Prediction of pressure losses in pipe flow of aqueous foams

This paper presents a model for predicting pressure losses in foams of various expansions and pressures, in pipes of any given diameter, once the foam behavior has been characterized at a single expansion and pressure. The model 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 also needs to be characterized to enable predictions of pressure losses. The couplings between foam flow and wall slip characteristics are investigated, and two models are presented to predict slip velocities for slow and fast flow rates. Experimentally we find that u(slip) proportional to epsilon(-3/2), where epsilon denotes the foam expansion ratio at the experimental pressure. Predicted results are compared with experimental observations, with good agreement.