Prediction of pressure losses in pipe flow of aqueous foams

This paper presents a model for predicting pressure losses in foams of vari ous expansions and pressures, in pipes of any given diameter, once the foam behavior has been characterized at a single expansion and pressure. The mo del incorporates a modified form of the power-law viscosity model of foam, which is obtained through the method of volume equalization. Since apparent wall slip contributes significantly to pipe now of foam, the wall slip als o needs to be characterized to enable predictions of pressure losses. The c ouplings between foam flow and wall slip characteristics are investigated, and two models are presented to predict slip velocities for slow and fast f low rates. Experimentally we find that u(slip) proportional to epsilon(-3/2 ), where epsilon denotes the foam expansion ratio at the experimental press ure. Predicted results are compared with experimental observations, with go od agreement.