Heat pipe and method of manufacturing the same

Abstract: A wick layer (21) is attached and fixed to one surface of a metal tape (1) without forming a gap with the metal surface, and thereafter, the tape is rolled so that the surface having the wick layer serves as an inner surface, thus forming a pipe shape, then the pipe wall is corrugated. According to the above process, the wick layer is completely and uniformly attached to the inner surface of the heat pipe.

Description: The present invention relates to a heat pipe used for heat conduction and a method for manufacturing a heat pipe. Conventionally, in order to manufacture a heat pipe, a wick such as a metal gauze is attached through an open end portion from the outside to an inner wall of an elemental heat pipe formed into a hollow shape. However, this method is cumbersome; it is difficult to uniformly attach the wick to the entire inner wall surface; it is not easy to check whether or not the wick is correctly attached; it is difficult to attach a wick to the inner wall of a corrugated pipe due to its corrugated surface shape, which results in deterioration of heat characteristics; and more specifically, as shown in Fig. 1, gap K is present between diameter D of inner crest portion and diameter d of inner root portion, thus causing deterioration of the heat characteristics. (in Fig. 1, a cross-hatched portion indicates a wick). In this invention, a wick layer is attached and fixed to one surface of a metal tape without forming a gap with the metal surface, and thereafter, the tape is rolled so that the surface having the wick layer serves as an inner surface, thus forming a pipe shape, then the pipe wall is corrugated. A pipe with corrugations is known from GB-A-409 933. A heat pipe according to the preamble of claim 22 is known from JP-A-56-133593 and includes a pipe wall with a wave-like pattern having spiral pleats. It is an object of the present invention to provide a method for manufacturing a heat pipe as well as a heat pipe by means of which the reinforcement effect against an external crushing force on the pipe and the heat efficiency can be increased. Further, it is also desired to provide a heat pipe, to an inner surface of which a wick is completely and uniformly attached, and a method of manufacturing the same using a simple process. This object is solved according to the present invention by a method of manufacturing a heat pipe including the features of claim 1 and by a heat pipe including the features of claim 22. Further embodiments are defined in the dependent claims. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 shows a conventional corrugated heat pipe; Fig. 2 shows an apparatus used for manufacturing a heat pipe according to an embodiment of the present invention; Figs. 3 to 5 show structures used for forming an wick layer on a metal tape; Fig. 6 shows a grooving machine for a groove-like pattern on a heat pipe; and Figs. 7 and 8 show groove-like patterns formed on a heat pipe. An embodiment of the present invention will now be described with reference to Fig. 2. Reference numeral 1 denotes a metal tape which is wound in a roll shape in a conventional feeding apparatus (not shown) and is therefrom. Metal tape 1 is formed into a heat pipe as a final product. Metal tape 1 is made of copper, aluminum, iron, or stainless steel, and has a width of 30 to 450 mm, and a thickness of 0.2 to 2.0 mm. Reference numeral 2 denotes a wick member comprising a tape to which a fibrous wick material is adhered. Wick member 2 is brought into close contact with and attached to one surface of metal tape 1 to form wick layer 21. Wick layer 21 has a capillary action, and the wick material includes an organic or inorganic metal fiber, glass fiber, animal/vegetable fiber, synthetic resin fiber, or the like. Wick layer 21 may be prepared by disposing the fibrous wick material on the tape. Wick layer 21 may also be prepared by forming the above-mentioned fiber into a net, nonwoven fabric, or porous material. In order to attach wick member 2 to one surface of metal tape 1, wick member 2 is wound into a roll shape in a feeding apparatus (not shown) in the same manner as in metal tape 1, and is fed therefrom at the same speed as the feeding speed of metal tape 1 to be brought into tight contact with and adhered to one surface of metal tape 1. In order to adhere wick member 2 to tape 1, adhesive 23 is sprayed and applied from nozzle 22 onto the surface of metal tape 1. When wick member 2 is attached, press roller 24 is preferably used. Reference numeral 3 denotes forming rollers, each of which forms metal tape 1, after being subjected to the above-mentioned process, into a pipe shape, so that wick layer 21 serves as an inner surface. Each forming roller 3 has an arcuated shape in order to form metal tape 1 into a pipe shape. A plurality of pairs of opposing forming rollers 3 are arranged along the moving direction of metal tape 1. Each of the rollers 3 has an arc configuration and is vertically rotatable around the axis. However, the roller 3 can be arranged in other forms, for example, in a staggered form. The arcs of the pairs of forming rollers 3 can be the same, but are preferably changed in accordance with the progress of metal tape 1 in the pipe forming process. For example, the first stage of forming rollers 3 may have a large radius of curvature, and the radius is gradually decreased to a size corresponding to a pipe diameter as the process progresses. Rollers 3 may have a shape other than the above-mentioned shape, and may be axially supported in a direction other than in the vertical direction. Reference numeral 31 denotes a welding means for welding the mating edges 10 at the start of the formation of heat pipe 41. A welding electrode of welding means 31 is arranged immediately above mating edges 10 to weld mating edges 10. Note that a process for cooling the pipe immediately after welding may be added so as not to damage already attached wick layer 21. The pipe obtained after the above process can be used as a finished product, or can further be corrugated. Reference numeral 4 denotes a corrugating machine for forming a groove-like or wave-like pattern. The pattern provides a flexibility on the outer surface of the heat pipe 41 and holds the working fluid in the heat pipe. More specifically, corrugating machine 4 comprises small disc 401 which is rotatably pressed along outer surface 42 of heat pipe 41, and ring 402 which holds the disc therein and is rotated along outer surface 42 of heat pipe 41. Ring 402 is rotated by rotating disc 403 arranged thereon. Small disc 401 has a rounded outer shape. In this case, when ring 402 is rotated, small disc 401 is also rotated while pressing elemental heat pipe 41, thus forming a smooth helically corrugated pattern on the outer surface of elemental heat pipe 41 at a constant pitch. When small disc 401 has a flat outer shape, a groove-like or wave-like pattern can be formed. If a groove-like or wave-like pattern is formed by corrugating machine 4 while moving heat pipe 41 is temporarily stopped, a wavy or groove-like pattern extending in the circumferential direction can be obtained on the outer surface of heat pipe 41. If pressing of small disc 401 is stopped with respect to elemental heat pipe 41, neither wavy nor groove-like pattern can be formed. If pressing is intermittently performed, a wavy or groove-like pattern can be intermittently formed on the outer surface of elemental pipe 41. More specifically, a wavy or groove-like pattern can be formed on an arbitrary portion of the outer surface of pipe 41, as needed. Mode of transferring the elemental pipe can be modified as desired. That is, the elemental pipe may be continuously, regularly, or irregularly transferred. Furthermore, the groove forming means can be transferred in correspondence to the transfer of the elemental pipe. The pipe formed as described above can be subjected to normal processes, e.g., cutting of the heat pipe, injection of working fluid, sealing of both ends, and the like, thus completing the heat pipe. Figs. 3 to 5 show other embodiments wherein wick layer 21 is formed on metal tape 1. Fig. 3 shows an embodiment wherein wick member 2 is made of a metal, e.g., a metal gauze. In this embodiment, wick member 2 is preformed into a tape-like shape, is fed from a state wherein it has been rolled, and is overlaid on moving metal tape 1. Spot welding electrodes 201 are arranged at both sides of the moving path of metal tape 1, so that tape-like wick member 2 is attached and fixed to metal tape 1 by spot welding electrodes 201. In this case, wick member 2 is preferably pressed against metal tape 1 by rollers 24, as in the above embodiment. This applies to the following embodiments. Fig. 4 shows an embodiment wherein wick member 2 is a powder, particles, or very fine fibers. In this embodiment, wick member 2 is accumulated in hopper 202. Wick member 2 can be any one of the powder, particle, or very fine fibers or may be a combination thereof. Prior to attachment of wick member 2 to metal tape 1, an adhesive is applied to the surface of tape 1, e.g. a plastic tape, by nozzle 5. Wick member 2 is fed to the applied surface by, e.g., spraying from hopper 202, thus attaching and fixing wick member 2 on the surface of tape 1. Fig. 5 shows an embodiment wherein wick member 2 comprises an organic or inorganic solid material. In this embodiment, solid wick member 2 is fused, brazed, or welded by nozzle 205 and the powder is attached and fixed to one surface of metal tape 1. Fig. 6 shows a grooving machine for forming a groove-like pattern on the surface of heat pipe 41 along its longitudinal direction. Grooving machine 501 has a hollow ring shape, and has an appropriate number of small discs 502 each having a groove forming function in its hollow portion toward the center. If heat pipe 41 is moved while grooving machine 501 is not rotated, grooves can be formed along the longitudinal direction of elemental pipe 41. If grooving machine 501 is rotated in the lateral direction, helical grooves can be formed. Figs. 7 and 8 are longitudinal sectional views of groove-like or wave-like patterns formed on elemental pipe 41. Fig. 7 shows an embodiment of a wavy pattern having bulges on the crest and trough portions. Inner diameter g of the crest portion and inner diameter G of the trough portion are respectively larger than their open end gaps h and H. Note that inner diameters g and G of the crest and root portions may be or may not be equal to each other. The groove pattern shown in Fig. 7 has a high working fluid holding force. According to the above embodiments, a wick layer can be uniformly and firmly attached and fixed to the entire inner wall of a heat pipe, thus improving the heat characteristics of the heat pipe. More specifically, since a wick layer is formed on a metal tape before being formed into a pipe shape, the contact state of the wick layer is not influenced even if machining and deformation are performed thereafter. Fig. 8 shows yet another embodiment of the present invention. In this embodiment, an Ω-shaped groove, in which the length of a wave of an outer projecting portion is larger than that of an inner recessed portion, is formed on the outer surface of a pipe in its radial or oblique direction. More specifically, reference numerals 601 and 602 denote grooves comprises Ω-shaped ridges and recesses. When the widths of the ridge and recess are given by Wa and Wb, they are formed to establish Wb < Wa. It is preferable that Wa is 1.01 to 5 times Wb, and more specifically, 1.1 to 2 times. These parameters are determined in consideration of an inner diameter, wall thickness, operation temperature, heat transfer amount, and the like, of the pipe. In the pipe of this structure, a reinforcement effect can be provided against an external crushing force. Since ridge 602 has a hollow portion, a working fluid moving along the wall surface in the heat pipe can be sufficiently stored in the inner hollow portion, and heat from the outside of the pipe can be quickly conducted to the working fluid, thus improving heat efficiency. The heat pipe is particularly suitable when the pipe is used in an uprightly set state. That is, it is particularly effective when the working fluid is uniformly distributed in an elongated heat absorbing portion of an elongated heat pipe used for absorbing terrestrial heat.

Claims: A method of manufacturing a heat pipe, comprising the steps of: feeding a tape (1) from a tape roll; forming a wick layer (21) on one surface of the fed tape; forming the tape having the wick layer thereon into a form of pipe (41); and forming on the inner and outer surfaces of said pipe a wavy pattern having bulges on the crest and trough portions, the inner diameter g of the crest portion and the inner diameter G of the trough portion being respectively larger than their respective open end gaps h and H. A method according to claim 1, characterized by feeding the tape in the form of a metal tape. A method according to claim 1, characterized by feeding the tape in the form of a tape of copper, aluminum, iron, or stainless steel. A method according to claim 1, characterized by feeding the tape in the form of plastic tape. A method according to claim 1, characterized by forming the wick layer on the tape in the form of a net, fabric, or nonwoven fabric made of organic or inorganic fiber as a major component, and attaching and fixing the wick layer to the fed tape by adhesion, fusing, brazing, or welding. A method according to claim 1, characterized by forming the wick layer on the tape in the form of an organic or inorganic powder or particle, and attaching and fixing the wick layer to the fed tape by adhesion or fusing. A method according to claim 1, characterized by forming the wick layer on the tape in the form of an organic or inorganic fine fiber, and attaching and fixing the wick layer to the fed tape by adhesion or fusing. A method according to claim 1, characterized by forming the wick layer on the tape in the form of a mixture of an organic or inorganic powder and a fine fiber, and attaching and fixing the wick layer to the fed tape by adhesion or fusing. A method according to claim 1, characterized by forming the wick layer on the tape in the form of an organic or inorganic solid linear member or powder or a combination thereof, and attaching and fixing the wick layer to the fed tape by spraying. A method according to claim 1, characterized by forming the bulge portions such that they extend helically in the longitudinal direction of the pipe. A method according to claim 1, characterized by forming the bulge portions such that they extend in a straight manner in the longitudinal direction of the pipe. A method according to claim 1, characterized by forming the bulge portions continuously or intermittently in the longitudinal direction of the pipe. A method according to claim 1, characterized by forming the bulge portions by pressing a shaping means to the outer surface of the pipe. A method according to claim 1, characterized by forming the bulge portions such that they extend in a ring form in the longitudinal direction of the pipe. A method according to claim 10, characterized by forming the helicoid of the bulge portions with a constant pitch. A method according to claim 14, characterized by forming the ring form of the bulge portions with a constant pitch. A method according to claim 1, characterized by bonding together mating edges of the tape having a wick layer formed thereon by welding or adhesion to form the pipe. A method according to claim 1, characterized by forming the bulge portions while transferring the pipe. A method according to claim 1, characterized by forming the bulge portions while continuously transferring the pipe. A method according to claim 1, characterized by intermittently transferring the pipe and forming the bulge portions when the pipe is stopped. A method of manufacturing a heat pipe according to claim 1, characterized by forming the maximum width of each of the bulge portions to be different to that of the respectively adjacent bulge portions. A heat pipe comprising a pipe (41) made of tape and a wick layer (21) formed on the inner surface of the pipe, the inner and outer surfaces of the pipe having a wavy pattern, characterized in that bulges are formed on the crest and trough portions of the wavy pattern, the inner diameter g of the crest portion and the inner diameter G of the trough portion being respectively larger than their respective open end gaps h and H. A heat pipe according to claim 22, characterized in that the tape is a metal tape. A heat pipe according to claim 22, characterized in that the tape is a tape of copper, aluminum, iron, or stainless steel. A heat pipe according to claim 22, characterized in that the tape is a plastic tape. A heat pipe according to claim 22, characterized in that the wick layer comprises a net, fabric, or nonwoven fabric made of organic or inorganic fiber as a major component, and is attached and fixed to the fed tape by adhesion, fusing, brazing, or welding. A heat pipe according to claim 22, characterized in that the wick layer comprises an organic or inorganic powder or particle, and is attached and fixed to the fed tape by adhesion or fusing. A heat pipe according to claim 22, characterized in that the wick layer comprises an organic or inorganic fine fiber, and is attached and fixed to the fed tape by adhesion or fusing. A heat pipe according to claim 22, characterized in that the wick layer comprises a mixture of an organic or inorganic powder and a fine fiber, and is attached and fixed to the fed tape by adhesion or fusing. A heat pipe according to claim 22, characterized in that the wick layer comprises an organic or inorganic solid linear member or powder or a combination thereof, and is attached and fixed to the fed tape by spraying. A heat pipe according to claim 22, characterized in that the bulge portions extend helically in the longitudinal direction of the pipe. A heat pipe according to claim 22, characterized in that the bulge portions extend in a straight manner in the longitudinal direction of the pipe. A heat pipe according to claim 22, characterized in that the bulge portions extend in a ring form in the longitudinal direction of the pipe. A heat pipe according to claim 31, characterized in that the helicoid of the bulge portions has a constant pitch. A heat pipe according to claim 33, characterized in that the ring form of the bulge portions has a constant pitch. A heat pipe according to claim 22, characterized in that the maximum width of each of the bulge portions differs from that of the respectively adjacent bulge portions.

Inventors: MASHIKO KOUICHI, MOCHIZUKI MASATAKA, OKIAI RYUICHI, SAKAYA MASUJI, MASHIKO, KOUICHI, MOCHIZUKI, MASATAKA, OKIAI, RYUICHI, SAKAYA, MASUJI
Applicants: FUJIKURA LTD, FUJIKURA LTD.
Application year: 1988
Main classification: F28D15
IPC codes: F28D15