FLOW IN AN ABRUPT EXPANSION AS A MODEL FOR BIOLOGICAL MASS-TRANSFER EXPERIMENTS

This paper describes and examines developing flows downstream of abrupt tubular expansions for tube diameter ratios 0. 63, 0. 79, and 0. 93. A solution for a linearized form of the Navier-Stokes equation for developing flows was expanded to deal with polynomial representations of upstream velocity profiles. Experimental velocity profiles were obtained via tracer particles and high-speed photography at two stations downstream of the vortex. These profiles in polynomial form were used as upstream boundary conditions for the Navier-Stokes equation for the purpose of computing velocity profiles, wall-shear rates and development lengths. The authors find a simple tubular expansion to be a good model for biological mass transfer experiments in that it provides a well controlled variable wall shear rate. It has been demonstrated that using a dia. ratio of 0. 63 it is possible to vary shear rate by a factor of two over a 30 cm length of test section.