Effect of Adsorption on Acoustic Boundary-Layer Losses

A theory accounting for the effect of surface adsorption of molecules on losses occurring in acoustic boundary layers has been developed. Results of this theory show that such losses can be a sizable fraction of losses due to viscosity and thermal conductivity. Interpretation of recently obtained sound-absorption measurements in H2, He, Ne, N2, CO, O2, and Ar by this means permits direct determination of adsorption times for these gases. Comparison of these results with existing data is not conclusive, since most adsorption measurements have been carried out at temperatures near that of liquid air whereas the data reported here was obtained at room temperature. In addition, it is almost certain that water vapor caused considerable contamination of the adsorbing surface.