| Summary: | 碩士 === 遠東科技大學 === 機械工程研究所 === 103 === The Sheet is not easy to be smooth by mechanical clamping. Its flatness is poorer than thick pieces. If the sheet is used as a heat sink, there are many voids in contact interface. The coefficient of thermal conductivity is 0.024 W/mK for the air inside the voids, these are caused heat accumulation. In the past, thermal grease was used to fill voids of interface for thermal conductivity. Because it is polymer materials and is easy to heat cracking, the lifespan is about 1~3 years for thermal grease. The coefficient of thermal conductivity is 2~10 W/mK for thermal grease. It is better than air, but is poorer than metal.
In this study, the defect of heat transfer of the thin porous aluminum is solved by developing low interfacial thermal resistance path. The surface of microporous sheet is porous. The heat convection structure is combined with the microporous sheet, heat source, and the interface. The heat convection transmits the accumulated heat at the interface. Compared with the traditional aluminum sheet, the heat transfer properties are listed below: the thermal resistance decreased 0.16 ℃/W, the heat-transfer coefficient improved 0.27 W/m2℃, and the temperature of heat source decreased 1.23 ％. Therefore, heat transmission of microporous sheet is better than aluminum sheet.
About the heat convection of microporous sheet, the thermal resistance and the heat-transfer coefficient of microporous sheet is better than that of aluminum sheet in 90 to 180 degrees of angle. The difference value is 0.193 ℃/W for the average thermal resistance between the microporous sheet and the aluminum sheet. The difference value is 0.419 W/m2℃for the average heat-transfer coefficient between the microporous sheet and the aluminum sheet. The peak value is happened at 180 degrees of angle. The temperature of heat source decreased 3.11 ％ at this angle.
The idea of the bismuth alloy for interfacial heat transfer is to use the bismuth alloy to fill the voids of interface, and to improve the heat-transfer coefficient at the interface. The temperature of heat source decreased 4.81 ％ after using the bismuth alloy at interface. The idea of the absorbing layer of infrared ray for interfacial heat transfer is to transferring thermal to the microporous sheet from heat source by radiant energy. The temperature of heat source decreased 3.7 ％ after using the absorbing layer at interface.
The effects of thermal radiation of composite carbon layer to improve emissivity of surface are listed below. At 0 degrees of angle, the temperature of the aluminum sheet decreased 18.98 ％, and the temperature of the microporous sheet decreased 16.51 ％. At 90 degrees of angle, the temperature of the aluminum sheet decreased 15.40 ％, and the temperature of the microporous sheet decreased 15.40 ％. Therefore, the composite carbon layer is helpful for the heat transfer of the aluminum sheet and the microporous sheet.
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