چكيده به لاتين
The numerical investigation is the main motivation of the present study. It means that different microchannel geometry is examined by numerical simulation (with Ansys fluent version 19.1) and the optimize geometry is used for experimental study. Four study cases with different barrier structures have been investigated to examine the effect of the Split and incorporate of fluid streams, fluid tortuosity, 2D vs 3D geometry and the symmetry of obstacle on fluid movement.
The geometrical parameters in the convergent-divergent microchannel are optimized by response surface method. Due to the obstacle place in the main channel and fluid movement (stretching of rhodamine-B solution to another side that occupied with pure water) the mixing quality can be improved. Besides, tracking the streamlines show that the vortices act as imaginary barriers which their asymmetric trends lead to enhanced mixing. The Reynolds number was considered between 0.05 - 93. At low Reynolds number (Re<2) the mass diffusion rate is greater than the mass advection rate. While at Re>2 mass advection rate is greater. The approximate mixing quality at Re=93 by numerical simulation and experimental procedure are 73 and 60, respectively. By increasing the Re number, the pressure drop increases in the main channel. The relation between the fluid tortuosity with lateral peclet number and MI is investigated in the second study cases. The results show that, by decreasing the winglet angle, the fluid tortuosity increases as well as lateral peclet number. Decreasing in winglet angle can increase the lateral velocity that is proper for homogenous mixing. Thus, the MI and fluid tortuosity have direct relation. The aim of the third case study was the comparison between 2D vs 3D numerical simulations. When the blockage ratio (hbarrier/Hchannel) of the barriers against the flow direction is close to 1 or zero, the results of a 2D simulation approach to the simulation results of the 3D case. In another case due to the depth of channel that has an important role for twisting the fluids, the 2D geometry cannot be used and the best geometry with the barrier height h=0.75H that was obtained. In the last cases, the effect of symmetry cylinder obstacle pairs is investigated. The geometry with asymmetric obstacles leads the fluid flows to more chaotic movement and increases the fluids merging.
The mixing efficiency is used for comparison of four study cases. The ideal microchannels have more MI and low-pressure drop. The third case has more mixing efficiency than the other ones.
