An acoustic levitation technique for measuring the rheology of foam

Abstract

Understanding the rheological behavior of foams is important as a basic problem in fluid physics, and as a practical problem in many industries. Foams are tremendously important in a variety of applications. The most important quality of a foam in many of these applications is its response to imposed strain, or its rheological behavior. However, there exists almost no experimental data on the rheological properties of real 3-D foams. This is due in large part to the earth-based requirements for contact containment, and to the fact that gravity-induced drainage quickly destroys all but the ‘‘driest’’ foams. A unique method to provide noncontact control and manipulation of foam samples, via acoustic levitation is described. The analysis is outlined which will allow determination of a foam’s yield stress, effective bulk modulus, and effective bulk viscosity from the observed response of a foam sample to quasistatic, step function, and periodic acoustic and ambient pressure changes. Preliminary data will also be presented. [Work supported by NASA.]