Tangential Momentum Accommodation Coefficient Measurements of Tetrafluoroethane in Metallic Microtubes
Résumé
The leakage of gas between the reed valve and the valve seat affects significantly the efficiency of household refrigeration compressors. These leakages are induced by differences of pressure between the compression chamber and the suction/discharge chamber and occur through small gaps in the order of few micrometers, formed as a result of surface imperfections. Given the small dimensions of these gaps, under some operating conditions of the compressor a rarefied flow of refrigerant occurs. Therefore, leakage models must account for the non-equilibrium effects near the walls which can result in viscous slip, thermal slip and temperature jump at the wall. A significant parameter that must be taken under account when defining the degree of slip at the wall for the case of isothermal micro gas flows is the tangential momentum accommodation coefficient (TMAC), which describes statistically the exchange of momentum between the gas molecules and the surface. Many works in the literature provide the value of TMAC for different conditions. However, the gases considered are usually nitrogen and noble gases. Also, the surface material is usually limited to glass and silicon due to restrictions of the manufacturing technologies. In this work we measured mass flow rates of R134a (Tetrafluoroethane), a gas commonly used in the refrigeration industry, through commercially-available capillaries of stainless steel and copper on the basis of the dynamic constant-volume technique.