Variable Conductance Heat Pipe

Abstract

A variable conductance heat pipe is provided. The variable conductance heat pipe includes a sealed container in which a working fluid and a noncondensable gas are sealed, the sealed container extending in an axial direction. The sealed container includes one end to be connected to a heating source and a part to be connected to a heat sink. On a cross section of the sealed container along a direction orthogonal to the axial direction, a portion having water conveying property better than other portions is provided. The portion having the better water conveying property extends in the axial direction.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from Japanese Patent Application No. 2008-219549, filed on Aug. 28, 2008, the entire subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a cooler for controlling the temperature of an electronic equipment and more particularly to a cooler which employs a variable conductance heat pipe.

[0004] 2. Description of the Related Art

[0005] In a related-art electronic equipment cooler, in order to obtain a desired function in a stable manner, it has been regarded important to cool the electronic equipment to a temperature equal to or lower than its permissible temperature. Although as coolers for electronic equipment, radiational cooling type, natural air cooling type, forced air cooling type, liquid cooling type and boiling cooling type coolers have been used, in recent years, heat pipes have also been used in many cases. These coolers have thermal resistances which are specific thereto. When the coolers are actually used, as the heating amount of electronic equipment increases or as the ambient environmental temperature increases, the temperature of the electronic equipment increases, whereas the flow rate of a cooling medium (such as air, water or the like) which flows through a heat radiating or radiating portion increases, the temperature of the electronic equipment decreases. Consequently, the temperature of the electronic equipment varies as the operating factor or environmental factor varies, and it is inevitable in practice that a heat cycle occurs. This heat cycle generates an inner stress attributed to a difference in linear expansion coefficient between respective materials which make up the electronic equipment, which causes a failure of the electronic equipment, that is, shortens the life of the electronic equipment.

[0006] In view of the above-described background, in order to extend the life of electronic equipment, coolers which can suppress the heat cycle has been required, and as one of such cooling equipment, there has been proposed a variable conductance heat pipe in which a noncondensable gas such as helium, argon, nitrogen or the like is put in an interior of the heat pipe (for example, JP-A-10-122775 (page 2, FIG. 1)).

[0007] In such a variable conductance heat pile, although a working fluid (liquid and vapor) and a noncondensable gas are sealed in an interior of a sealed container which is made up of a heat receiving portion, a heat insulating portion (a transport portion), a heat radiating portion and a gas reservoir, since the variable conductance heat pipe takes various postures during production, storage, transportation and installation, the working fluid flows into an interior of the gas reservoir, or the working fluid flows into the interior of the gas reservoir due to a drastic change in temperature. Accordingly, the working fluid does not always reside within the heat receiving portion, which causes a problem with the stable actuation and stable operation of the variable conductance heat pipe. Therefore, it has been difficult to mass produce variable conductance heat pipes.

SUMMARY OF THE INVENTION

[0008] According to an aspect of the invention, there is provided a variable conductance heat pipe comprising a sealed container in which a working fluid and a noncondensable gas are sealed, the sealed container extending in an axial direction, the sealed container including one end to be connected to a heating source and a part to be connected to a heat sink, wherein, on a cross section of the sealed container along a direction orthogonal to the axial direction, a portion having water conveying property better than other portions is provided, and wherein the portion having the better water conveying property extends in the axial direction.

[0009] According to the above-configuration, irrespective of conditions of the variable conductance heat pipe during storage, transportation and installation, the stable actuation and stable operation thereof can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments of the present invention will be described in detail based on the following figures, wherein:

[0011] FIG. 1 is a schematic sectional view showing a main part of a variable conductance heat pipe according to Embodiment 1 of the invention;

[0012] FIG. 2 is a schematic sectional view showing a main part of a related-art variable conductance heat pipe;

[0013] FIG. 3 is a schematic sectional view which describes the operation of the variable conductance heat pipe according to Embodiment 1 of the invention;

[0014] FIGS. 4A to 4C are sectional views showing modified examples to the variable conductance heat pipe according to Embodiment 1 of the invention;

[0015] FIG. 5 is a schematic sectional view showing a main part of a variable conductance heat pipe according to Embodiment 2 of the invention;

[0016] FIG. 6 is a schematic sectional view showing a modified example of an insertion member to that of Embodiment 2 of the invention;

[0017] FIG. 7 is a schematic sectional view showing a main part of a modified example to the variable conductance heat pipe according to Embodiment 2 of the invention;

[0018] FIG. 8 is a diagram showing an example of an insertion member according to Embodiment 2 of the invention;

[0019] FIG. 9 is a schematic sectional view showing a main part of another modified example to the variable conductance heat pipe according to Embodiment 2; and

[0020] FIG. 10 is a schematic sectional view showing an insertion member according to Embodiment 3 of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1

[0021] FIG. 1 is a sectional view showing a variable conductance heat pipe according to Embodiment 1 of the invention. In the figure, a left-hand part is a sectional view including an axis of a sealed container which makes up the variable conductance heat pipe and a right-hand part shows a section taken orthogonal to the axis, that is, an enlarged sectional view taken along the line A-A. From one end portion, a sealed container 1 includes a heat receiving portion 2 (an evaporating portion), a heat insulating portion 3 (a transporting portion), a heat radiating portion 4 (a condensing portion) and a noncondensable gas reservoir portion 5. A working fluid (a liquid 6 and vapor 7 thereof) and a noncondensable gas 8 are sealed in an interior of the sealed container 1. As shown in the enlarged sectional view taken along the line A-A, irregularities are provided partially on an inner wall of the sealed container 1, and the irregularities extend in an axial direction of the sealed container 1. The heat receiving portion 2 contacts (is connected to) a heating source 9 and the heat radiating portion 4 contacts (is connected to) a heat sink 10, whereby heat is transmitted from the heating source 9 whose temperature is high to the heat receiving portion 2 and is transmitted further to the liquid 6 residing within the heat receiving portion 2. The heat transmitted to the liquid 6 is absorbed by the liquid 6 in the form of latent heat or the liquid 6 is evaporated or boiled, whereby vapor 7 is generated, and the vapor 7 or the vapor 7 and the liquid 6 flow into the heat radiating portion 4 via the heat insulating portion 3, where latent heat possessed by the vapor 7 is emitted to the heat radiating portion 4 while the vapor 7 is condensed, the heat so emitted being radiated to the heat sink 10 whose temperature is lower than that of the heat radiating portion. As this occurs, the condensed liquid (the liquid 6) which is generated by the vapor 7 being condensed is returned to the heat receiving portion 2 from the heat radiating portion 4 via the heat insulating portion 3 by virtue of gravity or capillary force. Heat generated in the heating source 9 is transmitted (discharged) continuously to the heat sink 10 by circulation of these vapor 7 and liquid 6. On the other hand, the noncondensable gas 8 sealed within the interior of the sealed container 1 is caused to move to the noncondensable gas reservoir portion 5 or a portion of the heat radiating portion 4 which lies to face the noncondensable gas reservoir portion 5 via the heat insulating portion 3 and the heat radiating portion 4 as the vapor 7 or the vapor 7 and liquid 6 move and is accumulated to be retained therein. In the event that the noncondensable gas 8 so stays, the vapor 7 is made difficult to enter the noncondensable gas 8, thereby an interface 11 being formed between the vapor 7 and the noncondensable gas 8. The vapor 7 pushes the noncondensable gas 8 continuously, whereby the interface is caused to move, and the pressures of the vapor 7 and the noncondensable gas 8 reach an equilibrium state, whereupon the interface 11 stops moving, and its position is stabilized. Consequently, when the interface 11 reaches to be positioned in the noncondensable gas reservoir portion 5, since the vapor 7 is condensed over the whole heat radiating portion 4, a heat radiation capability of 100% can be obtained, while when the interface 11 is positioned within the heat radiating portion 4, since the area over which the vapor 7 is condensed (the heat radiating area) is reduced, the heat radiating capability decreases (the heat radiating capability is variable such that 0<heat radiating capability <100%). In addition, when the interface 11 is positioned within the heat insulating portion 3 or the heat receiving portion 2, heat can be insulated (the heat radiating capability becoming 0%. However, since part of heat is caused to move by conduction of heat which is transmitted through the wall of the sealed container 1, in reality, although it is not large, there is a capability of radiating heat. The description of the operation of the variable conductance heat pipe that has been made heretofore is based on the operation principle of the variable conductance heat pipe.

[0022] The variable conductance heat pipe is configured such that three types of fluids such as liquid, vapor and noncondensable gas are sealed in the interior of the sealed container 1. Although the noncondensable gas preferably stays within the interior of the noncondensable gas reservoir portion 5 in principle, in reality, the vapor and noncondensable gas stay therein in a mixed manner due to molecular diffusion. In addition, when looking at the molecular weights of gases which can be used as a noncondensable gas, the molecular weight of neon is 20, nitrogen is 28, and argon is 40. In the event that for example, water is used as a working fluid, the molecular weight of water is 18, which is lighter than those of the gases which can be used as the noncondensable gas, and therefore, it becomes easy for the noncondensable gas 8 to stay in the heat receiving portion 2 which is normally placed in the lower position as a result of the effect of gravity, whereas it becomes easy for the vapor 7 to stay in the noncondensable gas reservoir portion 5 which is normally placed in the upper position. Further, due to the fact that the vapor may be condensed within the interior of the noncondensable gas reservoir portion 5 or the liquid may flow into the interior of the noncondensable gas reservoir portion 5 via the heat radiating portion 4, in reality, there may be such a case that the aforesaid three types of fluids coexist within the noncondensable gas reservoir portion 5. These facts of the noncondensable gas tending to stay in the heat receiving portion 2 and the liquid, vapor and noncondensable gas tending to coexist in the noncondensable gas reservoir portion 5 do not cause any particular problem with the storage, transportation and installation of the variable conductance heat pipe. However, in actually actuating and operating the variable conductance heat pipe as a heat radiating device, due to the liquid residing in the interior of the noncondensable gas reservoir portion 5, there occurs a shortage of liquid in the interior of the heat receiving portion 2, and the interior of the heat receiving portion 2 is caused to be dried out, causing a problem of thermorunaway of the temperature within the heat receiving portion 2. Consequently, the variable conductance heat pipe must have the configuration in which the liquid residing in the interior of the noncondensable gas reservoir portion 5 always returns to the heat receiving portion 2 whenever the variable conductance heat pipe is put in use.

[0023] In a variable conductance heat pipe shown in FIG. 2 which has the related-art configuration (whose difference from the configuration according to Embodiment 1 will be described later), however, in the event that a sealed container 1 is thin, when liquid exists at an end portion of the sealed container 1, the liquid so staying is made difficult to flow downwards by a capillary force acting on a gas-liquid interface 14 which makes up a boundary between a gas section 12 which contains vapor and a noncondensable gas and a liquid section 13 in which liquid stays. In addition, as shown in FIG. 2, when the end portion of the sealed container 1 is filled with liquid, in the case of a normal heat pipe which employs no noncondensable gas, since the liquid at the end portion of the sealed container 1 is turned into vapor to be expanded, the liquid is made easy to move. However, in the case of the variable conductance heat pipe, since the noncondensable gas resides in the gas section 12, the internal pressure in the gas section 12 is not so small that the liquid at the end portion of the sealed container 1 is turned into vapor, and even though the liquid attempts to move towards the direction of the heat receiving portion 2, no gas (condensable fluid, that is vapor) is generated at the end portion of the sealed container 1 (vapor is attached to the end portion of the sealed container 1 due to vacuum), and therefore, it becomes difficult for the liquid to move as required. Further, in the event that the liquid attempts to move, in the case of the normal heat pipe which employs no noncondensable gas, there is produced a state in which the pressure within the gas section 12 is not increased while the vapor in the interior of the gas section 12 is being condensed. However, in the case of the variable conductance heat pipe, since the pressure within the gas section 12 is increased due to the noncondensable gas existing therein, the movement of the liquid is interrupted. Because of this, there is the possibility that the liquid within the heat receiving portion 2 to short, and the variable conductance heat pipe cannot be activated to operate properly as a result that the liquid is liable to stay in the noncondensable gas reservoir portion 5.

[0024] Hereinafter, the configuration and operation of Embodiment 1 will be described in detail by the use of FIG. 3. As shown in an enlarged sectional view taken along the line A-A in FIG. 3 (also in the enlarged sectional view taken along the line A-A in FIG. 1), in the variable conductance heat pipe of Embodiment 1, a portion 15 having water conveying property better than other portions is provided within the cross section of the sealed container. Specifically, the portion 15 having the better water conveying property than other portions 16 is formed by providing irregularities partially on an inner wall of the sealed container 1 in a circumferential direction as viewed in cross section thereof in such a manner that recessed portions and raised portions extend in an axial direction (a direction in which liquid and vapor move) of the sealed container. Due to the non-uniformity in water conveying property in the circumferential direction, a dome-shaped liquid-liquid interface 11 like one shown in FIG. 1 is not formed for some reason, and in the event that a liquid 6, that is, a liquid section 13 exists in the vicinity of the noncondensable gas reservoir portion 5 as shown in FIG. 3, the portion 15 having the better water conveying property forms a non-uniform configuration (a configuration that is not axisymmetric) where liquid sags and runs partially. This liquid sagging and running portion preferentially moves the liquid 6, and a gas section 12 and the liquid section 13 are switched over without causing any pressure increase within the gas section 12, whereby the liquid 6 moves to the heat receiving portion 2, thereby allowing the variable conductance heat pipe to operate properly.

[0025] On the other hand, the same advantage can also be provided in the heat receiving portion 2. In the variable conductance heat pipe having the related-art configuration as shown in FIG. 2 in which no treatment or machining is applied to the inner wall of the sealed container 1 so as to have the uniform water conveying property along the circumferential direction, due to the configuration inherent therein, the heat receiving portion 2 is not always filled with the liquid, and in the event of a worst case, there is a possibility that the heat receiving portion 2 is filled with the noncondensable gas. In the event that the heat receiving portion 2 is filled with the noncondensable gas, even though the liquid attempts to flow into the heat receiving portion 2 from the heat radiating portion 4, a gas-liquid interface 17 is formed between the noncondensable gas and the liquid as shown in FIG. 2, and a uniform capillary force is generated within the cross section of the heat receiving portion 2 in the position where the gas-liquid interface 17 is so formed, whereby the heat receiving portion 2 is closed by the liquid which functions as a lid thereon. When the heat receiving portion 2 is heated, the noncondensable gas in the interior of the heat receiving portion 2 expands, whereby the gas-liquid interface 17 is caused to move towards the heat insulating portion 3. As this occurs, unless liquid exists in the interior of heat receiving portion 2, the proper heat transport that has been described above is not performed, and the temperature within the heat receiving portion 2 is increased. As a result, since no liquid flows into the heat receiving portion 2, the normal operation of the variable conductance heat pipe is not attained. On the other hand, in the configuration of the variable conductance heat pipe according to Embodiment 1 shown in FIG. 3 (also in FIG. 1), being different from the related-art configuration shown in FIG. 2, since the portion 15 having the better water conveying property exists partially in the circumferential direction within the heat receiving portion 2 as viewed in cross section thereof, as in the case of liquid residing in the noncondensable gas reservoir portion 5, a dome-shaped gas-liquid interface 17 as one shown in FIG. 2 is not formed due to the non-uniformity in water conveying property in the circumferential direction, and the portion 15 having the better water conveying property forms a non-uniform configuration (a configuration that is not axisymmetric) where liquid sags and runs partially. This liquid sagging and running portion preferentially moves the liquid, whereby the liquid is caused to move to a distal end of the heat receiving portion 2. By the liquid which has flowed into the distal end of the heat receiving portion 2 being evaporated or boiled by being subjected to heat from the heating source 9, vapor is generated, which sends out the noncondensable gas which is staying in the heat receiving portion 2 to the heat insulating portion 3, and the noncondensable gas dispersed within the sealed container 1, in particular, the noncondensable gas residing in the interior of the heat receiving portion 2 is caused to move to the noncondensable gas reservoir portion 5 for accumulation therein by the action of the variable conductance heat pipe itself, so that the liquid can be continuously supplied to the heat receiving portion 2, and vapor can be continuously let out from the heat receiving portion 2, thereby making it possible to make stable the operation of the variable conductance heat pipe.

[0026] In addition to those shown in FIGS. 1 and 3, the portion 15 having the better water conveying property can be realized by deforming part of the inner wall of the sealed container 1 as viewed in cross section into an unsmoothed configuration (a configuration having a bent point as viewed in cross section, a configuration having a point angled at an angle of 180 degrees or larger or 180 degrees or smaller as viewed in cross section), or such configurations as a teardrop configuration shown in FIG. 4A, a gourd-like configuration shown in FIG. 4B, and a configuration shown in FIG. 4C in which there are provided a plurality of wedge-shaped flow paths. Further, the portion 15 having the better water conveying property can also be realized by applying a treatment for improving the water conveying property to part in the circumferential direction of the inner wall of the sealed container 1 as viewed in cross section which includes a treatment in which part of the inner wall is made to differ from the other portions thereof in terms of hydrophilic nature, for example, a treatment in which the surface roughness of the inner wall is partially roughened, a treatment in which a UV treatment (surface activation), oxidation treatment or ozonization treatment is applied to part of the inner wall, and a treatment in which a water repellent film is affixed to part of the inner wall.

[0027] The heating source 9 of Embodiment 1 may be such that heat can be applied to the heat receiving portion 2 thereby, and there is imposed no limitation on its dimensions and configuration. The heating source 9 may be made up of a heating portion of electronic equipment, a heater, a solid such as a heat radiating portion of a heat transport device, a heat pump or a heat exchanger, or a fluid such as a highly heated liquid and a highly heated gas. In addition, the heating source 9 may also be made up of an object which can apply heat to the heat receiving portion 2 through radiation, including the sun, a highly heated object and the like.

[0028] On the other hand, the heat sink 10 may be such that heat can be received thereby from the heat radiating portion 4, and there is no limitation on its dimensions and configuration. The heat sink 10 may be made up of a fluid such as water and air or a solid such as a heat receiving portion of a heat transport device, a heat pump or a heat exchanger, soil, and a structure. In addition, the heat sink 10 may also be made up of a substance lying far which can be reached by making use of radiation.

[0029] The sealed container 1 is an airtight container which stores liquid, vapor and noncondensable gas therein and may preferably be made of a metal which does not induce any chemical reaction between liquid and vapor and the inner wall of the sealed container 1. For example, in the case of water being used as the liquid, copper is preferably used as a material for the sealed container 1, and in the case of ammonia water being used as the liquid, it is recommendable to use a material such as aluminum or stainless steel which does not produce a noncondensable gas through a chemical reaction with the ammonia water as a material for the sealed container 1.

[0030] The heat from the light source 9 is applied to and received by the heat receiving portion 2 and has a function to conduct the heat to the liquid. In addition, the heat receiving portion 2 may have a structure (a porous material or a configuration provided on the surface by which vapor is trapped) which promotes the boiling of the liquid within in the heat receiving portion 2 provided on an inner surface thereof.

[0031] The heat insulating portion 3 is a passage through which the liquid, the vapor and the noncondensable gas move. The heat insulating portion 3 may have its periphery exposed to a fluid such as air or brought into contact with a structure to radiate heat thereto. On the contrary, the heat insulating portion 3 may have a heat insulating material provided thereon to insulate itself against the loss of heat. The heat radiating portion 4 has a function to get vapor condensed to be liquefied and radiate latent heat emitted at that time to the heat sink 10. As shown in FIGS. 1 and 3, fins may be provided on an outer circumferential surface of the heat radiating portion 4 in such a manner as to increase its heat conducting surface in order to promote the radiation of heat to the heat sink 10. It is noted that as has been described above, there may be a case where the gas-liquid interface 15 is produced to be positioned in the interiors of the heat insulating portion 3 and the heat radiating portion 4, and part of the gas-liquid interface 15 so positioned plays a role of a passage or a container which accommodates the noncondensable gas therein.

[0032] The noncondensable gas reservoir portion 5 has a function to accommodate the noncondensable gas therein. There may be a case where the noncondensable reservoir portion 5 accommodates therein the liquid, vapor and noncondensable gas when the variable conductance heat pipe is not in operation. The noncondensable gas reservoir portion 5 is provided at an end portion of the variable conductance heat pipe which lies farthest from the heat receiving portion 2 with respect to the fluid passageway of the variable conductance heat pipe. Preferably, a configuration may be adopted in which the noncondensable gas reservoir portion 5 is provided at an uppermost portion of the constituent part of the variable conductance heat pipe, so that the liquid that has flowed thereinto is allowed to flow downwards.

[0033] The liquid is a liquid which can boil, evaporate and condense and may consist of a single-component fluid such as water and ammonia or a multi-component fluid such as an anti-freeze. The vapor is a gas resulting from vaporization of the liquid or part thereof. The noncondensable gas is a gas which does not condense in the working environment, and under the normal environment, helium, argon, neon and nitrogen is used as the noncondensable gas. Preferably, the noncondensable gas is a gas which does not chemically react with the material of the sealed container 1, the liquid, and the vapor, and an inactive gas is further preferably used. In addition, a non-condensable gas may be used which is generated by challengingly causing the sealed container 1 to react with the liquid in an initial stage of sealing the liquid, vapor and noncondensable gas into the sealed container 1.

Embodiment 2

[0034] FIG. 5 is a sectional view showing schematically a variable conductance heat pipe according to Embodiment 2. This variable conductance heat pipe is configured such that an insertion member 19 is inserted into an interior of the variable conductance heat pipe having the related-art configuration as shown in FIG. 2. The interior of a sealed container 1 is divided into a flow path 20 having a larger cross-sectional area and a flow path 21 having a smaller cross-sectional area by the insertion member 19, and a gas-liquid interface is formed in each of those flow paths. In addition, the larger cross-sectional area flow path 20 and the smaller cross-sectional area flow path 21 have openings 18, and since these openings 18 are made to extend continuously in an axial direction (there will be no problem even in case there are partially discontinued portions, that is, portions where the insertion member 19 and an inner wall of the sealed container 1 contact each other), the openings 18 function as noncondensable gas discharge passages and circumferential liquid suction ports. A smaller capillary force is generated in the gas-liquid interface in the larger cross-sectional area flow path 20, and a larger capillary force is generated in the gas-liquid interface in the smaller cross-sectional area flow path 21, whereby a non-equilibrium state of capillary force is produced within the flow paths in the same cross section. Consequently, a liquid staying at an end portion of the sealed container 1 moves towards the larger capillary force flow path 21 (a gas-liquid interface 14 within the flow path 21 moves towards a heat receiving portion 2), and a gas-liquid interface in the smaller capillary force flow path 20 moves towards the end portion of the sealed container 1. Namely, the smaller cross-sectional area flow path 21 configures a portion which has water conveying property better than those of the larger cross-sectional area flow path 20 and configures a passage through which the liquid flows. By this configuration, when the variable conductance heat pipe is in operation, the same operating conditions as those described in Embodiment 1 are produced in which an appropriate amount of water exists within the heat receiving portion 2, thereby making it possible to establish stable actuation and operation of the variable conductance heat pipe.

[0035] On the other hand, the same advantage is also provided in the interior of the heat receiving portion, and being different from the variable conductance heat pipe having the related-art configuration which is shown in FIG. 2, an insertion member 19 is mounted within a heat receiving portion 2, so that the interior of the heat receiving portion 2 is divided into a flow path 20 having a larger cross-sectional area and a flow path 21 having a smaller cross-sectional area, whereby a non-equilibrium state of capillary force is produced within the flow paths in the same cross section. Consequently, the flow path 21 having a larger capillary force is filled with a liquid 6 (a distal end of the heat receiving portion 2 contacts the liquid 6), while a noncondensable gas stays within the flow path 20 having a smaller capillary force. In If the variable conductance heat pipe operates, when heat is applied to the heat receiving portion 2, due to the liquid being made to contact the distal end of the heat receiving portion 2, vapor is generated from an end portion of the heat receiving portion 2, and when the vapor so generated is caused to move to a heat radiating portion 4 via a heat insulating portion 3, the noncondensable gas staying in the flow path 20 is caused to move towards a noncondensable gas reservoir portion 5. In this way, the noncondensable gas which is being dispersed within the sealed container 1, in particular, the noncondensable gas residing in the interior of the heat receiving portion 2 is caused to move to the noncondensable gas reservoir portion 5 to be accumulated therein by the operation of the variable conductance heat pipe itself, whereby the liquid can be supplied to the heat receiving portion 2 continuously and the vapor can be sent out continuously from the heat receiving portion 2, thereby making it possible to make stable the operation of the variable conductance heat pipe.

[0036] The insertion member 19 only has to be inserted into the interior of the sealed container 1 in such a manner that the non-equilibrium state of capillary force is formed within the same cross section of the sealed container 1, that an exclusive passage for the liquid 6 is provided in such a manner as to extend along the inner wall of the sealed container 1, and that the insertion member 19 has openings 18 which extends axially along the full length or part of the exclusive passage to function as noncondensable gas discharge passages and circumferential liquid suction ports, and the insertion member 19 may be made up of a board which is inserted eccentrically into the sealed container 1. It is noted that in the event that an exclusive passage for the liquid 6 which does not have the openings 18 is provided in the cross section of the sealed container 1 in such a manner as to completely partition the cross section, the noncondensable gas flows into in an interior of the exclusive passage to stay therein so as to produce a gas-liquid interface between the liquid and the noncondensable gas within the exclusive passage, whereby the liquid 6 cannot flow through the exclusive passage due to a capillary force acting on the interface, and consequently, the variable conductance heat pipe becomes out of operation.

[0037] It is noted that while in FIG. 5, the board-like material having a concave surface is shown as the configuration of the insertion member 19, the insertion member 19 may be made up of a flat board-like material or may be made up of a material such as a piece of punched sheet metal or a wire mesh. Further, as the cross-sectional configuration of the insertion member 19, a V-shape configuration like one shown in FIG. 6 or a W-shape configuration may be adopted. In the case of these V-shape and W-shape configurations being adopted, there is provided an advantage that once inserted into the sealed container 1, the insertion member 19 is fixed in place and is made stationary. In this way, as long as the interior of the sealed container 1 is divided into the larger cross-sectional area flow path 20 and the smaller cross-sectional area flow path 21 which have the openings 18, as the cross-sectional configuration of the insertion member 19, any configuration may be adopted.

[0038] Further, while in FIG. 5, the sealed container 1 is illustrated as being made up of a straight tube, as shown in FIG. 7, the sealed container 1 may be bent at one end portion thereof so as to provide a bent portion somewhere along the length of the heat insulating portion 3. In this case, there is provided an advantage that once inserted into the interior of the sealed container 1, the insertion member 19 is fixed in place so as to be stationary therein. In addition, as shown in FIG. 8, a board-like material having a portion where its width is expanded at an intermediate position along the length thereof may be used as the insertion member 19, and in the event that the board-like material is inserted into the interior of the sealed container 1 in such a manner that the width expanded portion is positioned somewhere in the bent portion, there is provided an advantage that the insertion member is fixed in place. This insertion member 19 which has the configuration in which the intermediate portion is expanded in width is, needless to say, advantageous not only in the sealed container 1 having the bent portion shown in FIG. 7 but also in the straight tube shown in FIG. 3. Further, by bending or curving the width expanded portion of the insertion member 19 which is provided in the intermediate position thereof, there is provided an advantage, particularly when the insertion member 19 is inserted into the straight tube, that the insertion member 19 can be fixed in the eccentric position within the sealed container 1 in an ensured manner. In addition to the modified configurations of the insertion member 19, normally adopted various configuration can be adopted as the configuration in which the insertion member 19 is fixed in the eccentric position which include a configuration in which as shown in FIG. 9, the insertion member 19 can be inserted eccentrically into the sealed container 1 while being bent at end portions thereof, or the insertion member 19 is inserted to stay in the eccentric position within the sealed container 1 with a spacer or spacers which are disposed separately (to keep the insertion member 19 separate from the inner wall of the sealed container 1).

Embodiment 3

[0039] FIG. 10 is an enlarged cross-sectional view showing a cross section taken orthogonal to an axis of a variable conductance heat pipe according to Embodiment 3 of the invention. A rod 19 which is dense in cross section as shown in FIG. 10 may be inserted eccentrically in a sealed container 1. In this case, a space which is narrowed between the rod and the sealed container 1 configures a portion having water conveying property better than other portions. In place of the rod shown in FIG. 10, a stranded wire may be used, and in the stranded wire, narrow spaces defined between constituent twisted wires also configure portions having better water conveying property. Further, in place of the straight rod, an insertion member which is made of a thin wire which is formed into a spiral configuration may be used to be inserted in such a manner as to extend along an inner wall of the sealed container 1. In this case, a portion having better water conveying property is formed spirally.

[0040] An oxygen free copper is preferably used as the material of the insertion member 19 shown in Embodiments 2 and 3, and when an oxygen free copper is used which is washed using acetone to remove deposits on a surface thereof and is thereafter subjected to an oxidation treatment under a high temperature the water conveying property of the smaller cross-sectional area flow path 21 can be improved further.

[0041] In addition, in Embodiments 2 and 3, grooves may be provided axially on the inner wall of the sealed container 1 so as to produce an irregular surface thereon. The grooves may be provided uniformly in the circumferential direction or may be provided non-uniformly, and moreover, the grooves may be provided in a spiral manner.

[0042] As has been described heretofore, the portion having better water conveying property according to the invention can be realized by, as is described in Embodiment 1, providing partially the irregularities on the inner wall of the sealed container or deforming part of the inner wall so as to form on part of the surface of the inner wall the portion where liquid expands axially better than the other portions on the surface of the inner wall. In addition, the portion having better water conveying property can also be realized by applying to part of the surface of the inner wall a treatment which improves the hydrophilic nature. Further, as has been described in Embodiments 2 and 3, the portion having better water conveying property can also be realized by inserting the insertion member into the sealed container so as to define the narrow space between the insertion member and the inner wall of the sealed container. Note that to determine whether or not a specific portion on the inner wall has better water conveying property than the other portions thereon, liquid is dropped on to the specific portion to see whether or not the liquid expands axially longer than on the other portions, and if this is determined true, the specific portion can be determined as having the better water conveying property.

[0043] The invention described based on Embodiments 1 to 3 is largely advantageous particularly for a thin sealed container in which the movement of a working fluid is made difficult due to the surface tension of the working fluid. For example, in the case of the working fluid being water, the invention is advantageous when the diameter of the sealed container is on the order of 10 mm or smaller and is more advantageous particularly for a sealed container having a small diameter of the order of 6 mm or smaller. Consequently, the invention is suitable for an application where the quantity of heat is small which can be transported by a single variable conductance heat pipe and is suitable for cooling, for example, a semiconductor laser whose output is on the order of several watts. In the semiconductor laser, since the oscillation frequency and output of the semiconductor laser is largely affected by a change in temperature when it is actuated, the property of a variable conductance heat pipe in which a change in temperature at a heat receiving portion is small when a heating source is actuated can effectively be made use of, and from this view point, such a variable conductance heat pipe can be said to configure a suitable application for the invention.

[0044] While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A variable conductance heat pipe comprising a sealed container in which a working fluid and a noncondensable gas are sealed, the sealed container extending in an axial direction, the sealed container including one end to be connected to a heating source and a part to be connected to a heat sink, wherein, on a cross section of the sealed container along a direction orthogonal to the axial direction, a portion having water conveying property better than other portions is provided, and wherein the portion having the better water conveying property extends in the axial direction.

2. The variable conductance heat pipe according to claim 1, further comprising an insertion member inserted eccentrically into the interior of the sealed container so as to configure the portion having the better water conveying property between an inner wall of the sealed container and the insertion member.

3. The variable conductance heat pipe according to claim 2, wherein the insertion member is inserted eccentrically so that a flow path having a larger cross-sectional area and a flow path having a smaller cross-sectional area are configured along the axial direction of the sealed container between the inner wall of the sealed container and the inserted insertion member, and wherein the larger cross-sectional area flow path and the smaller cross-sectional area flow path communicate with each other at least partially.

4. The variable conductance heat pipe according to claim 3, wherein the insertion member is a board or a wire mesh.

5. The variable conductance heat pipe according to claim 3, further comprising a spacer so that the insertion member is kept separate from the inner wall of the sealed container.

6. The variable conductance heat pipe according to claim 2, wherein the insertion member includes a portion having a larger cross-sectional area than other portions.

7. The variable conductance heat pipe according to claim 2, wherein a rod is inserted eccentrically in the interior of the sealed container.

8. The variable conductance heat pipe according to claim 1, wherein a spiral fine wire is provided to extend along an inner wall of the sealed container to configure the portion having better water conveying property.

9. The variable conductance heat pipe according to claim 1, wherein a treatment for improving water conveying property is applied to a part of an interior wall of the sealed container to configure the portion having better water conveying property.

10. The variable conductance heat pipe according to claim 9, wherein irregularities including a recessed portion and a raised portion extending in the axial direction are provided at a part of the inner wall of the sealed container to configure the portion having better water conveying property.

11. The variable conductance heat pipe according to claim 1, wherein a part of an inner wall of the sealed container in cross section is deformed, so that the deformed portion configures the portion having better water conveying property.

12. The variable conductance heat pipe according to claim 1, wherein the heating source is a semiconductor laser.