CORRUGATED HEAT PIPE

Abstract: A corrugated heat pipe (1) sealed at both ends is disclosed, having a longitudinally corrugated peripheral wall (101) and containing operating liquid (102) therein. The corrugated heat pipe (1) comprises inside a rope-like tension member (2) extending therethrough in its longi­ tudinal direction and secured at both ends. The rope-­ like tension member (2) has the effect of preventing the corrugated heat pipe (1) from elongation due to the weight thereof when the pipe (1) is inserted in the ground (100), thus eliminating the possibility of local flattening of the corrugated outer periphery or of breakage of the pipe (1). Further, even when the coefficient of thermal expansion of the rope-like tension member (2) differs from that of the corrugated heat pipe (1), since the corrugated heat pipe (1) has its outer periphery corrugated in a wavy form in the longitudinal direction, it can sufficiently absorb the thermal expansion of the rope-like tension member (2). Thus, the corrugated heat pipe (1) will not be broken, even when the coefficient of thermal expansion of the corrugated heat pipe (1) differes from that of the rope-like tension member (2).

Description: This invention relates to a corrugated heat pipe according to the precharacterizing part of claim 1. Such a heat pipe is disclosed in JP-A-59 77 292. Heretofore, a corrugated heat pipe is used to conduct terrestrial heat onto the ground surface from hot water in the ground by heat conduction, without depriving the ground of hot water or steam. Several tens or hundreds rigid heat pipes of steel or alloy steel, each, for example of 10 m long are laid out at the installation site and connected one by one, using male and female screws, to obtain a single long heat pipe which is then inserted in the ground. A pipe having this structure can sufficiently withstand the hanging load and also radial pressure externally applied to it is the depth of the ground. This method of installation, however, has problems as regards operability. The operation performed when the pipes are connected on the installation site encounters great difficulties depending on status and evironments of the installation site. Nevertheless, the installing method is used in which the pipes are connected on the installation site. This is because if a single long steel or alloy steel heat pipe is completed in factory, it can not be transported to the installation site, because of its size and weight. There has been a proposal for improving the operability on the site. This proposal is to provide a heat pipe having flexibility and reduced wall thickness. If a single long corrugated heat pipe having flexibility and reduced wall thickness is completed in factory, it can be readily transported to the installation site by winding it onto a drum. In addition, the flexible material is very light in weight compared to steel or alloy steel. The flexible heat pipe is used as thermal siphon and is buried in the ground by inserting it into the ground to a depth of 200 to 5,000 m. However, this method has the following problems. Since a pipe as long as several hundred to several thousand meters is buried such that it is suspended at the ground surface into the ground, it is subject to elongation due to its own weight, resulting in flattening of its corrugated outer peripheral surface or breakage of it. The flattening of the corrugated outer peripheral surface leads to fluctuations of the heat transfer characteristics in the longitudinal direction. When in the ground, the pipe is liable to be crushed due to a radial external pressure applied to it. Generally, the pipe experiences as high pressure as 0.12 bar multiplied by the depth in meters. In the depth of several thousand meters, the pipe experiences an external pressure of several hundred bar, so that it will be crushed if it has reduced wall thickness. To solve the above problems, in the case of a power cable used for a mining pit, a steel wire is wound closely helically on the entire outer periphery of the inner sheath, and the helically wound steel wire is covered by an outer sheath of vinyl or polyethylene. In this case, however, the handling of a hanger at the top of heat pipe is a very difficult operation. In addition, when the heat pipe provided with this means is insertedly buried in the ground, its flexibility is spoiled due to its very great weight. Further, the use of the vinyl or polyethylene sheath gives rise to the problems of the resistance against the terrestrial heat at high temperatures of 200 °C or above and reduction of the heat conductivity. The JP-A-59-77 292 discloses a flexible corrugated heat pipe which can freely be bent and be fitted to any place in narrow space. The heat pipe is provided with a number of metallic or plastic filaments, annularly bundled in the longitudinal direction along the inner surface of the corrugated pipe. The bundle of filaments is pressed against the pipe from its inside by the tension of spring coils and is held between the spring coils and the corrugated pipe. Insofar the spring coils are effective as a reinforcing member inside the heat pipe which is able to take over externally applied radial pressure. However, the said structure of the heat pipe is rather stiff despite its corrugation. Further, quite apparently neither the aforementioned bundle of filaments nor the said longitudinally extending coil springs do comprise the effect of a tension member, which prevents the corrugated heat pipe from elongating due to the weight thereof when the pipe is inserted in the ground. The present invention has been intended in the light of the above, and it has an object of providing a corrugated heat pipe, which can be insertedly buried in the ground without possibility of elongation due to the weight, leading to flattening of its corrugated outer periphery or its breakage. According to the invention, there is provided a corrugated heat pipe sealed at both ends, having a longitudinally corrugated peripheral wall and containing operating liquid therein, a reinforcing member therein and wick means presenting a capillarity, which corrugated heat pipe includes inside a rope-like tension member extending therethrough in its longitudinal direction and secured at both ends. The rope-like tension member constitutes a simple and clear solution of preventing the corrugated heat pipe from elongating due to the weight thereof when the pipe is inserted in the ground, thus eliminating the possibility of local flattening of the corrugated outer periphery or of breakage of the pipe. Further, even when the coefficient of thermal expansion of the rope-like tension member differs from that of the corrugated heat pipe, since the corrugated heat pipe has its outer periphery corrugated in a wavy form in the longitudinal direction, it can sufficiently absorb the thermal expansion of the rope-like tension member. In addition to the above mentioned prior art it may be referred to the heat pipe assembly of US-A-4 090 555, comprising a straight tubular container having a charge of working fluid therein, wherein the said container is affixed to a separate support structure in form of a utility pole, building pile or the like for supporting the said tubular container within the ground. There is disclosed neither the use of a corrugated heat pipe nor the aforementioned structure of a corrugated heat pipe. Rather the same applies to the flexible heat pipe of US-A-3 604 503, which also does not disclose the use of a corrugated pipe structure having a rope-like tension member therein. Further, according to a particular embodiment of the invention, the reinforcing member comprises a substantially helically wound wire provided in contact with the inner wall of the corrugated heat pipe over the entire length thereof or portions of the length. Thus, even when a radial pressure is externally applied to the corrugated heat pipe inserted in the ground, the pipe will never be crushed. The direction of the helical winding is the same as that of the helical corrugation of the heat pipe if helically corrugated. The pitch of the helical winding of the helical reinforcing wire is the same as or smaller than that of the helical corrugation of the corrugated heat pipe. With this arrangement, the flexibility of the heat pipe is not spoiled, and the pipe can sufficiently absorb the thermal expansion of the rope-like tension member. Where the direction of the helical winding of the helical reinforcing wire is opposite to the direction of the helical corrugation of the corrugated heat pipe, the helical winding of the helical reinforcing wire may have any desired pitch. In this case, effects obtainable where the helical winding of the reinforcing wire and helical corrugation of the corrugated heat pipe are in the same direction, can be obtained without the reinforcing member received in the groove of the pipe corrugation. Still further, a liquid condensate receptacle is attached on a rope-like tension member extending through the corrugated heat pipe in the longitudinal direction thereof. The liquid condensate receptacle receives liquid condensate cooled in and dropped from an upper portion of the pipe. The liquid received in the receptacle is evaporated toward the pipe upper portion. This has an effect of preventing the pipe upper portion from drying. Further, a wick presenting a capillarity is provided on the rope-like tension member extending longitudinally through the corrugated heat pipe over the entire length of the member or portions of the length. The wick can retain liquid condensate, and the retained liquid condensate is evaporated toward the pipe upper portion to prevent the pipe upper portion from drying. With respect to some other preferred embodiments of the invention it is referred to the dependent claims 6 to 13. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic sectional view showing an embodiment of the corrugated heat pipe according to the invention; Fig. 2 is a schematic sectional view, to a reduced scale, showing the corrugated heat pipe of Fig. 1 in a state mounted in an on-ground building structure; Fig. 3 is a schematic elevational sectional view showing a further embodiment of the corrugated heat pipe according to the invention; and Figs. 4 to 7 are perspective views showing respective examples of a supporting member used for the corrugated heat pipe of Fig. 3. Now, preferred embodiments of the corrugated heat pipe according to the invention will be described with reference to the accompanying drawings. Fig. 1 is a schematic sectional view showing an embodiment of the corrugated heat pipe according to the invention, and Fig. 2 shows the corrugated heat pipe of Fig. 1 in a state mounted in an on-ground structure. In Fig. 2, the inner arrangement of the corrugated heat pipe is shown in a simplified form compared to Fig. 1 for the sake of simplicity. Corrugated heat pipe 1 as shown, has flexibility, and its upper portion including a hanger portion extends on the ground. Its main portion is inserted substantially vertically in the ground 100. Usually, the corrugated heat pipe is inserted into a depth of 200 to 3000 m. The corrugated heat pipe is made of such metal as steel, copper, aluminum and stainless steel and has an inner diameter of 50 to 300 mm. Its peripheral wall 101 is wavy, i.e., corrugated, in the longitudinal direction. The corrugated heat pipe contains therein operating liquid 102, e.g., "Furon" (a trademark). The form of corrugation of peripheral wall 101 may be either helical or non-helical, e.g., bellows-like. Rope-like tension member 2, which is composed of stranded steel or like wires, is provided inside the sealed corrugated heat pipe, and extends coaxially therethrough, and its upper and lower ends are fittedly secured in center holes in upper and lower end securement members 201 and 202 provided at the upper and lower ends of the corrugated heat pipe. Actually, the ends of rope-like tension member 2 are secured to the end securement members by means of press clamping, welding, etc. The operatio of securement is done in factory. The rope-like tension member 2 may be a stranded rope of fine steel wires, a hempen rope, a stranded rope of fine plastic fibers, a stranded rope of fine carbon fibers, or the like. Upper end securement member 201 has a disk-like sealing portion having a central hole and a coaxial cylindrical boss portion also having a central hole. A portion of the rope-like tension member inserted in the central hole of the sealing portion is welded to or screwedly coupled to the same, whereby the upper end of corrugated heat pipe 1 is sealed. A portion of the rope-like tension member inserted in the central hole of the boss portion is secured to the same by means of press clamping, whereby a great hanging load of the corrugated heat pipe is supported. Upper end securement member 201 is coaxially secured by means of screwing to hanger 203. Hanger 203 is provided with hole 204 formed therein for facilitating the operation when the corrugated heat pipe is transported and installed. The lower end of rope-like tension member 2, like the upper end, is inserted in the central hole of securement member 202 and secured to lower end thereof. The lower end of the corrugated heat pipe is thus sealed. The boss portion of lower end securement member 202 is protected by cap member 205. The means of securing the upper and lower ends of rope-like tension member 2 are not limitted to the above means. Reinforcing member 3 is composed of a steel or like metal strip which is wound helically. It is mounted in contact with the inner wall of corrugated heat pipe 1 such that it will not slip down. Before it is mounted, it may be contracted by cooling, so that it may be expanded to the normal size after the mounting. It may be mounted over the entire length of the corrugated heat pipe or a portion of the length. It is effective and desired that reinforcing member 3 is used for a portion of the corrugated heat pipe inner wall which is inserted deep in the ground. Where corrugated heat pipe 1 has a helical corrugation, the pitch of helical winding of reinforcing member 3 may be equal to or smaller than the pitch of helical corrugation of pipe 1. The metal strip constituting reinforcing member 3 may have any sectional profile, e.g., a circular or angular profile, so long as the flexibility of corrugated heat pipe is not spoiled. Liquid condensate receptacle 4 is a member having a recess open upward such as a dish or a cup. It may be attached on rope-like tension member 2 by fitting its central hole thereon. Liquid condensate receptacles may have size and be used in number determined by taking the inner diameter, length and heat transport capacity of the corrugated heat pipe. Receptacle 4 may be attached on rope-like tension member 2 over the entire length thereof or a portion or portions. Further, they may be provided closely or at an interval over the entire length or a portion or portions. They may be readily attached in factory. Rope-like tension member 2 is not limitative as corrugated heat pipe support means; for instance it is possible to use like rope extending through the corrugated heat pipe. Reference numeral 5 designates a wick. It is composed of a metal net or very fine wires and provided suitably on rope-like tension member 2. It may be provided on rope-like tension member 2 over the entire length thereof or a portion or portions. Further, it may be provided closely or at an interval over the entire length or a portion or portions. Furthermore, the wick may be constituted by rope-like tension member 2 itself. Further, it may be buried in rope-like tension member 2. Further, it may be provided on a rope substituted for rope-like tension member 2 over the entire length thereof or a portion or portions. Wick 6 which is provided between the inner wall of the corrugated heat pipe and reinforcing member 3 is composed of a metal net, fine wires, etc. It may be clamped between the inner wall of corrugated heat pipe 1 and reinforcing member 3 by making use of the contact pressure therebetween. Further, very fine wires may be preliminarily wound on the metal strip of reinforcing member, and then the resultant assembly may be wound into a helical form having a predetermined number of turns, thus obtaining wick 6. Wick 6, like wick 5, may be provided on the corrugated heat pipe inner wall over the entire length thereof or a portion or portions. Evacuation/liquid supply nozzle 206 is provided for evacuating and supplying liquid to corrugated heat pipe 1. Fig. 2 shows corrugated heat pipe 1 of Fig. 1 which is secured to and supported by on-ground building structure 10. Reference numeral 11 designates a terrestrial heat conducting pipe, through which the terrestrial heat is transferred to a cooler (not shown). Reference numeral 12 designates a return pipe, through which liquid condensate produced as a result of cooling in the cooler is recirculated to corrugated heat pipe 1. Reference numeral 13 designates a branch pipe, which is used for evacuation, exhausting as well as the operation and monitoring of pressure gauges, safety valves. etc. Corrugated heat pipe 1 may be provided with local heat insulation and/or corrosion-proof or other protective treatment, if necessary. Figs. 3 illustrates a further embodiment of the invention. In this Figure, parts like or corresponding to those in the embodiment of Fig. 1 are designated by corresponding like reference numerals, and their description is omitted. In this embodiment, supporting wire 43 is used instead of the reinforcing member in the embodiment of Fig. 1. Supporting wire 43 is an elastic or rigid wire, e.g., a steel wire. It is disposed helically between and in close contact with rope-like tension member 2 and recessed inner wall portion of corrugated heat pipe 1 (i.e., valleys of corrugation when viewed from the inner side of pipe 1). More specifically, some of supporting wire 43 is helically wound on predetermined portions of rope-like tension member 2 in the longitudinal direction thereof, while the remainder is received in and held in close contact with helically recessed inner wall 51 or valleys of corrugated heat pipe 1. Wick 53 is provided on some predetermined portions of supporting wire 43. It may be provided over the entire length of supporting wire 43 or portions of the lengths. Fig. 4 shows a way of securement of wick 53. In this case, wick 53 is held secured in the recessed inner wall of the pipe by supporting wire 43. The length, for which supporting wire 43 is wound on rope-like tension member 2, and the length, for which the supporting wire is held in close contact with the helical recessed inner surface of corrugated heat pipe 2 (i.e., the product of the number n of turns in close contact and the pitch p), are suitably selected such that the weight of the corrugated heat pipe is uniformly shared by the entire supporting wire. For example, the length, for which rope-like tension member 2 is held in close contact with recessed inner wall 51 of pipe 1, may be equal to or twice the pitch of corruagation of the corrugated heat pipe. The distribution of the supporting wire is determined by taking the size (i.e., length and diameter) of corrugated heat pipe 1 and the geology and terrestrial heat temperature distribution of the place of the pipe installation into considerations. The supporting wire may be provided over the entire length of rope-like tension member 2 or portions thereof. Particularly, in the depth of the ground the supporting wire is desirably disposed collectively for a great hanging load of the pipe applied. Further, the supporting member may be mounted in factory, or it may be mounted at the installation site by preparing a simple mounting device. In this case, the supporting member may be contracted in size by cooling it before mounting it. Steam passes through gaps defined by the supporting members toward upper portion of the corrugated heat pipe, that is, without being blocked by the supporting member, so that it is possible to ensure proper function of the heat pipe. Fig. 5 shows a further example of the supporting wire. In this case, the corrugated heat pipe (not shown), with which the supporting wire is held in close contact, is corrugated bellows-like. A portion of supporting wire 43 is wound on rope-like tension member 2, while the remainder is held in a ring-like form in the recessed inner peripheral wall of the pipe. In this case, opposite end portions C and D of a turn of supporting wire 43 are found at the same position in the direction of extension of the rope-like tension member. In this case, the method of mounting and distribution of the supporting wire may be the same as described before in conjunction with Figs. 3 and 4. Reference numeral 54 designates a supporting plate. Fig. 6 shows supporting plate 54. It is substantially disk-like, and is formed from a metal plate, a plastic plate, etc. It has notch 61. Rope-like tension member 2 is closely fitted in inner end 62 of notch 61, whereby the supporting plate is held in position without possibility of slide-down. Supporting plate 54 has a helical outer periphery, which is received and held in close contact with helical recessed inner wall of tee corrugated heat pipe (not shown). As shown in Fig. 6, the outer periphery of supporting plate 54 is inclined helically so that opposite ends A and B of notch 61 are spaced apart by a distance equal to the pitch P of the helical corrugation of the corrugated heat pipe. Supporting plate 54 is provided with holes 64 formed therein to permit passage of steam. Holes 64 may have any suitable shape, e.g., circular, oval, flaring, etc. The method of mounting and distribution of supporting plates 54 may be the same as for supporting wire 43 in the case of Figs. 4 and 5. Fig. 7 shows a different example of supporting plate. This supporting plate is provided in a corrugated heat pipe having a bellows-like corrugation (not shown). This example of supporting plate 75 is like a flat disk having notch 81. Rope-like tension member 2 is closely fitted in end 82 of supporting plate 75. The outer periphery of supporting plate 75 is closely mounted in a recessed inner peripheral wall of pipe. In this case, opposite ends E and F of notch 81 of supporting plate 75 are not spaced apart but at the same position in the direction of extension of the rope-like tension member. Supporting plate 75 has holes 84 for permitting passage of steam. Holes 84 may have any suitable shape as in the case of Fig. 6. Inside corrugated heat pipe 1, liquid condensate receptacle 4 having a recess open upward, e.g., like a cup or a dish, is attached on rope-like tension member 2. Further, wick 302 is attached on tension-resistant rope 2. The rope-like tension member itself may serve as wick instead of particularly providing wick 302. Further. the inner peripheral wall of pipe is provided with wick 53. In the above embodiment provided with the supporting member, there will hardly occur a slip-down between the corrugated heat pipe and supporting member due to thermal expansion. Liquid condensate will drop on the supporting member and temporarily retained on this part. The retained or collected liquid on the supporting member is evaporated toward upper portion of the pipe. This has an effect of preventing the upper portion of the pipe from drying. Reference numeral 206 designates an evacuation/liquid supply nozzle for evacuating and supplying liquid to corrugated heat pipe 1. The corrugated heat pipe, of course, is further provided with other, usually used accessory devices, e.g., a terrestrial heat conducting pipe, a liquid return pipe, branch pipes, etc. Further, corrugated heat pipe 1 is supported, if necessary, by an on-ground building structure, and also it may be partly provided with heat insulation, corrosion-proof and other protective treatments. While the above embodiments have concerned with cases where the corrugated heat pipe according to the invention is inserted vertically in the ground. This is, however, by no means limitative. For example, the corrugated heat pipe may be installed in the sea, or it may be installed such that it is inclined with respect to the ground surface. For example, where there is an obstacle in the ground, it may be installed in an inclined state to avoid such obstacle. Further, it may be installed horizontally. Where the corrugated heat pipe is installed horizontally, when a force of longitudinal thermal expansion is exerted, the rope-like tension member has an effect of preventing the corrugated heat pipe from elongaing and thus deforming. Thus, it is possible to maintain satisfactory heat transfer characteristics. As has been described in the foregoing, according to the invention it is possible to provide an elongate heat pipe, which can be readily transported. This elongate heat pipe can preclude low operability works on the installation site. Further, the elongate heat pipe may be factory provided with various components. With the functions of these components, it is possible to prevent the pipe from elongating due to the weight thereof, particularly prevent the pipe from crushing due to high radial external pressure applied to its portion extending deep in the ground, and also prevent an upper portion of the pipe from drying owing to positive promotion of evaporation by the liquid condensate receptacle, wick and other parts. Further, on the installation site, it is only necessary to insert and hang the corrugated heat pipe in a pit in the simplest case.

Claims: A corrugated heat pipe (1) sealed at both ends, having a longitudinally corrugated peripheral wall (101) and containing operating liquid therein, a reinforcing member (3; 43; 54; 75) therein, and having wick means (5) presenting a capillarity, characterized in that said corrugated heat pipe (1) comprises inside a rope-like tension member (2) extending therethrough in its longitudinal direction and secured at both ends. A corrugated heat pipe (1) according to claim 1, characterized in that said reinforcing member comprises a substantially helically wound wire (3) provided on its inner peripheral wall surface, along the entire length thereof or a portion of the length. The corrugated heat pipe (1) according to claim 2, characterized in that the direction of the helical winding of said wire (3) being the same as that of the corrugation of said corrugated heat pipe (1), and the pitch of the helical winding of said wire (3) being the same as that of the corrugation of said corrugated heat pipe (1). The corrugated heat pipe (1) according to claim 2, characterized in that said wire (3) is helically wound in the opposite direction to the direction of the helical corrugation of said corrugated heat pipe (1). A corrugated heat pipe (1) according to any of the claims 1 to 4, characterized in that liquid condensate receptacle means (4) are attached on the rope-like tension member (2) at least at one position thereof. A corrugated heat pipe (1) according to any of the claims 1 to 5, characterized in that said wick means (5) are provided on at least a portion of the rope-like tension member (2). A corrugated heat pipe (1), according to any of the claims 1 to 5, characterized in that said wick means (6) are provided between the reinforcing member (3) and its inner peripheral wall surface. The corrugated heat pipe (1), according to claim 1, characterized in that said reinforcing member is a wire-like member (43) having a portion secured to said rope-like tension member (2) and an extending portion received in and secured to a recessed inner wall portion of said corrugated heat pipe (1). The corrugated heat pipe (1), according to claim 8, characterized in that said extending portion of the wire-like member (43) is received helically in and secured to a helical recessed inner wall portion of said corrupted heat pipe (1). The corrugated heat pipe (1), according to claim 8, characterized in that said wire-like member (43) has an extending portion in a ring-like form in and secured to a bellows-like recessed inner wall portion of said corrugated heat pipe (1). The corrugated heat pipe (1) , according to claim 1, characterized in that said reinforcing member (54, 75) is a substantially disk-like member (75) having a notch (81), said rope-like tension member (2) being fittedly held in said notch (81), the outer periphery (83) of said disk-like support member (75) being received in a recessed inner wall portion of said corrugated heat pipe (1). The corrugated heat pipe (1), according to claim 11, characterized in that the outer periphery (64) of said disk-like support member (54) being received helically in a helical recessed wall portion of said corrugated heat pipe (1). The corrugated heat pipe (1), according to claim 11, characterized in that the outer periphery (83) of said disk-like support member (75) being received in ring-like form in a bellows-like recessed inner wall portion of said corrugated heat pipe (1).

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