Experimental Measurement of Energy Accommodation Coefficient by Low-Pressure Method

Heat transfer in micro flows has received much attention along with the development in micro- and nano-technology. In micro- and nano-flow fields, the Knudsen number, which is defined as a ratio of the molecular mean free path to the characteristic length of the system, becomes large because of the small characteristic length. In these so-called “high Knudsen number flows”, the number of the collision of gas molecules to the surface is much larger than that of intermolecular collisions. Therefore, it is important for the high Knudsen number flows to understand the gas-surface interaction. Since detailed science of the gas-surface interaction is complicated, the empirical parameter called the accommodation coefficient is widely used for flow analyses of the flows. In this study, the energy accommodation coefficient for metal surface has been measured experimentally by the Low-Pressure method, in which the energy accommodation coefficient is obtained from the pressure dependency of the heat flux in the free-molecular flow regime. It is not easy to realize the free-molecular flow condition, and, thus, the relation between the heat flux and the pressure extended to much higher pressure condition was employed in this study. Experimental geometry was designed as concentric cylinders, and heat flux between two cylinders, whose surface temperatures was different, was measured. Experimental results are reported for argon and oxygen in contact with a platinum surface. The surface temperature dependence of the energy accommodation coefficient was also studied, and verified by the results of previous work.