Paper Title
Numerical Investigation of Mixing Index for Three Novel Micro-Mixers With Experimental Validation

Abstract
In this work three dimensional three novel micro mixers are analyzed for mixing efficiency by numerical simulation. The simulations results are validated by experimental work. These novel micro-mixer designs are analyzed first by simulation before fabrication on chip for experimental purpose to ensure mixing is enhanced due to addition mixing units. The concentration gradient, flow pattern on the cross sectional plane and mixing index of these micro-mixers is numerically investigated for wide range of Reynolds number 0.5 ≤ Re ≤ 100. Mixing index and pressure drop for each micro-mixer is calculated from COMSOL 5.2a simulation. Mixing index is improved for each novel design as compared to straight micro-mixer SMM1. The reason for improvement in mixing index inside CMM2, RCMM3, and RMM4 is chaotic advection, which causes rotation and circulation in flow. Advection occurs parallel to flow, while chaotic advection perpendicular to the flow direction. The RCMM3 micro-mixer having mixing units of circle and rhombus type shows better mixing index of 0.99 at Reynolds number of 100.After simulation micro- mixers ,chips are fabricated for finalized designs from material of glass and silicon material. Experiment is performed with the help of red and blues dyes, as working fluids for evaluation of mixing performance. Comparison of simulation and experimental results shows that there is little difference in mixing index values ,though the overall trends for both cases is consistent. Also it is concluded that both experimentally and numerically at low Reynolds number below(< 20) mixing index is low showing very small mixing , however with increase in Reynolds number up to 40 mixing index increase to 0.8 which quite acceptable range. When Reynolds number is increased to 100 maxing is 0.99 showing almost complete mixing. Keywords - Microfluidics, mixing index, micro-mixer, CFD