Evaporator For Loop Heat Pipe System

Abstract

Provided is an evaporator for a loop heat pipe system including a condenser, a vapor transport line, and a liquid transport line, and more particularly, to an evaporator having an increased contact area between a sintered wick and a heating plate.

Description

FIELD OF THE INVENTION

The present invention relates to an evaporator for a loop heat pipe system including a condenser, a vapor transport line, and a liquid transport line, and more particularly, to an evaporator having an increased contact area between a sintered wick and a heating plate.

BACKGROUND OF THE INVENTION

Electronic parts such as CPUs or semiconductor chips used for various electronic devices such as computers generate a large amount of heat during operation. Such electronic devices are usually designed to operate at room temperature. Accordingly, when heat generated during the operation of an electronic device is not effectively cooled down, the performance of the electronic device is severely deteriorated and, in some cases, the electronic device itself may be damaged.

In order to cool down heat generated by various electronic parts, many approaches have been developed, such as a heat conduction method using a heat sink, a method of using natural convection or radiation of air, a force convection method using a fan, a method using circulation of liquid, or a submerged cooling method.

However, as nowadays many electronic products are made slim, an installation distance between electronic parts generating heat during operation is continuously decreased so that heat is not appropriately cooled down. Also, since the heat load of electronic parts has continuously increased due to the high integration and high performance of the electronic parts, the above-described cooling methods are not able to effectively cool down the electronic parts.

As a new technology to solve the above problem, a phase change heat transport system which can cool down an electronic part having a high heat load density per unit has been introduced. A thermosyphon system and a cylindrical heat pipe system are examples of the phase change heat transport system.

According to the thermosyphon system, cooling is achieved using a natural circulation method via a liquid-vapor phase change and a specific gravity difference of working fluid. In a conventional cylindrical heat pipe 100, as shown in FIG. 1, cooling is obtained by circulating the working fluid using a capillary pumping force generated by a sintered wick installed in an inner surface of a pipe. When heat is transported from a heat source 101, the working fluid included in the sintered wick 102 is evaporated and moved in a direction indicated by a plurality of arrows 103 as a flow of vapor. As the heat is dissipated by a heat sink 104, the operating fluid is changed back to a liquid state and moved along the sintered wick 102 in a direction indicated by a plurality of arrows 105, thereby circulating in the heat pipe 100.

However, there is a limitation in the positions of the constituent elements of the two systems, that is, the thermosyphon system requires a condensing portion located higher than an evaporating portion and, although this problem is less severe in the case of the heat pipe 100, a heat transport ability of the heat pipe 100 is quite deteriorated when a condensing portion is located lower than the evaporating portion. Accordingly, this limitation prevents electronic devices employing the above cooling systems from being made slim.

Also, since vapor and liquid flow in opposite directions in a linear pipe of the thermosyphon or the cylindrical heat pipe 100, the vapor and the liquid may be mixed in the middle of the pipe. Another problem is that the mixture may make the amount of heat actually transported less than that that can be ideally transported.

A loop heat pipe (LHP) system has been suggested as an ideal heat transport system which can solve these problems, that is, the positional limitation and the mixture between the vapor and liquid. The LHP system is a sort of a capillary pumped loop heat pipe (CLP) technology developed by the NASA, U.S.A., to cool down a large amount of heat generated from communications equipment or electronic equipment for an artificial satellite.

Korean Patent No. 671041 entitled “Loop Heat Pipe” discloses a technology about a compact loop heat pipe system. FIG. 2 illustrates a loop heat pipe system 110 according to this conventional technology. The conventional loop heat pipe system 110 includes a condenser 112, an evaporator 114, and a vapor line 116 and a liquid line 118, which form a loop. The vapor line 116 and the liquid line 118 are connected between the condenser 112 and the evaporator 114. In the loop heat pipe system 110, a sintered wick 120 is installed only in the evaporator 114 unlike the conventional linear heat pipe of FIG. 1.

In the present specification, the loop heat pipe is referred to as a loop heat pipe system and both terms have the same meaning. Also, the evaporator and the condenser, respectively, have the same meanings as the evaporator section and the condenser section.

The loop heat pipe system 110 operates in the following manner. Heat is applied to a heating plate 122 which is the bottom portion of the evaporator 114 which is inserted with the sintered wick 120. At that point the sintered wick 120 is saturated with the liquid phase of working fluid due because the heat transported to the sintered wick 120 contacting the heat plate 122. And the applied heat vaporizes the working fluid so that the phase of the working fluid is changed to a vapor state. The vapor is moved toward the condenser 112 along the vapor line 116 connected to a side of the evaporator 114. As the vapor passes through the condenser 112, heat is dissipated externally so that the vapor is liquefied. The liquefied working fluid is moved toward the evaporator 114 along the liquid line 118 at a side of the condenser 112. The above-described process is repeated so that the heat source can be cooled down.

In the evaporation of the working fluid permeated in the sintered wick 120, referring to FIG. 4 showing the sintered wick 120 of FIG. 3 rotated by 180° for the convenience of explanation, a surface 126 of the sintered wick 120 facing the heating plate 122 includes a contact surface 126b contacting the heating plate 122 and a plurality of micro-channels 126a working as a passage of the generated vapor. Accordingly, the sintered wick 120 receives heat via the contact surface 126b contacting the heating plate 120 so that the received heat makes the operating fluid permeated in the sintered wick 120 evaporate. The generated vapor is moved toward the condenser 112 along the vapor line 116 connected to a side of the evaporator section 114 through the micro-channels 126a formed in the surface 126 facing the sintered wick 120.

On the other hand, the performance of an evaporator taking heat from a heat source like an electronic part is determined according to how well the heat transported from the heat source to a heating plate is transported to a sintered wick. In this connection, contact conductance is a factor directly affecting the heat transport between the heat source and the heating plate.

The contact conductance is related to the thermal resistance generated when a metal has a surface contact with another metal and heat transport occurs between the metals. The contact conductance is proportional to the contact area between the two metals. That is, as the contact area increases, the contact conductance increases, and as the contact conductance increases, heat transport is generated further.

However, in the evaporator for the conventional loop heat pipe system, since the contact area between the sintered wick and the heating plate is decreased due to the existence of a vapor passage, that is, the micro-channels, the contact conductance is relatively small. That is, referring to FIG. 5 showing the sintered wick 120 having the micro-channels 126a coupled to the heating plate 122 in a direction rotated by 90° from the direction of the cross-section of FIG. 3, the contact surface 126b of the sintered wick 120 contacting the heating plate 122 is decreased due to the micro-channels 126a so that the amount of heat to be transported is reduced accordingly.

SUMMARY OF THE INVENTION

The present invention provides an evaporator for a loop heat pipe system, the evaporator having increased contact conductance by increasing a contact area between a metal sintered wick and a heating plate.

According to an aspect of the present invention, there is provided a According to an aspect of the present invention, there is provided an evaporator for a loop heat pipe system includes an evaporator section having a sintered wick formed by sintering a metal powder, in which a working fluid permeating through a plurality of pores in the sintered wick is heated so that the phase of the working fluid is changed to a vapor state, a condenser section in which the phase of the working fluid transported from the evaporator section is changed from a vapor state to a liquid state, a vapor transport line connecting between the evaporator section and the condenser section to transport the working fluid, whose phase is changed to a vapor state by the evaporator section, to the condenser section, and a liquid transport line connecting between the condenser section and the evaporator section to transport the working fluid, whose phase is changed to a liquid state by the condenser section, to the evaporator section, wherein the evaporator section includes a heating plate formed of metal and receiving heat from a heat source, a sintered wick coupled to a surface of the heating plate and receiving heat, a plurality of grooves formed in a surface of the heating plate contacting the sintered wick and functioning as a passage though which the working fluid whose phase is changed to a vapor state by the sintered wick is exhausted through the vapor transport line, wherein the grooves are formed in a side surface of the heating plate, each of the grooves having a bottom surface and two side surfaces, and the sintered wick is partially inserted in each of the grooves so as to contact at least a part of the two side surfaces of each of the grooves.

The part of the sintered wick inserted in each of the grooves may be an insertion portion, both side surfaces of the insertion portion contact the two side surfaces of each of the grooves, and a lower surface of the insertion portion is any one of a downwardly bulging shape, an inwardly depressed shape, and a flat shape.

The heating plate may include a lower plate portion having a circular disc shape and a wall portion extending from a circumferential portion of the lower plate portion, the sintered wick may be coupled to an inner surface having an upper surface of the lower plate portion and an inner surface of the wall portion of the heating plate, and a cover member is provided in an upper portion of the wall portion of the heating plate and the liquid transportation line is coupled to the cover member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the operation of a conventional cylindrical heat pipe;

FIG. 2 illustrates the concept of a conventional loop heat pipe;

FIG. 3 is a cross-sectional view of a conventional evaporator of FIG. 2;

FIG. 4 is a perspective view of the sintered wick of FIG. 3 rotated by 180°;

FIG. 5 is a cross-sectional view of a portion of the sintered wick and the heating plate of the conventional evaporator of FIG. 2;

FIG. 6 is a perspective view of a loop heat pipe system including an evaporator according to an embodiment of the present invention;

FIG. 7 is a cross-sectional view of the evaporator of FIG. 6;

FIGS. 8, 9, and 10 are cross-sectional views of the sintered wicks of FIG. 7 according to embodiments of the present invention;

FIG. 11 is a cross-sectional view illustrating a state in which the sintered wick and the heating plate are coupled to each other; and

FIG. 12 is a perspective view of the heating plate where a groove is formed.

DETAILED DESCRIPTION OF THE INVENTION

The attached drawings for illustrating exemplary embodiments of the present invention are referred to in order to gain a sufficient understanding of the present invention, the merits thereof, and the objectives accomplished by the implementation of the present invention. Hereinafter, the present invention will be described in detail by explaining exemplary embodiments of the invention with reference to the attached drawings. Like reference numerals in the drawings denote like elements.

The present invention is related to an evaporator for a loop heat pipe system including a condenser, a vapor transportation line, and a liquid transportation line. FIG. 6 illustrates the structure of a loop heat pipe system according to an embodiment of the present invention. Referring to FIG. 6, the loop heat pipe system includes an evaporator 1, a condenser 210, a vapor transport line 220, and a liquid transport line 230.

The condenser 210 changes the phase of a working fluid in a vapor state received from the evaporator 1 to a liquid state. The condenser 210 takes heat from the working fluid and exhausts the heat to the outside air.

The vapor transport line 220 is a pipe member connecting the evaporator 1 and the condenser 210 to supply the vapor whose phase is changed by the evaporator 1 back to the condenser 210. The liquid transport line 230 is a pipe member connecting the condenser 210 and the evaporator 1 to supply the liquid whose phase is changed by the condenser 210 back to the evaporator 1.

The general operations of the condenser 210, the vapor transport line 220, and the liquid transport line 230 are the same as those described in the background section. The evaporator 1, which is the subject matter of the present invention, is one of the constituent elements of the loop heat pipe system, together with the condenser 210, the liquid transport line 220, and the vapor transport line 230.

FIG. 7 is a cross-sectional view of the evaporator 1 of FIG. 6. Referring to FIG. 7, the evaporator 1 includes a sintered wick 20 that is formed by sintering metal powders. When the working fluid permeating through pores formed inside the sintered wick 20 is heated, the phase of the working fluid is changed to a vapor state. The evaporator 1 includes a heating plate 10, the sintered wick 20, and a plurality of grooves 30. The heating plate 10 is formed of metal and receives heat from a heat source such as electronic parts that generate heat during operation.

In the present embodiment, the heating plate 10 includes a lower plate portion 12 and a side wall portion 14. The lower plate portion 12 has a disc shape. The side wall portion 14 extends upwardly from the circumferential portion of the lower plate portion 12. The lower plate portion 12 and the side wall portion 14 may be integrally formed or coupled together after being manufactured separately. The lower surface of the lower plate portion 12 contacts the heat source and receives heat from the heat source. The heat transported to the lower plate portion 12 is transported to the side wall portion 14 connected to the lower plate portion 12 by conduction.

In the present embodiment, a cover member 16 is provided at an upper end portion of the side wall portion 14 of the heating plate 10. The liquid transport line 230 is connected to the cover member 16 so that the working fluid in a liquid state transported from the condenser 210 flows into an inner space of the evaporator 1. An inlet 17 to which the liquid transport line 230 is connected is formed in the cover member 16 of the evaporator 1 so that the working fluid can flow into the evaporator 1. An outlet 18 to which the vapor transport line 220 is connected is formed in the heating plate 10 so that a vapor can be exhausted.

In the present embodiment, the lower plate portion 12 of the heating plate 10 has a disc shape and the side wall portion 14 has a shape encompassing the lower plate portion 12. The cover member 16 has a disc shape and is provided on top of the heating plate 10. The evaporator 1 has a hollow cylindrical shape. However, the present invention is not limited to the above descriptions and, for example, the lower plate portion may have a polygonal plate shape such as a rectangle.

The sintered wick 20 is coupled to the upper surface of the lower plate portion 12 to receive heat therefrom. The working fluid in a liquid state included in the pores of the sintered wick 20 is evaporated into a vapor state by the received heat. The sintered wick 20 is formed by sintering a metal powder. A large number of spaces or pores are formed in the sintered wick 20 so that the working fluid in the liquid state can permeate in the sintered wick 20. The groves 30 are formed in a surface where the heating plate 10 and the sintered wick 20 contact each other and work as a passage for a vapor in the sintered wick 20 whose phase is changed to exhaust vapor through the vapor transport line 220 via the outlet 18. Thus, since the groves 30 are connected to the outlet 18, the vapor can be exhausted from the evaporator 1 through the vapor transport line 220.

In the present embodiment, the grooves 30 linearly formed in the upper surface of the lower plate portion 12 are separated from one another and parallel to one another. Each space (not shown) is circumferentially formed at both end portions of each of the grooves 30. Also, the grooves 30 are circumferentially formed in the side wall portion 14. Each space penetrating the grooves 30 and connected to the outlet 18 is formed in the side wall portion 14. Accordingly, the vapor generated in the grooves 30 formed in the lower plate portion 12 of the heating plate 10 flows toward the space formed in the circumferential portion of the lower plate portion 12 and then is exhausted via the outlet 18 toward the vapor transport line 220. Also, the vapor generated in the grooves 30 formed in the side wall portion 14 of the heating plate 10 flows toward the space penetrating the grooves 30 and the resultant vapor then travels via the outlet 18 toward the vapor transport line 220.

Each of the grooves 30 has a bottom surface 32 and side surfaces 34 and is formed on a side surface of the heating plate 10. In the present embodiment, the term “a surface” of the heating plate 10 has the same meaning as an “inner side surface” and indicates the upper surface of the lower plate portion 12 and an inner surface of the side wall portion 14. Accordingly, the grooves 30 are formed in the inner side surface, or the side surface, that is, in the upper surface of the lower plate portion 12 and the inner surface of the side wall portion 14 of the heating plate 10.

The sintered wick 20 is coupled to the inner side surface of the heating plate 10 to receive heat. In particular, the sintered wick 20 is partially inserted into each of the grooves 30 so as to contact at least part of both side surfaces 24 of each of the grooves 30. In the present embodiment, the part of the sintered wick 20 inserted in each of the grooves 30 is referred to as an insertion portion 22.

Both side surfaces 24 of the insertion portion 22 contact the upper portions of the side surfaces 34 of the grooves 30. The insertion portion 22 is inserted in each of the grooves 30 to a depth of about ⅓ of the height of each of the grooves 30. A lower surface 26 of the insertion portion 22 has a flat shape. An insertion length t of a portion of the insertion portion 22 inserted into each of the grooves 30 is defined as a length of both side surfaces of the insertion portion 22 coupled to both side surfaces of each of the grooves 30 assuming that both side surfaces of the insertion portion 22 are symmetrical.

However, the insertion length t of the insertion portion 22 and the shape of the lower surface 26 may be interdependently changed considering factors such as a contact area between the heating plate 10 and the sintered wick 20, a need for the space in the grooves 30 as the passage of the vapor, the size of a surface area where the working fluid can be evaporated. That is, the length t of the insertion portion 22 may be determined as a predetermined value considering the above factors.

For example, referring to FIG. 8, a lower surface 26a of an insertion portion 22a downwardly bulges in interrelation with a change in the insertion length t. Referring to FIG. 8, a lower surface 26b of an insertion portion 22b is inwardly depressed. Also, referring to FIG. 10, the insertion length t of an insertion portion 22c of the sintered wick 20 with respect to the side surfaces 34 of the grooves 30 is almost equal to the height of each of the grooves 30 and a lower surface 26c of the insertion portion 22c is inwardly depressed. The shape of the lower surface 26c of the insertion portion 22c can maximize the contact area between both side surfaces 24 of the sintered wick 20 and both side surfaces 34 of the grooves 30 of the heating plate 10 and simultaneously enables the grooves 30 to work as a vapor passage, and also facilitates securing a sufficient area of the lower surface 26c.

In the evaporator for a heat pipe system of the present embodiment, since the insertion portion 22 of the sintered wick 20 is inserted in each of the grooves 30 formed in the heating plate 10 and contacts both side surfaces of each of the grooves 30, the contact area increases. The increase in the contact area is described with reference to FIGS. 11 and 12.

FIG. 11 is a cross-sectional view illustrating a state in which a sintered wick 20d and the heating plate 10 are coupled to each other. FIG. 12 is a perspective view of the heating plate 10 where a plurality of grooves 30d are formed. In FIGS. 11 and 12, it is assumed that the sintered wick 20d and the heating plate 10 are not circular but rectangular for the convenience of calculation, an n-number of grooves, where n is an integer, each having the same length, are formed in the heating plate 10, and the lower surface of an insertion portion is flat. Accordingly, since the shapes of the sintered wick 20d and the grooves 30d are different from those shown in FIG. 7, a suffix “d” is added to reference numbers for the sintered wick 20d and the grooves 30d.

In FIGS. 11 and 12, the meanings of reference characters are as shown below.

W′: heating width	W: width of groove	H: height of groove
L: length of groove	n: number of grooves
rtw: permeation ratio of insertion portion
A′: contact area	rw: insertion length ratio
A: vapor evaporation	Atw: permeation area	At: total area
area

W′×L=A′, W×L=A, A_t=n(A′+A)

When the ratio of the heating area to the total area is that r_w=W/W′, nA′/A_t=nW′L/n(W′L+WL)=W′/(W′/W)=1/(1+r_w). If the sintered wick 20d is inserted into each of the grooves 30d by a depth of t and both side surfaces of an insertion portion are symmetrical, the amount of an increase in the contact area is as follows.

When r_tw=2t/W, A_tw=2tL=r_twWL. Accordingly, the contact area is that A′=n(W′L)+n(r_twWL)=nL(W′+r_twW). Thus, the ratio of a heating area increased as the sintered wick 20d intrudes into each of the grooves 30d is that nA′/A_t=nL(W′+r_twW)/nL(W′+W)=(W′+r_twW)/(W′+W)=(1+r_twr_w)/(1+r_w).

Generally, the size and number of the grooves 30d are determined according to the specification of a system. Since the increase in the contact area decreases the value of heat flux (W/m²), it is preferable that the contact area is increased. When the contact length ratio r_w is 0.5, as the permeation ratio r_tw increases to 0.1-0.5, the contact area ratio is increased to 0.7-0.83. Compared to a case when the permeation ratio is 0, the contact area ratio is increased to 0.7-0.83 from 0.67 by 0.03-0.17. Accordingly, when the permeation ratio r_w is 1, that is, t=W/2, or more, the contact area may correspond to an area of insertion may be larger.

A method of coupling the sinters wick 20 to a side surface of the heating plate 10 may be a sintering method of sintering metal powder to form the sintered wick 20 and simultaneously coupling the sintered wick 20 to the heating plate 10 and a coupling method of forming the sintered wick 20 and then coupling the sintered wick 20 to the heating plate 10 where the grooves 30 are formed. The coupling method includes a simple pressing coupling method and a metal coupling method.

According to the simultaneous sintering method, a plurality of grooves are formed in a metal heating plate and the grooves are filled with a sublimate solid material considering the insertion length of an insertion portion and the shape of a lower surface of a sintered wick. That is, in FIG. 7-9, a portion of each of the grooves, corresponding to an empty space, is filled with the sublimate solid material considering the insertion portion inserted in each of the groves. Then, a jig above the sintered plate is arranged to be separated from one another by the thickness of the sintered wick. The heating plate and the jig are packed with metal powder and heated at a predetermined temperature for a period of time according to the type of the metal powder to be sintered. As the metal powder is sintered, the metal powder is coupled to the heating plate. Also, simultaneously with the sintering of the metal powder, the sublimate solid material filling the grooves is sublimated and exhausted from the sublimate solid material. Accordingly, with an empty space having a desired shape, the insertion portion of the sintered wick inserted in each of the grooves is formed into a desired shape.

In the simple pressing coupling method, a previously manufactured metal sintered wick is prepared to contact the heating plate and then a predetermined load is applied to the sintered wick to be coupled to the heating plate. In the metal coupling method, a previously manufactured metal sintered wick is prepared to contact the heating plate and heated to be sintered again (or secondly sintering) so that the sintered wick is coupled to the heating plate. Any one of the above-described methods may be appropriately selected as a method of coupling the sintered wick 20 to the side surface of the heating plate 10.

As described above, according to the evaporator for a loop heat pipe system according to the present invention, since the contact area between the heating plate and the sintered wick is increased compared to the conventional technology, a contact conductance increases. That is, in the conventional technology, the heating plate and the sintered wick contact each other except for a surface corresponding to the width of each of the grooves functioning as a passage for vapor. In the evaporator of the present invention, since a portion of the sintered wick is inserted in each of the grooves and contacts both side surfaces of each groove, the contact area between the heating plate and the sintered wick increases.

Also, according to the evaporator for a loop heat pipe system of the present invention, since the shape of the lower surface of the insertion portion of the sintered wick inserted in each of the grooves can be variously formed, in a state in which the contact area between the heating plate and the sintered wick is increased, a sectional area of the vapor passage and a evaporation surface area can be additionally adjusted so that optimal efficiency suitable for the environment can be obtained.

Furthermore, according to the simultaneous sintering method, since a manufacturing process is simple, a cost for manufacturing an evaporator is low. In particular, since the coupling between the sintered wick and the heating plate is performed simultaneously with sintering, a contact state is improved so that contact conductance is increased. Also, by controlling a state of a sublimate material filling the grooves, the insertion portion of the sintered wick can be formed in any shape.

In addition, when the sintered wick is coupled to the heating plate in the coupling method, compared to the above-described simultaneous sintering method, the coupling state between the sintered wick and the metal heating plate is slightly deteriorated. However, since the side surface of the insertion portion is coupled to the side surface of each of the grooves, compared to the conventional technology, the contact area between the sintered wick and the heating plate can be increased. Also, the insertion portion of the sintered wick can be mechanically processed into a desired shape.

As described above, according to the evaporator for a loop heat pipe system according to the present embodiment, since the contact area between the sintered wick and the heating plate is increased compared to the conventional technology, the contact conductance is increased.

While this invention has been particularly shown and described with reference to 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. An evaporator for a loop heat pipe system comprising: an evaporator section having a sintered wick formed by sintering a metal powder, in which a working fluid permeating through a plurality of pores in the sintered wick is heated so that the phase of the working fluid is changed to a vapor state;a condenser section in which the phase of the working fluid transported from the evaporator section is changed from a vapor state to a liquid state;a vapor transport line connecting between the evaporator section and the condenser section to transport the working fluid, whose phase is changed to a vapor state by the evaporator section, to the condenser section; anda liquid transport line connecting between the condenser section and the evaporator section to transport the working fluid, whose phase is changed to a liquid state by the condenser section, to the evaporator section,wherein the evaporator section comprises:a heating plate formed of metal and receiving heat from a heat source;a sintered wick coupled to a surface of the heating plate and receiving heat;a plurality of grooves formed in a surface of the heating plate contacting the sintered wick and functioning as a passage though which the working fluid whose phase is changed to a vapor state by the sintered wick is exhausted through the vapor transport line,wherein the grooves are formed in a side surface of the heating plate, each of the grooves having a bottom surface and two side surfaces, and the sintered wick is partially inserted in each of the grooves so as to contact at least a part of the two side surfaces of each of the grooves.

2. The evaporator of claim 1 wherein the part of the sintered wick inserted in each of the grooves is an insertion portion, both side surfaces of the insertion portion contact the two side surfaces of each of the grooves, and a lower surface of the insertion portion is any one of a downwardly bulging shape, an inwardly depressed shape, and a flat shape.

3. The evaporator of claim 2, wherein the heating plate comprises a lower plate portion having a circular disc shape and a wall portion extending from a circumferential portion of the lower plate portion, the sintered wick is coupled to an inner surface having an upper surface of the lower plate portion and an inner surface of the wall portion of the heating plate, and a cover member is provided in an upper portion of the wall portion of the heating plate and the liquid transportation line is coupled to the cover member.