Effects of a plane wall above a pipe inlet on the entry flow of viscoelastic fluids.

An aqueous solution of Separan AP-30 (2 or 4 wt%) was pushed out through a circular pipe with a diameter d = 4 or 6 mm, attached to the bottom of a large reservoir. A plane wall was set in the reservoir parallel to the bottom, the distance z from the bottom being adjustable. The flow in the reservoir was observed and the pressure distribution along the channel was measured. The upper wall significantly affected the flow pattern above the pipe inlet ; the transition shear rates from the radial flow with vortex to the spiralling flow and from the spiralling flow to the random flow became lower with a decreasing z/d, and the period of the spiralling flow was shorter with a smaller z/d. For the random flow, the inlet pressure loss increased over a wide range of z/d. For the spiralling flow it decreased in the range z/d = 5 20.