JP6070036B2 - Loop thermosyphon and electronic equipment - Google Patents

Description

  The present invention relates to a loop thermosyphon and an electronic device including the loop thermosiphon.

  A semiconductor device (LSI: Large Scale Integration) such as a CPU used in a personal computer or server generates a large amount of heat as it operates. If the temperature of the semiconductor device exceeds the allowable temperature, malfunction or failure may occur, or the protection function may be activated to significantly reduce the processing capability. Therefore, it is important to cool the semiconductor device so that the temperature of the semiconductor device does not exceed the allowable range.

  For cooling a semiconductor device such as a CPU, an air cooling type or a water cooling type cooling device is generally used. The air-cooling type cooling device has metal fins mounted on the semiconductor device and a blower that sends air to the fins. The water-cooled cooling device has a metal hollow plate mounted on the semiconductor device, a heat exchanger, and a pump for circulating cooling water between the hollow plate and the heat exchanger.

  In recent years, due to the demand for higher performance, the appearance of semiconductor devices with power consumption of several hundred watts is expected. Since such a semiconductor device has a larger calorific value than a conventional semiconductor device, there is a possibility that it cannot be sufficiently cooled by an air-cooled or water-cooled cooling device. For this reason, a cooling device having a higher cooling capacity than the air-cooled or water-cooled cooling device is desired.

  One such cooling device is a loop thermosyphon. The loop thermosyphon transports heat using the latent heat of the refrigerant (working fluid). A general loop-type thermosyphon includes an evaporator that generates heat of a refrigerant by transferring heat from a heat source, a heat exchanger that is cooled by a blower or the like to return the refrigerant vapor to a liquid, and an evaporator and a heat exchanger. A gas-liquid two-phase pipe and a liquid pipe communicating with each other. In the case of a loop-type thermosyphon that uses water as a refrigerant, it has a heat transport capability that is five times or more that of a water-cooled cooling device.

JP-A-8-313178 JP 2008-134043 A Utility Model Registration No. 3170057

  An object of the present invention is to provide a loop-type thermosiphon having higher heat transport efficiency than conventional ones.

According to one aspect of the disclosed technology, an evaporator that generates refrigerant vapor, a heat exchanger that is disposed above the evaporator and that condenses the refrigerant vapor generated by the evaporator, and the evaporator A gas-liquid two-phase tube that communicates between the heat exchanger and the vapor of the refrigerant and has a smaller inner diameter than the gas-liquid two-phase tube, and communicates between the evaporator and the heat exchanger. A liquid pipe through which the refrigerant condensed in the heat exchanger passes, and the evaporator is disposed on the heat transfer section and is connected to the heat source, together with the heat transfer section There is provided a loop thermosyphon having a space in which the refrigerant is sealed and having a conical cover portion whose inner surface is subjected to hydrophobic treatment.

  According to the loop thermosyphon according to the above-described one aspect, the dryness of the steam in the evaporator is increased, and the heat transport efficiency is improved as compared with the conventional one.

FIG. 1 is a diagram showing the dryness of water vapor under atmospheric pressure. FIG. 2 is a diagram illustrating the loop thermosyphon according to the embodiment. FIG. 3 is a diagram illustrating a state where the loop-type thermosiphon according to the embodiment is mounted on a semiconductor device. FIG. 4 shows that droplets generated when the refrigerant evaporates in the evaporator and refrigerant that has condensed in the evaporator into a liquid adheres to the inner surface of the cover part and travels down along the wall surface of the cover part by gravity. It is a schematic diagram which shows the state which moves to. FIG. 5 is a diagram showing a loop thermosiphon according to the first modification. FIG. 6 is a diagram illustrating a loop thermosyphon according to the second modification. FIG. 7 is a diagram illustrating a loop thermosyphon according to the third modification. FIG. 8 is a schematic diagram illustrating an electronic device equipped with the loop thermosyphon according to the embodiment.

  Hereinafter, before describing the embodiment, a preliminary matter for facilitating understanding of the embodiment will be described.

  FIG. 1 is a diagram showing the dryness of water vapor under atmospheric pressure, with the horizontal axis representing enthalpy (calorie) and the vertical axis representing temperature.

  Under atmospheric pressure, water is in a liquid state when the temperature is from 0 ° C. to 100 ° C. And while the temperature is from 0 ° C. to 100 ° C., the temperature of water rises as the enthalpy rises.

  When the enthalpy exceeds 419 kJ / kg, the water becomes water vapor having a temperature of 100 ° C. While the enthalpy is between 419 kJ / kg and 2676 kJ / kg, the temperature of the water vapor remains at 100 ° C.

  Water vapor includes wet water vapor and dry water vapor. Water vapor having a temperature of 100 ° C. and an enthalpy of 419 kJ / kg has a dryness of 0% and is moist water vapor. In this case, water vapor has no latent heat.

  On the other hand, water vapor having a temperature of 100 ° C. and an enthalpy of 2676 kJ / kg has a dryness of 100% and is dry water vapor. In this case, the water vapor has a latent heat of 100%, ie 2257 kJ / kg.

  In a cooling device that uses latent heat to transport heat, such as a loop thermosyphon, more heat can be transported as the degree of dryness of steam increases, and cooling efficiency increases. However, in the loop thermosyphon, when the refrigerant (water in the above example) changes to vapor in the evaporator, splashing occurs due to boiling, or the vapor condenses in the evaporator and returns to liquid. For this reason, the dryness of the vapor | steam in an evaporator falls, heat transport efficiency becomes low, and cooling efficiency also becomes low.

  In the following embodiments, a loop thermosyphon having higher heat transport efficiency than the conventional one will be described.

(Embodiment)
FIG. 2 is a diagram illustrating the loop thermosyphon according to the embodiment. FIG. 3 is a diagram illustrating a state where the loop thermosyphon according to the embodiment is mounted on a semiconductor device.

  As shown in FIG. 1, the loop thermosyphon 10 includes an evaporator 11, a heat exchanger 12, a gas-liquid two-phase pipe 13, and a liquid pipe 14. The space in the loop thermosyphon 10 is filled with a refrigerant that changes into a liquid phase or a gas phase depending on the temperature. Furthermore, the space in the loop thermosyphon 10 is depressurized to about 1/100 atm, for example, and the refrigerant evaporates at a relatively low temperature.

  In the present embodiment, the case where water is used as the refrigerant will be described. However, alcohol, fluorine-based inert liquid, or other chemicals may be used as the refrigerant.

Evaporator 11 has a rectangular flat plate-like heat transfer part 21 is joined to the upper heat transfer section 21 together with the heat transfer portion 21 and a cover portion 22 that forms a quadrangular cone-shaped space.

  For example, a cylindrical space is provided inside the heat exchanger 12, and a large number of cooling fins 12a are provided outside. The heat exchanger 12 is disposed above the evaporator 11 as shown in FIG.

  The gas-liquid two-phase tube 13 communicates between the top of the evaporator 11 and one end of the space in the heat exchanger 12. The liquid pipe 14 communicates between the other end of the space in the heat exchanger 12 and a hole provided in the cover portion 22 of the evaporator 11.

  The inner diameter of the liquid pipe 14 is set smaller than the inner diameter of the gas-liquid two-phase pipe 13. The space in the heat exchanger 12 is wide on the gas-liquid two-phase tube 13 side and narrow on the liquid tube 14 side according to the inner diameters of the gas-liquid two-phase tube 13 and the liquid tube 14. The gas-liquid two-phase tube 13 and the liquid tube 14 are made of, for example, copper, copper alloy, stainless steel, aluminum, or aluminum alloy.

  As shown in FIG. 3, the heat transfer unit 21 of the evaporator 11 is disposed on a semiconductor device 32 mounted on a circuit board 31 via a heat transfer sheet 33. 3 is a semiconductor chip sealed in a package of the semiconductor device 32, and reference numeral 32b is solder for electrically and physically connecting the semiconductor device 32 and the circuit board 31.

  The heat transfer section 21 is formed of a metal having high thermal conductivity such as copper, copper alloy, aluminum, or aluminum alloy, and the lower surface that contacts the heat transfer sheet 33 is flat. In this embodiment, many unevenness | corrugations 23 are provided in the upper surface of the heat-transfer part 21, and the contact area of the heat-transfer part 21 and a liquid state refrigerant | coolant is enlarged. However, the unevenness 23 is not essential and may be provided as necessary.

  The upper surface of the heat transfer section 21 is subjected to hydrophilic treatment, and the inner surface of the cover section 22 is subjected to hydrophobic treatment. In the present embodiment, the upper surface of the heat transfer section 21 is covered with a hydrophilic film 24, and the inner surface of the cover section 22 of the evaporator 11 is covered with a hydrophobic film 25.

  As the film material of the hydrophilic film 24, for example, titanium oxide, aluminum oxide, silicon oxide, polyamide, or the like can be used. Further, as the film material of the hydrophobic film 25, for example, fluororesin, polypropylene, polyethylene, polysulfone, or the like can be used. Instead of forming the hydrophilic film 24, a hydrophilic surface may be imparted by providing fine irregularities on the upper surface side of the heat transfer section 21.

  As described above, it is possible to use a coolant other than water. However, in the present application, regardless of whether or not the coolant is water, the treatment that increases the contact angle with the liquid coolant is referred to as a hydrophobic treatment. The process in which the contact angle with the liquid refrigerant is reduced is called hydrophilic treatment.

  Hereinafter, the operation of the loop thermosyphon 10 described above will be described. Here, it is assumed that a certain amount of water (refrigerant) exists in a liquid state in the evaporator 11 in the initial state.

  Heat generated by the operation of the semiconductor device 32 is transmitted to the heat transfer section 21 via the heat transfer sheet 33, and the temperature of the heat transfer section 21 rises. As a result, the liquid refrigerant adhering to the heat transfer section 21 evaporates, and the heat transfer section 21 takes heat of evaporation.

  The steam generated in the evaporator 11 passes through the gas-liquid two-phase pipe 13 and enters the heat exchanger 12. Thereby, the temperature of the heat exchanger 12 rises. However, as described above, the heat exchanger 12 is provided with a large number of fins 12a, and the heat exchanger 12 is cooled by the wind passing between the fins 12a. Therefore, in the heat exchanger 12, the refrigerant | coolant vapor | steam condenses and returns to a liquid.

  In this case, in the heat exchanger 12, the diameter on the gas-liquid two-phase tube 13 side is large and the diameter on the liquid tube 14 side is small, so that a pressure difference is generated between the gas-liquid two-phase tube 13 and the liquid tube 14. . Due to this pressure difference, the refrigerant that has become liquid in the heat exchanger 12 moves toward the liquid pipe 14 and enters the liquid pipe 14. The liquid refrigerant that has entered the liquid pipe 14 then descends in the liquid pipe 14 due to gravity and enters the evaporator 11.

  In this way, the refrigerant circulates between the evaporator 11 and the heat exchanger 12 while changing between the liquid phase and the gas phase, whereby heat is transported from the evaporator 11 to the heat exchanger 12, and the semiconductor device 32 is cooled.

  By the way, in this embodiment, since the unevenness | corrugation 23 is provided in the upper surface side of the heat-transfer part 21, the contact area of the heat-transfer part 21 and a liquid state refrigerant | coolant is large, and the heat-transfer part 21 changes to a liquid state refrigerant | coolant. High heat transfer efficiency. Moreover, in this embodiment, since the hydrophilic film | membrane 24 is formed in the upper surface side of the heat-transfer part 21, even if the quantity of the refrigerant | coolant of the liquid state in the evaporator 11 decreases, the upper surface of the heat-transfer part 21 The liquid refrigerant wets and spreads to the side. For this reason, the heat transfer efficiency from the heat transfer part 21 to the liquid refrigerant is further improved.

Furthermore, in this embodiment, the hydrophobic film | membrane 25 is formed in the inner surface of the cover part 22 as a hydrophobic process. For this reason, as schematically shown in FIG. 4, droplets generated when the refrigerant evaporates in the evaporator 21 or refrigerant that has condensed into liquid in the evaporator 21 adheres to the inner surface of the cover portion 22. Then, it immediately moves down along the wall surface of the cover part 22 by gravity. In the present embodiment, since the space in the evaporator 11 has a conical shape with the heat transfer section 21 side as the base, the liquid refrigerant adhering to the vicinity of the ceiling in the evaporator 11 is also the wall surface of the cover section 22. Move down through.

  Thereby, the fall of the dryness of the vapor | steam in the evaporator 11 is suppressed, and heat transport efficiency becomes high. As a result, the semiconductor device 23 can be efficiently cooled.

(Experimental example)
As an experimental example, a loop thermosyphon 10 having the shape shown in FIG. 2 was produced. The evaporator 11 was made of copper, the height of the central portion was 30 mm, and the height of the outer peripheral portion was 5 mm. The inner surface of the cover portion 22 of the evaporator 11 was coated with a fluororesin film having a thickness of about 20 μm as a hydrophobic film 25. The contact angle between water and the fluororesin film is about 100 °.

  On the upper surface of the heat transfer section 21, 17 columnar protrusions were arranged in a grid pattern at intervals of 0.5 mm as the unevenness 23. The size of this protrusion is 1 mm (vertical) × 1 mm (horizontal) × 2 mm (height). A titanium oxide film having a thickness of 0.5 μm was formed as the hydrophilic film 24 on the upper surface of the heat transfer section 21 (including the top of the unevenness 23). The contact angle between water and the titanium oxide film is about 5 °.

  The heat exchanger 12 was also formed of copper. Transparent tubes were used for the gas-liquid two-phase tube 13 and the liquid tube 14 so that the inside could be observed. The gas-liquid two-phase tube 13 has an inner diameter of 4.3 mm, and the liquid tube 14 has an inner diameter of 2.1 mm.

  The loop type thermosiphon 10 shown in FIG. 2 is assembled by using the evaporator 11, the heat exchanger 12, the gas-liquid two-phase pipe 13 and the liquid pipe 14, and 70 cc of water is sealed therein as a refrigerant. The pressure in the loop thermosyphon 10 was set to a pressure lower by about 100 kPa than the atmospheric pressure.

  The evaporator 11 of the loop thermosyphon 10 was attached on a semiconductor device 32 with a heat transfer sheet 33 interposed therebetween as shown in FIG. The size of the semiconductor device 32 is 40 mm (vertical) × 40 mm (horizontal) × 10 mm (height), and the size of the semiconductor chip 32 a disposed therein is 25 mm (vertical) × 25 mm (horizontal).

  Moreover, the air blower was arrange | positioned in the vicinity of the heat exchanger 12, and the wind of the wind speed of 3 m / s was supplied to the heat exchanger 12 from the air blower. Further, the semiconductor device 32 was heated with power of 200 W, and the state inside the gas-liquid two-phase tube 13 and the liquid tube 14 was observed.

  As a result, it was confirmed that the vapor generated in the evaporator 11 moved to the heat exchanger 12 to become a liquid and moved downward in the liquid pipe 14. Also, almost no liquid refrigerant was observed in the gas-liquid two-phase tube 13.

  On the other hand, as a comparative example, a loop thermosyphon similar to the experimental example was prepared except that the hydrophilic film 24 and the hydrophobic film 25 were not provided, and the state inside the gas-liquid two-phase tube and the liquid tube was observed. As a result, a relatively large amount of liquid refrigerant was observed in the gas-liquid two-phase tube.

  By providing the hydrophilic film 24 and the hydrophobic film 25 in the evaporator 11 as in the experimental example, it is expected that the cooling performance is improved by about 15 to 20% compared to the comparative example.

(Modification 1)
FIG. 5 is a diagram showing a loop thermosiphon according to the first modification. 5, the same components as those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 5, in the loop-type thermosyphon 10a of the first modification, a hydrophobic continuous layer that is continuous with the hydrophobic film 25 of the evaporator 11 is formed on the inner surface of the gas-liquid two-phase tube 13 near the evaporator 11. A film 25a is formed.

  As a result, the splash that has entered the gas-liquid two-phase tube 13 and the refrigerant condensed in the gas-liquid two-phase tube 13 can be quickly removed from the gas-liquid two-phase tube 13, and the heat exchanger from the evaporator 11 can be removed. The dryness of the steam moving to 12 can be further increased. As a result, the cooling capacity of the loop thermosyphon 10a is improved as compared with the loop thermosyphon 10 shown in FIG.

(Modification 2)
FIG. 6 is a diagram illustrating a loop thermosyphon according to the second modification. 6, the same components as those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the loop-type thermosyphon 10b of the second modification shown in FIG. 6, the evaporator 40 has a rectangular parallelepiped shape. The size of the evaporator 40 is, for example, 40 mm (vertical) × 40 mm (horizontal) × 30 mm (height), for example, 40 mm (vertical) × 40 mm (horizontal) × 5 mm (thickness) rectangular plate-shaped heat transfer. It is formed by the part 41 and the cover part 42 which is arrange | positioned on it and forms the rectangular parallelepiped-shaped space 20 mm in height with the heat-transfer part 41. FIG.

  The inner surface of the cover part 42 is covered with a hydrophobic film 25 formed of fluororesin or the like.

The loop-type thermosiphon 10b of Modification 2 also has the same effect as the loop-type thermosiphon 10 shown in FIG. Further, since the shape of the evaporator 40 is a rectangular parallelepiped, it is easy to manufacture as compared to loop thermosyphon 10 shown in FIG. 2 formed in a square pyramidal shape.

(Modification 3)
FIG. 7 is a diagram illustrating a loop thermosyphon according to the third modification. In FIG. 7, the same components as those in FIG.

  In the loop-type thermosyphon 10c of Modification 3 shown in FIG. 7, the evaporator 50 is disposed on the heat transfer unit 51 and forms a dome-shaped space together with the heat transfer unit 51. 52. The inner surface of the cover portion 52 is covered with a hydrophobic film 25 formed of fluororesin or the like.

  The loop-type thermosiphon 10c of Modification 3 also has the same effect as the loop-type thermosiphon 10 shown in FIG. Further, in the third modification, the space in the evaporator 50 is a dome shape with the heat transfer section 21 side as the base, so that the liquid refrigerant adhering to the vicinity of the ceiling in the evaporator 11 is removed from the wall surface of the cover section 22. Easy to move down through.

(Electronics)
FIG. 8 is a schematic diagram illustrating an electronic device equipped with the loop thermosyphon according to the embodiment.

  The electronic device 60 is, for example, a blade server or a tower-type personal computer. As shown in FIG. 8, a circuit board 61 on which a CPU 62 and a memory (not shown) are mounted in a housing 66, and a housing 66 A blower 67 for taking in cold air is arranged.

  Further, the evaporator 62 of the loop thermosyphon 10 (see FIG. 2) according to the embodiment is connected to the CPU 62. The heat exchanger 12 of the loop thermosyphon 10 is disposed in the vicinity of the blower 67, and cold air is supplied from the blower 67. A gas-liquid two-phase pipe 13 and a liquid pipe 14 are connected between the evaporator 11 and the heat exchanger 12.

  The electronic device 60 according to the present embodiment cools the CPU 62 by the loop thermosyphon 10. Since the loop thermosyphon 10 has a high cooling capacity as described above, it is possible to prevent malfunction of the CPU 62 due to heat, occurrence of a failure, and reduction in processing capacity. Thereby, the reliability of the electronic device 60 is improved.

  The following additional notes are disclosed with respect to the above embodiments.

(Appendix 1) an evaporator that generates refrigerant vapor;
A heat exchanger for condensing the refrigerant vapor generated in the evaporator;
A gas-liquid two-phase tube that communicates between the evaporator and the heat exchanger and through which the refrigerant vapor passes;
A liquid pipe that communicates between the evaporator and the heat exchanger and through which the refrigerant condensed in the heat exchanger passes;
The evaporator includes a heat transfer portion thermally connected to a heat source, and a cover portion that forms a space in which the refrigerant is sealed together with the heat transfer portion and has an inner surface subjected to hydrophobic treatment. Loop type thermosyphon.

  (Additional remark 2) The loop-type thermosiphon of Additional remark 1 characterized by the hydrophilic process being given to the surface at the side of the said space of the said heat-transfer part.

  (Additional remark 3) The loop type thermosiphon of Additional remark 1 or 2 characterized by the internal diameter of the said gas-liquid two-phase pipe | tube being larger than the internal diameter of the said liquid pipe.

  (Appendix 4) Any one of appendices 1 to 3, wherein as the hydrophobic treatment, a resin film selected from fluororesin, polypropylene, polyethylene and polysulfone is formed on the inner surface of the cover portion. Loop type thermosiphon as described in 1.

  (Additional remark 5) As said hydrophilic process, the film | membrane of the material selected from the titanium oxide, the aluminum oxide, the silicon oxide, and the polyamide is formed in the surface of the said heat-transfer part, The loop type | mold of Additional remark 2 characterized by the above-mentioned Thermosiphon.

  (Additional remark 6) As said hydrophilic process, the unevenness | corrugation is provided in the surface of the said heat-transfer part, The loop type thermosiphon of Additional remark 2 characterized by the above-mentioned.

(Appendix 7) Any one of appendices 1 to 6, wherein the space formed by the heat transfer portion and the cover portion is a cone or dome shape with the heat transfer portion side as a base. Loop type thermosiphon as described in 1.

  (Supplementary note 8) The loop thermosyphon according to any one of supplementary notes 1 to 6, wherein the space formed by the heat transfer part and the cover part has a rectangular parallelepiped shape.

(Appendix 9) a circuit board on which electronic components are mounted;
A loop thermosyphon,
The loop thermosyphon
An evaporator that generates a vapor of refrigerant by heat generated in the electronic component;
A heat exchanger for condensing the refrigerant vapor generated in the evaporator;
A gas-liquid two-phase tube that communicates between the evaporator and the heat exchanger and through which the refrigerant vapor passes;
A heat transfer section that communicates between the evaporator and the heat exchanger and through which the refrigerant condensed in the heat exchanger passes, and the evaporator is thermally connected to a heat source; An electronic apparatus comprising: a cover portion that forms a space in which the refrigerant is sealed together with the heat transfer portion, and an inner surface is subjected to hydrophobic treatment.

  10, 10a, 10b, 10c ... Loop thermosyphon, 11, 40, 50 ... Evaporator, 12 ... Heat exchanger, 13 ... Gas-liquid two-phase pipe, 14 ... Liquid pipe, 21, 41, 51 ... Heat transfer section 22, 42, 52 ... cover part, 23 ... irregularities, 24 ... hydrophilic film, 25, 25 a ... hydrophobic film, 31 ... circuit board, 32 ... semiconductor device, 33 ... heat transfer sheet, 60 ... electronic equipment 61 ... Circuit board, 62 ... CPU, 66 ... Housing, 67 ... Blower.

Claims (4)

An evaporator that generates refrigerant vapor;
A heat exchanger disposed above the evaporator for condensing the refrigerant vapor generated in the evaporator;
A gas-liquid two-phase tube that communicates between the evaporator and the heat exchanger and through which the refrigerant vapor passes;
An inner diameter smaller than the gas-liquid two-phase tube, and a liquid tube that communicates between the evaporator and the heat exchanger and through which the refrigerant condensed in the heat exchanger passes,
The evaporator has a heat transfer part thermally connected to a heat source and a space disposed on the heat transfer part to enclose the refrigerant together with the heat transfer part, and is subjected to a hydrophobic treatment on the inner surface. A loop thermosyphon characterized by having a conical cover portion.   The loop thermosyphon according to claim 1, wherein a hydrophilic treatment is applied to the surface of the heat transfer section on the space side.   The loop thermosyphon according to claim 1 or 2, wherein a film of a resin selected from fluororesin, polypropylene, polyethylene and polysulfone is formed on the inner surface of the cover portion as the hydrophobic treatment. A circuit board with electronic components,
A loop thermosyphon,
The loop thermosyphon
An evaporator that generates a vapor of refrigerant by heat generated in the electronic component;
A heat exchanger disposed above the evaporator for condensing the refrigerant vapor generated in the evaporator;
A gas-liquid two-phase tube that communicates between the evaporator and the heat exchanger and through which the refrigerant vapor passes;
A liquid pipe having a smaller inner diameter than the gas-liquid two-phase pipe, communicating between the evaporator and the heat exchanger, and through which the refrigerant condensed in the heat exchanger passes, and the evaporator includes a heat source A heat transfer portion that is thermally connected to the heat transfer portion, and a conical cover portion that is disposed on the heat transfer portion to form a space in which the refrigerant is sealed together with the heat transfer portion, and whose inner surface is subjected to hydrophobic treatment And an electronic device.

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