US20100071880A1

US20100071880A1 - Evaporator for looped heat pipe system

Info

Publication number: US20100071880A1
Application number: US12/576,832
Authority: US
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
Current assignee: Zalman Tech Co Ltd; Sungkyunkwan University Foundation for Corporate Collaboration
Priority date: 2008-09-22
Filing date: 2009-10-09
Publication date: 2010-03-25

Abstract

An evaporator for a looped heat pipe (LHP) system, the evaporator including a plurality of wicks having pores formed therein; a plurality of heat transferring fins respectively having a wick coupler to be coupled to one of the plurality of wicks; a plurality of unit assemblies formed by respectively coupling each of the wicks and each of the heat transferring fins; an assembly structure formed by horizontally disposing the unit assemblies to enable a bottom surface of each of the unit assemblies to be located on a planar surface; a heat transferring plate coupled to a bottom part of the assembly structure; and a covering member coupled to the heat transferring plate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of pending International patent application PCT/KR2008/005694 filed on Sep. 25, 2008, which designates the United States and claims priority from Korean patent application 10 2008 0092421 filed on Sep. 25, 2008, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to 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 an evaporator for a LHP system, wherein the evaporator has a structure in which a wick and a heat transferring fin to be coupled to the wick are separately formed and then coupled to a heat transferring plate in a wing direction, and wherein the wick and the heat transferring fin are respectively formed having various shapes and sizes so that the thermal contact resistance between the wick and the heat transferring fin can be minimized.

BACKGROUND OF THE INVENTION

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 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 temperature gradient between the wick 410 and the protrusion 120 and the wick 410. 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.
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.

SUMMARY OF THE INVENTION

The present invention provides 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.
According to 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 separately formed, and an assembly structure formed by coupling the wick and the heat transferring fin is coupled to a heat transferring plate, so that it is easy to form the heat transferring fins and the wicks in a complicated shape and improve a contact state between the heat transferring fin and the wick.
According to an aspect of the present invention, there is provided an evaporator for a looped heat pipe (LHP) system, the evaporator including a plurality of wicks having pores formed therein; a plurality of heat transferring fins respectively having a wick coupler to be coupled to one of the plurality of wicks; a plurality of unit assemblies formed by respectively coupling each of the wicks and each of the heat transferring fins; an assembly structure formed by horizontally disposing the unit assemblies to enable a bottom surface of each of the unit assemblies to be located on a planar surface; a heat transferring plate coupled to a bottom part of the assembly structure; and a covering member coupled to the heat transferring plate.
The assembly structure may further include a spacer between neighboring unit assemblies so that the neighboring unit assemblies are separated from each other.
The assembly structure may further include a middle wick between the neighboring unit assemblies.
Each of the plurality of wicks may have a plate shape, and each of the plurality of heat transferring fins may include a bottom member and a plurality of protrusions, wherein the bottom member may be coupled to a bottom surface of the wick, and the protrusions separated from each other may be respectively upward protruded from either end of the bottom member so as to be located by either side surface of the wick.
Each of the plurality of wicks may have a plate shape, and each of the plurality of heat transferring fins may include a bottom member and a plurality of protrusions, wherein the bottom member may be coupled to a bottom surface of the wick, and the protrusions separated from each other may be upward protruded from one end of the bottom member so as to be located by one side surface of the wick.
The assembly structure may further include pressing means that horizontally applies pressure to the unit assemblies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a conventional 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 for a LHP system according to an embodiment of the present invention,

FIGS. 7, 8, and 9 are diagrams respectively corresponding to a wick, a heat transferring fin, and a unit assembly, which are of the evaporator of FIG. 6,

FIG. 10 is a diagram of an assembly structure of the evaporator of FIG. 6,

FIGS. 11 and 12 are diagrams of an assembly structure and its cross-sectional view according to another embodiment of the present invention,

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 through 17 are diagrams respectively corresponding to a heat transferring fin, a unit assembly, and an assembly structure according to another embodiment of the present invention,

FIG. 18 is a diagram of an assembly structure further including a quadrangle-shaped frame as a pressing means according to another embodiment of the present invention,

FIG. 19 is a diagram showing a case where a diameter length of a pore is shrunken by pressing means.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to 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.
A structure of an evaporator 1 for a LHP system according to an embodiment of the present invention will be described with reference to FIGS. 6 through 10. 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 unit assembly 30, an assembly structure 40, a heat transferring plate 50, and a cover member 60.
Referring to FIG. 7, each of the wicks 10 has a thin plate shape. The wicks 10 are respectively coupled to the heat transferring fins 20, and are horizontally disposed.
Each of the wicks 10 is a separate member, thus, it is easy to form the wicks 10 to have various shapes. The shape of the wick 10 may be changed when needed.
The wick 10 is porous and has a large number of pores formed therein. Working fluid that permeates into the pores is phase-changed into a vapor state by heat transferred from the heat transferring fin 20.
The wick 10 is formed to have a desired shape by 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 by applying either heat or pressure or both to the selected material. The wick 10 is formed by filling a frame with the selected material, and by applying one of heat and pressure to the frame or by using an injection molding method, etc.
As the selected material, a metal such as copper, brass, bronze, nickel, titanium, aluminum, stainless steel, etc., may be used. If the wick 10 is formed of the metal, the wick 10 has porosity due to sintering process. The sintering process may be performed when the wick 10 is formed, or may be performed when the wick 10 that was inserted into the heat transferring fin 20 is coupled to the heat transferring fin 20. Otherwise, the sintering process may be performed when the assembly structure 40 and the heat transferring plate 50 are cross-coupled.
If the wick 10 is formed of non-metal, examples of the non-metal include ceramic-based Al203, carbon-based active carbon, and carbon-based carbon graphite. A jig or a mold is filled with the non-metal powder or the non-metal fiber, and then either or both heat and pressure are applied to the jig or the mold to form the desired shape.
Each of the heat transferring fins 20 has a wick coupler 22 to which the wick 10 is inserted and coupled. The heat transferring fins 20 are disposed in parallel in a horizontal direction.
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 is produced by processing metal having a relatively high thermal conductivity by using a milling machine, etc. Different methods of processing the metal may be used
Referring to FIG. 8, 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 located at one side end are separated from each other to form spaces there between. These spaces function as passages for the vapor generated in the wick 10. The protrusions 28 located at the other side end are also separated from each other.
The heat transferring fins 20 are formed of materials which are different from the material of 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 in complicated shapes, and to adjust roughness of a processed surface to a desired level.
The unit assembly 30 is formed by coupling the wick 10 and the heat transferring fin 20.
In particular, if the wick 10 is formed of the metal, the wick 10 and the heat transferring fin 20 are cross-coupled via metallic coupling. The metallic coupling means that the wick 10 and the heat transferring fin 20 are cross-coupled by heat applied to a contact interface between the wick 10 and the heat transferring fin 20 so that metallic coupling is achieved at the contact interface, not by simply inserting or compulsorily putting the wick 10 into the heat transferring fin 20. By doing so, when the heat is transferred to the wick 10, thermal resistance in the contact interface is significantly reduced.
The assembly structure 40 is formed by horizontally disposing the unit assemblies 30. The horizontally disposed unit assemblies 30 are arranged in such a manner that each of bottom surfaces of the unit assemblies 30 is located on one virtual planar surface. Thus, the assembly structure 40 can be coupled to the heat transferring plate 50.
Meanwhile, in the current embodiment, the assembly structure 40 further includes a middle wick 12 between the unit assemblies 30 adjacent to each other. The middle wick 12 may be disposed in such a manner that a bottom surface of the middle wick 12 contacts the heat transferring plate 50. The middle wick 12 is equal to the wick 10, except a fact that the middle wick 12 is disposed in a position different from that of the wick 10.
The middle wick 12 receives heat from the heat transferring plate 50 coupled to the bottom surface of the middle wick 12, and from the heat transferring fins 20 coupled to either side of the middle wick 12. Working fluid in the middle wick 12 is phase-changed into a vapor state by the received heat so that the vapor is exhausted through the protrusions 26 and 28 of the heat transferring fins 20.
The heat transferring plate 50 is formed of metal, and is coupled to a bottom part of the assembly structure 40. A bottom surface of the heat transferring plate 50 contacts a heat source (not shown), 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.
A contact surface of the heat transferring plate 50 and a contact surface of the assembly structure 40 are cross-coupled via thermal and physical coupling. Here, 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 heat transferring plate 50 to the bottom surface of the assembly structure 40.
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.
Operations of the evaporator 1 having such a structure for the LHP system will be described.
The working fluid in a liquid state is injected into the evaporator 1 through the liquid line coupling hole 64 of the cover member 60, and is permeated into a large number of pores which are formed inside the wick 10 and the middle wick 12. The heat, which is transferred from the heat source to the heat transferring fins 20 via the heat transferring plate 50, is transferred to the wick 10 and the middle wick 12, thereby phase-changing the working fluid from a liquid state into a vapor state. Since the wick 10, the middle wick 12, and the protrusions 26 and 28 of the heat transferring fins 20 are cross-coupled to form vapor passages there between, the vaporized working fluid may pass through the vapor passages, and may be exhausted through the vapor line coupling hole 62 of the cover member 60.
In the structure of the evaporator 1 for the LHP system according to the current embodiment, the wick 10 and the transferring fin 20 to be coupled to the wick 10 are separately formed, and the unit assemblies 30 are disposed and coupled to the heat transferring plate 50, wherein the unit assemblies are respectively formed by coupling the wick 10 and the transferring fin 20.
Since the wick 10 and the transferring fin 20 are separately formed and then coupled to form the unit assembly 30, it is possible to form the wick 10 and the transferring fin 20 possibly in various shapes and sizes, and it is easy to rigidly cross-couple the wick 10 and the transferring fin 20 via heat or pressure, so that it is possible to minimize the thermal contact resistance in the contact interface between the wick 10 and the heat transferring fin 20.
That is, compared to the conventional technology wherein all protrusions are directly integrally formed on a heat transferring plate, according to the current embodiment of the present invention, since the heat transferring fin 20 is processed as a 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.
Such easiness in forming the heat transferring fin may maximize a heating area and the vapor generation area, and may minimize the thermal contact resistance between the wick 10 and the heat transferring fin 20 including the protrusions 26 and 28, thus, total thermal resistance of the LHP system may be reduced.
If the wick 10 is formed of the metal, coupling between the wick 10 and the heat transferring fin 20, and coupling between the heat transferring fin 20 and the heat transferring plate 50 are not achieved by simply physically contacting the corresponding contact surfaces but are achieved by metallic coupling via either heat or pressure or both. Thus, the contact thermal resistance in the contact interface is reduced.
However, according to the conventional technology, due to a limitation in forming the sintered wicks and protrusions integrally formed on a base in a desired shape, the sintered wicks are inserted into and simply coupled between the protrusions. Thus, even though a size of a contact surface between the sintered wicks and the base appears to be enlarged, coupling in the contact surface between the sintered wicks 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 wicks.
However, in the current embodiment of the present invention, the wick 10 and the heat transferring fin 20 do not directly contact the heat source, and thus, it is possible to freely adjust a structure of the heat transferring fin 20, the thickness and a width of the wick 10, etc. That is, with respect to forming the wick 10 and the heat transferring fin 20, a thickness of each of the wick 10 and the heat transferring fin 20, 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.
FIG. 11 is a diagram of an assembly structure 40 a modified in comparison to the previous embodiment of the present invention. Components which are not illustrated in FIG. 11 are the same as those in the previous embodiment. FIG. 12 is a cross-sectional view of the assembly structure 40 a of FIG. 11.
In the assembly structure 40 a according to the current embodiment, spacers 14 are arranged between unit assemblies 30 a adjacent to each other so as to separate the unit assemblies 30 a from each other. The spacer 14 is comb-shaped. A space formed by the spacer 14 between the unit assemblies 30 a is used as a vapor passage, thereby allowing the vapor generated in a wick 10 to be smoothly externally exhausted.
A plurality of heat transferring fins 20 a respectively coupled to the plurality of wicks 10 are formed to have a significantly thin thickness, compared to those in the previous embodiment. Since the heat transferring fins 20 a are individually processed, a plurality of bottom members 24 a and a plurality of protrusions 26 a and 28 a may also be processed to have a significantly thin thickness. A plurality of vapor passages 15 are secured between the unit assemblies 30 a due to the spacers 14.
FIG. 13 is a diagram of an assembly structure 40 b having spacers 16 different from those of the embodiment of FIG. 11. Components which are not illustrated in FIG. 13 are the same as those in the previous embodiment. FIG. 14 is a cross-sectional view of the assembly structure 40 b of FIG. 13.
In the assembly structure 40 b, a heat transferring fin 20 b includes a bottom member 24 b and a plurality of protrusions 26 b and 28 b which are formed to have a highly thinner thickness. A plurality of vapor passages 17 are formed between the unit assemblies 40 b due to the spacers 16.
Meanwhile, FIGS. 15 through 17 respectively show an altered heat transferring fin 20 c, a unit assembly 30 c, and an assembly structure 40 c according to another embodiment of the present invention. Compared to the heat transferring fin 20 of FIG. 8, the heat transferring fin 20 c according to the current embodiment does not include protrusions located at one side of the heat transferring fin 20 c but only includes protrusions 28 c located at the other side, and a bottom member 24 c. FIGS. 16 and 17 respectively show the unit assembly 30 c obtained by coupling the heat transferring fin 20 c and the wick 10, and the assembly structure 40 c obtained by horizontally disposing the unit assemblies 30 c.
FIG. 18 is a diagram of an assembly structure 40 further including a quadrangle-shaped frame 42 as pressing means according to another embodiment of the present invention.
The quadrangle-shaped frame 42 as the pressing means applies pressure to unit assemblies 30 constituting the assembly structure 40 in a horizontal direction. Here, the horizontal direction indicates a direction in which the unit assemblies 30 are disposed in parallel.
The pressing means applies pressure to the unit assemblies 30 in either side of the unit assemblies 30, and thus make the diameter of pores in the wick 10 shrink. Meanwhile, although not illustrated in FIG. 18, the pressing means may be a clamp capable of pressing the assembly structure 40 from either side via a screw, etc. Also, a penetration hole horizontally penetrating through the assembly structure 40 may be arranged, 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.
FIG. 19 is a diagram showing a case where a diameter of a pore 18 in the wick 10 is shrunken from D0 to D1 as the unpressured pore 18 is pressured in a direction indicated by arrows.
Meanwhile, the wick 10 transports the working fluid to an evaporation interface by a capillary pressure. At this time, if the diameter of the pore 18 is shrunken, the capillary pressure may increase, thereby smoothly transporting the working fluid to the evaporation interface.

Claims

1. An evaporator for a LHP (looped heat pipe) system, the evaporator comprising:

a plurality of wicks having pores formed therein;

a plurality of heat transferring fins respectively having a wick coupler to be coupled to one of the plurality of wicks;

a plurality of unit assemblies formed by respectively coupling each of the wicks and each of the heat transferring fins;

an assembly structure formed by horizontally disposing the unit assemblies to enable a bottom surface of each of the unit assemblies to be located on a planar surface;

a heat transferring plate coupled to a bottom part of the assembly structure; and

a covering member coupled to the heat transferring plate.

2. The evaporator of claim 1, wherein the assembly structure further comprises a spacer between neighboring unit assemblies so that the neighboring unit assemblies are separated from each other.

3. The evaporator of claim 1, wherein the assembly structure further comprises a middle wick between the neighboring unit assemblies.

4. The evaporator of claim 1, wherein each of the plurality of wicks has a plate shape, and each of the plurality of heat transferring fins includes a bottom member and a plurality of protrusions,

wherein the bottom member is coupled to a bottom surface of the wick, and the protrusions separated from each other are respectively upward protruded from either end of the bottom member so as to be located by either side surface of the wick.

5. The evaporator of claim 1, wherein each of the plurality of wicks has a plate shape, and each of the plurality of heat transferring fins includes a bottom member and a plurality of protrusions,

wherein the bottom member is coupled to a bottom surface of the wick, and the protrusions separated from each other are upward protruded from one end of the bottom member so as to be located by one side surface of the wick.

6. The evaporator of claim 1, wherein the assembly structure further comprises pressing means that horizontally applies pressure to the unit assemblies.