Numerical investigation of a curved micromixer using different arrangements of cylindrical obstacles

Abstract

Curved micromixers are one of the most widely used types of passive micromixers that perform better than straight micromixers. Yet the main disadvantage of these micromixers is low mixing efficiency at low Reynolds numbers. To overcome this drawback implementing obstacles with different configurations can be a solution to change the flow pattern and consequently boosting the mixing efficiency of system. To this purpose, in the present study, four curved passive micromixers with different arrangements of cylindrical obstacles alongside with simple curved channel are considered and assessed. Simulations are carried out at eight different Reynolds numbers ranging from 0.1 to 80 in steady state, with water as a working fluid. In this regard, geometrical parameters such as channel cross-section, channel length, number of pitches, dimensions of obstacles and number of obstacles are considered constant in all cases. The results showed that the special arrangement of the obstacles placed in the channels led to the deviation of the flow path of the fluid and as a result the contact surface between the two fluids increased at low Reynolds numbers, which resulted an increase in the efficiency of mixing between the two species. Namely Case-B and Case-E with uniform distribution of obstacles along the channel have 26% and 23.6% higher mixing efficiency at Reynolds 5 compared to simple unobstructed channel. This is because the arrangement of obstacles in these cases associates with layered mixing of species and better mixing on the corners. Also, among different cases, the Case-B shows the highest mixing index. At Reynolds 40, the mixing efficiency of Case-A, B, C, D and E are 95.54%, 91.52%, 89.96%, 76.39% and 89.7%, respectively. By comparing the introduced channels, considering the mixing efficiency and pressure drop, it can be said that the Case-B model, although its mixing efficiency is 1.8% higher than the Case-E model, but due to 14.5% higher pressure drop, Case-E has the best performance among the introduced channels.