JP2007180438A - Cooling medium, cooling apparatus, and electronic appliance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling medium whereby a cooling performance can be improved by leaps and bounds, a cooling apparatus using the cooling medium, and an electronic appliance using the cooling apparatus. <P>SOLUTION: The cooling apparatus has the constitution wherein there are connected in the form of a ring via pipings 5 with each other a heat receiving plate 1 for receiving the heat generated from an electronic component 21, a heat radiating plate 2 for radiating a heat to the external by attached heat radiating fins 7, a tank 3, and a pump 4; and a cooling medium 6 is circulated in the pipings 5 by the driving of the pump 4. The cooling medium 6 is a fluidic mixture (a) comprising such a liquid 11 as a water to be a base liquid and carbon fibers 12, or the cooling medium 6 is a fluidic mixture (b) comprising such a liquid 11 as a water to be a base liquid, and powder particles 13 made of a metal or a ceramic. The cooling medium 6 has a high heat conductivity and exhibits an excellent cooling performance since it contains the carbon fibers 12 or powder particles 13 of a high heat conductivity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cooling medium for cooling a heating element such as an electronic component, a cooling device for circulating the cooling medium to cool the heating element, and an electronic apparatus using the cooling apparatus.

  In electronic devices such as desktop computers, notebook computers, and mobile communication devices, a plurality of electronic components such as CPU elements, coil elements, and capacitors are provided on a printed circuit board. In recent years, the amount of heat generated during the operation of these electronic components tends to increase with the increase in processing speed, functionality, and performance of electronic devices. In order to maintain a stable operation of the electronic device, it is necessary to quickly release the heat generated from the electronic component to the outside to improve heat dissipation.

Therefore, a liquid cooling type cooling device that uses a liquid such as water having a higher specific heat than air as a cooling medium has been proposed (see, for example, Patent Documents 1, 2, and 3). In these cooling devices, a heat receiving plate (heat receiving portion) that receives heat from an electronic component (heating element), a heat radiating plate (heat radiating portion) that dissipates heat to the outside, and a pump are connected in an annular shape by piping. The cooling medium is circulated in the pipe by the action of the pump, and the heat received from the heating element in the heat receiving part is conducted to the heat radiating part through the cooling medium flowing in the pipe, and the heat is dissipated from the heat radiating part. The heating element is cooled.
JP 2004-1111829 A JP 2001-237582 A JP 2004-95891 A

  In the conventional cooling device as described above, a liquid such as water or antifreeze is used as the circulating cooling medium. However, since the heat generation amount of the electronic components is expected to increase further in the future, it is more efficient. Development of technology that can cool electronic components well is desired.

  The present invention has been made in view of such circumstances, and provides a cooling medium capable of dramatically improving the cooling performance, a cooling device using the cooling medium, and an electronic apparatus using the cooling device. For the purpose.

  Another object of the present invention is to provide a cooling device and an electronic apparatus that can be downsized in size as the cooling performance is improved.

  The cooling medium according to the present invention is a cooling medium for cooling a heating element, which is a mixture of a liquid and a solid having a higher thermal conductivity than the liquid.

  The cooling medium of the present invention is a fluid medium in which a liquid such as water or antifreeze is mixed with a solid having a higher thermal conductivity than this liquid. Therefore, compared with the case where water or antifreeze is used (conventional example), the thermal conductivity is increased, and excellent cooling performance is expected.

In the cooling medium according to the present invention, the solid includes one or more elements selected from the group consisting of carbon fiber, Cu, Al, Ag, Au, and Mg, and Cu, Al, Ag, Au, and Mg. It is characterized by being an alloy or a ceramic selected from Al ₂ O ₃ , AlN, CuO, ZnO, BeO, MgO, ZrO ₂ and SiC.

  The cooling medium of the present invention contains the material as described above as a solid having high thermal conductivity. Since these materials have high thermal conductivity, a cooling medium containing one or more of them has high thermal conductivity. Moreover, since carbon fiber has a specific gravity close to that of water, it can be uniformly dispersed in water.

  In the cooling device according to the present invention, a heat receiving part that receives heat from the heating element and a heat radiating part that dissipates heat to the outside are connected by a pipe, and a cooling medium is circulated in the pipe to cool the heating element. In the cooling device, the cooling medium is a mixture of a liquid and a solid having a higher thermal conductivity than the liquid.

  In the cooling device of the present invention, a fluid medium in which a liquid having a higher thermal conductivity than that of a liquid such as water or an antifreeze is mixed as a cooling medium. Therefore, compared with the case where water or antifreeze is used (conventional example), the thermal conductivity of the cooling medium is increased and the cooling performance is improved. Further, since the cooling performance is improved, a sufficient cooling effect can be obtained even if the size of the heat receiving portion, the heat radiating portion, etc. is reduced, and the apparatus configuration can be reduced in size.

In the cooling device according to the present invention, the solid includes one or more elements selected from the group consisting of carbon fiber, Cu, Al, Ag, Au, and Mg, and Cu, Al, Ag, Au, and Mg. It is characterized by being an alloy or a ceramic selected from Al ₂ O ₃ , AlN, CuO, ZnO, BeO, MgO, ZrO ₂ and SiC.

  In the cooling device of the present invention, the material as described above is used as a solid having a high thermal conductivity contained in the cooling medium. Since these materials have high thermal conductivity, excellent cooling performance can be obtained. Moreover, since carbon fiber has a specific gravity close to that of water, it can be uniformly dispersed in water.

  An electronic apparatus according to the present invention is characterized by using the cooling device as described above.

  In the electronic apparatus of the present invention, since a cooling device with excellent cooling performance is used, heat generated from the electronic component is quickly released to the outside, heat dissipation is improved, and stable operation can be performed. In addition, since the cooling performance is high even with a small cooling device, the size of the configuration can be reduced.

  In the present invention, since the cooling medium is composed of a mixture of a liquid and a solid having a higher thermal conductivity than the liquid, the thermal conductivity of the cooling medium can be increased compared to the conventional example using water or antifreeze. Thus, the cooling performance can be dramatically improved.

  Further, in the present invention, since the cooling performance can be improved without increasing the device configuration, it is possible to reduce the size of the cooling device by reducing the size of the heat receiving portion, the heat radiating portion, and the like.

  Hereinafter, the present invention will be specifically described with reference to the drawings. Note that the present invention is not limited to the following embodiments.

  FIG. 1 is a diagram showing a configuration of a cooling device according to the present invention. In FIG. 1, the cooling device has a configuration in which a heat receiving plate 1 as a heat receiving portion, a heat radiating plate 2 as a heat radiating portion, a tank 3, and a pump 4 are annularly connected via a pipe 5. The cooling medium 6 circulates in the pipe 5 in the direction indicated by the arrow by driving the pump 4.

  The heat receiving plate 1 is connected to an electronic component 21 as a heating element. The heat radiating plate 2 is provided with heat radiating fins 7 that dissipate heat, and in the vicinity of the heat radiating fins 7, a blower fan 8 that sends air toward the heat radiating fins 7 is provided. The tank 3 stores a cooling medium 6 that circulates in the pipe 5.

  The cooling medium 6 has a composition as shown in FIG. 1 (a) or (b). In the example of FIG. 1A, the cooling medium 6 is a mixture of a liquid 11 serving as a base liquid and a carbon fiber (carbon fiber) 12, and has fluidity. As the liquid 11, liquids such as water, antifreeze, ethylene glycol, and propylene glycol can be used. The carbon fiber 12 has a cylindrical shape with a diameter of about 10 μm and a length of about 50 μm, for example, and is contained in the cooling medium 6 by about 10 to 20% by weight. Since the specific gravity (about 2.1) of the carbon fiber 12 is close to that of water, the carbon fiber 12 can be uniformly dispersed in the liquid 11.

On the other hand, in the example of FIG. 1B, the cooling medium 6 is a mixture of a liquid 11 serving as a base liquid and metal or ceramic powder particles 13 and has fluidity. As the liquid 11, liquids such as water, antifreeze, ethylene glycol, and propylene glycol can be used. As the metal of the powder particles 13, a metal such as Cu, Al, Ag, Au, or Mg having a high thermal conductivity, or an alloy containing one or more elements such as Cu, Al, Ag, Au, or Mg can be used. These metal powder particles 13 have a spherical shape with a diameter of about 3 to 5 μm, and are contained in the cooling medium 6 at about 10 to 20% by weight. In order to prevent condensation and increase dispersibility in the liquid 11, it is preferable to attach silica powder to the surface of the metal powder particles 13. As the ceramic of the powder particles 13, ceramics such as Al ₂ O ₃ , AlN, CuO, ZnO, BeO, MgO, ZrO ₂ , and SiC can be used. These ceramic powder particles 13 have a spherical shape with a diameter of about 30 to 50 nm, and are contained in the cooling medium 6 by about 10 to 20% by weight.

  A cooling process of the heating element 21 using the cooling medium 6 that is a mixture slurry of liquid and solid as described above in the cooling device will be described. The cooling medium 6 is circulated in the pipe 5 by driving the pump 4. The heat from the heating element 21 is conducted to the cooling medium 6 flowing in the pipe 5 inside the heat receiving plate 1 (white arrow in FIG. 1), and the cooling medium 6 whose temperature has increased flows in the pipe 5 and the cooling medium 6 Is dissipated to the outside through the heat radiating plate 2 and the heat radiating fins 7. At this time, air is sent from the blower fan 8 toward the heat radiating fins 7 to obtain a larger heat radiating effect. The cooling medium 6 whose temperature has decreased due to heat dissipation flows through the pipe 5 through the tank 3 and is circulated to the heat receiving plate 1 again. As a result, the heating element 21 is cooled.

  As described above, in the present invention, the slurry, which is a mixture of a liquid and a solid having a high thermal conductivity, is used for the cooling medium 6, so that the thermal conductivity of the cooling medium 6 can be increased, Compared to the conventional example using a cooling medium made of antifreeze, the cooling performance can be dramatically improved. Further, since the cooling performance is improved, if the cooling performance of the same level as when only water or antifreeze is used is used, the heat receiving plate 1, the heat radiating plate 2, etc. can be obtained by using the cooling medium 6 of the present invention. The size of the member can be reduced, and the cooling device can be configured compactly. Moreover, in the electronic device of the present invention using the cooling device as described above, the cooling performance of the cooling device to be used is excellent, so heat generated from the electronic components in the device is quickly dissipated to the outside. And high heat dissipation can be obtained. Moreover, in the electronic device of the present invention using the cooling device having a high cooling performance even with a compact configuration, the configuration can be downsized.

  Hereinafter, specific examples of the cooling medium 6 of the present invention and its thermal characteristics will be described. Two kinds of carbon fibers (CF1 and CF2) manufactured by Mitsubishi Chemical Industries, Ltd. were respectively contained in water at 10 wt% and 20 wt% to prepare a cooling medium. The carbon fibers CF1 and CF2 each have a diameter of 10 μm and a length of about 50 μm. Further, the thermal conductivity in the axial direction is 140 W / mK for CF1 and 400 W / mK for CF2. The heat transfer coefficient was calculated for the four types of prepared cooling media and water as a reference. The calculation results are shown in Table 1 below together with other physical properties.

The heat transfer coefficient h was calculated according to the following formula. FIG. 2 is a schematic diagram of a portion (corresponding to the heat receiving plate 1 and the heat radiating plate 2 in the example of FIG. 1) where the cooling medium flows and heat transfer is performed.
h = (Nuk) / L
Experimental formula: Nu = 3.66 + [0.0668 (d / L) RePr]
/{1+0.04[(d/L)RePr] ^2/3 }
RePr = (vdρCp) / k
However,
h: Heat transfer coefficient Nu: Nusselt number
k: thermal conductivity of cooling medium L: length of flow path (see FIG. 2)
Re: Reynolds number = (vdρ) / μ
Pr: Prandtl number = (μCp) / k
d: width of flow path (see FIG. 2) μ: viscosity at fluid temperature
v: Flow velocity (see Fig. 2) ρ: Density of cooling medium
Cp: Specific heat of the cooling medium The amount of heat Q to be transferred is given by Q = DAΔT, where D is the proportionality constant, A is the surface area in contact with the cooling medium, and ΔT is the temperature difference.

  In the cooling medium containing 10% by weight and 20% by weight of carbon fiber in water, the thermal conductivity is 2.9 to 13.9 W / mK, which is 4.5 to 21 times that of water. It has become. Also, the heat transfer coefficient is improved to 3.8 to 17.1 times.

  Thus, it can be seen that the cooling medium, which is a mixture of water and carbon fiber, exhibits a high heat transfer coefficient and can exhibit excellent cooling performance. By adding carbon fiber to water, the apparent viscosity of the cooling medium increases and the flow rate and Reynolds number decrease. However, the thermal conductivity of the cooling medium increases, and as a result, the heat transfer coefficient improves.

Next, in order to confirm the above-described calculation results, the thermal resistance of a plurality of types of cooling media was measured using a cooling device having a configuration as shown in FIG. The cooling medium used was water as a control example, a cooling medium in which carbon fibers CF1 and CF2 as described above were added to water by 10 wt% and 20 wt%, respectively, Cu, Al, and Ag powder (particle size: 3 ˜5 μm), a cooling medium prepared by adding 20% by weight of silica powder and about 1% by weight of silica powder for preventing condensation to water, powder of Al ₂ O ₃ , CuO, ZnO made by NanoTek (particle size: 30 to 50 nm) is a cooling medium prepared by adding 20 wt% each to water.

Moreover, the operating conditions of the cooling device which measured thermal resistance were as follows.
Pump: 5V drive Flow rate: 150ml / min Flow path diameter: 5mm
Flow path length: 500mm Heat generation amount of heating element: 50W
Fan: 5V drive, diameter 50mm, air volume 100 liters / minute

  FIG. 3 shows the results of measuring the thermal resistance between the room temperature (about 25 ° C.) and the heating element when the above 11 kinds of cooling media are used. It is understood that any of the ten types of cooling media of the present invention has a lower thermal resistance than water, and that an excellent cooling effect can be realized by using the cooling media of the present invention.

Regarding the above embodiment, the following additional notes are disclosed.
(Supplementary note 1) A cooling medium for cooling a heating element, which is a mixture of a liquid and a solid having a higher thermal conductivity than the liquid.
(Supplementary note 2) The solid is carbon fiber, any metal in Cu, Al, Ag, Au, Mg, an alloy containing one or more elements in Cu, Al, Ag, Au, Mg, or The cooling medium according to appendix 1, wherein the cooling medium is any one of Al ₂ O ₃ , AlN, CuO, ZnO, BeO, MgO, ZrO ₂ , and SiC.
(Supplementary note 3) The cooling medium according to Supplementary note 1 or 2, wherein the liquid is any one of water, antifreeze, ethylene glycol, and propylene glycol.
(Additional remark 4) In the cooling device which connects the heat receiving part which receives the heat of a heat generating body, and the heat radiating part which dissipates heat outside by piping, circulates a cooling medium in the piping, and cools the heating element, The cooling device, wherein the cooling medium is a mixture of a liquid and a solid having a higher thermal conductivity than the liquid.
(Supplementary note 5) The solid is carbon fiber, any metal in Cu, Al, Ag, Au, Mg, an alloy containing one or more elements in Cu, Al, Ag, Au, Mg, or The cooling device according to appendix 4, wherein the cooling device is any one of Al ₂ O ₃ , AlN, CuO, ZnO, BeO, MgO, ZrO ₂ , and SiC.
(Appendix 6) The cooling device according to appendix 4 or 5, wherein the liquid is any one of water, antifreeze, ethylene glycol, and propylene glycol.
(Additional remark 7) The electronic device characterized by using the cooling device in any one of Additional remark 4-6.

It is a figure which shows the structure of the cooling device which concerns on this invention. It is a schematic diagram of the part by which a cooling medium flows and heat transfer is made. It is a graph which shows the measurement result of thermal resistance.

Explanation of symbols

1 Heat receiving plate (heat receiving part)
2 Heat sink (heat sink)
3 Tank 4 Pump 5 Piping 6 Cooling Medium 7 Radiating Fin 8 Blower Fan 11 Liquid 12 Carbon Fiber (Solid)
13 Powder particles (solid)
21 Electronic components (heating elements)

Claims (5)

  A cooling medium for cooling a heating element, which is a mixture of a liquid and a solid having a higher thermal conductivity than the liquid. The solid is carbon fiber, any metal in Cu, Al, Ag, Au, Mg, an alloy containing one or more elements in Cu, Al, Ag, Au, Mg, or Al ₂ O _3. The cooling medium according to claim 1, wherein the cooling medium is any one of ceramics of AlN, CuO, ZnO, BeO, MgO, ZrO ₂ , and SiC.   In the cooling device for connecting the heat receiving part that receives heat of the heating element and the heat radiating part that dissipates heat to the outside by piping, and circulating the cooling medium in the pipe to cool the heating element, the cooling medium is A cooling device, which is a mixture of a liquid and a solid having a higher thermal conductivity than the liquid. The solid is carbon fiber, any metal in Cu, Al, Ag, Au, Mg, an alloy containing one or more elements in Cu, Al, Ag, Au, Mg, or Al ₂ O _3. , AlN, CuO, ZnO, BeO , MgO, cooling apparatus according to claim 3, characterized in that the one of the ceramic in the ZrO _2, SiC.   An electronic apparatus using the cooling device according to claim 3 or 4.

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