The flow of gas-liquid foams through pipe fittings

Pipe fittings introduce complex phenomena in foam structure and flow. The dynamic effects resulting from the interaction of foam with a fitting are a function of the type of foam generator used and, hence, depend on the initial foam structure. A sudden change in the flow area or flow direction can alter the foam liquid holdup and foam homogeneity, and hence affect how upstream and downstream of the fitting. This paper reports a study on the flow of pneumatically generated foams through a variety of pipe fittings: pipe bend, pipe elbow, perforated plate and orifice plates. The orifice plate was the only flow constriction which had negligible effects on the foam flow. Other fittings generated large differences in liquid holdup and pressure gradient between the flows in the upstream and downstream pipe sections. The perforated plate introduced a substantial local pressure drop especially in the case of foams with an initial large polyhedral bubble structure. In such a case, bubble size was also significantly reduced. Foam rheology in the straight pipe sections was successfully described by a power-law model and the friction factor for foam flow could be described by a simple explicit relationship, both in horizontal and vertical hows, regardless of the foam structure and flow regime. (C) 2001 Elsevier Science Inc. All rights reserved.