Energy and tangential momentum accommodation coefficients on gas covered tungsten

Abstract

The sum of the energy (EAC) and tangential momentum (TMAC) accommodation coefficients has been measured acoustically for Ne on W exposed to the following adsorbates: CO, CO2, O2, N2, H2O, and D2; for He on W with O2 and D2 as adsorbates; and for each of these adsorbates on itself on W. An effort has been made to infer separate values of EAC and TMAC from the measured values of their sum. Good agreement is obtained with EAC values obtained from thermal conductivity cell measurements if TMAC is assumed to have a value of 0.75 for He and Ne on all the gas covered surfaces, and a value of 1.0 for all the adsorbates except D2 on itself on W. The acoustical method which was used has the capability of determining AC values under gas dynamic conditions where the surface and the gas are at essentially the same temperature. For CO2, since the acoustical measurments were made at frequencies far above the vibrational relaxation frequency, the EAC value obtained is for the translational and rotational energy only. The measurements in D2 reveal rotational relaxation.