Numerical Simulation of Mixing Two Fluids of Different Viscosities in a Micromixer at Different Aspect Ratios of Stirrer by LBM

In the present study, mixing of two fluids of different viscosities in a micromixer with oscillating stirrer was simulated by MRT-LBM and the effect of aspect ratio (AR) of stirrer on mixing efficiency was analyzed. The simulation was performed at Re=50, Sc=10. The results showed that at low values of amplitude (K), at low values of Strouhal number (St), increase of AR causes increase in mixing efficiency and at other values of St it decreases and then increases. At intermediate values of K, at low and intermediate St, mixing efficiency decreases with the increase of AR and at high values of St, it first decreases and then increases. At high values of K, at low and high St, increasing AR causes no improvement in mixing efficiency and at intermediate values of St, mixing efficiency decreases and then increases. In this research, the best mixing efficiency for viscosity logarithmic ratio (R) =2 is at AR=0.7, St=1, K=0.5. The effect of AR and St on mixing efficiency at different R was analyzed and results revealed that for two fluids of different viscosities, at very low values of St, mixing efficiency increases with the increase of R and at others decreases considerably. In general, for two fluids of different viscosities, stirrer with low values of AR has better mixing efficiency.