Effect of couple stresses on the unsteady convective diffusion in fluid flow through a channel

Abstract

A generalized dispersion model is used to obtain exact solution for unsteady convective diffusion in the presence of couple stresses. The effect of the couple stress parameter ‘a’ on the most dominant dispersion coefficient is clearly depicted. The dimensionless mean concentration distribution is obtained as a function of dimensionless axial distance, time and ‘a’. The results for ‘pure convection’ are also reported. It is shown that the effect of couple stress is predominant only for small values of ‘a’ and when $\mathit{a}\to \infty$ the flow characteristics tend to their equivalents in Newtonian theory. The results of Taylor’s dispersion model are recovered as a particular case in the limit $\mathit{\tau }\to \infty$ .