JP2008004606A - Cooling apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling apparatus which can establish high cooling efficiency inside a PC enclosure inexpensively, low noise and high reliability, in comparison with the conventional cooling measures using microbubble emission boiling for an MPU for PC as a super-high density heat source, which requires a large-scales mechanism for necessary cooling capacity and too much cost and large occupancy volume. <P>SOLUTION: A pump 4 is used to increase the velocity of a refrigerant passing over a heating surface, thus establishing stable microbubble emission boiling state even in a cooling circulation system wherein the degree of subcool is not large enough. Then, an auxiliary pump is used together, so as to realize microbubble emission boiling state even in still smaller subcool environment. In addition, a protective film is provided on the heating surface to ensure high reliability. Furthermore, the operation state of the PC is reflected on the rotational frequency of a fan 6 to prevent noises. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cooling device that cools a semiconductor that generates heat, such as a microprocessing unit (hereinafter abbreviated as MPU) used in a personal computer or the like, or an electronic component having another heat generating portion, mainly by an endothermic action due to a phase change of the refrigerant. It is about.

  In recent years, in electronic devices, the contact temperature of each electronic component has been reduced for the normal operation of the electronic component against the increase in heat generation due to higher integration of electronic components such as semiconductors and higher operating clock frequencies. How to keep within the operating temperature range has become a major issue. For this reason, it is not sufficient to perform air cooling with a heat sink as in the conventional case, and a more efficient cooling device is indispensable. Therefore, as such a cooling device, the present applicant has proposed a cooling device that cools the generated electronic components with high efficiency by circulating the refrigerant (see Patent Document 1). However, although the calorific value does not change greatly in the technical evolution of the MPU, the integration of electronic components has further increased, the chip area of the components has decreased, and the heat density has increased accordingly. The representative value of the wiring rule (minimum distance) on the chip in the MPU for personal computer in 2005 is 90 nanometers, but this is expected to be 65 nanometers around 2007. This means that if the MPU mounting circuit amount and power consumption are not changed, the chip area is halved and the heat density is doubled to about 300 W per square centimeter. As a cooling device corresponding to such a high heat density, a cooling method using refrigerant phase change and more efficient bubble micronization boiling has been proposed (see Patent Document 2).

Hereinafter, a cooling device using an endothermic action accompanying a phase change caused by bubble miniaturization boiling of the refrigerant will be described. As in the case of the MPU that has been integrated, the increase in the heat density in the heat transfer section can be seen everywhere, and a cooling method that achieves a higher cooling effect and cooling efficiency than before is required. As a method for cooling such a high heat load surface, it is conceivable to use nucleate boiling heat transfer of the refrigerant. According to this boiling cooling method, as is clear from the boiling curve diagram illustrated in FIG. 10, there is a critical heat flux (the maximum value P1 of the heat flux when transitioning from nucleate boiling I1 to transition boiling I2), which is practically used. It is the upper limit. That is, under nucleate boiling, the amount of heat transferred to the cooling water increases as the heat transfer surface temperature rises, but eventually reaches a peak at the critical heat flux P1, and under transition boiling, the amount of heat transferred to the refrigerant decreases rapidly and heat transfer. It is known that the surface temperature rises rapidly. Furthermore, when transition to boiling through the film shown by I3 over the point P2 in the figure after transition boiling, the steam covers the heat transfer surface and the heat transfer surface temperature increases discontinuously and burns down the MPU, etc. It is known that there is. For this reason, the critical heat flux has been regarded as a practical upper limit. It is a boiling form called bubble refinement boiling that realizes a heat flux exceeding the upper limit. In this boiling mode, a heat flux higher than the critical heat flux in a general boiling phenomenon can be obtained under a specific boiling accompanied by intense injection of fine bubbles. This conventional example is a cooling method that removes heat from a heat generation source using boiling of the refrigerant on the heat transfer surface, and the refrigerant can condense large bubbles generated on the heat transfer surface and directly supply the surrounding refrigerant to the heat transfer. Heat transfer that has a subcool degree, the contact interface temperature when large bubbles are condensed and the heat transfer surface comes into contact with the refrigerant is less than the minimum film boiling temperature, and the heat source side of the heat transfer surface is lower than the melting point It has a surface thickness so that bubble refinement boiling is continuously generated on the heat transfer surface so that it can be stably cooled under a heat flux exceeding the critical heat flux. Thereby, the heat of the heat source is removed by boiling on the surface of the heat transfer surface of the refrigerant having a subcool degree that condenses large bubbles covering the heat transfer surface, for example, bubbles having a diameter of 2 to 4 cm. And when a heat flux becomes large, the big bubble which covers a heat-transfer surface will come to appear frequently according to it. If this large bubble covers the heat transfer surface, the surface temperature of the heat transfer surface rises and transitions to film boiling, but it immediately condenses and disappears by the refrigerant that has secured the degree of subcooling. Do not migrate. In other words, large bubbles instantly repeat the formation and collapse, which promotes mixing of the refrigerant that ensures a sufficient degree of subcooling over a wider area of the heat transfer surface, making the temperature distribution uniform and increasing the amount of subcooling. The secured refrigerant touches the heat transfer surface and a large amount of heat is removed from the heat transfer surface, and even under high heat flux far exceeding the critical heat flux, bubble micronization boiling can be stably maintained and heat can be removed. it can. In the conventional example, in the cooling method using the above-described bubble micronization boiling, the refrigerant is water having a subcool degree of 15K to 85K under atmospheric pressure. In this case, the bubbles covering the heat transfer surface can be grown and collapsed instantaneously, and a large amount of refrigerant touches the heat transfer surface to remove a large amount of heat from the heat transfer surface. I can do it.
JP 2005-327776 A JP 2002-26210 A

  As described above, in order to cool the MPU for PC which is an ultra-high heat density heat source, it is necessary to remove heat from the heat transfer surface by phase change due to bubble refinement boiling. Therefore, as described above, it is necessary to secure a cooling capacity that allows the refrigerant to have a sufficient degree of subcooling. FIG. 11 shows a configuration example of a conventional PC MPU cooling apparatus that has been implemented. In this example, the refrigerant circulation type PC cooling device without phase change is considered, but the size of the casing will not change greatly in the future. In FIG. 11, reference numeral 111 denotes a PC housing on which a cooling device is mounted, 112 denotes a heat exchange means for exchanging heat in contact with a heating element to constitute the cooling device, and 113 denotes an MPU. 114 is a substrate on which the MPU 113 is mounted, 115 is a radiator that is provided on the inner side surface of the casing 111 and radiates the heat of the refrigerant received from the MPU 113 to the outside, and 116 is a refrigerant that connects the heat exchanging means 112 and the radiator 115. It is a closed pipe line for circulating. Reference numeral 117 denotes a pump for circulating the refrigerant under pressure. A thermal conductive grease (not shown) is applied to the contact surface between the MPU 113 and the heat exchanging means 112 to reduce the contact thermal resistance at the contact surface. As the refrigerant circulating in the circulation path 116, an antifreeze liquid such as an ethylene glycol aqueous solution or a propylene glycol aqueous solution is usually used. The radiator 115 is made of a material having high thermal conductivity and good heat dissipation, for example, a thin plate material such as copper or aluminum, and a refrigerant passage and a reserve tank are formed therein. Further, a fan may be provided to increase the cooling effect by forcibly applying air to the radiator 115 for cooling. The pipe line 116 is made of a rubber tube such as a flexible rubber having a low gas permeability, for example, butyl rubber, in order to ensure flexibility in piping layout. The heat exchanging means 112 is composed of a metal part such as aluminum or copper having excellent heat conductivity and a resin part that does not leak the refrigerant to the outside and has a strength that can withstand a fixed stress given from the outside. However, since the amount of air blown by the fan is limited because it is installed in such a closed narrow space and the noise is suppressed, the cooling ability of the refrigerant by the radiator 115 is also limited. Furthermore, reliability is required to maintain performance without tens of thousands of hours and without extensive maintenance work. On the other hand, in order to cool an ultra-high heat density heat source, a conventional cooling device using bubble micronization boiling has a large-scale mechanism, particularly a radiator, for realizing a cooling capacity necessary to obtain a sufficient subcooling degree. Therefore, the cost and occupied volume become enormous, and regular maintenance work may be required. For this reason, it is very difficult to fit the above-mentioned size and generated noise in a PC housing, and thus a cooling device using bubble micronization boiling cannot be realized. Accordingly, an object of the present invention is to provide a reliable cooling device that can realize high cooling efficiency using bubble micronized boiling at a low cost inside a PC housing with minimal noise generation.

In order to achieve the above object, according to the present invention, a heat dissipating means and a heat exchanging means are provided in a closed circuit for circulating a refrigerant, and the heat exchanging means is brought into contact with a heat generating electronic component so that A cooling device that draws heat from the heat generating electronic component by heat exchange with phase change and releases heat from the heat dissipating means, using a refrigerant pump as the refrigerant pressure feeding means, and a heat transfer portion of the heat exchanging means In this case, if the temperature of the refrigerant flowing in is lower than the boiling point of the refrigerant at the pressure and the temperature difference is ΔT, the average speed of the refrigerant passing through the heat transfer section is 2 × 10 ¹⁰ × ΔT ^(−8.958) or more. The cooling device is characterized by this.

Further, in the present invention, a heat dissipating means and a heat exchanging means are provided in a closed circuit for circulating the refrigerant, and the heat accompanying the heat exchange means is brought into contact with the heat generating electronic component to cause heat accompanying phase change with the refrigerant in the closed circuit. A cooling device for removing heat from the heat generating electronic component by exchanging action and radiating heat from the heat dissipating means, comprising a first refrigerant pump in the closed circuit and communicating from the refrigerant outlet of the heat exchanging means to the refrigerant inlet A refrigerant flow path and a second refrigerant pump in the flow path are provided, and in the heat transfer portion of the heat exchanging means, the temperature of the refrigerant flowing in is lower than the boiling point of the refrigerant at the pressure there, and the temperature difference is ΔT. For example, the cooling device is characterized in that the average speed of the refrigerant passing through the heat transfer section is 2 × 10 ¹⁰ × ΔT ^(−8.958) or more.

  Moreover, in this invention, the heat conductivity of the member between a heat receiving surface and a heat radiating surface is lower than the heat conductivity of the member of a part other than that in a heat exchange means. As a cooling device. In the present invention, the cooling device according to any one of claims 1 to 3, further comprising a refrigerant agitating means in the refrigerant flow immediately above the heat receiving surface of the heat exchange means.

  Further, in the present invention, the cooling device according to claim 1 or 4 further comprising a turbulent flow promoting structure upstream of the heat exchange means immediately before the position where the refrigerant flows into the heat receiving surface.

In the present invention, all or part of the heat radiating means, the refrigerant pump, and the plurality of heat exchanging means are provided in series or in parallel in a closed circuit for circulating the refrigerant, and the heat exchanging means is brought into contact with the heat generating electronic component. A cooling device that removes heat from the heat generating electronic component by heat exchange action or convective heat transfer accompanied by phase change of the refrigerant in the closed circuit, and radiates heat from the heat radiating means, and has at least the highest heat density heat. If the exchanging means is at the most upstream with respect to the heat dissipating means, the refrigerant temperature flowing in is lower than the boiling point of the refrigerant at the pressure there, and the temperature difference is ΔT, the average speed of the refrigerant passing through the heat transfer section is 2 It is a cooling device characterized by being not less than × 10 ¹⁰ × ΔT ^(-8.958) .

In the present invention, all or part of the heat radiating means, the refrigerant pump, and the plurality of heat exchanging means are provided in series or in parallel in a closed circuit for circulating the refrigerant, and the heat exchanging means is brought into contact with the heat generating electronic component. A cooling device that removes heat from the heat generating electronic component by heat exchange action or convective heat transfer accompanied by a phase change of the refrigerant in the closed circuit and radiates heat from the heat radiating means. A refrigerant flow path communicating from the refrigerant outlet to the refrigerant inlet and a separate refrigerant pump in the flow path are provided, and if the temperature of the refrigerant flowing in is lower than the boiling point of the refrigerant at the pressure and the temperature difference is ΔT, heat transfer The cooling device is characterized in that the average speed of the refrigerant passing through the section is 2 × 10 ¹⁰ × ΔT ^(−8.958) or more.

  Further, in the present invention, the cooling device according to any one of claims 1 to 7, further comprising a coating layer having a high intermolecular bonding degree on at least a heat transfer surface of the heat exchange means.

  Further, in the present invention, the heat radiation from the heat radiating means is due to the air blown by the fan, and includes means for detecting the temperature and pressure in the vicinity of the heat transfer surface inside the heat exchange means and means for detecting the heat transfer surface temperature. 9. The cooling device according to claim 1, further comprising means for controlling the rotational speed of a fan that blows air to the heat radiating means based on the value.

  Even in a small cooling device that cannot obtain a sufficient degree of subcooling according to the cooling device of the present invention, when a large bubble covering the heat transfer surface is formed, it immediately condenses and disappears by the surrounding subcooled refrigerant. In other words, the formation and collapse of large bubbles can be instantaneously repeated to promote sufficient mixing and supply of subcooled refrigerant over a wider area on the surface of the heat transfer surface, thereby making the temperature distribution uniform. In addition, a large amount of subcooled refrigerant touches the heat transfer surface to remove a large amount of heat from the heat transfer surface, so that heat can be removed even under a high heat flux far exceeding the general limit heat flux. Therefore, high cooling efficiency can be realized at a low cost with respect to a high heat density PC MPU or the like that has conventionally been difficult to cool. In addition, even when the subcool degree is small and the flow rate of the refrigerant generated by the pump in the heat exchanging portion is small, the above-described bubble micronization boiling can be stably maintained, and high cooling efficiency can be realized at low cost. Furthermore, it is possible to provide a cooling device that prevents deterioration of the heat transfer surface due to erosion due to shock waves generated accompanying the formation and collapse of bubbles that are instantaneously repeated, and maintains stable performance over a long period of time. In addition, noise generated by the cooling device can be minimized.

According to the first aspect of the present invention, a heat dissipating means and a heat exchanging means are provided in a closed circulation path for circulating the refrigerant, and the heat exchanging means is brought into contact with a heat generating electronic component so that A cooling device that takes heat from the heat generating electronic component by heat exchange action accompanied by phase change and radiates heat from the heat radiating means, and uses a refrigerant pump as a refrigerant pressure feeding means, and in the heat transfer section of the heat exchange means, If the temperature of the refrigerant flowing in is lower than the boiling point of the refrigerant at the same pressure and the temperature difference is ΔT, the average speed of the refrigerant passing through the heat transfer section is 2 × 10 ¹⁰ × ΔT ^(−8.958) or more. By adopting such a configuration, the refrigerant boiling mode in the heat exchange portion can be changed to bubble micronization boiling, thereby significantly improving the heat exchange efficiency of the heat exchange portion. be able to.

According to the second aspect of the present invention, the closed circuit for circulating the refrigerant is provided with a heat dissipating means and a heat exchanging means, and the heat exchanging means is brought into contact with the heat generating electronic component so as to contact the refrigerant inside the closed circuit. A cooling device that removes heat from the heat generating electronic component by heat exchange action accompanied by phase change and dissipates heat from the heat radiating means, and includes a first refrigerant pump in the closed circuit and from a refrigerant outlet of the heat exchange means A refrigerant flow path communicating with the refrigerant inlet and a second refrigerant pump in the flow path are provided, and in the heat transfer section of the heat exchanging means, the temperature of the refrigerant flowing in is lower than the boiling point of the refrigerant at the pressure therein, and the temperature If the difference is ΔT, the cooling device is characterized in that the average speed of the refrigerant passing through the heat transfer section is 2 × 10 ¹⁰ × ΔT ^(-8.958) or more. Efficient heat exchange means even with the refrigerant pump of the output The average flow velocity of the refrigerant can be enhanced in the parts, the boiling mode of the refrigerant in the heat exchange portion can be a microbubble boils, thereby, it is possible to remarkably improve heat exchange efficiency of the heat exchange portion.

  The invention according to claim 3 of the present invention is characterized in that the heat conductivity of the member between the heat receiving surface and the heat radiating surface of the heat exchange means is lower than the heat conductivity of the other members. The cooling device according to claim 1 or claim 2 having such a configuration makes it possible to make the boiling mode of the refrigerant in the heat exchange part a more stable bubble micronization boiling. Significant heat exchange efficiency can be improved and stabilized.

  Invention of Claim 4 of this invention is a cooling device of Claims 1-4 which has a refrigerant | coolant stirring means in the refrigerant | coolant flow just above a heat receiving surface among heat exchange means, Such a cooling device, By adopting the configuration, the boiling mode of the refrigerant in the heat exchange part can be changed to bubble refined boiling, and thereby the heat exchange efficiency of the heat exchange part can be remarkably improved.

  Invention of Claim 5 of this invention is a cooling device of Claim 1 to 4 which has a turbulent flow promotion structure in the upstream just before the position where a refrigerant | coolant flows in into a heat receiving surface among heat exchange means, By adopting such a configuration, it is possible to make the boiling mode of the refrigerant in the heat exchange part more stable bubble refinement boiling, thereby stabilizing the improvement of the remarkable heat exchange efficiency of the heat exchange part. Can do.

According to a sixth aspect of the present invention, all or a part of the heat dissipating means, the refrigerant pump, and the plurality of heat exchanging means are provided in series or in parallel in a closed circuit for circulating the refrigerant, and the heat exchanging means generates heat. A cooling device that is brought into contact with an electronic component to remove heat from the heat generating electronic component by heat exchange action or convective heat transfer accompanied by a phase change of the refrigerant inside the closed circuit, and radiates heat from the heat radiating means. Refrigerant that passes through the heat transfer section when the heat exchange means having a high heat density is at the most upstream with respect to the heat dissipating means, and the temperature of the refrigerant flowing in is lower than the boiling point of the refrigerant at that pressure and the temperature difference is ΔT. The cooling device is characterized in that the average speed of the ^refrigerant is 2 × 10 ¹⁰ × ΔT ^(−8.958) or more. By ^adopting such a configuration, the refrigerant in the heat exchange means can be efficiently used with the minimum number of parts. Mean flow velocity Can Mel, this makes it possible to best heat exchange efficiency of the other of the plurality of heat exchange parts with remarkably improve heat exchange efficiency in a large heat exchange means of the thermal load is also improved.

According to a seventh aspect of the present invention, all or part of the heat radiating means, the refrigerant pump, and the plurality of heat exchanging means are provided in series or in parallel in a closed circuit for circulating the refrigerant, and the heat exchanging means generates heat. A cooling device that takes heat from the heat generating electronic component by heat exchange action or convective heat transfer accompanied by a phase change of the refrigerant inside the closed circuit in contact with the electronic component and radiates heat from the heat radiating means, alone or The plurality of heat exchanging means is provided with a refrigerant flow path communicating from the refrigerant outlet to the refrigerant inlet and a separate refrigerant pump in the flow path, and the temperature of the refrigerant flowing in is lower than the boiling point of the refrigerant at the pressure, and the temperature difference is ΔT In this case, the cooling device is characterized in that the average speed of the refrigerant passing through the heat transfer section is 2 × 10 ¹⁰ × ΔT ^(−8.958) or more. The refrigerant pump Can effectively increase the average flow rate of the refrigerant inside the heat exchange means, thereby significantly improving the heat exchange efficiency of the heat exchange means with the largest heat load and the heat exchange efficiency of other heat exchange parts. Can also be improved.

  The invention according to claim 8 of the present invention has a coating layer having a high degree of intermolecular bonding at least on the heat transfer surface of the heat exchange means. With such a configuration, it is possible to provide a cooling device that prevents deterioration of the heat transfer surface and maintains stable performance over a long period of time.

  According to the ninth aspect of the present invention, the heat radiation from the heat radiating means is by air blown by a fan, and means for detecting the temperature and pressure in the vicinity of the heat transfer surface inside the heat exchange means and means for detecting the heat transfer surface temperature are provided. The cooling device according to claim 1, further comprising means for controlling the number of rotations of a fan that blows air to the heat radiating means based on the detected value. Noise generated by the cooling device can be minimized.

(Embodiment 1)
The heat exchange means of the cooling device in Embodiment 1 of the present invention will be described. FIG. 1 is a configuration diagram of a cooling device according to Embodiment 1 of the present invention. DESCRIPTION OF SYMBOLS 1 is MPU, 2 is the board | substrate with which MPU1 was mounted, 3 is a heat exchange means, 4 is a pump which supplies a refrigerant | coolant to the heat exchange means 3, 5 is heat dissipation which radiates the heat received from MPU1 by the heat exchange means 3 to outside air 6 is a fan for blowing outside air to the radiator 5, and 7 is a pipe line connecting the heat exchange means 3, the pump 4 and the radiator 5. Consideration is also required for the member in contact with the refrigerant in the cooling device and the refrigerant. For non-condensable gas generated from the member, the overall pressure of the circulating system in the cooling device rises, the boiling point of the refrigerant rises, and the heat equilibrium temperature in the heat exchange means rises. It becomes impossible. For example, when the coolant is water, a metal that reacts chemically such as aluminum to generate a non-condensable gas, or an organic substance that emits a non-condensable gas by decomposing even a little should be used as the material of the wetted part I can't. As for the refrigerant, Freon organic refrigerant such as R134a, propane, water and the like can be used for the cooling device for PC. However, water is the most suitable for the cooling device for PC in consideration of environmental problems related to global warming of Freon refrigerant, safety of propane, and performance as a refrigerant. Therefore, if water is used as the refrigerant, the heat exchange means 3, the liquid contact part of the pump 4, the radiator 5, the pipe line 7, etc. inevitably become the best constituent material. As described above, the heat generation density of the MPU 1 has been greatly increased with the improvement of the circuit density as described above, and the heat flux at the heat transfer surface exceeds 300 W (3 MW / m ² ) per square centimeter. In addition, although the board | substrate 2 and surrounding air can be considered as a path | route which radiates the heat | fever generated in MPU1, neither has a low thermal conductivity and cannot become an effective heat-transfer path | route. For example, when water is used as the refrigerant, in order to transfer the heat using the phase change, the pressure at the heat transfer section is kept low so that the refrigerant is evaporated by the required heat exchange means 3. To do. Therefore, in order to keep the airtight permanently against the external atmospheric pressure, all the members that contact the refrigerant as well as the conduit 7 are made of metal such as copper, and welding is not used for joining the parts. Special considerations such as Metals that react chemically with the refrigerant to produce non-condensable gas, such as aluminum, cannot be used as a material for parts in contact with liquid. Now, Research Paper 1: Proceedings of the Japan Society of Mechanical Engineers (Part B), Vol. 91-0492 “Occurrence and Stability of Bubble Micronization Boiling” and Research Paper 2: Transactions of the Japan Society of Mechanical Engineers (Part B), Vol. 63, No. 637. 98-1221 “Subcooled boiling heat transfer in rectangular channel (observation and generation conditions for bubble refinement boiling)” describes conditions that cause bubble refinement boiling. According to Research Paper 1, “In strong subcooled boiling, the nucleate boiling region is located on the extension line of saturation boiling, but even if the DNB point is exceeded, it does not immediately transition to film boiling, but shifts to the bubble refinement region. At this time, the boiling curve is different from the normal boiling curve in which the bubble refinement phenomenon does not occur, that is, in the normal boiling, the curve has a positive slope in spite of the heat transfer surface temperature in the transition boiling region. In addition, in this paper, we decided to classify this phenomenon of bubble miniaturization into two types according to the strength when the micronized bubble is ejected from the heat transfer surface. Named “Storm Microbubble Emission Boiling”, Calm Microbubble Emission Boiling "Which form of bubble refinement phenomenon depends largely on the degree of subcooling and flow velocity, and depending on the conditions, fluctuations reciprocating between the two may occur. It was clarified from the results of simultaneous measurement of “(NNB: Departure from Nucleate Boiling”, “nuclear boiling limit”). 2MW / m ² about a quiet microbubble boiling in the same paper, it was confirmed by experiment heat flux up to about 10 MW / m ² is intense microbubble boiling.

FIG. 2 shows two morphological regions of bubble micronization boiling (MEB) shown in Research Paper 2. From this figure, when the conditions for transition to bubble refinement boiling are formulated for subcool degree ΔTsub and flow velocity (Flow velocity) U, the conditions for transition to quiet bubble refinement boiling (Calm-MEB) are:
U = 2 × 10 ¹⁰ × ΔT ^(-8.958) (Formula 1)
The conditions for transition to intense bubble refinement boiling (Storm-MEB) are:
U = 1 × 10 ⁹ × ΔTsub ^-6.9972 (Expression 2)
It becomes. Note that the above superscript indicates power. Therefore, in FIG. 1, air outside the PC housing is blown to the radiator 6 by the fan 6, the internal refrigerant temperature is lowered, the refrigerant is pressurized by the pump 4, and sent to the heat exchanger 3. If Formula 1) is satisfied, even if the general critical heat flow rate is exceeded, transition to film boiling does not occur, and the boiling mode there is bubble refined boiling. That is, by doing so, a large amount of heat is removed from the heat transfer surface, and even under a high heat flux far exceeding the general limit heat flux, the bubble micronization boiling can be stably maintained and heat can be removed.

(Embodiment 2)
Here, if the required heat flux at the heat transfer surface is large, the flow velocity is increased or the subcooling degree is increased to satisfy (Equation 2) as much as possible. However, it is difficult to secure a larger subcooling degree as described above, so it is a good idea to increase the flow rate.

  FIG. 3 is a configuration diagram of a cooling device according to Embodiment 2 of the present invention. The difference from the first embodiment is that a pump 4 ′ is added as a second pump in addition to the pump 4. The pump 4 ′ has a suction port in the middle of the conduit 7 connecting the heat exchange means 3 and the radiator 5, and a discharge outlet in the middle of the conduit 7 in the middle of the first pump 4 and the heat exchange means 3. Be prepared to have. For the pump 4, the operating load is a fluid resistance corresponding to the circulation flow rate of the pipe 7 connecting the heat exchanging means 3, the radiator 5, and the respective components, but the operating load of the pump 4 ′ is the heat exchanging means 3. As a result, it is possible to move more refrigerant if it is assumed that the same pump performance and the same driving power are obtained. That is, by operating the pump 4 ′ simultaneously with the pump 4, the flow rate passing through the heat exchange means 3 can be remarkably increased. As a result, the flow rate in the heat exchanging means 3 becomes higher, and a stable bubble refined boiling state can be created even when the subcool degree cannot be ensured greatly. Furthermore, since the load corresponding to the heat exchange means 3 is substantially removed from the pump 4, the overall circulation flow rate is increased somewhat. Thereby, since the heat dissipation efficiency of the radiator 5 is slightly improved, there is also an advantage that the degree of subcooling can be secured somewhat large. Note that the pump 4 and the pump 4 ′ do not have to have the same performance, and can be appropriately selected for installation space and other reasons.

(Embodiment 3)
A cooling device according to Embodiment 3 of the present invention will be described. In the research paper 2 mentioned above, in bubble miniaturization boiling when the heat transfer surface length is long, “the liquid flowing on the heat transfer surface is heated and subcooling is reduced, so that ΔTsub = 10K occurs in any U. It is considered that film boiling occurs through transition boiling. " From this, it can be seen that it is important to secure the subcooling degree by avoiding the rise in the refrigerant temperature as much as possible until reaching the heat transfer surface. Considering heat exchange means made only of copper as an example, especially in the vicinity of a substantial heat transfer surface, a boundary layer is formed in the refrigerant flow, and the temperature rise of the refrigerant becomes significant, and the refrigerant receives heat from the heat receiving surface that contacts the MPU. While heat is transferred to the heat transfer surface in contact with the liquid, the heat is also diffused in a direction (surface direction) perpendicular to the heat transfer surface. That is, the temperature distribution on the heat transfer surface has an isotherm on a concentric circle centered on the center of the heat receiving surface. This means that the temperature of the refrigerant in contact with the heat transfer part gradually rises, and like the long heat transfer surface in the paper, the subcooling degree of the refrigerant is locally reduced and film boiling tends to occur. It becomes a state.

  FIG. 4 is a partial configuration diagram of heat exchange means 3 in the cooling device according to Embodiment 3 of the present invention. Reference numeral 8 denotes a heat transfer member from a surface (heat receiving surface) in contact with the MPU 1 of the heat exchanging means 3 to a surface (heat transfer surface) in contact with the refrigerant. The heat transfer member 8 is made of a material having a higher thermal conductivity than the other parts of the heat exchange means 3. If the other part of the heat exchanging means 3 is made of copper, the heat transfer member 8 can be made of a material having higher thermal conductivity than gold, such as gold and silver. If the other part of the heat exchanging means 3 is made of stainless steel, the heat transfer member 8 can obtain substantially the same effect at low cost if copper is used. Furthermore, the other part of the heat exchange means 3 is made of ceramic or the like that has been subjected to a treatment for suppressing the generation of non-aggregating gas and ensuring airtightness by metallizing the surface, and brazing the heat transfer member 8 and the like. If integrated, it is more effective. Further, the heat transfer member 8 is made of a material having the same thermal conductivity as that of the heat exchanging means 3, and a member made of the above-mentioned metallized ceramic or the like that inhibits the heat flow is interposed at the boundary, or a groove is provided. Alternatively, the heat flow may be blocked.

(Embodiment 4)
A cooling device according to Embodiment 4 of the present invention will be described. As described above, in order to make the transition from the nucleate boiling to the bubble miniaturization boiling state and maintain it stably, the bubbles generated by the phase change due to the boiling are rapidly dispersed in the refrigerant with the subcool degree secured, It is necessary to condense quickly. For this purpose, the bubbles are dispersed efficiently by increasing the flow rate of the refrigerant in the vicinity of the heat transfer surface and creating a turbulent flow.

  FIG. 5 shows a partial configuration diagram of the heat exchange means of the cooling device according to Embodiment 4 of the present invention. In FIG. 5, 9 is a stirring means for stirring the refrigerant, 10 is a drive magnet integrated with the stirring means 9, and 11 is a drive member comprising a coil and a core. The drive magnet 10 integrated with the stirring means 9 is rotated by the drive member 11 and a current control circuit (not shown). Needless to say, the partition walls of the heat exchange means 3 between the drive magnet 10 and the drive member 11 are magnetically permeable. Due to this rotational movement, the stirring means 9 also rotates and stirs the refrigerant in the heat exchange means 3. Since the refrigerant pressurized by the pump sequentially flows into the heat exchange means 3 from the pipe line 7, the refrigerant in the heat exchange means 3 continues to move from the inlet to the outlet while being stirred. The relative speed with respect to the heat transfer surface in the vicinity of the heat transfer surface of the refrigerant stirred by the stirring means 9 increases, and the temperature boundary layer also becomes thinner accordingly. In other words, the bubbles of the refrigerant evaporated on the heat transfer surface immediately pass through the temperature boundary layer and come into contact with the refrigerant having a low temperature, and can be quickly condensed there. Further, by physically stirring, the flow in the vicinity is disturbed, and heat exchange in the refrigerant around the bubbles is also activated, so that the condensing action proceeds more smoothly. The stirring means 9 is rotatably held in the vicinity of the heat transfer surface immediately above the heat receiving surface from the MPU 1, but it is desirable that the distance between the stirring means 9 and the heat transfer surface be as close as possible. Further, if there is a margin in the driving force due to the driving method and no problem due to wear due to contact between the stirring means 9 and the heat transfer surface occurs, it is more effective to drive in the contacted state. Further, according to the fourth embodiment, the driving is based on a rotational motion, but it may be a reciprocating motion. Furthermore, the same effect can be obtained even when the spherical body or the cylindrical body rolls on the heat transfer surface as the stirring means.

(Embodiment 5)
A cooling device according to Embodiment 5 of the present invention will be described. In the fourth embodiment, it has been described that the stirring of the refrigerant in the vicinity of the heat transfer surface is effective for generating and maintaining the bubble micronized boiling state, but providing the stirring mechanism in the vicinity of the heat transfer surface is cooling. Problems such as the reliability of the device itself, cost, and flexibility during mounting may occur. In that case, it is effective to enhance the turbulent flow of the refrigerant flow in the vicinity of the heat transfer surface as a next best measure. That is, the effect close to that of the fourth embodiment can be obtained by providing a turbulent flow promoting structure with a simple configuration upstream of the heat transfer surface in the refrigerant flow.

  FIG. 6 shows a partial configuration diagram of the heat exchange means of the cooling device in the fifth embodiment of the present invention. 12 is a turbulent flow promoting structure, and 13 is a wire type turbulent flow promoting structure. FIG. 6A shows a configuration example in the case where there is a space in the upper part of the MPU 1 and there is a capacity in the pump for feeding the refrigerant. The refrigerant from the pipe 7 hits the turbulent flow promoting structure 12. When the refrigerant exceeds the turbulent flow promoting structure 12, a relatively large scale of turbulence occurs due to the shear force in the flow. Bubbles generated by the phase change due to the boiling of the refrigerant that has secured the subcool degree by the action of the turbulent flow can be quickly dispersed and condensed quickly in the refrigerant. This turbulence dissipates as it goes downstream, but it is necessary to maintain sufficient strength to stir the refrigerant in the vicinity of the bubbles generated at the upper part of the heat transfer surface. Therefore, the cross-sectional shape of the turbulent flow promoting structure 12 is not limited to the shape shown in the figure, and the turbulent flow strength is increased by giving the turbulent flow a three-dimensional structure by changing the cross-sectional shape in the direction orthogonal to the flow. It can be sufficient. However, the effect of increasing the turbulent flow promoting structure 12 as close as possible to the heat transfer surface is greater, but if it is positioned on the heat transfer surface, flow separation occurs there, and the film boils or approximates it, resulting in a decrease in heat transfer efficiency. This is not preferable. FIG. 6B shows a configuration example in the case where there is no space in the upper part of the MPU 1 or there is no capacity in the pump for feeding the refrigerant. The wire-type turbulent flow promoting structure 13 is a needle-like member stretched so as to be orthogonal to the refrigerant flow. When the refrigerant exceeds the wire-type turbulent flow promoting structure 13, a distribution of shear force in the flow is periodically generated, thereby generating a vortex array. These vortex streets flow downstream in a state where they are regularly arranged upstream, but break in the middle and become a flow having a uniform turbulence state. The turbulent flow promotion by the wire type turbulent flow promoting structure 13 does not increase the scale and strength of the turbulent flow as compared with the turbulent flow promoting structure 12 described above, but can reduce the pump power used because it has a relatively small fluid resistance. The number of wire-type turbulent flow promoting structures 13 is one in FIG. 6B, but depending on the size of the heat transfer surface, it can be added to the refrigerant flow above the heat transfer surface to expand the turbulent flow range. May be.

(Embodiment 6)
A cooling device according to Embodiment 6 of the present invention will be described.

  FIG. 7 shows a schematic configuration diagram of a cooling device according to Embodiment 6 of the present invention. In FIG. 7, 1 ′ is an MPU having the same heat generation amount and heat density as MPU 1, 3 ′ is a heat exchanging means, 14 and 14 ′ are auxiliary board heat exchanging means, 15 and 15 ′ are auxiliary boards, and 16 and 16 ′. Is a sub-chip mounted on an auxiliary substrate. Some recent server PCs have a plurality of MPUs 1 and MPUs 1 'mounted on a single substrate 2 to improve the processing capability. Further, the sub chip 16 for improving the image display capability of the PC is mounted on the auxiliary substrate 15 and inserted into a slot provided on the substrate 2. Recently, there are PCs that further enhance the image display capability by adding more subchips 16 'and auxiliary boards 15'. The sub-chip 16 and the sub-chip 16 ′ independently perform high-level drawing processing at a high speed, the built-in circuit is increased in scale, and the drive frequency is increased. As a result, the MPU 1 and MPU 1 ′ have a considerable amount of heat during operation, although they do not reach the heat generation amount and heat density. Conventionally, the sub chip on the auxiliary substrate is cooled by air cooling with a heat sink and a small fan. However, as a result of the increase in the amount of heat generated as described above, air cooling has become insufficient. In the sixth embodiment, such a situation is dealt with by using the surplus cooling capacity after cooling MPU1 and MPU1 ′. Since the heat exchanging means 1 and the heat exchanging means 1 ′ are in series with the pipe line 7, the flow rate of the refrigerant passing therethrough is higher than the condition of the (Expression 1) or (Expression 2). Therefore, heat exchange is performed by bubble micronization boiling with a refrigerant having a sufficiently high subcooling degree, and MPU1 and MPU1 ′ having a large amount of heat and high heat density can be cooled. The auxiliary board heat exchanging means 14 and the auxiliary board heat exchanging means 14 ′ are arranged in parallel downstream of this. Therefore, since the flow rate of the refrigerant passing therethrough is not high, the fluid resistance in the auxiliary substrate heat exchanging means 14 and the auxiliary substrate heat exchanging means 14 ′ is suppressed as compared with the case where they are connected in series. It is done by. As described above, the subchip 16 and the subchip 16 'are not as large in heat quantity and high heat density as the MPU1 and MPU1', and therefore can be sufficiently cooled by heat exchange by nucleate boiling or convective heat transfer. In the sixth embodiment, the auxiliary board heat exchanging means 14 and the auxiliary board heat exchanging means 14 'are arranged in parallel to reduce the load on the pump. Absent. In the sixth embodiment, the cooling target other than the MPU 1 is the MPU 1 ′, the sub chip 16, and the sub chip 16 ′, but the same applies when cooling more or less cooling targets in the same refrigerant circulation path. If the heat exchange means 3 having the highest heat density is the most upstream with respect to the heat dissipating means 5, and the flow rate is higher than the condition of (Equation 2) at the subcooling degree, efficient cooling with minimum pump power is possible. A device is feasible.

(Embodiment 7)
A cooling device according to Embodiment 7 of the present invention will be described.

  FIG. 8 shows a schematic configuration diagram of a cooling device according to Embodiment 7 of the present invention. The seventh embodiment is roughly similar to the sixth embodiment, but in addition to the main circulation system pump 4, a pump 4 ′ is provided so as to bypass the heat exchanging means 3 ′. Since the operation load of the pump 4 ′ is only the heat exchanging means 3 ′ as in the second embodiment, it is possible to move more refrigerant if it is assumed that the same pump performance and the same operation power are obtained. By operating the pump 4 ′ simultaneously with the pump 4, the flow rate passing through the heat exchanging means 3 ′ can be remarkably increased. As a result, the flow rate in the heat exchanging means 3 ′ becomes higher, and a stable bubble refined boiling state can be created even when the subcool degree cannot be ensured greatly. That is, since the temperature of the refrigerant flowing into the heat exchanging means 3 ′ is slightly increased by the amount received by the heat exchanging means 3, the subcooling degree is reduced, and at least the above (formula) on the heat transfer surface of the heat exchanging means 3 ′. By moving the refrigerant at a speed exceeding the flow rate of 2), heat exchange by bubbling refined boiling in the heat exchanging means 3 ′ is possible. In the seventh embodiment, similarly to the sixth embodiment, the number of objects to be cooled can be increased or decreased, and the number of installations and positions of pumps having the same configuration and effect as the pump 4 ′ can be increased or decreased.

(Embodiment 8)
A cooling device according to Embodiment 8 of the present invention will be described. In the research paper (1) and the research paper (2), corrosion of the heat transfer surface due to bubbling of finer bubbles is reported. Taking research paper (1) as an example, “The intense bubble miniaturization phenomenon at a high degree of subcooling leads to countless erosion erosion like a needle attached to the heat transfer surface. Sometimes it is similar to what is found in a nearby solid wall. " Since the bubbles are originally generated by the phase change of the same refrigerant as the surroundings, the bubbles rapidly return to liquid when the gas inside the bubbles is cooled by the surrounding refrigerant. The contraction at this time is rapid, and as a result, a shock wave is generated in the refrigerant. This shock wave erodes the nearby solid surface. This phenomenon is particularly severe when the coolant is water. In order to avoid this, a member that absorbs shock or resists erosion by shock waves may be interposed on the solid surface. However, it is not appropriate to provide a cushion member with a thickness capable of absorbing shock on the heat transfer surface in the heat exchange means 3 because it deteriorates the heat transfer characteristics, and a member that resists erosion by coating the solid surface. It is a good idea to provide it. For such a member, for example, hard chromium carbide plating in which a base material is coated with a chromium carbide alloy having a high degree of intermolecular bonding using a mixed catalyst is effective.

(Embodiment 9)
A cooling device according to Embodiment 9 of the present invention will be described. The actual load state of the PC changes every moment, and the amount of heat generated in the MPU increases or decreases accordingly. If the number of fan rotations is set in accordance with the maximum amount of heat that can be generated, the blowing sound can be large and unsuitable for general PC usage environments.

  FIG. 9 shows a schematic configuration diagram of a cooling device according to Embodiment 9 of the present invention. In FIG. 9, 17 is a refrigerant temperature detection means provided near the heat transfer surface inside the heat exchange means 3, 18 is a refrigerant pressure detection means provided similarly near the heat transfer surface inside the heat exchange means 3, and 19 is heat transfer. Heat transfer surface temperature detection means 20 for detecting the surface temperature, 20 controls the rotational speed of the fan 6 based on the detection values obtained from the refrigerant temperature detection means 17, the refrigerant pressure detection means 18, and the heat transfer surface temperature detection means 19. Control circuit. The control by the control circuit 20 first obtains the boiling point of the refrigerant based on the refrigerant pressure detection value from the refrigerant pressure detection means 18. There is a method of calculating or interpolating from an approximate expression or a numerical table. The difference between the boiling point and the refrigerant temperature detection means 17 is the subcool degree. When the operating state of the PC changes and the heat transfer surface temperature obtained by the heat transfer surface temperature detecting means 19 exceeds a predetermined set temperature, the control circuit 20 increases the rotational speed of the fan 6 to increase the refrigerant temperature. Control the lowering direction. By doing this, the degree of subcooling increases, so even if the flow rate of the refrigerant is constant, the condition of (Equation 2) is satisfied. Therefore, the boiling mode in the heat exchange means 3 is completely intense bubble refinement boiling, and the cooling performance is maximum. It becomes a constant temperature below the allowable value. By setting the maximum cooling performance to a level that slightly exceeds the maximum amount of heat that can be generated by the MPU 1, the maximum rotational speed of the fan can be suppressed. When the load on the PC decreases and the heat transfer surface temperature decreases, the control circuit 20 controls the direction in which the rotational speed of the fan 6 is decreased and the refrigerant temperature is increased. By doing so, the subcooling degree is reduced, and the boiling mode changes from complete intense bubble refinement boiling to quiet bubble refinement boiling or nucleate boiling, and cooling performance corresponding to the PC load at that time. Thus, the noise generated by controlling the rotation speed of the fan 6 can be minimized. If the capacity of the pump 4 is sufficient, the upper limit of the rotational speed of the fan 6 can be suppressed by controlling the operation state of the pump, which is more effective. As an alternative to the heat transfer surface temperature detection means 19, a temperature sensor built in the MPU 1, a temperature sensor mounted on the substrate 2, or a means for detecting the MPU operating status on the PC by software can be used.

  Since the present invention can enable the cooling of a heat source having a heat density that greatly exceeds the critical heat density of a conventional cooling device by phase change even with a small cooling device, as a cooling device for a small and highly exothermic electronic component. Preferably used.

Configuration diagram of cooling device in Embodiment 1 of the present invention Two bubble refined boiling (MEB) morphological region diagrams shown in Research Paper 2 Configuration diagram of cooling device according to Embodiment 2 of the present invention Partial configuration diagram of heat exchange means in the cooling device in Embodiment 3 of the present invention Partial block diagram of the heat exchange means of the cooling device in Embodiment 4 of the present invention Partial block diagram of the heat exchange means of the cooling device in Embodiment 5 of the present invention Schematic block diagram of the cooling device in Embodiment 6 of the present invention Schematic configuration diagram of a cooling device in Embodiment 7 of the present invention Schematic configuration diagram of a cooling device in Embodiment 9 of the present invention Boiling curve diagram Configuration diagram of conventional MPU cooling device for PC

Explanation of symbols

1, 1 'MPU
2 Substrate 3, 3 'Heat exchange means 4, 4' Pump 5 Radiator 6 Fan 7 Pipe line 8 Heat transfer member 9 Stirring means 10 Drive magnet 11 Drive member 12 Turbulence promotion structure 13 Wire type turbulence promotion structure 14, 14 ′ Auxiliary board heat exchange means 15, 15 ′ Auxiliary board 16, 16 ′ Subchip 17 Refrigerant temperature detection means 18 Refrigerant pressure detection means 19 Heat transfer surface temperature detection means 20 Control circuit 111 PC housing 112 Heat exchange means 113 MPU
114 Substrate 115 Radiator 116 Pipe line 117 Pump

Claims (9)

Heat dissipating means and heat exchanging means are provided in a closed circulation path for circulating the refrigerant, and the heat exchanging means is brought into contact with the heat generating electronic component, and the heat is generated by a heat exchanging action involving a phase change with the refrigerant inside the closed circulation path. A cooling device for removing heat from an electronic component and radiating heat from the heat radiating means, using a refrigerant pump as a refrigerant pressure feeding means, and flowing in at a heat transfer portion of the heat exchanging means above the boiling point of the refrigerant at that pressure. A cooling device characterized in that if the refrigerant temperature is low and the temperature difference is ΔT, the average speed of the refrigerant passing through the heat transfer section is 2 × 10 ¹⁰ × ΔT ^(-8.958) or more. Heat dissipating means and heat exchanging means are provided in a closed circulation path for circulating the refrigerant, and the heat exchanging means is brought into contact with the heat generating electronic component, and the heat is generated by a heat exchanging action involving a phase change with the refrigerant inside the closed circulation path. A cooling device for removing heat from the electronic component and radiating heat from the heat radiating means, comprising a first refrigerant pump in the closed circuit, and a refrigerant flow path communicating from the refrigerant outlet of the heat exchanging means to the refrigerant inlet; A second refrigerant pump is provided in the flow path, and in the heat transfer section of the heat exchanging means, if the refrigerant temperature flowing in is lower than the boiling point of the refrigerant at the pressure and the temperature difference is ΔT, the heat transfer section is A cooling device characterized in that the average speed of the refrigerant passing therethrough is 2 × 10 ¹⁰ × ΔT ^(−8.958) or more. The cooling device according to claim 1 or 2, wherein, of the heat exchange means, the thermal conductivity of the member between the heat receiving surface and the heat radiating surface is lower than the thermal conductivity of the other members. The cooling device according to any one of claims 1 to 3, further comprising a refrigerant stirring means in the refrigerant flow immediately above the heat receiving surface among the heat exchange means. 5. The cooling device according to claim 1, further comprising a turbulent flow promoting structure upstream immediately before a position where the refrigerant flows into the heat receiving surface of the heat exchange means. All or part of the heat dissipating means, the refrigerant pump, and the plurality of heat exchanging means are provided in series or in parallel in a closed circuit for circulating the refrigerant, and the heat exchanging means is brought into contact with the heat generating electronic component to thereby form the closed circuit A cooling device that removes heat from the heat generating electronic component by heat exchange action or convective heat transfer accompanied by a phase change of an internal refrigerant and radiates heat from the heat radiating means, and at least the heat exchange means having the highest heat density is radiated. If the temperature of the refrigerant flowing upstream of the means is lower than the boiling point of the refrigerant at the pressure and the temperature difference is ΔT, the average speed of the refrigerant passing through the heat transfer section is 2 × 10 ¹⁰ × ΔT. ^(-8.958) Cooling device characterized by being above. All or part of the heat dissipating means, the refrigerant pump, and the plurality of heat exchanging means are provided in series or in parallel in a closed circuit for circulating the refrigerant, and the heat exchanging means is brought into contact with the heat generating electronic component to thereby form the closed circuit A cooling device that draws heat from the heat generating electronic component by heat exchange action or convective heat transfer accompanied by a phase change of an internal refrigerant and dissipates heat from the heat radiating means, and the refrigerant inlet from the refrigerant outlet to the single or plural heat exchange means A refrigerant flow path that communicates with the refrigerant, and a separate refrigerant pump in the flow path, and if the refrigerant temperature is lower than the boiling point of the refrigerant at the pressure and the temperature difference is ΔT, the refrigerant that passes through the heat transfer section The cooling device is characterized in that the average speed of is 2 × 10 ¹⁰ × ΔT ^(−8.958) or more. 8. The cooling device according to claim 1, further comprising a coating layer having a high intermolecular bond degree on at least a heat transfer surface of the heat exchange means. The heat radiating from the heat radiating means is due to the air blown by the fan, and it has means for detecting the temperature and pressure in the vicinity of the heat transfer surface inside the heat exchange means and means for detecting the heat transfer surface temperature, and based on the detected value 9. The cooling device according to claim 1, further comprising means for controlling the rotational speed of a fan that blows air to the heat dissipating means.

Images