Evaluation of slip effects in the capillary flow of foams

Abstract

Foams have been prepared from water added with a surfactant (Sodium-Dodecyl-Sulfate, SDS) and a polymer (Poly-Ethylene-Oxide, PEO) at different concentrations. This work was devoted to a study of the flow properties of the foams. The pressure drops were measured during flow in capillary tubes (2.5, 3.5 and 4 mm) in laminar regime. It was found a strong dependence of the flow curves on capillary diameter showing that pronounced wall slip effects exist. Two known approaches were applied to quantify the slip velocity: (a) the Mooney method, in which the key assumption is that the slip velocity depends only on the wall shear stress, was not applicable and (b) the Oldroyd-Jastrzebski method, in which the assumption is that the slip velocity depends not only on the wall shear stress but also on the flow geometry, yielded satisfactory results. The determination of the pressure drop coefficient showed that the Metzner and Reed correlation, i.e., the Reynolds analogy based on the generalised Reynolds number, could be applied if the data are corrected for slip effects.