Abstract
An innovative method for determining the thermal-accommodation coefficients of gases by means of monitoring the Mie scattering from a single suspended water droplet is described. The heat exchange between the gas molecules and the suspended droplet is analyzed by considering the simultaneous mass- and heat-transfer processes during droplet growth by condensation in a gaswater-vapor environment. Measurements have been carried out for helium with water-vapor-to-helium ratios in the range of 1:0.5 to 1:2.5. The thermal conductivity of this mixture is found to be best represented by its reciprocal average. The thermal-accommodation coefficient of helium on water surfaces is determined to be 0.65±0.05, as compared to unity for water vapor on water surfaces.