The effect of inclination angles on foam rheology in pipes

Foams are regarded as a versatile means in many industrial applications due to its high viscosity and low density. Recent experimental studies in horizontal pipes show the existence of two flow regimes: the high-quality regime exhibits a repetition of fine-textured foams and free gas sections (i.e. "slug flow" pattern) with fluctuating pressure responses; and the low-quality regime exhibits stable foams (either "plug flow" pattern with homogenous foams, or "segregated flow" pattern with upper foam layer and lower liquid layer) with stable pressure responses. In continuation with these previous studies, this study investigates the effects of inclination angles on foam rheology in pipes within the context of two-flow-regime concept. The results showed that foam rheology was not significantly altered as long as the slug flow or plug flow pattern was formed because of a viscous-force dominant environment. However, if flow conditions fell within the segregated flow pattern, foam rheology was governed by the gravitational force rather than the viscous force, and therefore the flow characteristics were sensitive to inclination angles. These findings were supported by visual observations as well as pressure responses.