. 10 is a broken-away schematic side view of a construction similar to that of the heat pipe of Fig. IA, and illustrating operation thereof, but wherein the illustrated construction is used for cold transfer;

Fig. 11 is a schematic view of a heat pipe used for cold transfer, of which the evaporation portion has a tubular, zigzag, helical configuration;

Fig. 12 is a schematic side-sectional view of a heat pipe used for heat dissipation, constructed in accordance with a further embodiment ofthe invention;

Fig. 13 is a partially cut-away perspective view of a heat pipe used for heat dissipation, of which the evaporation portion is constituted by a plurality of evaporation tubes mounted in heat transfer association with a split coupling;

Fig. 14A is a schematic side view of an improved horizontal heat pipe which is generally similar to that of Fig. IA, but which is modified in accordance with an alternative embodiment ofthe present invention;

Fig. 14B is an enlarged, side-sectional view ofthe evaporation portion ofthe heat pipe of Fig. 14A, taken along line B-B therein; and

Fig. 14C is an enlarged cross-sectional view ofthe heat pipe of Fig. 14 A, taken along line C-C therein, at right angles to the view of Fig. IB. DETAILED DESCRIPTION OF THE INVENTION

Referring now to Figs. 1A-1C, there is seen a heat pipe, referenced generally 10, constructed and operative in accordance with a preferred embodiment of the invention. Heat pipe 10 is used typically for cooling electronic systems and components, and for cooling the hot side ofa thermoelectric element. As will become apparent from the following description, heat pipe 10 is constructed for operation in a horizontal orientation, and may thus also be referred to as a "horizontal" heat pipe.

As seen in the drawings, heat pipe 10 is formed of a tube 12 which is sealed at one end by a first plug 14, and at the other end by a second plug 16; second plug 16 being provided with a valve 18 via which any fluid in the interior of the tube is purged, and replaced with a low-temperature-boiling liquid and its vapor. This liquid may be any such liquid known for use in the art. The tube 12 has a central portion, referenced generally 20, which is configured for connection to a heat source via a coupling or saddle, referenced 22, and end portions, referenced generally 24, each having mounted thereon a plurality of cooling fins, referenced 26.

As will be understood by persons skilled in the art, and as will become apparent from the following description, all heat-conducting components of the heat pipe 10, may be formed from any solid substance having good thermal conduction properties. Accordingly, these components are preferably formed of metal, although this is not intended to exclude from use any other materials having satisfactory thermal conduction properties.

As seen, coupling 22 is formed of two portions 28, which are fastened together about central portion 20 of tube 12 via appropriate, typically threaded fasteners 30, extending through flanges 31 of coupling portions 38. Each coupling portion 28 is, in the present example, configured as a parallelepiped, but having formed on an inner face thereof a semi-cylindrical recess, referenced 32, configured for maximum surface contact with the exterior ofthe tube 12. Each coupling portion 28 further defines a preferably flat exterior surface, referenced 34, for placement in thermally conductive contact with a heat source, shown at block 36 in Fig. 4, and which may be any heat-generating body, such as an electronic component or an electronic unit. Referring now particularly to Figs. IB and IC, it is seen that, in the present embodiment, central portion 20 ofthe tube 12 is the evaporation portion of the heat pipe 10. Enclosed within this evaporation portion is a stack, referenced generally 40, of heat transfer disks 42. In the present embodiment, these disks are used as evaporation disks, and are thus referred to as such herein. However, as described below in conjunction with other embodiments ofthe invention, heat transfer disks 42 may alternatively operate as condenser disks.

Referring now briefly to Figs. 14 A, 14B, 14C, there is provided a heat pipe construction, referenced generally 1000, having a generally similar construction to that of Figs. lA-lC. Accordingly, components and portions of heat pipe 1000 having counterpart components or portions in the embodiment of Figs. 1 A-1C, are generally not described again in conjunction with the present embodiment, and are indicated with the same reference numerals as in Figs. 1A-1C, but with the addition ofa prime (') notation.

The difference between heat pipe 1000 of the present embodiment and heat pipe 10, described above in conjunction with Figs. 1A-1C, is in the construction of the tube and apparatus for thermally coupling the heat pipe to an external heat source.

In accordance with the present embodiment, there is provided a tube 1012 which is formed of two generally similar portions, referenced 12a and 12b, respectively, which are separated by a central connector ring 1022. Ring 1022, which extends longitudinally along the longitudinal axis 1023 (Fig. 14B) of tube 1012, has a cylindrical interior surface 1024 extending contiguously with the interior of portions 12a and 12b, and exterior surfaces 1026, which are shaped so as to be easily positionable in heat transfer connection with a heat source. As seen in Fig. 14B, ring 1022 is joined and sealed together with adjacent portions of tube potions 12a and 12b as by fillet welds 1028. It will be appreciated that the illustration of fillet welds 1028 is for example only, and that the described joining may be equally well provided by other suitable sorts of welding, soldering, fusion, adhesion, or the like.

Aparticular advantage ofthe present construction of tube 1012 is that, ring 1022 provides a direct heat transfer connection between an exterior thermal source and the interior ofthe tube, and that the heat transfer path does not have to pass across an interface between an exterior connector member mounted about a tube, and the tube itself, thereby rendering the efficiency of the entire device dependent on the mechanical precision with which the tube and the connector member are formed or positioned.

It will also be appreciated that, while the construction of tube 1012 is shown and described in conjunction with present embodiment only, it is intended that a similar construction can be used in place of any of the other constructions shown and described herein in conjunction with any ofthe various embodiments.

Referring now also to Figs. 2A and 2B, each disk 42 is formed with lower and upper openings or fluid flow ports, respectively referenced 44 and 46, and a central opening 48. The provision of central opening 48 facilitates mounting of disks 42 along an axially-positioned carrying rod 50, as seen in Fig. IB. The disks 42 are axially separated by spacer members 52, located along the carrying rod 50 between each two adjacent disks 42. The ends 54 of the carrying rod 50 are preferably provided with screw threads 56, thereby facilitating fastening of the disks 42 and spacer members 52 by nuts 58. In the present embodiment the diameter ofthe disks 42 may be somewhat smaller than the inner diameter of tube 12.

While tube 12 has a generally straight configuration, it may be bent into any preferred non-linear shape, so long as it remains in a horizontal plane.

As seen in Figs. 2A and 2B, there is preferably also provided capillary wetting apparatus. In the present embodiment, the capillary wetting apparatus may be provided on the faces 59 of each evaporation disk 42 as a porous coating, referenced 60. Coating 60 may be any suitable coating known in the art, including, by way of example, sintered copper powder.

The porous coating 60 serves to continuously wet, via capillary action, the surface of disk 42 when a portion thereof (as shown and described below in conjunction with Fig. 4) is immersed in a low-temperature-boiling liquid. The lower fluid flow port 44 of each disk 42 permits flow of the liquid through the bottom of the stack 40, thereby enabling causing immersion of the bottom portion of each disk 42, and the consequent wetting thereof, via coating 60. The upper fluid flow port 46 permits evaporated vapors ofthe liquid to flow through the stack 40 and to the end portions 24 ofthe tube 12. The disk faces 59 may also, or alternatively, be provided with micro-grooves, referenced 61, thereby respectively providing or enhancing the above-described wetting action provided by the porous coating 60.

As seen in Fig. 4, heat-releasing bodies 36 and heat pipe 10 may be connected via flat interfaces 70, thereby to transfer heat from the heat-releasing bodies to heat pipe 12 via coupling 22.

In accordance with a further embodiment of the invention, in addition to the fastening of coupling portions 28 about tube 12 by use of threaded fasteners, or in place thereof, the coupling portions 28 may be connected to the tube 12 so as to provide maximum heat transfer therebetween, by way of soldering or gluing the recesses 32 of coupling portions 28 to the exterior of tube 12. Preferably, the soldering or gluing is performed under pressure, thereby to cause a desired deformation ofthe tube 12, and thereby to improve the thermal conductivity between the connected members. Alternatively, or additionally, a paste with good thermal conductivity should be introduced between the recesses 32 ofthe coupling portions 28 and the external surface of tube 12.

Referring now particularly to Figs. 1A-1C, good thermal contact of disks 42 with the inner face of tube 12 is ensured by a deformation of tube 12 by application thereto of mechanical pressure while tightening threaded fasteners 30. It is also possible, so as to further ensure good thermal contact between the tube wall and disks 42, to solder the edges. Furthermore, edges 72 of disks 42 may also be soldered to the inner surface of tube 12. In the case when the disks 42 are compressed into tube 12, or when they are glued or soldered to the internal wall ofthe tube, a non-split coupling may be used as an alternative to the illustrated split coupling 22.

Referring now to Fig. 3, a unitary stack, referenced 74, may be employed in place of the above-described multiple component disk stacks, thereby obviating necessity of use of disks, spacers, fasteners and carrying rod. Unitary stack 74 is configured as a truncated cylinder, it has first and second generally flat end faces, respectively referenced 76 and 78, and it has formed therein a plurality of radially extending slots 80, formed typically about a central spine 81, thereby forming a plurality of disk-shaped teeth 82. Preferably, the diameter D of at least the end faces 76 and 78 is approximately equal to the internal diameter of tube 12. Furthermore, the planar surfaces ofthe teeth

82, parallel to the end faces 76 and 78, are provided with a porous coating such as porous coating 60, described above in conjunction with Kg.2B. ernanvery, or additionally, vertical micro-grooves may be formed on the planar surfaces of the teeth, thereby to provide or enhance the required capillary actioa

Referring now to Figs. 4A and 4B, in accordance with an alternative embodiment ofthe invention, there are provided heat transfer disks, referenced 442, characterized by having an initial diameter Dl (Fig. 4 A), prior to insertion into tube 12, that is slightly greater than the diameter D2 (Fig. 4B) of tube 12. Accordingly, disks 442 are sufficiently flexible so as to permit a required deformation thereof when forced into the tube^' 12. Disks 442 are further characterized by having a rim 444. It will thus be appreciated that, in the present embodiment, the disks 442 are forced into the tube 12 such that their rims 444 engages the interior surface of the tube wall, thereby providing good heat-conductive contact between the disks 442 and the tube wall, thus obviating the necessity of provision of central openings and a carrying rod, as required in disks 42, described above in conjunction with Figs. 1A-2B. The rims 444, furthermore, which, in the present embodiment, extend along the entire circumference, and in a single direction, serve as spacers, thereby obviating the necessity of provision of separate spacers as shown and described in conjunction with the embodiment of Figs. 1 A-2B.

It is of great importance to provide touching contact between the edges of the heat transfer disks and the wall of tube 12, thereby facilitating maximum heat transfer therebetween. Accordingly, while the disk 442, illustrated in Fig. 4A, provides the required touching contact, the rims thereof may be modified in any suitable manner. Accordingly, the rim, instead of extending along the entire circumference in a single direction, may be split, such that portions thereof extend in a first direction, parallel to the tube wall, and other portions ofthe rim extend in the opposite direction, also parallel to the tube wall.

Referring now to Fig. 5, operation ofthe heat pipe 10 is now described.

Heat transferred to the flat exterior surface 34 of coupling 22 from a heat source 36, is transferred to disks 42, thereby to cause evaporation of the low-temperature boiling liquid with which the disk surfaces is soaked, as described. The evaporated vapors pass through the upper ports

46 ofthe disks and flow outwardly, as indicated by arrows 84. The vapors then condense on the inward- facing surfaces 86 at end portions 24 of tube 12, resulting in an accumulation of condensate in the bottom part ofthe tube 12. The provision of lower disk ports 44 permits free flow ofthe condensate through the disk stack 40, thereby enabling further wetting ofthe disks 42.

It will thus be appreciated that heat pipe 10 of the invention functions as a two phase thermosyphon, wherein the condensate returns to the disk stack by means of gravitational forces. Accordingly, so as to ensure that the evaporation portion ofthe present heat pipe is higher than the condensation portion thereof, the heat pipe ofthe present embodiment must be held in a substantially horizontal position in order to function properly.

Referring now to Fig. 6, it will be appreciated, however, that, in accordance with an alternative embodiment ofthe invention, there may be provided a heat pipe, referenced generally 86, which also functions as a two-phase thermosyphon, but which is modified so as to facilitate retum of condensate to the evaporation portion from the condensing portion or portions, by capillary forces.

In the present embodiment, there are provided evaporation disks 88 which may be formed in accordance with any of the disk embodiments shown and described above in conjunction with Figs. 1A-4B, and may thus either be mounted on an axial carrying rod 89, as in the illustrated embodiment, or formed as a unitary stack. A modification ofthe present disks 88, however, is that they are formed with first and second cutouts or recesses 90 and 91, thereby defining a pair of first and second, parallel, lateral channels, referenced 93 and 95, parallel to the longitudinal axis of the tube 92 within which the disks are located. First channel 93 permits a required circulation of evaporated vapor from the evaporation portion to the condenser portion of the heat pipe. Furthermore, in order to provide retum of condensate from the condenser portion to the evaporation portion ofthe heat pipe, as described, a wick 94 is located in second channel 95, along its entire length.

In order to provide good thermal contact between the various components ofthe illustrated construction, there is provided a coupling 96 which is formed typically of two portions 98 and 100, of different shapes, as seen in the drawing. This allows a desired deformation ofthe tube 92 upon tightening at portions ofthe tube adjacent to channels 93 and 95, thereby providing good thermal contact between the disks and the tube, and further, between the tube and the wick 94. Coupling portions 98 and 100 are also provided with flat surfaces 102 and 104, so as to permit positioning thereagainst of heat sources.

With reference now to Fig. 7A, in order to reduce the size of a heat pipe constructed in accordance with the present invention, a heat pipe arrangement may be provided in the form of a tubular, zigzag constmction. This zigzag constmction, referenced generally 110, includes a lower horizontal evaporation tube, referenced 112, in which is located an evaporation stack (not shown) whose constmction is similar to that shown and described above in conjunction with any of Figs. 1 A-3B, and on which is mounted a split coupling 114. The evaporation tube 112 also includes a plug and valve, respectively referenced 113 and 115.

The evaporation tube 112 is connected to and communicates with a condensation portion, referenced generally 116, which has a helical form, as seen, and which is formed of a plurality of tubes 118 which, preferably, are located in a common vertical plane, and which are connected in series by pipe bends 120. Tubes 118 are provided with cooling fins 122. As seen, each tube 118 has a predetermined inclination with respect to the horizontal so as to ensure a sufficiently fast downward drainage of condensate into the horizontal evaporation tube 112.

Referring now to Figs. TB, there is provided a heat pipe constmction which, except as specifically described below, is identical to constmction 110. Accordingly, the present constmction bears the same reference numerals as used for corresponding portions in the constmction of Fig. IA, with the addition of an apostrophe (') siiffix- Accordingly, the constmction of Fig. 7B is labeled 110'.

Fig. 7B is characterized by the provision of condensation tubes 118' in a generally horizontal position, such that a wick, referenced 124 is required to provide drainage of condensate from the topmost condensation tube 118 to the entire stack of heat transfer disks, labeled generally 121. It will also be noted that each ofthe cooling fins 122' is common to all ofthe condensation pipes 118', thereby providing a desired -rtiffening to the condensation portions 116' ofthe illustrated heat pipe 110'.

Referring now to Figs. 8A and 8B, there is provided a heat pipe construction, referenced generally 140, which is formed of a preferably horizontal evaporation tube, referenced 142, and a condenser portion, referenced generally 144. Evaporation tube 142 is generally as described in conjunction with Fig. 7A and is thus not described specifically herein, except in as far as it differs from evaporation tube 112. Condensation portion 144 is constituted, in the present embodiment, by a manifold having a plurality of generally upwardly extending condensation tubes 146, connected to the interior of evaporation tube 142 via suitable connectors, referenced 148. Condenser tubes preferably have mounted thereon a plurality of cooling fins 150, which not only assist condensation ofthe vapor in the condensation tubes, but also provide desired mechanical stiffening to the manifold.

Referring now to Fig. 9, there is provided a substantially vertical heat pipe constmction, referenced generally 160. Heat pipe 160 is formed ofa single, generally vertical tube 162 in which both evaporation and condensation occur. Accordingly, the heat pipe includes a lower, evaporation portion, referenced 164, and an upper, condensation portion 166 extending upwardly therefrom.

The evaporation portion 164 includes a lower tube portion 168, sealed at its bottom end by a first plug 170, and an evaporation stack 172, which may be any of the evaporation stacks described above in conjunction with Figs. 1A-4B. A split coupling 174, which may be similar to coupling 22 shown and described above in conjunction with Figs. 1A-1C, is mounted onto the evaporation portion so as to surround the lower tube portion 168 in registration with the evaporation stack 172. The condensation portion 166 is constituted by upper tube portion 162 on which are mounted cooling fins 178. A second plug 180 is provided to seal the top end ofthe tube.

In accordance with an altemative embodiment ofthe invention, the condensation portion 166 may be replaced by a zigzag arrangement as shown and described in the embodiment of Fig. 7A

While the present embodiment is employed for heat transfer, it may altematively be employed for cold transfer from the cold side ofa thermoelectric element to a space to be cooled, or for the cooling of various electronic components.

Referring once more to Figs. IA, IB and 10, when the illustrated constmction is employed for cold transfer, it is modified such that the heat transfer disks (whether these be formed as separate disks or as part of a unitary evaporation stack) are not provided with porous coatings. However, a porous coating is provided on the internal walls 113 ofthe extreme sections of tube 12 thereby to ensure wetting of the internal wall surfaces of end portions 24 with the low-temperature boiling liquid by capillary forces. This is indicated by arrows 115 in Fig. 10. As a result, when the cold side of a thermoelectric element is in good thermal contact with the flat surface of coupling 22, the heat transfer disks are cooled so as to cause condensation of vapors ofthe low-temperature boiling liquid on the disk surfaces. The condensate flows downwards, as shown by arrows 117 (Fig. 10), so as to be collected in the bottom part ofthe tube 12, passing through lower disk ports 44 and flowing to the tube ends. At the tube ends, the condensate wets the intemal surfaces, from which it is evaporated, thereby cooling the outer surfaces ofthe tube ends 24. Resulting vapors return to the surfaces ofthe disks through the upper ports 46, whereat they are again condensed.

Referring now to Fig. 11, there is provided a heat pipe used for cold transfer, referenced generally 200, constmcted in accordance with a further embodiment ofthe invention. Heat pipe 200 includes a condensation portion 202, formed substantially as described above in conjunction with Figs. 1A-1C with respect to central portion 20 thereof, but modified for cold transfer as described above. In the present embodiment, an evaporation portion 204 is provided, and is constructed substantially as described above in conjunction with Fig. 7 with respect to condensation portion 116, but is located below condensation portion 202. In operation, condensate accumulating in condensation portion 202 flows downward, under the force of gravity, into the evaporation portion 204, whereat it is evaporated. The resulting vapors rise upward so as to retum to the condensation portion 202, whereat they are cooled and condensed. The present embodiment provides, as will be appreciated, a greatly increased condensation capability relative to the construction of Fig. IA due to the much larger area ofthe heat transfer surfaces ofthe heat transfer disks in condensation portion 202, relative to the size ofthe exterior surface thereof, thereby increasing the cold transfer capacity ofthe present embodiment.

In a modification to the present embodiment, the tubes 206 of the evaporation portion, may be arranged in parallel so as to form a construction similar to that shown in Fig. 7B, in which case a wick is introduced into the intemal space ofthe evaporation portion. Provision ofthe wick facilitates drainage of the condensate downwards when the tubes 206 are inclined at a small or zero angle relative to the horizontal.

It will be appreciated by persons skilled in the art that any ofthe heat pipe constmctions described above in conjunction with any of Figs. 8A 8B and 9, for heat transfer, may be modified in a similar manner to that described above for the constmctions of Figs. 1A-1C and 6, such that the roles of the respective evaporation and condensation portions are reversed.

Referring now to Fig. 12, there is illustrated an evaporation assembly, referenced 220, defining a surface 221 against which a heat source (not shown) may be placed. It will be appreciated that the present evaporation assembly may be used in conjunction with any of the condensation portions shown and described hereinabove.

More particularly, the evaporation portion 220 is composed of lower vertical or inclined tube 224, an interconnecting tube 226 via which vapors and condensate flow between evaporation portions 220 and a condenser portion (not shown), and a lower plug 228 which defines surface 221. There is further provided an axial pin member 230 which is brazed or otherwise connected to plug 228, and which has formed thereon a screw thread 232. A coil 234 formed from a metal strip with high thermal conductivity is placed in ώermally conductive contact with plug 228. Coil 234 is provided with a porous coating not shown), preferably on both sides, and is formed with indentations 238 and corresponding openings 240. Indentations 238 serve as spacers between mutually adjacent portions ofthe coil 234, and openings 240 facilitate removal of vapors from the coil surface to a condensation portion (not shown), constmcted, for example, as per the condensation portion of the embodiment of Fig. 8, via interconnecting tube 226. Cutouts, referenced 242, are also provided in the lower edge ofthe coil 234, thereby to facilitate access of the condensate to all the coil portions. There is also provided a packing washer 244 with openings 245, and a fastener 246 which is fastened to pin member 230 via thread 232, thereby to retain coil 234 in heat- conductive contact with plug 228.

Referring now finally to Figs. 13A and 13B, there is illustrated a portion ofa heat pipe, referenced 250, constmcted in accordance with yet a further embodiment ofthe invention As seen, heat pipe 250 is formed from a plurality of generally vertical evaporation portions 252 and a corresponding plurality of condensation portions 254. The individual evaporation and condensation portions are substantially as described above in conjunction with Fig. 9, and are therefore not described herein again in detail.

The evaporation portions 252 are enclosed within a single split coupling 256, each portion thereol referenced 258, being provided with semi-cylindrical recesses 260 which are fastened about the evaporation portions 252. In the present embodiment, the mutually opposite surfaces ofthe coupling portions 258 are first coated with a soldering material, such as tin. Subsequently, evaporation portions 252 are placed in the recesses 260 of one ofthe coupling portions 258, after which the two coupling portions are soldered together under pressure. This ensures, in addition to connection of tiie two coupling portions, that the tubes become sufficiently deformed so as to ensure good thermal contact between the tube walls and the edges of the disks. Preferably, a single set of cooling fins 264, is mounted onto all ofthe condensations portions 254 so as to be common thereto.

It will be appreciated that, although the present embodiment is described as being vertical, it may be adapted to a horizontal construction, provided that additional measures, namely, provision of wicks and/or a porous coating, are taken.

It will further be appreciated, by persons skilled in the art that the scope of the present invention is not limited by what has been specifically shown and described hereinabove, merely by way of example. Rather, the scope of the present invention is defined solely by the claims, which follow.

Claims

CLAIMS 1. An improved heat pipe constmction which comprises: evaporation means for evaporating a low-temperature boiling fluid in liquid form so as to generate vapors thereof; and condensing means for condensing said vapors so as to provide a condensate; wherein a predetermined one of said evaporation means and said condensing means comprises a first heat transfer arrangement and the other one of said evaporation means and said condensing means comprises a second heat transfer arrangement, and wherein said first heat transfer arrangement includes: a generally tubular housing; a plurality of substantially flat heat transfer portions each having heat transfer surfaces operative to exchange thermal energy with said fluid when in contact therewith, thereby to convert said fluid from a first fluid form to a second fluid form, wherein said heat transfer portions also have fluid flow ports provided therein for permitting fluid circulation transversely through said plurality of heat transfer portions between said first and second heat transfer arrangements, and said heat transfer portions are arranged within said housing so as to be in thermally conductive touching contact with said wall surfaces and such that said heat transfer surfaces are oriented transversely with respect to said wall surfaces; capillary wetting means for causing wetting of a predetermined one of said inner housing surface and said heat transfer surfaces of said heat transfer portions; and means for thermally coupling said housing with an external mass having a temperature in a known range, wherein the other one of said evaporation means and said condensing means comprises said second heat transfer arrangement which includes tubular means having an inward-facing surface for receiving said fluid in said second fluid form from said first heat transfer arrangement and for thermally coupling said fluid with an external mass having a temperature in a known range, thereby to convert said fluid back to said first fluid form.

2. A constmction according to claim 1, wherein said capillary wetting means comprises at least one ofa porous coating and microgrooves formed on said predetermined one of said inner housing surface and said heat transfer surfaces of said heat transfer portions.

3. A constmction according to claim 1, wherein said plurality of heat transfer portions comprises a stack of heat-conductive disk-shaped members.

4. A constmction according to claim 3, wherein said tubular housing has a longitudinal axis and said stack comprises: a plurality of disk-shaped members; and means for mounting said plurality of disk-shaped members transverse to said longimdinal axis.

5. A constmction according to claim 3, wherein said stack also comprises spacer means for providing spaces between adjacent ones of said disk-shaped members, and means for permitting flow of said fluid to and from said disk-shaped members.

6. A constmction according to claim 3, wherein said stack comprises a unitary stack member having a plurality of disk-shaped protmsions extending radially outward therefrom.

7. A constmction according to claim 3, wherein each said disk-shaped member has an edge portion in touching contact with said tubular housing.

8. A constmction according to claim 1, wherein said plurality of heat transfer portions comprises: a coil formed from a thermally conductive strip so as to define edge portions, and spacer means disposed between layers of said coil, wherein said coil is arranged in said housing such that said edge portions are in thermally conductive contact with said inner surface thereof.

9. A constmction according to claim 1, wherein a predetermined one of said first and second heat transfer arrangements is vertically beneath the other of said heat transfer arrangements.

10. A constmction according to claim 1, wherein said first and second heat transfer arrangements also include means for encouraging liquid flow in a direction contrary to the direction of gravitational acceleration.

11. A constmction according to claim 9, wherein said means for encouraging flow comprises wicking means.

12. A constmction according to claim 1, wherein said first heat transfer means is said evaporation means, and said second heat transfer means is said condensing means.

13. A constmction according to claim 1, wherein said first heat transfer means is said condensing means, and said second heat transfer means is said evaporation means.

14. A constmction according to claim 1, wherein said tubular housing and said means for thermally coupling are formed integrally.