The turbulent diffusion of drag-reducing polymer solutions from a point source in flow through a pipe

Abstract

Solutions containing salt(NaCI) were injected into water flow through a fine tube at the centre of a pipe. Tests were made to ensure that the flow was turbulent and well developed at the injection point; and that neither the injection process nor the injector caused any appreciable flow disturbance. Radial concentration profiles were measured at various downstream distances by withdrawing samples from the flow and measuring their electrical conductivity. A comparison was made between water, and aqueous solutions of polyethyleneoxide and polyacrylamide. Results for the eddy diffusivity in water agreed with those from previous investigations. Turbulent diffusivities were found to be greatly reduced in the polymer solutions (even after allowance had been made for the reduced wall shear stress) compared to the values for water alone. There were detailed differences in the effects of the two different kinds of polymer and these were attributed to their different viscoelasdc properties in the concentration ranges studied.