KR20090131533A - Evaporator for loop heat pipe system - Google Patents

Abstract

PURPOSE: An evaporator for a loop heat pipe system is provided to increase contact conductance by improving a contacting state by connecting a sintered wick and a heating plate simultaneously with sintering. CONSTITUTION: The evaporator for a loop heat pipe system includes: a heating plate(10) of a metal material transmitted heat from a heating source; a sintered wick(20) transmitted the heat by being connected to one side of the heating plate; and a groove(30) formed on the contact surface of the heating plate and the sintered wick, and functioning as a path that a gas phase-changed in the sintered wick can flow out through a gas transfer tube(220). The groove is formed on one side of the heating plate in the shape of a groove with the bottom side and both sides. The sintered wick is touched to at least one of both sides of the groove by a part thereof inserted in the groove.

Description

Evaporator for loop heat pipe system

The present invention relates to an evaporator which forms a loop heat pipe system together with a condenser, a gas conveying tube and a liquid conveying tube, and more particularly, to an evaporator capable of increasing the contact area between a sinter wick and a heating plate constituting the evaporator.

Electronic components such as CPUs and semiconductor chips used in various electronic devices such as computers generate a lot of heat during operation. Since such electronic products are usually designed to function properly at room temperature, if the heat generated during operation is not effectively cooled, their performance may be remarkably degraded and, in some cases, even damage to the product.

Various technologies such as heat conduction method using heat sink, natural convection and radiation method of air, steel convection method using fan, liquid circulation method or submersible cooling method have been developed as a cooling method for cooling the heat of electronic components. It is used.

However, as electronic products become slimmer, installation intervals between electronic components that generate heat during operation continue to narrow, and thus, heat generated when using electronic products is not properly cooled. In addition, since the heat load of the electronic components continues to increase due to the high integration and high performance of the electronic components, the above-described conventional cooling method may not effectively cool the electronic components.

As a new technology to solve this problem, the introduction of a phase change heat transport system capable of cooling an electronic component having a high heat load density per unit has recently been expanded. Examples of such phase change heat transfer systems include thermal siphon (thermosyphon) and cylindrical heat pipes.

Thermal siphon is a method in which the cooling is performed in a natural circulation method in the gravitational field according to the liquid-vapor phase change of the working fluid and the difference in specific gravity, and a typical cylindrical heat pipe 100 is illustrated in FIG. 1. By using the capillary pumping force of the sinter wick installed on the inner wall of the pipe, the working fluid is circulated and cooled. When the heat is transferred from the heat source 101, the working fluid contained in the sintered wick 102 is vaporized and moved along the arrow 103 indicated by the steam flow, and then liquefied again while losing heat to the heat sink 104. The sintering wick 102 is circulated while moving along the arrow 105 indicating the liquid flow by capillary pumping force.

However, thermosiphons require condensation to be higher than the evaporator, while bottom pipes are less dependent on the gravitational field than thermal siphons. Since the system has a limited positional relationship between the components, it has a disadvantage that it acts as a constraint on the slimming of electronic products employing it as a cooling system.

In addition, in the heat siphon and the cylindrical heat pipe, since the vapor and the liquid flow in opposite directions in the straight tube, the mixing of the vapor and the liquid occurs in the middle of the tube. There is also a big problem that this mixing makes a substantial amount of heat actually delivered rather than theoretically transferable.

The Loop Heat Pipe (LHP) system has been proposed as an ideal heat transfer system that can solve these problems, namely, space and location constraints, and steam and liquid mixing.

Loop heat pipe system is a kind of CLP (Capillary Pumped Loop Heat Pipe) technology developed by NASA in USA to cool large amount of heat generated from satellite communication equipment and electronic equipment.

As a related art related to a miniaturized loop heat pipe system, Korean Patent No. 671041 (name of the invention: loop hip pipe) is provided. 2 is a conceptual diagram of the loop heat pipe system 110 disclosed in the prior art, in which the conventional loop heat pipe system 110 includes a condenser 112, an evaporator 114, and a vapor line 116 and a liquid connecting them. Lines 118 are each connected to form a loop. In the case of the loop heat pipe system 110, unlike the conventional straight heat pipe (see FIG. 1), the sinter wick 120 is installed only in the evaporator 114.

Meanwhile, in the present specification, the loop heat pipe is also referred to as a loop heat pipe system, and both names are used interchangeably in the same sense, and the evaporator and the condenser have the same meaning as the evaporator and the condenser, respectively.

The principle of the operation of the loop heat pipe system 110 of this configuration is as follows.

First, when the lower member of the evaporator into which the sintered wick 120 is inserted is heated by a heat source as the heating plate 122, the sintered wick 120 penetrates into the sintered wick 120 by the heat transferred to the portion in contact with the heating plate 122. The working fluid is heated to saturation temperature and changes phase into gas. At this time, the generated gas is moved to the condenser 112 along the steam line 116 connected to one side of the evaporator 114. Subsequently, when the gas liquefies by releasing heat to the outside while passing through the condenser 112, the liquefied working fluid is moved back to the evaporator 114 along the liquid line 118 on one side of the condenser 112, The process is repeated and the heat source is cooled.

On the other hand, it will be described in more detail the process in which the working fluid infiltrated into the sintering wick 120 evaporates. Referring to FIG. 4, in which the sintered wick illustrated in FIG. 3 is flipped 180 degrees for convenience of description, the surface 126 of the sintered wick 120 facing the heating plate 122 may have a surface in contact with the heating plate 122. There is a contact surface 126b, and a microchannel 126a is formed to serve as a passage for the generated steam. Therefore, the sintered wick 120 receives heat from the surface 126b which is in contact with the heating plate 122, and the working fluid that has penetrated the sintered wick 120 is vaporized by this heat. The generated gas is moved to the condenser 112 along the steam line 116 connected to one side of the evaporator 114 through the fine channel 126a formed on the surface 126 facing the sintered wick 120.

At this time, the performance of the evaporator, which is an object of interest of the present invention and serves to take heat away from a heat source such as an electronic component, greatly depends on how well the heat generated from the heat source and transferred to the heating plate is transferred to the sintering wick. do. One factor that directly affects heat transfer between them is contact conductance.

Contact conductance is related to the thermal resistance that occurs when a metal is in surface contact with another metal and heat transfer occurs between them. Contact conductance is proportional to the contact area of the two metals in contact. In other words, as the contact area increases, the value of the contact conductance increases, and as the value of the contact conductance increases, heat transfer occurs better.

However, the conventional evaporator for a loop heat pipe system has a disadvantage in that the contact area between the sinter wick and the heating plate is reduced due to the existence of a vapor passage (microchannel), so that the value of the contact conductance is relatively small. That is, referring to FIG. 5, which schematically illustrates a cross section of a state in which a heating plate 122 and a sintered wick 120 having a steam passage 126a are coupled to each other in a cross sectional direction that is 90 degrees from the cross sectional direction of FIG. 3. In this case, the contact surface 126b contacting the sintered wick 120 and the heating plate 122 is reduced by the vapor passage 126a, thereby reducing the amount of heat that can be transferred.

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above problems, and an object thereof is to provide an evaporator having an increased value of contact conductance by increasing the contact area between a heating plate and a metal sintered wick in an evaporator for a loop bottom pipe system. have.

An evaporator according to the present invention comprises an evaporator including a sinter wick formed by sintering a metal powder, wherein the working fluid permeated between the pores of the sinter wick is heated to change into a gas; A condenser in which the gas delivered from the evaporator is changed into a liquid; A gas transfer pipe connecting the evaporator and the condenser so that the gas changed in the evaporator is transferred to the condenser; And a liquid transfer pipe connecting the condenser and the evaporator so that the phase-change liquid in the condenser can be fed back to the evaporator. The evaporator employed in a loop heat pipe (LHP) system configured to include A heating plate made of metal receiving heat from the heat source; A sintered wick coupled to one side of the heating plate to receive heat; And a groove formed on a surface where the heating plate is in contact with the sintered wick, and formed to serve as a passage through which the gas changed in the sintered wick may escape through the gas transfer pipe. A groove is formed on one side of the heating plate in a groove shape having a bottom surface and both sides, and the sintered wick is inserted into the groove to be in contact with at least a portion of both sides of the groove.

On the other hand, a portion of the sintered wick inserted into the groove is an insertion portion, each of the both sides of the insertion portion is in contact with each other on both sides of the groove, the lower surface of the insertion portion is convex down, convex up and It is preferable that it is either of the flat forms.

On the other hand, the heating plate is composed of a disk-shaped lower plate portion and a wall portion extending upward from the circumference of the lower plate portion, the sintered wick is coupled to an inner surface composed of the upper surface of the lower plate portion of the heating plate and the inner surface of the wall portion, The upper end of the wall portion of the heating plate is provided with a cover member, it is preferable that the liquid transfer pipe is coupled to the cover member.

According to the evaporator for a loop heat pipe system according to the present invention, the area in which the heating plate and the sintered wick are in contact with each other is increased, and thus the value of the contact conductance can be increased.

The present invention relates to an evaporator comprising a condenser, a gas conveying tube and a liquid conveying tube forming a loop heat pipe system. 6 schematically shows the overall configuration of a loop heat pipe system including the evaporator 1 of the present invention. The loop heat pipe system includes an evaporator 1, a condenser 210, a gas transfer tube 220, and a liquid transfer tube 230.

The condenser 210 is a place where the working fluid in the gaseous state received from the evaporator 1 is changed into a liquid. The condenser 210 takes heat from the working fluid and sends it to the outside atmosphere.

The gas transfer pipe 220 is a pipe member connecting the evaporator 1 and the condenser 210 so that the gas phase changed in the evaporator 1 is transferred to the condenser 210, the liquid transfer pipe 230 is a condenser It is a pipe member connecting the condenser 210 and the evaporator 1 so that the liquid phase-changed at 210 can be supplied to the evaporator 1 again.

On the other hand, with respect to the general description and operation of the condenser 210, the gas transfer pipe 220 and the liquid transfer pipe 230, what has been described in the background section above is applied as it is.

The evaporator 1, which is the object of the present invention, is one of the components constituting the loop heat pipe system together with the condenser 210, the liquid, and the gas transport pipes 220 and 230.

Referring to FIG. 7, which is a schematic cross-sectional view of the evaporator 1 of FIG. 6, the evaporator 1 includes a sintered wick 20 formed by sintering metal powder therein. The working fluid that has infiltrated between the pores formed in the sintered wick 20 is phase-changed to gas when heated by heat.

The evaporator 1 includes a heating plate 10, a sintered wick 20, and a groove 30.

The heating plate 10 is made of metal and receives heat from a heat source such as an electronic component that generates heat during operation.

In the present embodiment, the heating plate 10 is composed of a lower plate portion 12 and a wall portion 14. The lower plate part 12 has a disk shape, and the wall part 14 extends upward from the circumference of the lower plate part 12.

The lower plate part 12 and the side wall part 14 may be integrally formed, or may be separately manufactured and then combined.

The lower surface of the lower plate 12 is in contact with the heat source receives the heat. The heat transferred to the lower plate portion 12 is also transmitted by conduction to the wall portion 14 connected to the lower plate portion 12.

In addition, in the present embodiment, the cover member 16 is provided at the upper end of the side wall portion of the heating plate 10. The liquid transport tube 230 is coupled to the cover member 16 such that the working fluid in the liquid state from the condenser 210 flows into the internal space of the evaporator 1.

In addition, the cover member 16 of the evaporator 1, the liquid transfer pipe 230 is connected to the inlet port 17 through which the liquid can be formed, the heating plate 10 is connected to the gas transfer pipe 220 is An outlet 18 through which gas can flow is formed.

On the other hand, in the present embodiment, the lower plate portion 12 is in the shape of a disc and the side wall portion 14 has a shape surrounding the lower plate portion 12, and the upper portion is made of a cover member 16 in the form of a disc, so that the evaporator ( Looking at 1) as a whole, it has a hollow cylindrical shape. However, the present invention is not limited to such a shape, and various shapes, for example, the lower plate portion may be modified into a polygonal plate shape such as a rectangle.

The sintered wick 20 is coupled to one side of the heating plate 10 to receive heat. The working fluid in the liquid state contained in the pores of the sintered wick 20 is vaporized in the gaseous state by the received heat. The sintered wick 20 is formed by sintering metal powder, and a large number of spaces (= voids) are formed therein, so that a working fluid in a fluid state can be permeated.

The groove 30 is formed on the surface in contact with the heating plate 10 and the sintered wick 20, the gas phase change in the sintered wick 20 can exit through the gas transfer pipe 220 through the outlet 18. It is formed to serve as a passage. Therefore, the formed grooves 30 are formed to be in communication with the outlet 18, so that the gas can exit to the outside of the evaporator 1 through the gas transfer pipe 220.

In the present embodiment, the linear grooves 30 formed on the upper surface of the lower plate part 12 are spaced apart from each other and are arranged side by side, and spaces are formed at both ends of the grooves 30 along the circumference. In addition, grooves 30 are formed along the circumference of the wall portion 14, and a space penetrating them and communicating with the outlet 18 is formed. Therefore, the gas generated in the groove 30 formed in the lower plate portion 12 of the heating plate 10 is discharged into the space formed in the circumferential portion, the gas flows through the outlet port 18 along the space through the gas delivery pipe 220 It is configured to be discharged. In addition, the gas generated in the groove 30 formed in the wall portion 14 of the heating plate 10 is also configured to be discharged to the outside after moving to the outlet port 18 along the space therethrough.

Each groove 30 has a groove shape having a bottom surface 32 and both side surfaces 34, and is formed on one side surface of the heating plate 10.

On the other hand, in the present embodiment, the "one side" of the heating plate 10 has the same meaning as the "inner side" pointing together the inner surface facing the upper surface of the lower plate portion 12 and the inside of the wall portion 14. Therefore, the groove 30 is formed in the inner surface (= one side surface) which points to the upper surface of the lower board part 12 of the heating plate 10, and the inner surface of the wall part 14. As shown in FIG.

The sintered wick 20 is coupled to the inner surface of the heating plate 10 so as to receive heat. Particularly, the sintered wick 20 is partially inserted into the groove 30 to form the groove 30. It is in contact with at least a portion of both sides 34.

In the present embodiment, a portion of the sintered wick 20 inserted into the groove 30 is called the insertion portion 22. Each of the two side surfaces 24 of the insertion portion 22 is in contact with the top of the two side surfaces 34 of the groove 30, respectively. The insertion part 22 is inserted by about 1/3 of the height of the groove 30, and the lower surface 26 of the insertion part 22 is flat. At this time, the insertion length t of the insertion portion 22 into the groove 30 assumes that both sides of the insertion portion 22 are symmetrical, and both sides of the insertion portion 22 are coupled to both sides of the groove 30. Defined as meaning the length.

However, the insertion length t of the insertion portion 22 and the shape of the lower surface 26 have a necessity of securing a space for the contact area between the heating plate 10 and the sintered wick 20 and the role of the groove as a gas passage. It can be modified in consideration of factors such as the area of the surface area where the working fluid can be vaporized.

That is, the length of the insertion portion 22 may be determined to a predetermined value in consideration of the above elements, and the shape of the lower surface 26a of the insertion portion 22a is convex downward in combination with the change of the insertion length. (See FIG. 8) or the shape of the lower surface 26b of the insertion portion 22b may be formed to have a convex shape (see FIG. 9) upward.

Referring to FIG. 10, the contact length t with the groove side surface 34 of the insertion portion 22c of the sintered wick 20 is substantially the same as the height of the groove 30, and the lower surface 26c of the insertion portion is Convex up. This shape maximizes the contact area between the two side surfaces 24 of the sintered wick 20 and the two side surfaces 34 of the groove 30 of the heating plate 10, and also serves as a gas passage of the groove 30 and the vaporization surface thereof. It will be referred to as a shape to enable the area secured to the lower surface of the insertion portion 26c.

On the other hand, in the evaporator for a loop heat pipe system of the present invention, the insertion portion of the sintered wick is inserted into the groove formed in the heating plate to be brought into contact with the weak side surface of the groove, so that the contact area increases with respect to FIGS. 11 and 12. It is explained with reference to.

FIG. 11 is a schematic cross-sectional view of a state in which a sintered wick and a heating plate are coupled, and FIG. 12 is a perspective view schematically illustrating a heating plate in which grooves are formed. However, the sintered wick and the heating plate shown in FIGS. 11 and 12 are in the form of a square plate rather than a circular shape for ease of calculation, respectively, and grooves of the same length are formed by an integer n on the heating plate, and the lower surface of the insertion part is flat. Assume that Therefore, since it is not the same shape as the embodiment illustrated in FIG. 7, it is distinguished by attaching 'd' to the reference number.

The meanings of the indicators shown in FIGS. 10 and 11 are as follows.

W ': heating width W: groove width H: groove height

L: Groove length n: Number of grooves r _tw : Penetration rate of insertion part

A ': contact area r _w : contact length ratio

A: vapor evaporation area A _tw : penetration area A _t : total area

W '× L = A', W × L = A, A _t = n (A '+ A)

* Ratio of heating area to total area

If r _w = W / W ',

nA '/ A _t = nW'L / (n (W'L + WL) = W' / (W '+ W) = 1 / (1 + r _w ),

Assuming that the sintered wick penetrates into the reversible groove and is coupled by t depth, and is symmetrically on both sides of the groove, the increase in the contact area is as follows.

If r _tw = 2t / W, A _tw = 2tL = r _tw WL

Therefore, the contact area is

A '= n (W'L) + n (r _tw WL) = nL (W' + r _tw W).

Therefore, the ratio of the heating area to the sintered wick that penetrates into the groove increases.

nA '/ A _t = nL (W' + r _tw W) / (nL (W '+ W) = (W' + r _tw W) / (W '+ W) = (1 + r _tw r _w ) / (1 + r _w )

Becomes

In general, the size and number of grooves are determined by the specifications of the system, but the increase in contact area lowers the value of heat flux (W / ㎡), so the larger the value is, the better. If the contact length ratio r _w is 0.5, the penetration area ratio r _tw increases from 0.1 to 0.5, and the contact area ratio increases from 0.7 to 0.83. Compared to the case where the penetration ratio is 0, it increases from 0.67 to 0.7 ~ 0.83, so it increases by 0.03 ~ 0.17. Therefore, when the penetration ratio r _w is 1, that is, when t = W / 2, or 1 or more, the contact area has a contact area corresponding to or larger than the incident area.

Meanwhile, in the method of bonding the sintered wick 20 to one side of the heating plate 10, the metal powder is sintered to form the sintered wick 20, and at the same time, the sintered wick 20 is applied to the heating plate 10. There is a co-sintering method to be bonded, and a bonding method for bonding the sintered wick 20 to the heating plate 10 on which the grooves 30 are formed after forming the sintered wick 20. Joining methods are simple compression bonding method and metal bonding method.

First, the simultaneous sintering method will be briefly described.

A groove is formed in the metal heating plate, and the sublimable solid material is filled into the groove in consideration of the insertion length of the insertion portion of the sintered wick to be formed and the shape of the bottom surface thereof. That is, in consideration of the insertion portion inserted into the groove in FIGS. 7 to 9, the sublimable solid material is filled by the portion corresponding to the empty space of the groove. Then, the jig is placed on the heating plate, spaced apart by the thickness of the sintered wick. After the metal plate is filled with the heating plate and the jig, it is heated and sintered at a suitable temperature and time according to the type of the metal powder. The metal powder is sintered and bonded to the heating plate. In addition, as the metal powder is sintered, the sublimable solid material that is filled in the grooves is sublimed and exited to the outside, and the insertion portion of the sintered wick inserted into the groove is formed into the intended shape together with the empty space of the intended shape. Will be.

Next, the simple compression bonding method and the metal bonding method of the bonding method will be described.

The simple compression bonding method is a method in which a metal sintered wick prepared in advance is brought into contact with a heating plate and then bonded by applying a constant load. The metal bonding method is a method of bonding a sintered wick to a heating plate by contacting a previously prepared metal sintered wick with a heating plate and then applying heat to resinter (or secondary sintering).

The method of bonding the sintered wick 20 to one side of the heating plate 10 may be appropriately selected from any of the above-described methods.

As described above, according to the evaporator for a loop heat pipe system according to the present invention, the area in which the heating plate and the sintered wick are in contact with each other is increased, and the value of the contact conductance is increased. That is, in the prior art, the heating plate and the sintered wick were in contact with each other, except for the width corresponding to the width of the groove that serves as a steam passage. Therefore, the contact area between the heating plate and the sintered wick increases.

Further, according to the evaporator for the loop heat pipe system of the present invention, it is possible to vary the shape of the lower surface of the sintered wick portion (insertion portion) inserted into the groove, thereby increasing the contact area between the heating plate and the sintered wick. In addition, it is possible to adjust the cross-sectional area and gasification surface area of the gas passage additionally to obtain the optimum efficiency according to the conditions considering the role of mutual elements.

In addition, according to the simultaneous sintering method of bonding the sintered wick to the heating plate, the manufacturing process is simple and the cost of manufacturing the evaporator is low, and in particular, the contact state is improved because the bonding between the sintering wick and the heating plate proceeds simultaneously with the sintering. There is an advantage that the contact conductance is increased. In addition, by controlling the state of filling the groove of the sublimable material, there is an advantage that any shape of the insertion portion of the sintered wick can be formed.

On the other hand, when the sintered wick is bonded to the heating plate by the bonding method, the bonding state between the sintered wick and the metal heating plate is slightly lower than the co-sintering method described above. Compared with the prior art, it is still possible to obtain the advantage that the contact area between the sintered wick and the heating plate is increased. In addition, there is an advantage that the insert portion of the sintered wick can be processed into a desired shape by mechanical processing.

1 is a schematic diagram illustrating the operation of a conventional cylindrical heat pipe;

2 is a conceptual diagram of a conventional loop heat pipe system;

3 is a schematic cross-sectional view of the conventional evaporator of FIG.

4 is a schematic perspective view of rotating the sintered wick of FIG. 3 by 180 degrees;

5 is a schematic cross-sectional view of a sinter wick and a heating plate portion of the conventional evaporator of FIG.

6 is a schematic preliminary diagram of a loop heat pipe system including the evaporator of one embodiment according to the present invention;

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

8, 9 and 10 are modified examples of the sintered wick of FIG. 7, respectively.

11 is a schematic cross-sectional view of a state in which the sintered wick and the heating plate are combined;

12 is a perspective view schematically showing a heating plate in which grooves are formed.

Claims (3)

An evaporator configured to include a sintered wick formed by sintering a metal powder, wherein the working fluid permeated between the pores of the sintered wick is heated to change into a gas; A condenser in which the gas delivered from the evaporator is changed into a liquid; A gas transfer pipe connecting the evaporator and the condenser so that the gas changed in the evaporator is transferred to the condenser; and An evaporator employed in a loop heat pipe (LHP) system including a liquid conveying pipe connecting the condenser and the evaporator so that the liquid phase-changed in the condenser can be supplied to the evaporator again. The evaporator, A metal heating plate receiving heat from a heat source; A sintered wick coupled to one side of the heating plate to receive heat; And a groove formed on a surface where the heating plate and the sintered wick contact each other, and formed to serve as a passage through which the gas changed in the sintered wick may escape through the gas transfer pipe. The groove is formed on one side of the heating plate in a groove shape having a bottom surface and both sides, The sintered wick is evaporator for a loop heat pipe system, characterized in that a portion of the groove is inserted into the groove in contact with at least a portion of both sides of the groove. The method of claim 2, A portion of the sintered wick inserted into the groove is an insertion portion, Each of both sides of the insertion portion is in contact with each other on both sides of the groove, The bottom surface of the insertion portion is an evaporator of the loop heat pipe system, characterized in that any one of the convex shape, the convex shape and the flat shape. The method of claim 2, The heating plate is composed of a disk-shaped lower plate portion and a wall portion extending upward from the circumference portion of the lower plate portion, The sintered wick is coupled to an inner surface composed of an upper surface of the lower plate portion and an inner surface of the wall portion of the heating plate, An upper end of the wall portion of the heating plate is provided with a cover member, the cover member is evaporator for a loop heat pipe system, characterized in that the liquid transfer pipe is coupled.

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