Velocity of sound in two-phase media

A theory is developed for calculating the velocity of sound in solid-gas and liquid-gas systems. Using mass and momentum balances, an equation is obtained which shows that the velocity of sound depends on the relative velocity between the two phases, on the ratio of densities, on the porosity, on the particle diameter, on the drag coefficient, and on the frequency of sound.

The theory can be applied only if the one phase is distributed in the other homogeneously in the form of particles, droplets or bubbles of equal size. The experimental results agree very well with the theory.

Based on Hert'z equation for the deformation of spheres, a further theory is described which enables calculation of the velocity of sound in gas-solid systems of low porosity, such as packings or porous bodies.