JP7115091B2 - Evaporator and loop heat pipe - Google Patents

Description

The present invention relates to evaporators and loop heat pipes.

2. Description of the Related Art In recent years, in electronic devices, as a cooling means for cooling an object to be cooled, a method of cooling by inflowing a fluid serving as a coolant is known.
As one of such cooling methods, a loop-type heat pipe is known in which a fluid is circulated through a pipe between an evaporator and a condenser for cooling.
In such a loop heat pipe, a liquid-phase fluid is generally made to flow into an evaporator so that it permeates a porous body called a wick inside the evaporator by capillary action, and heat from the object to be cooled is transferred to the fluid seeping out from the surface of the wick. By receiving heat, the fluid undergoes a phase transition from the liquid phase to the gas phase. Then, the object to be cooled is cooled using the heat of vaporization at the time of phase transition.
The vaporized fluid is cooled in the condenser, returns to the liquid phase, and circulates by moving again to the evaporator side due to the pressure of the vaporized fluid.

By the way, the inventors found that when the heat from the object to be cooled is transmitted to the liquid phase fluid before permeating the wick in the evaporator through the housing of the evaporator, the liquid phase before permeating the wick of the fluid is superheated and creates bubbles. They also discovered that if air bubbles are generated in the liquid-phase fluid before it permeates the wick, the permeation of the liquid-phase fluid into the wick by capillary action is inhibited, and the cooling efficiency is reduced.

The present invention has been made based on the problems described above, and suppresses the phenomenon in which bubbles are generated in the liquid-phase fluid before penetrating the wick, which inhibits the penetration of the fluid into the inside of the porous wick. The purpose is to improve the cooling efficiency of the mold heat pipe.

The evaporator used in the loop heat pipe according to the present invention is an evaporator that causes a phase transition of a fluid inside a housing from a liquid phase to a gas phase by receiving heat from a heat receiving part of the housing, wherein the housing a porous member disposed inside; and a retention portion for retaining the fluid inside the housing separated from the inner wall surface of the housing by the porous member, wherein the porous member is and a connection portion formed between the retention portions, the connection portion connecting the heat receiving portion side of the porous member and the side opposite to the heat receiving portion side so as to connect the heat receiving portion side and the heat receiving portion side in the circulation direction. It is characterized by having an extending space .

According to the present invention, it is possible to improve the cooling efficiency of the loop heat pipe by suppressing the phenomenon in which air bubbles are generated in the liquid-phase fluid before penetrating the wick, which inhibits the penetration of the fluid into the inside of the porous wick. can be done.

It is a figure showing an example of composition of a loop type heat pipe which is an embodiment of the present invention. 2 is a diagram showing an example of the configuration of an evaporator of the loop heat pipe shown in FIG. 1; FIG. 3 is a diagram showing an example of the internal configuration of the evaporator shown in FIG. 2; FIG. It is a figure which shows the conventional example of an evaporator. FIG. 4 is a diagram showing an example of heat leak in an evaporator; FIG. 5 is a diagram showing an example of means for improving the evaporator shown in FIG. 4; FIG. 4 is a diagram showing an example of behavior of a refrigerant in the evaporator shown in FIG. 3; FIG. 4 shows a first modification of the evaporator shown in FIG. 3; FIG. 4 shows a second modification of the evaporator shown in FIG. 3; FIG. 4 shows a third modification of the evaporator shown in FIG. 3; Fig. 2 shows a second embodiment of an evaporator; FIG. 12 is a diagram showing another example of the evaporator shown in FIG. 11; FIG. 10 illustrates another embodiment of the invention;

As a first embodiment of the present invention, FIG. 1 shows a cooling device 100 which is a loop heat pipe.
The cooling device 100 includes an evaporator 10, a condenser 20, a pipe-shaped tube portion 30 connecting the evaporator 10 and the condenser 20, and a liquid reservoir arranged upstream of the evaporator 10 in the circulation direction. 40 , and the working fluid Q as a refrigerant flowing inside circulates while undergoing a phase transition between the gas phase and the liquid phase, thereby cooling the heat source 200 to be cooled.
In the following description, the Z direction is the front side perpendicular to the plane of FIG. 1, the Y direction is the upward direction perpendicular to the Z direction, and the X direction is the right-hand direction perpendicular to the Z direction. conduct.

In the cooling device 100 of the present invention, the working fluid Q enclosed inside the cooling device 100 circulates in the circulation direction indicated by A in FIG. there is
Of the pipes 30 connecting the evaporator 10 and the condenser 20, the pipe through which the working fluid Q moves in the vapor phase from the evaporator 10 to the condenser 20 is the vapor pipe 31, and the condenser 20 to the liquid reservoir 40. A pipe leading to the evaporator 10 is called a liquid pipe 32 .

When heat is conducted from the heat source 200 to the evaporator 10 , the phase of the working fluid Q changes from the liquid phase to the gas phase inside the evaporator 10 . The volume of the working fluid Q expands due to the phase change from the liquid phase to the gas phase. Since the porous wick 4 as a porous member is arranged in the evaporator 10 , the gas phase working fluid Q moves not to the porous wick 4 but to the vapor pipe 31 . That is, the working fluid Q in the gas phase passes through the evaporator 10 and moves from the vapor pipe 31 to the condenser 20 due to the pressure generated by the phase change.
The condenser 20 is a so-called radiator, and radiates the heat of the working fluid Q to change the phase of the working fluid Q from a vapor phase to a liquid phase. The liquid-phase working fluid Q is pushed in the direction of circulation by the pressure from the gas phase side, and therefore moves along the liquid pipe 32 to the liquid reservoir 40 .

As shown in FIG. 2, the evaporator 10 is an evaporator that changes the phase of the fluid inside the housing 11 from the liquid phase to the gas phase by bringing the heat receiving portion 1 of the housing 11 into contact with the heat source 200 .
The evaporator 10 has a flat plate shape, and the surface on which the heat receiving part 1 is formed has a flat shape.
The evaporator 10 includes a porous wick 4 as a porous member arranged inside a housing 11 , steam grooves 3 as grooves formed between the porous wick 4 and the heat receiving part 1 , and the porous wick 4 . and a retention portion 5 that is separated from the heat receiving portion 1 and holds the working fluid Q inside the housing 11 . Especially in FIG. 2 , the liquid-phase working fluid inflow space occupied by the working fluid Q corresponds to the retention portion 5 .
In this embodiment, the evaporator 10 has a flat plate configuration, but is not limited to such a configuration, and may have various shapes such as a cylindrical shape, depending on the design.
Moreover, in the present embodiment, the steam grooves 3 are formed at least between the porous wick 4 and the heat receiving section 1, but they may be formed in other places.
A plurality of steam grooves 3 are formed on the inner wall surface of the evaporator 10 on the side of the heat receiving part 1 , and the porous wick 4 is inserted into the evaporator 10 to surround the housing 11 and the porous wick 4 . function as a vented airway.

The porous wick 4 is a porous member formed on a substantially flat plate so as to match the shape of the inner surface of the housing 11 of the evaporator 10, as shown in FIG. For the material of the porous wick 4, it is preferable to use, for example, rubber with low thermal conductivity such as silicone rubber, or resin such as PTFE. Alternatively, if a metal is used, a sintered body of stainless steel powder having a relatively low thermal conductivity, or the like may be used. Note that the porous wick 4 in FIG. 3A is a perspective view simulating an example of a state in which the retaining portion 5 is filled with the working fluid Q. As shown in FIG. FIG. 3(b) shows a state before the working fluid Q is filled in a state arranged inside the housing 11. As shown in FIG. In addition, in FIG. 3A, hatching with oblique lines is omitted to improve visibility.
It is more preferable that the porous wick 4 is made of a material having flexibility, and in such a case, it is press-fitted into the housing 11 to improve adhesion.

When the porous wick 4 is inserted into the housing 11, the retention portion 5 is arranged so as to connect a wall surface 41 on the heat receiving portion side and a surface 42 on the non-heat receiving portion side facing the wall surface 41 on the heat receiving portion side. It has a connecting portion 6 formed by inserting the .

In the ZY section of the evaporator 10 at least in the region where the steam grooves 3 are formed, the retention portion 5 is formed so as to be surrounded by the porous wick 4, and the working fluid Q is in a liquid phase state and flows into the inner wall of the evaporator 11. It functions as an inflow space for a liquid-phase working fluid that is accommodated without direct contact.
The retention portion 5 is connected to the liquid reservoir portion 40 via the liquid pipe 32 .

Next, a conventional example of an evaporator in a circulation heat pipe is illustrated in FIG. 4 as an evaporator 10'.
The evaporator 10' includes a housing 11' mounted in contact with the heat source 200, a porous member 4', and steam grooves 3' formed in the wall surface of the housing 11' on the side in contact with the heat source 200. ,have.
Normally, when the working fluid Q flows in the liquid phase from the liquid tube 32', it permeates the micropores of the porous member 4' by capillary action and evaporates due to the heat from the housing 11'. The working fluid Q in vapor phase is discharged from the vapor pipe 31'.
At this time, the liquid-phase working fluid Q that permeates the porous member 4' is prevented by the presence of a gap, ie, a vapor groove 3', between the surface of the porous member 4' on the side of the heat source 200 and the housing 11'. It becomes easy to evaporate, and heat exchange efficiency improves.

In such an evaporator 10', when all the heat from the heat source 200 is thus used to evaporate the working fluid Q that has oozed out onto the surface of the porous member 4' in the steam grooves 3', the heat exchange Efficiency can be said to be in an ideal state.
However, in such an evaporator 10' that receives heat only on one side, as shown in FIG. A so-called heat leak, in which the previous working fluid Q is heated, may occur.

Due to this heat leak, the liquid-phase working fluid Q is overheated at a location other than the heat-receiving portion, for example, a location shown as a non-heat-receiving portion 2' in FIG. 5, and bubbles are generated in the liquid-phase working fluid Q. was there.
As a result, the cooling operation becomes unstable due to adverse effects such as hindrance of the capillary action for permeation of the working fluid Q into the porous member 4′, loss of pressure due to phase change, and decrease in fluidity of the working fluid Q. It is not preferable because there is a concern that

As a countermeasure, for example, as shown in FIG. 6, a configuration is considered in which steam grooves 3' are formed on both sides of a housing 11'. However, the steam groove 3' requires microfabrication of the housing 11', which complicates the housing 11 and increases the cost.

Therefore, the porous wick 4 according to the present embodiment has a connection portion 6 formed by inserting the retention portion 5 as already shown in FIG.
The effect of the connecting portion 6 will be described in detail.
In the conventional example shown in FIG. 5, bubbles are generated in the non-heat-receiving portion 2' because the working fluid Q is heated by heat leakage.
First, the porous wick 4 covers the wall surface including the heat-receiving part 1 as shown in FIG. Direct heating of the phases can be suppressed.

By the way, the working fluid Q that permeates the porous wick 4 in the vicinity of the wall surface 42 on the non-heat-receiving side is permeated by capillary action, so it is difficult for the working fluid Q to return to the retention section 5 under normal conditions.
In other words, it has been found that the working fluid Q tends to stay for a long time only by enclosing the working fluid Q directly with the porous wick 4 so as not to contact the inner wall surface of the housing 11 . In particular, the working fluid Q tends to stay on the wall surface 42 on the side of the non-heat-receiving portion, which is the opposite side across the retaining portion 5 from the heat-receiving portion 1 .
Furthermore, according to detailed studies by the inventors, the porous wick 4 not only covers the wall surface 41 on the side of the heat receiving portion and the surface 42 on the side of the non-heat receiving portion when the porous wick 4 is inserted into the housing 11. It has been found that by providing the connection portion 6 formed by inserting the retention portion 5 so as to be connected, the generation of air bubbles can be further suppressed and the fluidity of the working fluid Q can be improved.
For the liquid-phase working fluid Q in the retention portion 5, the connecting portion 6 functions as a bypass path through which the connecting portion 6 flows from the wall surface 42 to the wall surface 41, as schematically shown in FIG. It depends.

In this way, even if heat leakage occurs, the working fluid Q moves to the wall surface 41 on the side of the heat receiving portion via the connecting portion 6 without remaining on the non-heat receiving portion side such as near the wall surface 42 . This suppresses the generation of air bubbles due to heat leakage, suppresses the generation of heat leakage, and makes it possible to eliminate the instability of the cooling operation.
In this embodiment, since the shape of the evaporator 10 and the shape of the porous wick 4 are rectangular parallelepipeds, the expressions "wall surface 41 on the side of the heat-receiving part" and "wall surface 42 on the side of the non-heat-receiving part" are used. However, it is not limited to such wall surfaces. However, as described above, the connecting portion 6 is the position where the working fluid Q undergoes a phase change from the liquid phase to the gas phase by receiving heat from the object to be cooled, and is the farthest from this position in the evaporator 10 in the heat transfer path. It is considered that the effect of improving fluidity is the highest by connecting the Therefore, it is desirable that the connecting portion 6 be configured to connect the position corresponding to the vicinity of the heat receiving portion 1 and the position facing the heat receiving portion 1 .
With such a configuration, the evaporator 10 more efficiently transfers heat to the working fluid Q, so that the cooling operation is stabilized and the cooling efficiency of the cooling device 100 can be improved.

In addition, in the flat evaporator as in the present embodiment, the connecting portion 6 "stands vertically" from the wall surface 41 on the heat receiving portion side, and extends to the wall surface 42 on the non-heat receiving portion side in the shortest distance, so efficiency is improved. This facilitates the movement of the working fluid Q from the wall surface 42 on the non-heat-receiving portion side to the wall surface 41 on the heat-receiving portion side.
With such a configuration, it is possible to promote the permeation of the working fluid Q into the porous wick 4 and suppress the generation of air bubbles due to heat wraparound, thereby improving the cooling efficiency of the cooling device 100 .

Further, in the present embodiment, the thermal conductivity of the porous wick 4 is lower than that of the metal material such as aluminum that constitutes the heat receiving portion 1 .
With such a configuration, the porous wick 4 serves as a heat insulating material for the retention portion 5, so that heating due to heat leakage of the working fluid Q in the retention portion 5 can be suppressed.

Now, one or more such connecting portions 6 may be provided.
For example, as shown in FIG. 8 as a first modification, connecting portions 6b formed like polygonal prisms may be provided at a plurality of locations along the X direction.
As shown in FIG. 3, in the present embodiment, the porous wick 4 is formed over the entire Y direction. It is good as

Alternatively, as shown in FIG. 10 as a third modified example, a plurality of cylindrical connecting portions 6 may be provided. Note that the porous wick 4 shown in FIGS. 9B and 10 is a perspective view simulating an example of a state in which the retaining portion 5 is filled with the working fluid Q, similar to that shown in FIG. 3A. , and hatching with oblique lines indicating the porous wick 4 is omitted for improved visibility. FIG. 9(a) shows a state before the working fluid Q is filled in a state arranged inside the housing 11. FIG.

Further, in the first embodiment and the first to third modifications, the case where the shape of the evaporator 10 is flat was described, but as shown in FIG. 11 as the second embodiment, a cylindrical evaporator It may be used for the vessel 10 as well.
Also in the second embodiment, the heat source 200 is arranged in contact with the local heat receiving portion 1 as in the first embodiment.
The evaporator 10 includes a porous wick 4 as a porous member arranged inside a housing 11, a steam groove 3 as a groove formed between the porous wick 4 and the heat receiving part 1, and a porous wick and a retention portion 5 that is separated from the heat receiving portion 1 by 4 and holds the working fluid Q inside the housing 11 . That is, in the present embodiment, "the surface on which the heat receiving portion is formed has an arc shape".

In this embodiment, as shown in FIG. 11, the steam grooves 3 are arranged radially along the inner periphery of the housing 11 around the heat receiving section 1 . FIG. 11(a) shows the state before the working fluid Q is filled in the retention portion 5, and FIG. is filled with the working fluid Q.
In addition, as shown in the AA' cross section of FIG. It extends toward the wall surface 44 .
With such a configuration, it is possible to promote the permeation of the working fluid Q into the porous wick 4 and suppress the generation of air bubbles due to heat wraparound, thereby improving the cooling efficiency of the cooling device 100 .

When the evaporator 10 has a cylindrical shape, the connecting portion 6 may be formed radially from the wall surface 43 on the side of the heat-receiving portion so as to form an AA' cross section as shown in FIG. 12, for example. 12(a) and (b) are similar to FIGS. 11(a) and (b), FIG. 12(a) shows the state before the working fluid Q is filled in the retention portion 5, and FIG. 12(a) is an AA' cross section showing a state in which the retention portion 5 is filled with the working fluid Q. FIG.
With such a configuration, the penetration of the working fluid Q into the inside of the porous wick 4 is also promoted, and the generation of air bubbles due to heat wraparound is suppressed, thereby improving the cooling efficiency of the cooling device 100 .
When the evaporator 10 has a cylindrical shape as described above, the heat receiving portion 1 may be in point contact, or may be in contact with the circumferential surface. can be said to be any point on the circumference other than the heat receiving portion 1 .

Although the preferred embodiment has been described in detail above, it is not limited to the above-described embodiment, and various modifications and substitutions can be made to the above-described embodiment without departing from the scope of the claims. can be added.
For example, in the above-described embodiment, the steam grooves 3 are formed on the inner peripheral surface of the housing 11, but as shown in FIG. Also good.
Moreover, it is good even if it uses combining each modification mentioned above.

1 heat receiving part 4 porous member (porous wick)
5 retention part 6 connection part (connection part)
10 Evaporator 11 Housing 20 Condenser 30 Pipe 31 Steam pipe 32 Liquid pipe 41 Wall surface 42 on the side of the heat-receiving part Wall surface 100 on the side of the non-heat-receiving part Cooling device

Japanese Patent No. 5699452 JP 2014-062658 A JP 2016-211767 A

Claims (8)

An evaporator that causes a phase transition of a fluid inside a housing from a liquid phase to a gas phase by receiving heat from a heat receiving part of the housing,
a porous member disposed inside the housing;
a retaining portion for retaining the fluid inside the housing separated from the inner wall surface of the housing by the porous member;
The porous member has a connection portion formed between the retention portions, and the connection portion connects the heat receiving portion side of the porous member and the side opposite to the heat receiving portion side, and the circulation direction an evaporator having a space extending to the The evaporator of claim 1, wherein
The evaporator, wherein the surface on which the heat receiving portion is formed is planar. The evaporator of claim 1, wherein
The evaporator, wherein a surface of the housing on which the heat receiving portion is formed has an arc shape. The evaporator according to any one of claims 1 to 3,
a steam groove formed between the surface on which the heat receiving portion is formed and the porous member;
The evaporator, wherein the steam groove is not formed on the side facing the heat receiving portion . An evaporator according to any one of claims 1 to 4,
The evaporator, wherein the connecting portion is formed over the entire length of the retention portion. An evaporator according to any one of claims 1 to 4,
The evaporator, wherein the connecting part is formed in the shape of at least one column. An evaporator according to any one of claims 1 to 6,
The evaporator, wherein the heat conductivity of the porous member is lower than the heat conductivity of the material forming the heat receiving portion. an evaporator according to any one of claims 1 to 7;
a condenser into which the fluid is in a gaseous phase and is cooled;
a tube connecting the evaporator and the condenser to form a loop;
a working fluid circulating between the evaporator, the condenser, and the tube while changing between a gas phase and a liquid phase;
A loop heat pipe characterized by comprising:

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