Casson fluid flow in a microchannel containing a flow disturbing rib

• Casson-fluid flow in a μ-channel with a flow-disturbing rib (FDR) was studied.
• A validated CFD code is used to assess the effect of key design parameters.
• The blockage ratio and the Re greatly affect the formation of recirculation zones.
• An algorithm is proposed to predict the length of the bottom recirculation zone.
• Two new correlations facilitate the optimal design of μ-devices with FDRs.

This work numerically studies the flow of a Casson liquid over a flow-disturbing rib in a rectangular μ-channel. The aim is to investigate, using a previously validated CFD code, the effect of the non-Newtonian behavior on the fluid flow characteristics, i.e. the size of the reattachment length at the bottom of the channel and downstream from the rib, in a μ-channel equipped with a Flow Disturbing Rib (FDR). The effect of the type of fluid, the Re number and key geometrical parameters on the size of the bottom reattachment length of the primary recirculation zone is investigated by performing a parametric study based on the Design of Experiments and the Response Surface Methodology. The results show that the reattachment length is mainly affected by the Re value and the rib height. It was also found that for Re<50 the reattachment length decreases up to 35% for the non-Newtonian fluid compared to a Newtonian one, whose viscosity is equal to the asymptotic value of the non-Newtonian fluid. Based on the results two new and properly validated correlations are proposed, which can serve as a useful tool for designing microfluidic devices.

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