On the Use of Viscous Micropumps for the Transport of Yield-Stress Liquids in Microfluidic Systems

Abstract

• A fluid's yield stress is predicted to negatively affect the performance of viscous micropumps. • The drop in performance depends on the Bn number and is estimated to be around 60% for Bn = 10 and 20% for Bn = 2. • Viscous micropumps can be used for pumping weakly-viscoplastic liquids in microfluidic systems. The effect of a fluid's yield stress is numerically studied on the performance of a single-rotor, I-shaped viscous micropump. The device comprises a long cylindrical rotor which rotates in a two-dimensional rectilinear channel filled with a yield-stress fluid. A net flow is established for viscous fluids provided that the cylinder is installed in an off-center position across the channel. Having assumed that the viscoplastic fluid of interest obeys the Bingham-Papanastasiou model we have obtained converged results for Bingham numbers (Bn) up to 10. Numerical results obtained at low Reynolds numbers (typical of microfluidic systems) have revealed that a fluid's yield stress has a negative effect on the device performance. Specifically, the flow rate of the micropump is decreased while its driving torque is increased the larger Bn number. At the maximum Bn number tried in this work (i.e., Bn = 10) the drop in performance is predicted to be around 60%. For Bn < 1, however, it is predicted to be less than 20% suggesting that viscous micropumps can still be regarded as a viable option for the transport of weakly-viscoplastic liquids in microfluidic systems.