Interplay of fluid rheology and flow actuation for modulation of mixing characteristics in T-shaped microchannels

Microfluidic applications demand mixing of fluids in a small span of length and time, which remains a challenging task due to the low Reynolds number flows at these scales. The mixing analysis becomes further complex with non-Newtonian fluids, which often have high effective viscosity. Such fluids are frequently encountered in practical applications. In the present study, we numerically analyze an effective way of mixing time-independent inelastic liquids using pulsatile velocity inlet conditions using COMSOL Multiphysics. The fluids are considered to obey the power law model for the rheological analysis. We demonstrate enhanced mixing using pulsing velocity inlet condition and achieve superior values of mixing by tuning the interplay of pulsed input velocity and phase difference between the input pulses. The analysis is done for both shear-thinning and shear-thickening fluids, and enhanced mixing is demonstrated. It was observed that upon pulsing, a mixing of 86%, 84.4% and 82.9% for n = 0.6, n = 1, and n = 1.4 respectively occurred. It was also observed that by introducing a phase difference of 180°, the mixing index increased by 13.2%, 5.8% and 3.9% for n = 0.6, n = 1, and n = 1.4 respectively. Maximum mixing of 97.6% was observed for shear thinning liquid (n = 0.6) at a pulsatile input conditions having a phase difference of 180°. It was also observed that upon increasing the frequency of pulsation, the mixing decreases. This study will be helpful in designing micromixers for the effective mixing of non-Newtonian liquids in a small span of length and time.