Patent Publication Number: US-2011073284-A1

Title: Evaporator for loop heat pipe system

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2009-0091141, filed on Sep. 25, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     One or more aspects of the present invention relate to an evaporator for a loop heat pipe (LHP) including a condenser, a vapor transport line, a liquid transport line, and the evaporator, and more particularly, to an evaporator for an LHP system having an improved structure in which bubbles are prevented to from being formed in a working fluid due to heat generated from a heat component when the working fluid in a vapor phase is changed into a liquid while passing through a condenser and then accommodated in a first chamber. 
     2. Description of the Related Art 
     Electronic parts such as central processing units (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 operation of an electronic device is not effectively removed, performance of the electronic device is severely deteriorated and, in some cases, the electronic device itself may be damaged. 
     As a method of removing 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 of air or radiation, a forced convection method using a fan, a method using circulation of a liquid, and a submerged cooling method. 
     However, nowadays, as many released electronic products are being made slimmer, an installation distance between electronic parts that generate heat during operation is continuously decreasing and thus heat may not be appropriately removed. Also, since a heat load of electronic parts has continuously increased due to 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 problems, a phase change heat transport system that 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 a working fluid. As illustrated in  FIG. 1 , in a conventional cylindrical heat pipe  100 , cooling is obtained by circulating the working fluid using a capillary pumping force generated by a sintered wick  102  installed in an interior wall of the pipe  100 . When heat is transferred to the working fluid contained in a heat source  101  from a heat source  101 , the working fluid is vaporized, and is moved in a direction of an arrow  103  indicating a flow of a vapor. Then, the working fluid is liquefied again while a heat sink  104  takes heat from the working fluid, moves through the sintered wick  102  in a direction of an arrow  105  indicating a flow of a liquid due to a capillary pumping force, and circulates throughout the conventional cylindrical heat pipe  100 . 
     However, in the thermosyphon system, a condenser section needs to be located higher than an evaporator section. Although this problem is less severe when using a heat pipe of the thermosyphon system, a heat transport ability of the heat pipe is quite deteriorated when a condenser section thereof is located lower with respect to gravity than an evaporator section thereof. Accordingly, since there is a limitation in a positional relationship between the constituent elements in the above two systems, this limitation prevents electronic devices employing the above cooling systems from being made slim. 
     Also, since a vapor and a liquid flow in opposite directions in a linear pipe of the thermosyphon system or the cylindrical heat pipe system, the vapor and the liquid may mix together in a middle portion of the pipe. 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 that can solve these problems, that is, a positional limitation and mixing between a vapor and a liquid. 
     The LHP system is a sort of capillary pumped loop heat pipe (CLP) technology developed by NASA, U.S.A., to remove a large amount of heat generated from communications equipment or electronic equipment used for artificial satellites. 
       FIG. 2  is a conceptual view of a conventional LHP system  110 .  FIG. 3  is a cross-sectional view of an evaporator  114  of the conventional LHP system  110 . The conventional LHP system  110  includes a condenser  112 , an evaporator  114 , 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 addition, the evaporator  114  includes a chamber portion  1144  that accommodates and buffers a liquefied working fluid before the working fluid permeates into a sintered wick  1142  inserted into the evaporator  114 . In the conventional LHP system  110 , the sintered wick  1142  is installed only in the evaporator  114  unlike in a conventional linear heat pipe (refer to  FIG. 1 ). 
     The conventional LHP system  110  operates in the following manner. 
     Heat is applied to a contact surface  1148  of the evaporator  114  that contacts a heat source such as a heating component. In this case, at a point of time when the sintered wick  1142  is saturated with the working fluid in a liquid phase, due to the heat applied to the sintered wick  1142 , the applied heat vaporizes the working fluid and thus the working fluid changes into a vapor. The vapor is moved towards 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 and thus the vapor is liquefied. The liquefied working fluid is moved towards 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. As illustrated in  FIG. 3 , the sintered wick  1142  is coupled onto an inner surface of the evaporator  114 . A space within an inner surface of the sintered wick  1142  functions as a vapor path along which the working fluid changed into a vapor is moved towards the vapor line  116 . 
     The working fluid liquefied while passing through the condenser  112  moves back to the evaporator  114 . In this case, the working fluid is accommodated in the chamber portion  1144  before being absorbed into the sintered wick  1142 . The liquefied working fluid stays in the chamber portion  1144  until it is absorbed into the sintered wick  1142  through a through hole  1146  of the chamber portion  1144  due to a capillary pressure of the sintered wick  1142 . In addition, the chamber portion  1144  prevents the liquefied working fluid, which is to flow towards the evaporator  114  along the liquid line  118 , from flowing backwards along the liquid line  118 . 
     However, the evaporator  114  of the conventional LHP system  110  makes the conventional LHP system  110  unstable due to the working fluid accommodated in the chamber portion  1144 . 
     In detail, all of heat generated from heating components needs to be transferred to the evaporator  114  as vaporization energy. However, some sensible heat is transferred to the evaporator  114  through an outer wall of the evaporator  114  and the sintered wick  1142  and thus bubbles are generated in the working fluid accommodated in the chamber portion  1144 . These bubbles forms a bubble layer around the liquid line  118  connected to the chamber portion  1144 , and acts as a boundary layer that prevents the working fluid from smoothly moving into the chamber portion  1144 . Thus, since the working fluid does not smoothly permeate into the sintered wick  1142  of the evaporator  114 , the sintered wick  1142  may dry, and the conventional LHP system  110  may not operate any more. 
     In addition, the working fluid in the chamber portion  1144  is vaporized and thus may flow backwards along the liquid line  118 , or bubbles in the working fluid may flow backwards along the liquid line  118  and collide with an inner surface of the liquid line  118 . Thus, since a temperature of each component of the conventional LHP system  110  oscillates, the conventional LHP system  110  may become unstable. 
     If, except for the through hole  1146 , the chamber portion  1144  is not completely sealed, the working fluid accommodated in the chamber portion  1144  may excessively flow into a space in which the sintered wick  1142  is inserted. That is, if an amount of the working fluid in the space is greater than an ideal amount of the working fluids due to the capillary pressure of the sintered wick  1142 , bubbles may be generated in the space by the heat source, and the generated bubbles may prevent the working fluid accommodated in the sintered wick  1142  from being vaporized. Accordingly, an overall temperature of the conventional LHP system  110  may be increased, and the conventional LHP system  110  becomes unstable, thereby reducing the cooling efficiency of the conventional LHP system  110 . 
     SUMMARY OF THE INVENTION 
     One or more aspects of the present invention provide evaporators for a loop heat pipe (LHP) system, the evaporators including a porous capillary structure inserted into a chamber portion so that a working fluid in a liquid phase passes through the capillary structure along a liquid line and permeates into a sintered wick, thereby preventing bubbles from being formed so as to increase cooling efficiency of the LHP system. 
     According to an aspect of the present invention, there is provided an evaporator for a loop heat pipe (LHP) system, the evaporator including an evaporator body for accommodating a sintered wick formed by sintering metal powders, a discharging hole for discharging a working fluid filled into voids formed between particles of the sintered wick and changed into a vapor due to being heated, and an inlet hole for introducing the working fluid changed into a liquid; a first chamber portion coupled to a side of the inlet hole, and including an inlet for introducing the working fluid in a liquid phase, and an accommodation space portion for accommodating the working fluid in a liquid phase; and a capillary structure that is porous and that is inserted into the accommodating space portion, wherein the working fluid in a liquid phase introduced through the inlet is introduced to the evaporator body through the capillary structure. 
     At least a portion of the capillary structure may contact the sintered wick. 
     The capillary structure may occupy all portions of the accommodation space portion. 
     A capillary pressure of the sintered wick may be greater than a capillary pressure of the capillary structure. 
     A transmittance of the sintered wick may be smaller than a transmittance of the capillary structure. 
     The evaporator may further include a second chamber portion including an outlet coupled to the discharging hole, for discharging the working fluid changed into a vapor, and a vapor accommodation portion for accommodating the working fluid changed into a vapor. 
     The sintered wick may include a space portion, and may have a rectangular parallelepiped shape with an open surface, and an outer surface of the sintered wick may be coupled to an inner surface of the sintered wick accommodating portion, wherein the open surface may be connected to the discharging hole. 
     The sintered wick may have a rectangular parallelepiped shape, the sintered wick may include a plurality of vapor paths for guiding the working fluid changed into a vapor, and the plurality of vapor paths may be connected to the discharging hole, and may each have a circular cross section. 
     The sintered wick may include first sub-sintered wicks that connect top and bottom surfaces of the sintered wick and are spaced apart from each other by a predetermined interval. 
     The sintered wick may include protrusions that protrude from top and bottom surface of the sintered wick and are spaced apart from each other by a predetermined interval. 
     The sintered wick may include plate-type first sub-sintered wicks that connect top and bottom surfaces of the sintered wick and are spaced apart from each other by a predetermined interval; and second sub-sintered wicks of a pin type that protrude from the bottom surface of the sintered wick, wherein the second sub-sintered wicks may be disposed between the first sub-sintered wicks and are spaced apart from each other by a predetermined interval. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a schematic view for explaining an operation of a conventional cylindrical heat pipe; 
         FIG. 2  is a conceptual view of a conventional loop heat pipe (LHP) system; 
         FIG. 3  is a cross-sectional view of an evaporator of the conventional LHP system; 
         FIG. 4  is a schematic perspective view of an LHP system including an evaporator according to an embodiment of the present invention; 
         FIG. 5  is a disassembled perspective view of an evaporator for an LHP system, according to an embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of the evaporator taken along a line VI-VI of  FIG. 5 ; 
         FIG. 7  is a cross-sectional view of the evaporator taken along a line VII-VII of  FIG. 5 ; 
         FIGS. 8 and 9  are cross-sectional views for explaining capillary pressure and transmittance. 
         FIG. 10  is a cross-sectional view of an evaporator for an LHP system, according to another embodiment of the present invention; 
         FIGS. 11 through 14  illustrate a sintered wick of an evaporator for an LHP system, according to various embodiments of the present invention 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
     The present invention relates to an evaporator  200  for a loop heat pipe (LHP) system including a condenser  20 , a vapor transport line  40 , and a liquid transport line  30 . 
     Referring to  FIG. 4 , the LHP system includes the evaporator  200 , the condenser  20 , the vapor transport line  40 , and the liquid transport line  30 . 
     The condenser  20  changes a working fluid received from the evaporator  200  from being in a vapor phase. The condenser  20  takes heat from the working fluid and exhausts the heat to outside air. 
     The vapor transport line  40  is a pipe member for connecting the evaporator  200  and the condenser  20  to each other so as to guide the working fluid in a vapor phase due to the evaporator  200  to the condenser  20 . The liquid transport line  30  is a pipe member for connecting the condenser  20  and the evaporator  200  to each other so as to guide the working fluid in a liquid phase due to the condenser  20  back to the evaporator  200 . 
     General operations of the condenser  20 , the vapor transport line  40 , and the liquid transport line  30  are the same as those described in the Description of the Related Art. 
     The present invention is directed to the evaporator  200 . The evaporator  200  as well as the condenser  20 , the liquid transport line  30 , and the vapor transport line  40  is one of components of the LHP system. 
     The evaporator  200  for the LHP system will be described in detail with reference to  FIGS. 5 through 9 . 
       FIG. 5  is a disassembled perspective view of the evaporator  200  for the LHP system, according to an embodiment of the present invention.  FIG. 6  is a cross-sectional view of the evaporator  200  taken along a line VI-VI of  FIG. 5 .  FIG. 7  is a cross-sectional view of the evaporator  200  taken along a line VII-VII of  FIG. 5 .  FIGS. 8 and 9  are cross-sectional views for explaining capillary pressure and transmittance. 
     Referring to  FIG. 5 , the evaporator  200  includes an evaporator body  210 , a first chamber portion  220 , and a capillary structure  230 . 
     The evaporator body  210  contacts a heating component  1  so as to receive heat from the heating component  1 . As illustrated in  FIG. 4 , the heating component  1  contacts an outer surface of the evaporator body  210 . 
     The evaporator body  210  includes a sintered wick accommodation portion  212  for accommodating a sintered wick  214  formed by sintering metal powders, a discharging hole  218  for discharging the working fluid filled in voids of the sintered wick  214  and changed into a vapor due to being heated, and an inlet hole  216  for introducing the working fluid changed into a liquid. 
     The sintered wick accommodation portion  212  is a space for accommodating the sintered wick  214 , and has a rectangular parallelepiped shape. 
     The discharging hole  218  is formed in the evaporator body  210  so as to discharge the working fluid filled in the voids of the sintered wick  214  and vaporized due to being heated by the heating component  1 . According to the present embodiment, an open surface of the sintered wick accommodation portion  212  is the discharging hole  218 . 
     The inlet hole  216  is formed in the evaporator body  210  so that the working fluid in a vapor phase changed into a liquid by passing through the condenser  20  may flow to the evaporator body  210  along the liquid transport line  30 . According to the present embodiment, the inlet hole  216  is formed in a top surface of the evaporator body  210 . Of course, a position of the inlet hole  216  may be variously changed. For example, the inlet hole  216  may be formed opposite to the discharging hole  218 . 
     The sintered wick  214  formed by sintering metal powders is inserted into the sintered wick accommodation portion  212 . According to the present embodiment, the sintered wick  214  includes a space formed therein, and has a rectangular parallelepiped shape with an open surface. An outer surface of the sintered wick  214  is coupled to an inner surface of the sintered wick accommodation portion  212 . The open surface functions as a vapor path  214   a  along which the working fluid changed into a vapor flows. 
     Numerous voids are formed in the sintered wick  214 . The working fluid in a liquid phase permeates into the voids. Generally, the working fluid may be water, acetone, pentane, ammonia, refrigerant (R-134a), or the like. 
     The first chamber portion  220  is coupled to a side of the inlet hole  216 , and accommodates the working fluid in a liquid phase moved to the evaporator body  210  along the liquid transport line  30 . The first chamber portion  220  includes inlets  222 , and an accommodation space portion  224 . 
     The inlets  222  are connected to the inlet hole  216  of the evaporator body  210 , and are portions for coupling the first chamber portion  220  to the liquid transport line  30 . The accommodation space portion  224  accommodates the working fluid in a liquid phase until the working fluid is introduced to the evaporator body  210 . As illustrated in  FIG. 6 , two inlets  222  are formed in a top surface of the first chamber portion  220 . The accommodation space portion  224  is formed below the inlets  222 . The accommodation space portion  224  includes an open surface that is open downwards. 
     The capillary structure  230  is formed of a porous material, and is inserted into the accommodation space portion  224 . In this case, the working fluid in a liquid phase introduced through the inlet  222  is introduced to the evaporator body  210  through the capillary structure  230 . According to the present embodiment, the capillary structure  230  occupies all portions of the accommodation space portion  224 . In addition, a bottom surface of the capillary structure  230  contacts the sintered wick  214  inserted into the evaporator body  210 . 
     A capillary pressure of the capillary structure  230  is smaller than that of the sintered wick  214 , and a transmittance of the capillary structure  230  is greater than that of the sintered wick  214 . 
     Capillary pressure and transmittance will be described in detail with reference to  FIGS. 8 and 9 .  FIG. 8  is a magnified diagram of a portion “A” of  FIG. 6 , and is a schematic cross-sectional view of particles constituting the sintered wick  214 .  FIG. 9  is a magnified diagram of a portion “B” of  FIG. 8 , and is a schematic cross-sectional view of particles constituting the capillary structure  230 . 
     A capillary pressure is given by the following equation. 
     
       
         
           
             P 
             = 
             
               
                 2 
                  
                 σ 
               
               r 
             
           
         
       
     
     In this equation, ‘P’ is a capillary pressure, ‘σ’ is a surface tension, and ‘r’ is an effective radius of a void formed between particles. 
     Since a surface tension of a working fluid is constant, a capillary pressure is determined according to an effective radius of a void formed between particles. 
     As illustrated in  FIGS. 8 and 9 , an effective radius of a void formed between particles  2  constituting the sintered wick  214  is ‘r 1 ’, and an effective radius of a void formed between particles  3  constituting the capillary structure  230  is ‘r 2 ’. In this case, since r 1 &lt;r 2 , the capillary pressure of the sintered wick  214  is greater than that of the capillary structure  230 . In addition, since r 1 &lt;r 2 , the working fluid may permeate more easily into the capillary structure  230  than in the sintered wick  214 . That is, the transmittance of the capillary structure  230  is greater than that of the sintered wick  214 . 
     Likewise, when the capillary pressure of the sintered wick  214  is greater than that of the capillary structure  230 , and the transmittance of the capillary structure  230  is greater than that of the sintered wick  214 , the working fluid in a liquid phase introduced in the first chamber portion  220  may permeate into the sintered wick  214  through the capillary structure  230 . If the capillary pressure of the sintered wick  214  is smaller than that of the capillary structure  230 , since the working fluid in a liquid phase introduced into the first chamber portion  220  permeates more into the capillary structure  230  than into the sintered wick  214 , and thus is not easily moved to the sintered wick  214 , the working fluid does not circulate smoothly. 
     As illustrated in  FIGS. 4 and 5 , the evaporator  200  for the LHP system includes a second portion  240 . 
     The second portion  240  is coupled to a side of the discharging hole  218 , and includes an outlet  242 , and a vapor accommodation portion  244 . The outlet  242  is a portion for discharging the working fluid changed into a vapor, and is coupled to the vapor transport line  40 . The vapor accommodation portion  244  accommodates the working fluid in a liquid phase introduced via the vapor path  214   a  of the sintered wick  214 . The vapor accommodation portion  244  prevents a sudden drop in pressure when the working fluid in a vapor phase is moved to the vapor transport line  40 . Since a sudden drop in pressure may momentarily increase a moving speed of the working fluid in a vapor phase, which makes the LHP system unstable, the vapor accommodation portion  244  accommodates the working fluid in a vapor phase so as to prevent a sudden drop in pressure in advance. 
     Hereinafter, operations and effects of the evaporator  200  for the LHP system will be described in detail. 
     Heat generated from the heating component  1  while a surface of the evaporator body  210  is in contact with the heating component  1  is applied to the sintered wick  214  inserted into the evaporator body  210 . The working fluid permeated in the sintered wick  214  is changed to a vapor due to the heat applied to the sintered wick  214 . 
     The working fluid in a vapor phase is moved towards the second portion  240  through the discharging hole  218 , is temporally accommodated in the vapor accommodation portion  244  of the second portion  240 , and then is moved to the condenser  20  along the vapor transport line  40 . 
     Heat is taken from the working fluid in a vapor phase and thus the working fluid is changed to a liquid in the condenser  20 , and then the working fluid is moved to the first chamber portion  220  along the liquid transport line  30 . 
     The capillary structure  230  inserted into the accommodation space portion  224  of the first chamber portion  220  absorbs the working fluid in a liquid phase. In addition, the working fluid permeates into the sintered wick  214 , which contact the capillary structure  230 . 
     In this case, since a bottom side of the accommodation space portion  224  is open downwards, and the bottom surface of the capillary structure  230  inserted into the accommodation space portion  224  contacts the outer surface of the sintered wick  214 , the working fluid in a liquid phase is absorbed into the capillary structure  230 , and then permeates into the voids of the sintered wick  214  due to the capillary pressure of the sintered wick  214 . 
     The working fluid in a liquid phase permeated into the voids of the sintered wick  214  is heated by heat generated by the heating component  1 , and is changed to a vapor. The working fluid in a vapor phase cools down the heating component  1  while circulating through the LHP system. 
     Likewise, since the evaporator  200  for the LHP system according to the present embodiment includes the capillary structure  230  inserted into the first chamber portion  220 , which has a greater transmittance than the sintered wick  214  and a smaller capillary pressure than the sintered wick  214 , the working fluid in a liquid phase introduced through the inlet  222  may be absorbed into the capillary structure  230  in a relatively short time, and the working fluid in a liquid phase absorbed into the capillary structure  230  may permeate into the voids of the sintered wick  214  due to the capillary pressure of the sintered wick  214 . 
     Thus, bubbles are prevented from being formed in the working fluid in a liquid phase absorbed into the capillary structure  230  of the first chamber portion  220  even though heat generated by the heating component  1  is transmitted to the first chamber portion  220 . In addition, since the capillary structure  230  absorbs the working fluid in a liquid phase in a relatively short time, time taken to heat the working fluid using heat generated by the heating component  1  is reduced, thereby preventing bubbles from being formed. 
     Even if heat of the heating component  1  is transmitted to the sintered wick  214  or the evaporator body  210 , bubbles may be prevented from being formed in the working fluid accommodated in the first chamber portion  220 . Thus, the working fluid is prevented from flowing backwards along the liquid transport line  30  due to bubbles. Introduction of the working fluid is not interrupted by a bubble layer formed in the first chamber portion  220 . In addition, the sintered wick  214  is prevented from being dried. Thus, the LHP system is maintained more stably than a conventional LHP system. 
     In order to prevent the working fluid absorbed into the capillary structure  230  of the first chamber portion  220  from being introduced in a coupling gap between the sintered wick  214  and the evaporator body  210 , the sintered wick  214  is formed directly on the evaporator body  210 , or the sintered wick  214  and the evaporator body  210  are coupled by using a thermal coupling manner, a metallic bonding manner, or the like, thereby preventing bubbles from being formed between the sintered wick  214  and the evaporator body  210 . Thus, since bubbles are prevented from being formed in the coupling gap between the sintered wick  214  and the evaporator body  210 , introduction of the working fluid is not interrupted by a bubble layer formed in the first chamber portion  220 , and the sintered wick  214  is prevented from being dried due to a bubble layer in advance. 
     Accordingly, heat generated from the heating component  1  is used only as vaporization energy for the working fluid permeated in the sintered wick  214 , and thus the vaporization energy is effectively ensured, thereby increasing cooling efficiency. 
       FIG. 10  is a cross-sectional view of an evaporator for an LHP system, according to another embodiment of the present invention. In  FIG. 10 , components having the same function as components in  FIG. 6  are denoted by the same numerals as shown in  FIG. 6 , and thus a detailed description thereof will not be repeated. 
     Referring to  FIG. 10 , the evaporator according to the present embodiment includes the capillary structure  230 , which unlike as in  FIG. 6 , occupies only a portion of the accommodation space portion  224 . That is, at least a portion of the capillary structure  230  contacts the sintered wick  214 . 
     According to the present embodiment, a top surface of the capillary structure  230  is coupled to the first chamber portion  220  with the inlet  222 , and an edge portion of the capillary structure  230  extends downwards so as to contact the sintered wick  214 . The working fluid in a liquid phase introduced through the inlet  222  is absorbed directly by the top surface of the capillary structure  230 , and is transmitted to the sintered wick  214  through the edge portion of the capillary structure  230 . 
     The working fluid in a liquid phase may be accommodated between the top surface and the edge portion of the capillary structure  230 . Although bubbles are formed in the working fluid in a liquid phase accommodated in a space formed between the sintered wick  214  and the capillary structure  230 , since the top surface of the capillary structure  230  coupled to the first chamber portion  220  with the inlet  222 , bubbles are prevented from flowing backwards through the inlet  222 . In addition, since the top surface of the capillary structure  230  coupled to the first chamber portion  220  with the inlet  222 , introduction of the working fluid is not interrupted by bubbles. 
     In order to prevent the working fluid from being introduced in a coupling gap between the sintered wick  214  and the evaporator body  210  and bubbles being formed therebetween, the sintered wick  214  is formed directly on the evaporator body  210 , or the sintered wick  214  and the evaporator body  210  are coupled by using a thermal coupling manner, a metallic bonding manner, or the like. 
     Operations and effects of the evaporator according to the present embodiment are similar to in  FIG. 6 , and thus a detailed description thereof will be omitted. 
       FIGS. 11 through 14  illustrate a sintered wick  214  of an evaporator for an LHP system, according to various embodiments of the present invention. In  FIGS. 11 through 14 , components having the same function as those in  FIG. 6  are denoted by the same numeral as shown in  FIG. 6 , and thus a detailed description thereof will not be repeated. 
     Referring to  FIG. 11 , the sintered wick  214  inserted into the evaporator body  210  has a rectangular parallelepiped shape, and includes a plurality of vapor paths  214   b  for guiding the working fluid permeated into the voids of the sintered wick  214  and changed into a vapor. The vapor paths  214   b  are connected to the discharging hole  218 , and has a circular cross section. 
     Referring to  FIG. 12 , the sintered wick  214  inserted into the evaporator body  210  has a rectangular parallelepiped shape, and includes first sub-sintered wicks  215  of a plate type that connect top and bottom surfaces of the sintered wick  214 . The first sub-sintered wicks  215  are spaced apart from each other by a predetermined interval. Spaces formed between the first sub-sintered wicks  215  may form vapor paths  214   c  for the working fluid in a vapor phase. 
     Referring to  FIG. 13 , the sintered wick  214  inserted into the evaporator body  210  has a rectangular parallelepiped shape, and includes protrusions  215  that protrude from top and bottom surfaces of the sintered wick  214 . The protrusions  215  are spaced apart from each other by a predetermined interval. Spaces formed between the protrusions  215 , and spaces formed by the top and bottom surfaces may form vapor paths  214   d  for the working fluid changed into a vapor. 
     Referring to  FIG. 14 , the sintered wick  214  inserted into the evaporator body  210  has a rectangular parallelepiped shape, and includes first sub-sintered wicks  215  of a plate type that connect top and bottom surfaces of the sintered wick  214 , and second sub-sintered wicks  219  of a pin type that are disposed between the first sub-sintered wicks  215 . 
     Like in  FIG. 11 , the first sub-sintered wicks  215  connect the top and bottom surfaces of the sintered wick  214 , and are spaced apart from each other by a predetermined interval. The second sub-sintered wicks  219  are of a plate type protruding from the bottom surface. Upper ends of the second sub-sintered wicks  219  are spaced apart from the top surface of the sintered wick  214 . The second sub-sintered wicks  219  are spaced apart from each other by a predetermined interval between the first sub-sintered wicks  215 . Spaces formed by the upper ends of the second sub-sintered wicks  219 , the top surface of the sintered wick  214 , and the first sub-sintered wicks  215  may form vapor paths  214   e  for the working fluid changed into a vapor. 
     Of course, although an outer appearance of the sintered wick  214  illustrated in  FIGS. 11 through 14  has a rectangular parallelepiped shape, the sintered wick  214  may be changed so as to correspond to the sintered wick accommodation portion  212  by changing a shape of the sintered wick accommodation portion  212 . 
     Operations and effects of evaporator of  FIGS. 11 through 14  are similar to those in  FIG. 6 , and will not be repeated. 
     According to one or more embodiments of the present invention, since an evaporator for an LHP system includes a capillary structure that is inserted into a chamber portion, a working fluid in a liquid phase may primarily pass through the capillary structure. In addition, since a capillary pressure of the capillary structure is smaller than that of a sintered wick, the working fluid in a liquid phase passed through the capillary structure may permeate into the sintered wick, instead of staying in the chamber portion for a long time, thereby preventing the working fluid from being heated and forming of bubbles in the chamber portion. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.