On convection-diffusion in non-Newtonian fluid flow in an annulus with wall oscillations

Dispersion of a solute in a Casson fluid flow in an annulus is studied by considering the flow unsteadiness due to the pulsatile pressure gradient and wall oscillations. The expression for velocity is derived under the assumption of low Womersley frequency parameter and also yield plane locations are estimated. Generalized dispersion method is used to solve the convective diffusion equation and hence estimated the dispersion coefficient. With this approach mean concentration is able to express in terms of convection and dispersion coefficients. Effects of yield stress, unsteadiness of the flow, annular gap and wall oscillations on axial velocity, yield plane locations of the flow, dispersion coefficient and mean concentration are analysed. Due to combined action of wall oscillations and flow oscillations, the dispersion coefficient is observed to be changing cyclically and took both positive and negative values which differs from the case of no wall oscillations where the dispersion coefficient seen to be taking only positive values. Both qualitative and quantitative changes are seen in mean concentration in the case of wall movement when compared with the case of no wall oscillations