Hydrodynamic description of fast and slow sound in binary fluids

A simple hydrodynamic mode analysis for disparate-mass binary fluid mixtures is given using a set of hydrodynamic equations which was generalized by the present author. In the small wavevector limit, as well-known four hydrodynamic modes and a friction mode are obtained, while, for the larger wavevector regime, there appear the fast and slow propagating modes which have been observed in experiments. Comparison of the theory with an experiment is performed for a dilute H-2-Ar gaseous mixture as a simple example. (C) 1997 Elsevier Science B.V.