WO2010032894A1

WO2010032894A1 - Method for manufacturing evaporator for looped heat pipe system

Info

Publication number: WO2010032894A1
Application number: PCT/KR2008/005693
Authority: WO
Inventors: Chul-Ju Kim; Min-Whan Seo; Byung-Ho Sung; Jung-Hyun Yoo; Jee-Hoon Choi; Jung Rae Jo
Original assignee: Zalman Tech Co., Ltd.; Sungkyunkwan University Foundation For Corporate Collaboration
Priority date: 2008-09-22
Filing date: 2008-09-25
Publication date: 2010-03-25
Also published as: KR20100033872A; TW201020498A; TWI382146B; KR101164611B1

Abstract

Provided is a method of manufacturing an evaporator for a looped heat pipe (LHP) system, the method including the operations of forming a plurality of wicks having pores; forming a plurality of heat transferring fins respectively having a wick coupler to be coupled to one of the plurality of wicks; inserting each of the wicks into the wick coupler of each of the heat transferring fin, thereby forming a plurality of unit assemblies; applying at least one of heat and pressure to the unit assemblies, and cross-coupling a contact surface of the wick and a contact surface of the heat transferring fin; horizontally disposing the unit assemblies to enable a bottom surface of each of the unit assemblies to be located on a planar surface, and forming an assembly structure; applying at least one of heat and pressure to the assembly structure, and cross-coupling the unit assemblies; and disposing the assembly structure on a top surface of a heat transferring plate having a planar plate shape, applying heat or heat and pressure to the assembly structure on the top surface, and coupling a contact surface of the assembly structure and a contact surface of the heat transferring plate.

Description

METHOD FOR MANUFACTURING EVAPORATOR FOR LOOPED HEAT PIPE

SYSTEM

TECHNICAL FIELD

The present invention relates to a method of manufacturing an evaporator for a looped heat pipe (LHP) system including a condenser, a vapor transport line, and a liquid transport line, and more particularly, to a method of manufacturing an evaporator for a LHP system, wherein a wick and a heat transferring fin are cross-coupled to form a unit assembly, and a plurality of the unit assemblies are arrayed and then coupled to a heat transferring plate so as to form the evaporator, whereby the wick and the heat transferring fin can be manufactured in various shapes and sizes, thereby minimizing the thermal contact resistance between the wick and the heat transferring fin.

BACKGROUND 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. Since such electronic devices are usually designed to operate at room temperature, it is necessary to cool down heat generated in the operation.

One of the many techniques to cool down electronic devices is the use of a phase change heat transport system, and a newly introduced technique in this regard is a looped heat pipe (LHP) system.

FIG. 1 is a diagram of a general LHP system 110. The LHP system 110 includes a condenser 112, an evaporator 114, and a vapor line 116 and a liquid line 118 which connect the condenser 112 and the evaporator 114. Working fluid is injected into the LHP system 110. Unlike a heat pipe usually having a cylindrical shape, a plurality of wicks having pores are arranged only in the evaporator 114 of the LHP system 110. The LHP system 110 operates in the following manner.

First, the evaporator 114 contacting an electronic part (not shown), that is, a heat source, is heated. When the evaporator 114 is heated, the working fluid in a liquid state permeating through the wicks is phase-changed into a vapor state.

The generated vapor is moved toward the condenser 112 via the vapor line 116 connected to a side of the evaporator 114. As the vapor passes through the condenser 112, heat is externally dissipated so that the vapor is liquefied. The liquefied working fluid is moved toward the evaporator 114 via the liquid line 118 at a side of the condenser 112. The above-described process is repeated so that the electronic part, that is, the heat source, can be cooled down. Meanwhile, for high performance and compactness of the LHP system 110, the total thermal resistance should be reduced. When the total thermal resistance is reduced, the heat source, that is, the electronic part can operate at a low temperature.

In order to reduce the total thermal resistance of the LHP system 110, it is necessary to consider various factors. The most important factor is the thermal contact resistance between a contact surface of the wicks and a contact surface of a base of the evaporator 114. The thermal contact resistance is affected not only by the apparent area sizes of contact surfaces of two objects between which a heat transfer is occurred. That is, although the apparent area sizes of the contact surfaces are flat, a size of an actual contact interface constituted between the contact surfaces of the two objects physically contacting each other may vary according to a state of the contact surfaces, thus, it is necessary to consider the size of the actual contact interface by referring to the state of the contact surfaces. Heat transfer between the contact surface of the wicks and the contact surface of the base of the evaporator 114 occurs by heat conduction in an actual contact interface constituted between the contact surfaces of the wicks and the base of the evaporator 114, and by heat conduction in a void area between the contact surfaces of the wicks and the base of the evaporator 114. Most of the thermal contact resistance is generated due to the void space between the contact surfaces of the wicks and the base of the evaporator 114. By increasing areas of the contact surfaces of the wicks and the base of the evaporator 114, the thermal contact resistance may be reduced. That is, the thermal contact resistance is related to the thermal resistance generated when a metal surface contacts another metal surface, and has a substantial difference according to an area of a contact surface.

In general, in order to enlarge an area of an actual contact interface between two objects, the contact surfaces of the two objects are polished and then cross-contacted, or a thermal grease having high heat conduction is applied thereto.

The thermal contact resistance of the LHP system 110 highly depends on a state of a heating interface of the evaporator 114, and on a state of a contact interface between the evaporator 114 and sintered wicks. Also, the thermal contact resistance is a highly important factor when the working fluid in a liquid state is phase-changed into a vapor state in response to heat.

Even though the sintered wicks and the base functioning as a heat plate apparently form a large cross-contact area, if a state of an actual contact interface between the sintered wicks and the base is not desirable, a heat transfer toward the sintered wicks is not smoothly performed. If so, a temperature of the base functioning as the heat plate of the evaporator 114 rises to increase a temperature of vapor to a working level of the LHP system 110 . Since the vapor functions to transport heat to the condenser 112, when the LHP system 110 operates with the high temperature vapor, the total thermal resistance of the LHP system 110 increases.

Thus, a key point with respect to the evaporator 114 is to enlarge an actual contact area between the sintered wicks arranged in the evaporator 114 and an inner structure of the evaporator 114, and then to lower a thermal contact resistance value so that an electronic part can be cooled down to a low temperature.

With respect to the evaporator 114, Korean Patent Application No. 10-2006-0024388 discloses a technology for enlarging a contact area between a wick and a structure in an evaporator. Referring to this application, such a conventional technology discloses a structural consideration to enlarge an area of a contact surface between a wick 410 and protrusions 120 which are inner structures of the evaporator. However, there is a limit in forming the inner structures in the desired shapes, and in this case, a state of the contact surface is not desirable such that heat transfer is not effectively performed.

That is, in the conventional technology, referring to FIGS. 1 , 5, and 6 of this application (which respectively correspond to FIGS. 2, 3, and 4 of the present invention) , it is apparent that the wick 410 and the protrusions 120 contact each other in a relatively larger area than that in a previous technology. In fact, the wick 410 is simply inserted into and coupled between the protrusions 120 and thus a state of an actual contact surface between the wick 410 and the protrusions 120 is not desirable. That is, point contact not surface contact occurs such that the heat transfer from the protrusions 120 to the wick 410 is not effectively performed.

FIG. 5 illustrates a contact surface between the wick 410 and the protrusion 120, and a graph of temperature gradient between the wick 410 and the protrusion 120. The graph is obtained by magnifying the contact surface via an electron microscope. Referring to FIG. 5, the wick 410 and the protrusion 120 are cross-coupled mainly via a point contact, and thus, it can be seen that a temperature decreases at a contact interface. Accordingly, in the case of an evaporator that operates under a constant heat load, a temperature of a heating surface may vary according to a thermal contact resistance value of the evaporator, a temperature of a heating interface becomes high when the thermal contact resistance value is great, and the temperature of the heating interface becomes low when the thermal contact resistance value is small. According to the conventional technology, the protrusions 120 are integrally formed on an inner side surface of a heat source contact unit 110, wherein the inner side surface is a metal plate, and thus, there is a limit in adjusting the shapes or surface roughness of the protrusions 120. Also, the wicks 410 to be inserted into the protrusions 120 correspond to a shape of the protrusions 120, and thus, there is a limit in selecting the material or a shape of the wicks 410. Such limits are major factors that make improvement of a contact surface state difficult.

In other words, according to the conventional technology, the protrusions 120 and the heat source contact unit 110 are integrally formed in the evaporator 114, and the shape of the wicks 410 inserted in such protrusions 120 corresponds to the shape of the protrusions 120. Thus, there is a limit in obtaining the various shapes of the wicks 410. Accordingly, the thermal contact resistance is high due to an undesirable state of a contact interface between the protrusion 120 and the wick 410, and cooling of an electronic part is not effectively performed.

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL PROBLEM

The present invention provides a method of manufacturing an evaporator for a looped heat pipe (LHP) system, wherein heat transferring fins of the evaporator can be formed in various shapes, and wicks of the evaporator can be formed in various shapes and of various materials, thereby improving a contact state between the heat transferring fins and the wicks.

TECHNICAL SOLUTION According to an aspect of the present invention, there is provided a method of manufacturing an evaporator for a looped heat pipe (LHP) system, the method including the operations of forming a plurality of wicks having pores; forming a plurality of heat transferring fins respectively having a wick coupler to be coupled to one of the plurality of wicks; inserting each of the wicks into the wick coupler of each of the heat transferring fin, thereby forming a plurality of unit assemblies; applying at least one of heat and pressure to the unit assemblies, and cross-coupling a contact surface of the wick and a contact surface of the heat transferring fin; horizontally disposing the unit assemblies to enable a bottom surface of each of the unit assemblies to be located on a planar surface, and forming an assembly structure; applying at least one of heat and pressure to the assembly structure, and cross-coupling the unit assemblies; and disposing the assembly structure on a top surface of a heat transferring plate having a planar plate shape, applying heat or heat and pressure to the assembly structure on the top surface, and coupling a contact surface of the assembly structure and a contact surface of the heat transferring plate.

The operation of forming the plurality of wicks may include the operation of using a material selected from the group consisting of a metal powder, a non-metal powder, a metal fiber, and a non-metal fiber, and then applying at least one of heat and pressure to the selected material, thereby forming the plurality of wicks having a desired shape.

The operation of forming the plurality of wicks may include the operation of mixing the selected material with one of a thermoplastic polymer and an organic solvent, and then applying one of heat and pressure to the mixture, thereby forming the plurality of wicks having a desired shape.

After the plurality of wicks having the desired shape are formed, the operation of forming the plurality of wicks may include the operation of removing the mixed thermoplastic polymer or the mixed organic solvent by using one of a solvent extraction method and a pyrolysis method. Before the wick is inserted into the wick coupler of the heat transferring fin, the operation of forming the unit assembly may further include the operation of inserting a coupling promoter selected from a metal powder and a coupling material whereby the coupling promoter can be located on at least a portion of a contact interface between the wick and the heat transferring fin.

The operation of forming the assembly structure may further include the operation of disposing at least one of a middle wick and a spacer between the unit assemblies adjacent to each other.

The operation of forming the assembly structure may further include the operation of horizontally applying pressure to the assembly structure, thereby shrinking a diameter of the pores in the wick.

The operation of forming the assembly structure may further include the operation of arranging pressing means capable of applying pressure to the assembly structure in either side directions of the assembly structure, and capable of shrinking a diameter of the pores in the wick.

After the operation of forming the plurality of wicks, the operation of forming the plurality of heat transferring fins, the operation of forming the unit assembly, and the operation of forming the assembly structure are performed, the operation of cross-coupling the contact surfaces of the wick and the heat transferring fin, the operation of cross-coupling the unit assemblies, and the operation of coupling the contact surfaces of the assembly structure and the heat transferring plate may be simultaneously performed as one procedure; the operation of cross-coupling the contact surfaces of the wick and the heat transferring fin, and the operation of cross-coupling the unit assemblies may be simultaneously performed, and then the operation of coupling the contact surfaces of the assembly structure and the heat transferring plate may be performed; or, the operation of cross-coupling the contact surfaces of the wick and the heat transferring fin may be performed, and then the operation of cross-coupling the unit assemblies, and the operation of coupling the contact surfaces of the assembly structure and the heat transferring plate may be performed.

ADVANTAGEOUS EFFECTS

According to a method of manufacturing an evaporator for a looped heat pipe (LHP) system according to one or more embodiments of the present invention, a wick and a heat transferring fin are first manufactured, and a plurality of the wicks and the heat transferring fins are arrayed and then attached to a heat transferring plate that is a metal planar plate, so that the evaporator is manufactured. Thus, it is easy to form the heat transferring fin in a complicated or desired shape, it is possible to improve a contact state between the heat transferring fin and the wick, and as a result, it is possible to enlarge a heating area and a vapor generation area and to minimize the contact thermal resistance between the heat transferring fin and the wick. DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a general looped heat pipe (LHP) system, FIGS. 2 through 4 are diagrams related to a conventional technology, FIG. 5 illustrates a state of a contact surface between an interface and a wick, which are related to FIGS. 2 through 4,

FIG. 6 is an exploded perspective view of an evaporator manufactured by a method of manufacturing an evaporator for a LHP system according to an embodiment of the present invention, FIG. 7 is a flowchart of a method of manufacturing an evaporator for a LHP system, according to an embodiment of the present invention,

FIGS. 8, 9, and 10 are diagrams respectively corresponding to a wick, a heat transferring fin, and a unit assembly,

FIG. 11 is a magnified cross-sectional view in which a metal powder is located on a contact interface via which a wick and a heat transferring fin mutually contact, FIG. 12 is a diagram of an assembly structure,

FIGS. 13 and 14 are diagrams of an assembly structure and its cross-sectional view according to another embodiment of the present invention,

FIGS. 15 and 16 are diagrams of an assembly structure and its cross-sectional view according to another embodiment of the present invention,

FIGS. 17 and 18 are diagrams in which pressure are horizontally applied to an assembly structure,

FIG. 19 is a diagram of an assembly structure further including a quadrangle-shaped frame as pressing means according to another embodiment of the present invention,

FIG. 20 is a diagram of an assembly structure coupled to a heat transferring plate,

FIGS. 21 through 23 are diagrams respectively corresponding to a heat transferring fin, a unit assembly, and an assembly structure according to another embodiment of the present invention.

MODE OF THE INVENTION

The present invention relates to a method of manufacturing an evaporator for a looped heat pipe (LHP) system including a condenser, a vapor transport line, and a liquid transport line. Operations of the LHP system correspond to those described above in relation to the conventional technology.

First, a structure of an evaporator 1 will be described with reference to FIG. 6, the evaporator 1 being manufactured using a method of manufacturing an evaporator for a LHP system according to an embodiment of the present invention. FIG. 6 is an exploded perspective view of the evaporator 1. The evaporator 1 includes a plurality of wicks 10, a plurality of heat transferring fins 20, a heat transferring plate 50, and a cover member 60.

Referring to FIG. 8, the plurality of wicks 10 has pores, and each has a thin plate shape. Each of the plurality of heat transferring fins 20 has a wick coupler 22 (refer to FIG. 9) to which the wick 10 may be coupled. The wick 10 and the heat transferring fin 20 are cross-coupled to form a unit assembly 30 (refer to FIG. 10).

A plurality of the unit assemblies 30 are horizontally disposed to form an assembly structure 40 (refer to FIG. 12).

The heat transferring plate 50 is coupled to a bottom part of the assembly structure 40.

The heat transferring plate 50 is formed of metal, and a bottom surface of the heat transferring plate 50 contacts a heat source and receives heat from the heat source. The heat source is an electronic part that generates heat during operation, and examples of the electronic part include a Central Processing Unit (CPU) of a computer, a chipset of a graphic card, etc.

The cover member 60 is coupled to a top surface of the heat transferring plate 50. The cover member 60 and the heat transferring plate 50 form an inner space there between in which the assembly structure 40 is to be positioned. A vapor line coupling hole 62 to be coupled to a vapor line is formed on a side surface of the cover member 60, and a liquid line coupling hole 64 to be coupled to a liquid line is formed on a top surface of the cover member 60.

Meanwhile, in the assembly structure 40, the wick 10 and the heat transferring fin

20 are cross-coupled in such a manner that vapor passages are formed between the wick 10 and protrusions 26 and 28 of the heat transferring fin 20, and thus, vapor generated in the wick 10 may be exhausted through the vapor line coupling hole 62 of the cover member 60.

Operations of the evaporator 1 having such a structure will be described. Working fluid in a liquid state is injected into the evaporator 1 through the liquid line coupling hole 64, and permeates into a large number of pores which are formed inside the wick 10. The heat, which is transferred from the heat source to the heat transferring fin 20 via the heat transferring plate 50, is transferred to the wick 10 and phase-changes the working fluid from the liquid state to a vapor state. The vaporized working fluid passes through the vapor passages, and is externally exhausted from the evaporator 1 through the vapor line coupling hole 62. Hereinafter, a method of manufacturing an evaporator having the aforementioned structure for a LHP system, according to an embodiment of the present invention, will be described with reference to FIGS. 7 through 12.

The method of manufacturing the evaporator for the LHP system according to the current embodiment includes operations of forming a plurality of wicks (operation S1), forming a plurality of heat transferring fins (operation S2), forming a unit assembly (operation S3), coupling the unit assemblies (operation S4), forming an assembly structure (operation S5), coupling the assembly structure (operation S6), and coupling a heat transferring plate (operation S7).

In the operation of forming the wicks (operation S1), a plurality of wicks 10 having pores are formed. Each of the wicks 10 has a porous structure having a large number of internal pores. Working fluid permeated into the pores is phase-changed into a vapor state by heat that is transferred from the heat transferring fin 20. As illustrated in FIG. 8, a shape of the wick 10 according to the current embodiment is a thin quadrangle-plate shape but the shape of the wick 10 may vary when needed. The wick 10 may be formed to have the desired shape by using at least one material selected from the group consisting of a metal powder, a non-metal powder, a metal fiber, and a non-metal fiber, and then by applying at least one of heat and pressure to the selected material. That is, either heat or pressure or both are applied to the selected material to obtain the desired shape. This operation of forming the wicks (operation S1) may be referred to as a pre-forming process.

The wick 10 is formed in the following manner by using the metal powder and the metal fiber. The operation of forming the wicks (operation S1), in order to obtain a porous member, is performed by using a material such as a metal wire/fiber and a metal power particle including copper, brass, bronze, nickel, titanium, aluminum, stainless steel, etc.

In general, the material is selected from the metal powder and the metal fiber but if necessary, the material may include two or more types selected from the metal power, or may include a mixture of the metal powder and the metal fiber. At least one of the heat and the pressure is applied to the selected material to obtain the desired shape. That is, a jig or a mold is filled with a metal or a metal fiber, and then either or both heat and pressure are applied to the jig or the mold to form the desired shape. When heat is used, heat at a sintering temperature may be applied to sinter the metal, or heat at a preliminary sintering temperature lower than the sintering temperature may be applied to sinter the metal.

The preliminary sintering temperature is from about 80% to about 90% of the sintering temperature at which the metal is sintered.

Also, in order to obtain the desired shape by applying the pressure to the metal, an injecting molding method or a method of filling a jig or a mold and applying pressure to the jig or the mold may be used.

Meanwhile, when the wick 10 is formed of the metal powder or the metal fiber, the wick 10 is a porous sintered body due to the sintering operation. However, the sintering operation with respect to the wick 10 may be performed in operation S1 , or the wick 10 may be heated at the sintering temperature when the sintering operation is performed in one of subsequent operations such as the operation of coupling the unit assemblies (operation S4), the operation of coupling the assembly structure (operation S6), and the operation of coupling the heat transferring plate (operation S7).

That is, in the case where the sintering operation is already performed in the operation of forming the wicks (operation S1), heat at a temperature lower than the sintering temperature is applied in the subsequent operations so as to achieve an excellent coupling state with respect to a contact surface. However, in the case where the sintering operation is not performed in the operation of forming the wicks (operation

S1), the sintering operation has to be performed in the subsequent operations so that heat at the sintering temperature is applied to one of the subsequent operations, and at this time, an excellent coupling state with respect to the contact surface is achieved.

Meanwhile, the wick 10 may be formed to have a desired shape by selecting at least one material from the non-metal powder and the non-metal fiber, and then by applying at least one of heat and pressure to the selected material.

Examples of the non-metal powder include a ceramic-based AI203 powder, a carbon-based active carbon powder, and a carbon-based carbon graphite powder. A jig or a mold is filled with the non-metal powder or the non-metal fiber, and then either heat or pressure or both are applied to the jig or the mold to form the desired shape.

However, in the case where the non-metal material is selected to form the wick 10, the wick 10 formed of the non-metal material and the heat transferring fin formed of metal may not achieve desired coupling by using the heat in the subsequent operation of coupling the unit assemblies (operation S4) in which the wick 10 and the heat transferring fin are cross-coupled to form the unit assembly, and thus, the wick 10 and the heat transferring fin are formed to enlarge their contact area via the pressure.

In the operation of forming the wicks (operation S1) according to the current embodiment, the wick 10 is formed to have a desired shape by mixing the selected material with one of a thermoplastic polymer and an organic solvent, and then by applying one of heat and pressure to the mixture. The thermoplastic polymer corresponds to an adhesive polymer material including polyethylene (PE), polypropylene (PP), acryl resin, and styrene resin. Such a thermoplastic polymer is used to increase a powder adhesive property required before the sintering operation is performed, and to minimize damage and volume change which are occurred when the sintering operation is performed.

The wick 10 is formed by mixing the material selected from the non-metal powder and the non-metal fiber with one of the thermoplastic polymer and the organic solvent that is a sublimate material, and then by performing injection or pressurization.

The organic solvent, that is the sublimate material, is in a solid state at room temperature, and is phase-changed from the solid state to the vapor state by being heated at a predetermined temperature. As the organic solvent, a sublimated material such as naphthalene, or either ether or alcohol or both may be used. The organic solvent is used to manufacture a complicated shape that is generally difficult to obtain. Thus, when the organic solvent is added before a forming operation is performed, a portion of the shape, to which the organic solvent is added, is sublimated during the sintering operation so that the desired shape may be manufactured.

Also, in the case where the metal is mixed with one of the thermoplastic polymer and the organic solvent in the operation of forming the wicks (operation S1), when forming of the wick 10 having a desired shape is completed, the mixed thermoplastic polymer or the mixed organic solvent may be removed by using one of a solvent extraction method and a pyrolysis method.

When the LHP system operates at a later time, residue from the thermoplastic polymer or the organic solvent may react with the working fluid, which may cause corrosion, fouling, or non-condensable gas. Thus, the residue has to be removed.

In the operation of forming the heat transferring fins (operation S2), a plurality of heat transferring fins 20 respectively having a wick coupler 22 are formed, and the wick

10 may be coupled to the wick coupler 22 (refer to FIG. 9). The heat transferring fin 20 is generated by processing metal having a relatively high thermal conductivity by using a milling machine, etc. Different methods of processing the metal may be used. The heat transferring fin 20 receives heat from the heat transferring plate 50, and transfers the received heat to the wick 10.

The heat transferring fin 20 includes a bottom member 24 and a plurality of protrusions 26 and 28. A top surface of the bottom member 24 contacts a bottom surface of the wick 10, and inner side surfaces of the protrusions 26 and 28 contact either side surface of the wick 10. The protrusions 26 located at one side end of the bottom member 24, and the protrusions 28 located at the other side end are respectively upward protruded from either end of the bottom member 24. The protrusions 26 and 28 are separated from each other to form spaces there between. These spaces function as passages for vapor generated in the wick 10. The heat transferring fins 20 are formed of materials which are different from the heat transferring plate 50, and thus, it may be easy to process a relatively complicated shape including the protrusions 26 and 28 and the wick coupler 22, and to adjust roughness of a processed surface to a desired level.

Meanwhile, the order of the operation of forming the wicks (operation S1) and the operation of forming the heat transferring fins (operation S2) may be reversed. Next, the operation of forming the unit assembly (operation S3) is performed.

In the operation of forming the unit assembly (operation S3), the wick 10 is inserted into the wick coupler 22 of the heat transferring fin 20 so that a unit assembly 30 is formed, as illustrated in FIG. 10.

Meanwhile, in the current embodiment, the operation of forming the unit assembly (operation S3) further includes an operation of inserting a coupling promoter to be located on at least a portion of a contact interface between the wick 10 and the heat transferring fin 20 before the wick 10 is inserted into the wick coupler 22 of the heat transferring fin 20. In the operation of inserting the coupling promoter, the coupling promoter is located on the contact interface via which the wick 10 and the heat transferring fin 20 mutually contact. Due to the coupling promoter, the contact interface between the wick 10 and the heat transferring fin 20 reaches metallic bond.

As the coupling promoter, one of a metal powder and a coupling material is selected. In the case where the coupling promoter is used, heat has to be applied to the unit assembly in the operation of coupling the unit assemblies (operation S4) in which one of heat and pressure is applied to the unit assembly.

The metal powder may be used as the coupling promoter in the following manner.

Before the wick 10 is inserted into the wick coupler 22 of the heat transferring fin 20, the metal powder is sprayed between the protrusions 26 and 28, and on the top surface of the bottom member 24. After that, the wick 10 is inserted between the protrusions 26 and 28. Since the metal powder has very small particles with a micro-sized diameter, if the metal powder is sprayed on a corresponding surface of the heat transferring fin 20 and then the wick 10 is inserted, the metal powder may be located on the contact interface between the wick 10 and the heat transferring fin 20. Otherwise, the metal powder may be sprayed on a corresponding surface of the wick 10, and then the wick 10 may be inserted into the heat transferring fin 20.

FIG. 11 is a magnified cross-sectional view when a metal powder 11 is located on a contact interface via which a wick 10 and a heat transferring fin 20 mutually contact each other. Meanwhile, the metal for the metal powder may be the same as or different from that used in the forming operation.

The coupling material may be used as the coupling promoter. The coupling material includes a solder-based material.

The solder-based material or another material is inserted into a space formed when the wick 10 is inserted into the heat transferring fin 20. That is, a material selected according to melting points of base materials of the wick 10 and the heat transferring fin 20 is inserted into the space and then soldered. For example, when the wick 20 and the heat transferring fin 20 are formed of copper, or when the wick 20 is formed of nickel and the heat transferring fin 20 is formed of copper, the coupling material includes the solder-based material such as Sn-Pb, Sn, or Pb. When the wick 20 is formed of stainless steel and the heat transferring fin 20 is formed of aluminum, the coupling material includes silver-solder, brass-solder, nickel-solder, gold-solder, platinum-solder, aluminum-solder, iron-solder, etc. Meanwhile, a polymer adhesive, or an adhesive polymer material, that is, a thermoplastic polymer including polyethylene (PE), polypropylene (PP), acryl resin, and styrene resin may be used as the coupling promoter.

In the operation of coupling the unit assemblies (operation S4), at least one of the heat and the pressure is applied to the unit assembly 30 so that the contact surface of the wick 10 and the contact surface of the heat transferring fin 20 are cross-coupled. That is, the heat may be applied to the unit assembly 30, the pressure may be applied to the unit assembly 30 in up and down-right and left directions of the unit assembly 30, or both heat and pressure may be applied to the unit assembly 30, whereby the contact surfaces of the wick 10 and the heat transferring fin 20 are cross-coupled. Meanwhile, if the operation of forming the unit assembly (operation S3) includes the operation of inserting the coupling promoter, coupling of the contact surfaces may become highly rigid.

A temperature of the heat to be applied is appropriately set according to a material for forming the wick 10 and, if the material for forming the wick 10 is metal, the temperature of the heat is appropriately set according to whether a sintering operation is to be performed in a current operation or in an operation to be performed at a later time.

In the operation of forming the assembly structure (operation S5), a plurality of unit assemblies 30 are horizontally disposed in such a manner that all bottom surfaces 29 of the unit assemblies 30 are located on one virtual planar surface, and an assembly structure 40 is formed thereof. By disposing all of the bottom surfaces 29 of the unit assemblies 30 to be located on one virtual planar surface, the unit assemblies 30 may be easily coupled to a planar top surface of the heat transferring plate 50 to be described later. Meanwhile, in the current embodiment, the operation of forming the assembly structure (operation S5) further includes an operation of disposing middle wicks 12 between unit assemblies 30 adjacent to each other. FIG. 12 is a diagram of an assembly structure 40 in which the middle wicks 12 are disposed between unit assemblies 30 adjacent to each other. By adding the middle wicks 12, a heat transfer area and a vapor generation area may be enlarged.

Also, spacers may be used instead of the middle wicks 12. FIGS. 13 through 16 are diagrams of two assembly structures 40a and 40b in which spacers are disposed between unit assemblies. Spaces formed by the spacers between the unit assemblies function as vapor passages, thereby allowing vapor generated in the wick 10 to be smoothly externally exhausted.

In the assembly structure 40a of FIGS. 13 and 14, comb-shaped spacers 14 are arranged between a plurality of unit assemblies 30a. Here, a plurality of heat transferring fins 20a respectively coupled to a plurality of wicks 10 are formed to have a significantly thin thickness, compared to those in the previous embodiment. Since the heat transferring fins 20a are individually processed, a plurality of bottom members 24a and a plurality of protrusions 26a and 28a may also be processed to have a significantly thin thickness. A plurality of vapor passages 15 are formed between the unit assemblies 30a due to the spacers 14.

FIGS. 15 and 16 are diagrams of the assembly structure 40b including a plurality of spacers 16 different from those of the embodiment of FIGS. 13 and 14. In the assembly structure 40b, a heat transferring fin 20b includes a bottom member 24b and a plurality of protrusions 26b and 28b which are formed to have a highly thinner thickness. A plurality of vapor passages 17 are formed between the unit assemblies 40b due to the spacers 16. Meanwhile, in order to form the vapor passages 15 and 17, jigs (not shown) having a shape similar to that of the spacers 14 and 16 may be used as the spacers 14 and 16. After the operation of coupling the heat transferring plate (operation S7) is performed, wherein an assembly structure is coupled to the heat transferring plate 50, the jigs are removed from the assembly structure. Also, the operation of forming the assembly structure (operation S5) may further include an operation of applying pressure to the assembly structure 40 in a horizontal direction, that is, in a direction toward which unit assemblies are disposed in a row, thereby shrinking a diameter of pores in the wicks 10. FIG. 17 is a diagram in which pressure applying directions are indicated by arrows. FIG. 18 is a diagram of a case where a diameter length of a pore 18 in the wick

10 is shrunken from DO to D1 as the unpressured pore 18 is pressured in a direction indicated by arrows. The shrunken pore 18 maintains its shrunken state even after the pressure is removed because of plastic deformation occurring according to a material of the wick 10. Meanwhile, the wick 10 functions to transport working fluid to an evaporation interface by the capillary pressure. At this time, if the diameter of the pore 18 is shrunken, that is, when the diameter is reduced, the capillary pressure may increase, thereby rapidly transporting the working fluid to the evaporation interface in which evaporation is occurred. Thus, cooling efficiency may increase. Moreover, according to other embodiments, the operation of forming the assembly structure (operation S5) may further include an operation of arranging pressing means capable of applying pressure to the assembly structure 40 in either side directions of the assembly structure 40. The pressing means may apply the pressure to the assembly structure 40 in horizontal either side directions of the assembly structure 40, and may shrink a diameter of pores in the wick 10.

As illustrated in FIG. 19, the pressing means may be a quadrangle-shaped frame 42, or may be a clamp (not shown) capable of being engaged to the assembly structure 40 in either side directions of the assembly structure 40 and capable of tightening the assembly structure 40 via a screw, etc. Also, a penetration hole horizontally penetrating through the assembly structure 40 may be formed, and a screw bolt may be placed in the penetration hole so as to apply pressure to the assembly structure 40 in a horizontal direction.

In the operation of coupling the assembly structure (operation S6), one of heat and pressure is applied to the assembly structure 40 so that the unit assemblies 30 are cross-coupled.

That is, by applying the heat to the assembly structure 40, by horizontally applying the pressure toward either side of the assembly structure 40, or by applying both heat and pressure to the assembly structure 40, contact surfaces of the unit assemblies 30 contacting each other are cross-coupled.

As illustrated in FIG. 12, in the operation of coupling the heat transferring plate

(operation S7), the assembly structure 40 is disposed on a top surface of the heat transferring plate 50, and then heat or both heat and pressure are applied to couple a contact surface of the assembly structure 40 with a contact surface of the heat transferring plate 50.

At this time, according to a property of a material of the heat transferring plate 50, a metal hot-melting method such as a brazing method or a soldering method may be used to couple the assembly structure 40 and the heat transferring plate 50.

After the operation of coupling the heat transferring plate (operation S7) is performed, the cover member 60 is coupled to the top surface of the heat transferring plate 50 (refer to FIG. 6).

Meanwhile, the aforementioned operations of the method of manufacturing the evaporator for the LHP system according to the embodiment of the present invention may be sequentially performed in an order of operation S1 through operation S7. However, the order of operation S1 through operation S7 may not be necessarily respected. That is, the operation of forming the wicks (operation S1), the operation of forming the heat transferring fins (operation S2), the operation of forming the unit assembly (operation S3), and the operation of forming the assembly structure (operation S5) may be first performed, and then the operation of coupling the unit assemblies (operation S4), the operation of coupling the assembly structure (operation S6), and the operation of coupling the heat transferring plate (operation S7) may simultaneously performed as one procedure, wherein one of the heat and the pressure, or both heat and pressure are used in operations S4, S6, and S7.

Otherwise, the operation of forming the wicks (operation S1), the operation of forming the heat transferring fins (operation S2), the operation of forming the unit assembly (operation S3), and the operation of forming the assembly structure (operation S5) may be first performed, subsequently, the operation of coupling the unit assemblies (operation S4) and the operation of coupling the assembly structure (operation S6) may be simultaneously performed as one procedure, and then the operation of coupling the heat transferring plate (operation S7) may be separately performed.

Otherwise, the operation of forming the wicks (operation S1), the operation of forming the heat transferring fins (operation S2), the operation of forming the unit assembly (operation S3), and the operation of forming the assembly structure (operation S5) may be first performed, subsequently, the operation of coupling the unit assemblies (operation S4) is performed, and then the operation of coupling the assembly structure (operation S6) and the operation of coupling the heat transferring plate (operation S7) may be simultaneously performed as one procedure. Hereinafter, operations of the evaporator for the LHP system manufactured by the aforementioned method according to the embodiment will be briefly described.

The heat transferring plate 50 is coupled to an electronic part (not shown) that is a heat source, thereby receiving heat from the electronic part. The received heat is transferred to the heat transferring fin 20, and then is transferred to the wick 10. Due to the heat transferred to the wick having the pores, the liquid working fluid existing in interior pores of the wick 10 is vaporized, is subsequently transported through the vapor passages arranged above the wick 10, and then is moved to a condenser via a vapor line. The working fluid is liquefied after externally dissipating the heat in the condenser, and then is supplied to the wick 10 via the liquid line. The above-described process is repeated so that the electronic part is cooled down.

Hereinafter, the performance of the aforementioned method of manufacturing the evaporator for the LHP system will be described.

According to the embodiments of the present invention, the heat transferring fin to be coupled to the wick is formed as a separate member, the wick and the heat transferring plate are cross-coupled to form the unit assembly, the plurality of unit assemblies are horizontally disposed to achieve the assembly structure, and then the assembly structure is coupled to the heat transferring plate. Thus, it is possible to manufacture the wick and the heat transferring fin, each possibly having various shapes and sizes, and to minimize a thermal contact resistance between the wick and the heat transferring fin.

That is, compared to the conventional technology where all protrusions are directly integrally formed on the heat transferring plate, according to the embodiments of the present invention, since the heat transferring fin is processed as the separate member, it may be possible to form a relatively complicated shaped heat transferring fin, and to form a heat transferring fin having a significantly thin thickness.

According to the conventional technology, adhesion between the wick and the heat transferring fin can be increased only by adjustment for tolerance between the wick and the heat transferring fin or the like, and there is a limit in the increase of the adhesion between the wick and the heat transferring fin. However, according to the embodiments of the present invention, the adhesion between the wick and the heat transferring fin may be increased so that vapor generation may be given impetus and as a result, the evaporator may have an excellent function.

Also, according to the embodiments of the present invention, it is possible to easily adjust the thickness of the heat transferring fin so that it is possible to find and use an appropriate size for the vapor passages. Moreover, it is possible to manufacture the heat transferring fin according to a thickness of the wick, thus, it is possible to employ a thin wick and to adequately adjust a vapor generation area and a heat transfer area so that an optimal structure may be easily embodied.

In the embodiments of the present invention, the aforementioned easiness in embodying the optimal structure can maximize a heating area and the vapor generation area and can minimize the thermal contact resistance between the wick and the heat transferring fin including the protrusions, thus, total thermal resistance of the LHP system can be reduced.

If the wick is formed of metal, coupling between the wick and the heat transferring fin and coupling between the heat transferring fin and the heat transferring plate are not achieved by simply physically contacting the corresponding contact surface but are achieved by metallic coupling via one of heat and pressure or both heat and pressure. Thus, the contact thermal resistance at the contact interface is reduced.

According to the conventional technology, after a sintered wick is formed, this sintered wick is physically inserted into and coupled between protrusions of a base functioning as the heat transferring fin. Thus, even though a size of a contact surface between the sintered wick and the base appears to be enlarged, coupling in the contact surface between the sintered wick and the protrusions of the base is performed by point contacts, not by surface contacts, and thus, a state of the contact surface deteriorates such that actual thermal resistance in the contact surface is relatively high, and it is difficult to smoothly transfer heat from a heat source to the sintered wick.

However, according to the embodiments of the present invention, the contact surface between the wick and the heat transfer fin is not achieved via simple physical coupling but is achieved via metallic coupling wherein the metal is slightly hot-melted. Thus, compared to the conventional technology, the thermal resistance can be significantly reduced in the embodiments of the present invention, enabling the electronic part, that is, the heat source, to operate at a low temperature.

Meanwhile, in the embodiments of the present invention, the wick and the heat transferring fin do not directly contact the heat source, and thus, it is possible to freely adjust a structure of the heat transferring fin, the thickness and a width of the wick, etc. That is, with respect to forming the wick and the heat transferring fin, a thickness of each of the wick and the heat transferring fin, and an entire width of them may be easily adjusted to secure the heat transfer area and the vapor generation area as large as possible. When heat and the pressure are simultaneously applied to cross-couple the wick and the heat transferring fin, the cross-coupling becomes very rigid so that the thermal resistance at the contact interface is reduced.

Also, since the assembly structure is horizontally pressured, the diameter of the pores in the wick is shrunken, thereby increasing the capillary pumping force and as a result, the working fluid can be smoothly moved.

According to the embodiments of the present invention, the shape of the heat transferring fin may vary and the spacers may be disposed between the unit assemblies.

Due to such a structure, it is possible to freely change shapes of each of components, in order to make the vapor be smoothly externally exhausted.

FIGS. 21 through 23 are diagrams respectively corresponding to a modified heat transferring fin 20c, a unit assembly 30c, and an assembly structure 40c according to another embodiment of the present invention. Compared to the heat transferring fin of

FIG. 9, the heat transferring fin 20c according to the current embodiment does not include protrusions located at one side of the heat transferring fin 20c but only includes protrusions 28c located at the other side, and a bottom member 24c.

FIGS. 22 and 23 are diagrams respectively corresponding to the unit assembly

30c obtained by coupling such a heat transferring fin 20c and the wick 10, and to the assembly structure 40c achieved by horizontally disposing the unit assemblies 30c. The aforementioned method according to the embodiment of the present invention is identically applied to manufacture the assembly structure 40c.

Claims

1. A method of manufacturing an evaporator for a LHP (looped heat pipe) system, the method comprising: forming a plurality of wicks having pores; forming a plurality of heat transferring fins respectively having a wick coupler to be coupled to one of the plurality of wicks; inserting each of the wicks into the wick coupler of each of the heat transferring fin, thereby forming a plurality of unit assemblies; applying at least one of heat and pressure to the unit assemblies, and cross-coupling a contact surface of the wick and a contact surface of the heat transferring fin; horizontally disposing the unit assemblies to enable a bottom surface of each of the unit assemblies to be located on a planar surface, and forming an assembly structure; applying at least one of heat and pressure to the assembly structure, and cross-coupling the unit assemblies; and disposing the assembly structure on a top surface of a heat transferring plate having a planar plate shape, applying heat or heat and pressure to the assembly structure on the top surface, and coupling a contact surface of the assembly structure and a contact surface of the heat transferring plate.

2. The method of claim 1 , wherein the forming of the plurality of wicks comprises using a material selected from the group consisting of a metal powder, a non-metal powder, a metal fiber, and a non-metal fiber, and then applying at least one of heat and pressure to the selected material, thereby forming the plurality of wicks having a desired shape.

3. The method of claim 2, wherein the forming of the plurality of wicks comprises mixing the selected material with one of a thermoplastic polymer and an organic solvent, and then applying one of heat and pressure to the mixture, thereby forming the plurality of wicks having a desired shape.

4. The method of claim 3, wherein, after the plurality of wicks having the desired shape are formed, the forming of the plurality of wicks comprises removing the mixed thermoplastic polymer or the mixed organic solvent by using one of a solvent extraction method and a pyrolysis method.

5. The method of claim 1 , wherein, before the wick is inserted into the wick coupler of the heat transferring fin, the forming of the unit assembly further comprises inserting a coupling promoter selected from a metal powder and a coupling material whereby the coupling promoter can be located on at least a portion of a contact interface between the wick and the heat transferring fin.

6. The method of claim 1 , wherein the forming of the assembly structure further comprises disposing at least one of a middle wick and a spacer between the unit assemblies adjacent to each other.

7. The method of claim 1, wherein the forming of the assembly structure further comprises horizontally applying pressure to the assembly structure, thereby shrinking a diameter of the pores in the wick.

8. The method of claim 1, wherein the forming of the assembly structure further comprises arranging pressing means capable of applying pressure to the assembly structure in either side directions of the assembly structure, and capable of shrinking a diameter of the pores in the wick.

9. The method of claim 1 , wherein, after the forming of the plurality of wicks, the forming of the plurality of heat transferring fins, the forming of the unit assembly, and the forming of the assembly structure are performed, the cross-coupling of the contact surfaces of the wick and the heat transferring fin, the cross-coupling of the unit assemblies, and the coupling of the contact surfaces of the assembly structure and the heat transferring plate are simultaneously performed as one procedure, the cross-coupling of the contact surfaces of the wick and the heat transferring fin, and the cross-coupling of the unit assemblies are simultaneously performed, and then the coupling of the contact surfaces of the assembly structure and the heat transferring plate is performed, or the cross-coupling of the contact surfaces of the wick and the heat transferring fin is performed, and then the cross-coupling of the unit assemblies, and the coupling of the contact surfaces of the assembly structure and the heat transferring plate are performed.