Measurement of surface roughness dependence of thermal contact resistance under low pressure condition

Recently, thermal design of electrical equipment is important. Thermal contact resistance is one of the important parameters in the thermal design. However, thermal contact resistance is dependent on various factors, for example surface roughness, the contact pressure and the hardness of the material. Therefore, quantitative evaluation is difficult, and a little information can be obtained under high pressure conditions. In this study, we examine surface roughness and material hardness dependence of thermal contact resistance under low pressure condition. The materials to be measured are Al1070 and S45C, and three patterns (Ra = 0.2, 3.2, 12.5) of surface roughness are examined. Range of the contact pressure is 7.8 - 78 kPa. And, we have investigated the thermal resistance changed by contact pressure. From the experimental results, the reduction rate of the thermal contact resistance by increasing in pressure is dependent on the surface roughness, and thermal resistance of low hardness sample is saturated at higher contact pressure. Further, we discuss the relationship between the contact pressure and thermal resistance by the “Hertzian contact theory”. As a result, we confirm that the experimental results can be approximated by this equation.