Circumferential Diffusion in Pipe Mixing

A method is presented and used for evaluating an average circumferential mass diffusivity for steady, uniform, turbulent pipe flow. The method is based on the analytical solution of the conservation equation for a source at an arbitrary point in a pipe cross section. This solution shows that the asymptotic longitudinal variation of the coefficient of variation of the concentration distribution is a function only of the ratio of the circumferential and the radial diffusivities. Thus, empirical information on this variation can be used to evaluate mass diffusivity. The value obtained for mass diffusivity depends on the value used for radial diffusivity. The eddy viscosity was used to evaluate the latter. Fifteen sets of concentration measurements from three references were used in the analysis.