JP7415540B2 - Evaporator and loop heat pipe - Google Patents

Description

The present invention relates to an evaporator and a loop heat pipe.

BACKGROUND ART In recent years, in electronic devices, a method of cooling an object by flowing a fluid as a refrigerant has been known as a cooling means for cooling an object to be cooled.
As one such cooling method, a loop heat pipe is known that circulates fluid between an evaporator and a condenser through a tube for cooling.
Such loop heat pipes generally allow liquid-phase fluid to flow into the evaporator, causing it to permeate a porous body called a wick inside the evaporator by capillary action, and the fluid seeping out to the wick surface absorbs heat from the object to be cooled. By receiving heat, the fluid undergoes a phase transition from the liquid phase to the gas phase. Then, the heat of vaporization during this phase transition is used to cool the object to be cooled.
The vaporized fluid is cooled in the condenser and returns to a liquid phase, and is circulated by being transferred to the evaporator again due to the pressure of the vaporized fluid.

Now, these porous wicks are particularly susceptible to deformation at the points where they come into contact with the inner wall of the evaporator case, but as a result of excessive pressure being applied at these points of contact, the internal structure of the porous wick collapses. It becomes difficult to transport the working fluid to a region where active evaporation occurs, and there is a risk that cooling efficiency will decrease.

The present invention has been made based on the above-mentioned problems, and an object of the present invention is to suppress a decrease in cooling efficiency due to deformation even when a porous wick is made of a material that easily deforms.

The evaporator according to the present invention is an evaporator that changes the phase of the fluid inside the casing from a liquid phase to a gas phase by receiving heat in a heat receiving part of a casing, and the evaporator has an inner wall of the evaporator in the heat receiving part. The porous member has a groove formed between the porous member and the fluid, the inner wall has at least one convex portion having a width smaller than the width of the concave portion of the groove, and the porous member includes: The longitudinal elastic modulus of the portion of the porous member that can be inserted into the housing and in which the recess is formed is smaller than the longitudinal elastic modulus of the convex portion, and the convex portion provided on the inner wall side of the heat receiving portion has a height equal to or less than the depth of the recess of the groove before the porous member is inserted into the housing, and is compressively deformed when the porous member is inserted into the housing. As a result, the height of the convex portion and the depth of the concave portion of the groove portion match, so that the tip of the convex portion formed on the inner wall of the evaporator comes into contact with the bottom of the concave portion of the groove portion, and It is characterized by having a gap formed on both sides of the convex part with the side wall of the concave part.

According to the present invention, even when a porous wick is made of a material that easily deforms, it is possible to suppress a decrease in cooling efficiency due to deformation and improve the cooling efficiency of a loop-type heat pipe.

1 is a diagram showing an example of the configuration of a loop-type heat pipe according to an embodiment of the present invention. 2 is a diagram showing an example of the configuration of an evaporator of the loop-type heat pipe shown in FIG. 1. FIG. 3 is a diagram showing an example of a cross-sectional configuration of the evaporator shown in FIG. 2. FIG. It is a figure which shows the modification of an evaporator. 4 is an enlarged view showing an example of the uneven shape shown in FIG. 3. FIG. 4 is a diagram showing an example of the configuration of the porous member shown in FIG. 3. FIG. It is a figure showing a comparative example of an evaporator. It is a figure which shows typically the deformation|transformation of the convex part formed in a porous member. FIG. 4 is a diagram showing an example of the flow of working fluid during operation of the evaporator shown in FIG. 3; FIG. 6 is a diagram showing an example of a shape change during press-fitting caused by the size of unevenness. It is a figure which shows an example of the combination of the uneven|corrugated shape of the inner wall of an evaporator, and a porous member. 12 is a diagram showing a first modification of the evaporator shown in FIG. 11. FIG. 12 is a diagram showing a second modification of the evaporator shown in FIG. 11. FIG. 12 is a diagram showing a third modification of the evaporator shown in FIG. 11. FIG. 12 is a diagram showing a fourth modification of the evaporator shown in FIG. 11. FIG. 12 is a diagram showing a fifth modification of the evaporator shown in FIG. 11. FIG. It is a figure which shows the 6th modification of the evaporator shown in FIG.

As a first embodiment of the present invention, FIG. 1 shows a cooling device 100 that is a loop-type heat pipe.
The cooling device 100 includes an evaporator 10, a condenser 20, a pipe-shaped tube section 30 that connects the evaporator 10 and the condenser 20, and a liquid reservoir section disposed upstream of the evaporator 10 in the circulation direction. 40, and is a circulation type heat pipe that cools the heat source 200 to be cooled by circulating the working fluid Q as a refrigerant flowing inside while undergoing a phase transition between a gas phase and a liquid phase.
In the following description, the upper side of FIG. 1 is assumed to be the Z direction, the direction perpendicular to the Z direction is the Y direction, and the right hand direction of the page perpendicular to the Z direction is the X direction.

In the cooling device 100 of the present invention, the working fluid Q sealed inside the cooling device 100 circulates in the circulation direction shown by A in FIG. There is.
Among the pipe sections 30 that connect the evaporator 10 and the condenser 20, in particular, the pipe through which the working fluid Q moves in the gas phase from the evaporator 10 to the condenser 20 is the steam pipe 31, and the pipe from the condenser 20 to the liquid reservoir section 40 is called the steam pipe 31. The pipe that reaches the evaporator 10 via the liquid pipe is called a liquid pipe 32.

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

As shown in FIG. 2, the evaporator 10 causes a phase transition of the fluid inside the casing 11 from a liquid phase to a gas phase by bringing a heat source 200, which is a heating element, into contact with the heat receiving part 1, which is the surface of the casing 11. It is an evaporator.
In this embodiment, the evaporator 10 has a cylindrical shape with a circular cross section as shown in FIG. 3, and the surface on which the heat receiving part 1 is formed has a curved surface forming a side surface of the cylinder.
The evaporator 10 includes a porous wick 4 which is a porous member disposed inside a housing 11, a steam groove 3 which is a groove formed between the porous wick 4 and the heat receiving part 1, and a porous wick 4. It has a retention part 5 that is separated from the heat receiving part 1 and holds the working fluid Q inside the casing 11. Particularly in FIGS. 2 and 3, the liquid-phase working fluid inflow space occupied by the working fluid Q corresponds to the retention section 5.

Although the evaporator 10 has a cylindrical configuration in this embodiment, it is not limited to this configuration, and may have various shapes depending on the design, such as a flat plate shape or a cylindrical shape as shown in FIG. It's okay.
Further, in this embodiment, the steam groove 3 is formed at least between the porous wick 4 and the heat receiving section 1, but it may be formed at other locations as well.
As shown in an enlarged view in FIG. 5, a plurality of convex portions 13 are formed on the inner wall surface 12 of the heat receiving portion 1 of the evaporator 10, and the porous wick 4 is attached to the evaporator 10. By being inserted, the ventilation path surrounded by the housing 11 and the porous wick 4 functions as the steam groove 3.
That is, the inner wall surface 12 of the evaporator 10 in the heat receiving section 1 has at least one protrusion 13 having a width smaller than the width of the recess formed on the outer surface of the opposing porous wick 4.

The porous wick 4 is a porous member formed to match the inner surface shape of the casing 11 of the evaporator 10, as shown in FIG.
As the material for 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 metal is used, a sintered body of stainless steel powder or the like having relatively low thermal conductivity may be used.
It is more preferable that the porous wick 4 is made of a flexible material, and in such a case, it is press-fitted into the housing 11 to improve adhesion.

The porous wick 4 has a plurality of grooves formed on its outer surface. That is, the porous wick 4 has a groove formed with unevenness along the X direction, which is the stretching direction, and the porous wick 4 has a plurality of porous protrusions 41 and a porous recess 42. There is.
When the porous wick 4 is inserted into the housing 11, the porous protrusions 41 enter between the protrusions 13 as shown in FIG. 3 or 5, thereby creating voids on both sides of the porous protrusions 41. 43 is formed. In other words, the void portion 43 represents a space surrounded by the side surface of the porous convex portion 41 , the side surface of the convex portion 13 , the inner wall surface 12 , and the porous concave portion 42 .
At this time, the top of the protrusion 13 is placed in contact with the bottom surface 42a of the porous recess 42 so as to butt against it.
Similarly, the top portion 41a of the porous convex portion 41 is arranged so as to abut against the inner wall surface 12 of the housing 11.
In this way, it is most preferable that the depth d of the porous recess 42 and the height of the convex part 13 are provided to match. Further, it is more preferable that the height of the porous convex portion 41 and the height of the convex portion 13 are similarly provided to match.

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

Now, when such an evaporator 10 is used, heat is transmitted from the heat receiving part 1 in contact with the heat source 200, and the heat transmitted to the inner wall of the casing 11 heats the working fluid Q, so that the working fluid Q is evaporated. Heat exchange is performed by cooling with the heat of vaporization.

A comparative example of an evaporator in a circulation type heat pipe is illustrated in FIG. 7 as an evaporator 10'.
The evaporator 10' includes a casing 11' that is attached in contact with the heat source 200, a porous member 4', and a steam groove 3' formed in the wall surface of the casing 11' on the side that is in contact with the heat source 200. ,have.
Normally, when the working fluid Q flows in a liquid phase from the liquid pipe 32', it permeates into the fine pores of the porous member 4' by capillary action, and is evaporated by the heat from the housing 11'. The working fluid Q in the gas phase is discharged from the steam pipe 31'.
At this time, because there is a gap, that is, a steam groove 3', between the surface of the porous member 4' on the heat source 200 side and the housing 11', the liquid phase working fluid Q that has permeated into the porous member 4' It becomes easier to evaporate and improves heat exchange efficiency.

In such an evaporator 10', when all the heat from the heat source 200 is used to evaporate the working fluid Q that has thus seeped out onto the surface of the porous member 4' in the steam groove 3', heat exchange is performed. Efficiency can be said to be in an ideal state.

That is, for efficient cooling, a passage is required when the working fluid Q is vaporized, and a vapor groove 3' may be formed between the porous member 4' and the housing 11'. It was important.
However, it is difficult to process and form fine steam grooves 3 in a porous wick 4 made of foamed rubber as in this embodiment, and it is extremely difficult to process the groove width and pitch to a level of 1 mm or less. .
Furthermore, there is a known problem that it is difficult to achieve both cooling efficiency and size reduction because the number of grooves per unit area cannot be increased.

To address these problems, a configuration may be considered in which steam grooves 3' are formed on the inner wall surface of the casing 11', as shown in FIG. That is, the structure has a convex portion 13' that protrudes toward the inside of the housing 11', similar to that formed in this embodiment. However, even in this case, there is a problem in that the thickness of the metal housing 11' varies from part to part.
Furthermore, since the casing 11' needs to be resistant to internal pressure, it is difficult to keep the thickness d1 of the thin part of the inner wall surface constituting the recess of the steam groove 3' to a predetermined thickness or more due to the design. .
Furthermore, if the thickness of the thick portion of the inner wall surface is set to d2, the distance from the heat source 200 to the working fluid Q becomes wide.
The temperature difference caused by the thickness d2 to the top of the convex portion 13', which is the thick part of the housing 11', is calculated assuming, for example, that the heat source 200 is an object with a high heat generation density of 10 W/cm2 or more. The temperature may reach 10 degrees or more, which is not preferable.

In addition, when providing the steam groove 3 in the porous wick 4, since the porous wick 4 itself has flexibility, the protruding portion of the porous wick 4 is compressively deformed as shown surrounded by a broken line in FIG. There is also the problem that the porous fine structure is crushed and the effect of supplying the working fluid Q by capillary force is reduced.

Therefore, in the evaporator 10 of the present embodiment, the porous convex portion 41 and the porous concave portion 42 are formed in the porous wick 4, and the width of the adjacent porous concave portion 42 is also formed on the inner wall surface 12 of the housing 11. A convex portion 13 having a width smaller than that is formed.
Further, the tips of the protrusions 13 formed on the inner wall surface 12 abut the bottoms of the porous recesses 42, and voids 43 are formed on both sides of the protrusions 13 between the side walls of the porous recesses 42. .
As shown in FIG. Since the void 43 formed between the porous wick 4 and the housing 11 functions as the evaporation groove 3, the number of evaporation grooves 3 per unit area can be increased, improving heat exchange efficiency. Contribute to
In addition, as shown in FIG. 9 surrounded by a dashed line, the evaporation of the working fluid Q occurs at a thin part with a thickness d1 (i.e., the bottom of the recess 12) and a thick part with a thickness d2 (i.e., the top of the convex part 13). Since heat exchange can be performed at a position close to the heat source 200, the influence of the thermal resistance of the casing 11 can be suppressed to a small extent, contributing to improved cooling performance.

Furthermore, since the top of the metal protrusion 13 made of the same material as the housing 11 abuts against the bottom surface 42a of the porous recess 42, unnecessary pressure is not applied to the porous protrusion 41. The effect of preventing compressive deformation of the porous convex portion 41 and maintaining the capillary force due to the porous microstructure can also be expected.

Now, the height d of the protrusion 13 formed on the inner wall surface 12 of the casing 11 should ideally completely match the height d' of the porous protrusion 41 formed on the porous wick 4. is desirable, but in reality it is difficult to achieve a perfect match.

Consider a case where the height d of the convex portion 13 and the height d' of the porous convex portion 41 are different.
As shown in FIG. 10(a), when the height d of the convex part 13 is longer than the height d' of the porous convex part 41 (d>d'), as shown in FIG. 10(b), When pressure is applied during assembly, the porous recesses 42 are pressed by the protrusions 13, making the shape of the porous wick 4 unstable, and there is a possibility that the expected contact state may not be obtained.

On the other hand, when the height d of the convex part 13 is equal to or less than the height d' of the porous convex part 41 (d'≧d), as shown in FIGS. 10(c) and 10(d). As the porous convex part 41 is distorted due to the flexibility of the porous wick 4, the porous convex part 41 comes into contact with the inner wall surface 12 of the housing 11, and the convex part 13 comes into contact with the porous concave part 42. We will come into contact with each other.
According to this configuration, heat exchange is performed in a state close to the ideal configuration shown in FIG. 8, so that a decrease in heat exchange efficiency can be prevented.
At this time, as explained with reference to FIG. 8, it is not preferable if the difference is such that the porous convex portion 41 is crushed excessively, so it is specifically determined to the extent that the microstructure of the porous wick 4 is not crushed. It is desirable to appropriately set each numerical value of d and d' within the range of d'≧d so that the amount of squeezing of the porous convex portion 41 is within 20%.

As described above, in this embodiment, the height d of the convex portion 13 provided on the inner wall side of the casing 11 is equal to the depth of the porous concave portion 42 (that is, the height of the porous convex portion 41: d'). The longitudinal elastic modulus of the porous convex portion 41, which is the portion of the porous wick 4 where the steam groove 3 is formed, is smaller than the longitudinal elastic modulus of the convex portion 13.
According to this configuration, heat exchange is performed in a state close to the ideal configuration shown in FIG. 8, so that a decrease in heat exchange efficiency can be prevented.

Further, the shape of the porous convex portion 41 and the porous concave portion 42 of the porous wick 4 and the shape of the casing 11 are, for example, if the shape is a flat plate, convex portions extending linearly from each other as shown in FIG. Although a configuration having a concave portion and a concave portion is conceivable, it is also possible to have a discontinuous convex shape in which the convex portions 13 stand up in the form of independent columns, as shown in FIG.
In addition, the number of porous convex portions 41 and porous concave portions 42 formed in the porous wick 4 and the number of convex portions 13 formed in the housing 11 are different from each other when the porous wick 4 is press-fitted into the housing 11. The protrusions 13 may be provided alternately so as to mesh with each other when the porous recesses 42 are disposed, as shown in FIG. 41 may be in contact with the inner wall surface 12 between the convex portions 13.
In addition, in FIGS. 10 to 14, a part of the porous wick 4 has been extracted to simplify the explanation, and the combination in a flat plate shape has been described. It can be formed in a configuration.

According to this configuration, since the steam grooves 3 are formed on both sides of the combined convex portions 13 or on both sides of the porous convex portions 41, the pitch of the steam grooves 3 formed in the porous wick 4 can be made smaller. This makes it possible to improve the heat exchange efficiency of the evaporator 10.

Now, in this configuration, the positional relationship between the porous convex part 41 and the porous concave part 42 formed in the porous wick 4 and the housing 11 are such that the void part 43 is formed on both sides of the convex part 13. It is necessary to correctly establish the positional relationship between the convex portions 13 and the convex portions 13 formed therein before assembly.
Specifically, it is desirable to adjust the positional relationship so that the protrusion 13 is located between the side walls of the porous recess 42 (or the side walls of the porous protrusion 41).
However, as in this embodiment, when it is desired to provide the steam grooves 3 at a pitch of 1 mm or less, it is difficult to assemble them visually.

Therefore, as shown in FIG. 15(a), if the shape of the convex part 13 is made to stand up with an inclination from the direction perpendicular to the inner wall surface 12, in other words, the convex part 13 has an inclined part 13a. , it is formed into a tapered shape. According to this configuration, when the inclined part 13a and the porous convex part 41 come into contact during assembly, the elastic force of the porous wick 4 is applied along the inclined part 13a, as shown by the broken line in FIG. 15(b). Since the direction is changed, positioning is automatically performed to some extent by pressing as shown in FIG. 15(a), and assembly is facilitated.
In addition, in the case of such a configuration, the slope of the slope portion 13a is determined so that the width L of the flat portion 12a of the inner wall surface 12 matches the width L′ of the flat portion of the top portion 41a of the porous convex portion 41. It is more preferable.

Note that, in addition to providing the slope portion 13a on the convex portion 13 formed on the casing 11, this configuration also provides a slope portion on the porous convex portion 41 side of the porous wick 4 as shown in FIG. 16 to create a tapered shape. It's fine if you do it. Further, since the purpose is to easily perform mutual positioning, the tops of the convex portions 13 and the porous concave portions 42 may be provided in contact with each other by a combination of curved surfaces in addition to the tapered shape.
Needless to say, when the shape of the evaporator 10 is cylindrical, the "direction perpendicular to the inner wall surface 12" is a direction toward the central axis of the cylinder, and the evaporator 10 is inclined with respect to the central axis of the cylinder. part is formed.

In this way, at least one of the porous convex portion 41 provided on the porous wick 4 and the side surface of the convex portion 13 is inclined from the direction perpendicular to the inner wall surface 12 of the heat receiving portion 1. If the structure is made to stand up, it is possible to easily solve problems such as the steam groove 3 being blocked due to misalignment of the unevenness during assembly.

For example, even if both the porous convex portion 41 and the convex portion 13 have an inclined portion, as shown in FIG. By making the difference, a void portion 43 is formed. With this configuration, the steam groove 3 can be formed on either side of the porous convex portion 41 or the convex portion 13.

Although the preferred embodiments have been described in detail above, they are not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. can be added.
Furthermore, the above-mentioned modifications may be used in combination as appropriate.

1 Heat receiving part 3 Steam groove 4 Porous member (porous wick)
5 Retention part 10 Evaporator 11 Housing 20 Condenser 30 Pipe part 31 Steam pipe 32 Liquid pipe 41 Porous convex part 42 Porous concave part 43 Cavity part 100 Cooling device Q Working fluid

JP2019-007725A

Claims (6)

An evaporator that changes the phase of the fluid inside the housing from a liquid phase to a gas phase by receiving heat in a heat receiving part of the housing,
a porous member having a groove formed between an inner wall of the evaporator and the fluid in the heat receiving part;
The inner wall has at least one convex portion having a width smaller than the width of the concave portion of the groove,
The porous member is insertable into the housing,
The longitudinal elastic modulus of the portion of the porous member where the concave portion is formed is smaller than the longitudinal elastic modulus of the convex portion, and the height of the convex portion provided on the inner wall side of the heat receiving portion is such that the porous member The depth is equal to or less than the depth of the recess of the groove before being inserted into the housing,
The convex portion is formed on the inner wall of the evaporator so that the height of the convex portion matches the depth of the concave portion of the groove portion due to compression deformation of the porous member when inserted into the casing. The evaporator has a distal end thereof in contact with a bottom of the concave portion of the groove, and a gap portion formed on both sides of the convex portion with a side wall of the concave portion. The evaporator according to claim 1,
An evaporator characterized in that a difference in the depth of the recessed portion of the groove portion before and after the insertion is within 20% . The evaporator according to claim 1 or 2,
At least one of a side wall of the recess provided in the porous member and a side surface of the convex portion is inclined from a direction perpendicular to the inner wall of the heat receiving portion and stands upright. evaporator. The evaporator according to any one of claims 1 to 3,
An evaporator characterized in that the heat receiving section includes a planar heat receiving surface. The evaporator according to any one of claims 1 to 3,
An evaporator characterized in that the heat receiving section includes a heat receiving surface having a curved shape. The evaporator according to any one of claims 1 to 5,
a condenser into which the fluid flows in a vapor phase and is cooled;
a pipe connecting the evaporator and the condenser to form a loop;
a working fluid that circulates between the evaporator, the condenser, and the pipe while changing into a gas phase and a liquid phase;
A loop-type heat pipe characterized by having.

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