Separation of gas mixtures in the acoustic boundary layer

Abstract

Spatial separation of binary gas mixtures in the presence of a sound wave has been reported by various experimenters in the last half-century, and is usually attributed to static pressure or temperature gradients. The authors suggest an additional mechanism, a ‘‘concentration pumping’’ in the acoustic boundary layer analagous to thermoacoustic heat pumping. Data from a simple acoustic mixture-separation experiment will be compared with predictions of this new theory. Observation of mixture separation between two acoustically coupled thermoacoustic engines will also be discussed.