Wall Shear Stress Generated by Aqueous Flowing Foam

Abstract

Aqueous foam flow over horizontal channels present significant pressure losses originated by the wall shear stress. Understanding this phenomenon is of paramount importance for the oil, food and cosmetic industries. In this study, we validate the use of the innovative polarographic method, used to measure the wall shear stress. It measures an oxy-reduction reaction controlled by the convection and diffusion phenomenon. The most reliable way of obtaining the wall shear stress is through the pressure losses. They allow obtaining the pressure gradient along the length of the channel, which can be related to an averaged wall shear stress. These measurement techniques were applied over a horizontal foam flow enclosed in a square duct of section 21 × 21 mm2; with a velocity of 2, 4 and 6 cm/s; and a void fraction of 70%. Results validate the use of the polarographic method to obtain the wall shear stress produced by foam flow inside a channel.