In the present paper, a double multiple-relaxation-time lattice Boltzmann simulation and response surface optimization are performed to optimize the performance of a novel active micropump-mixer at high Peclet number flows. The mixer and pump systems are comprised of rotationally oscillating rectangular stirrer with a constant aspect ratio of AR = 0.1, with a variable diameter, and two identical square rotors, respectively. Effects of three important non-dimensional parameters of the stirrer, including its diameter 〖(D〗_S), maximum velocity (U_S), and amplitude (K) are investigated on the mean mixing efficiency (ε_out), the time-averaged of the instantaneous dimensionless averaged velocity (U_ave), mixing energy cost (mec) and pumping energy cost (pec). All calculations are carried out for the non-dimensional U_S and K in the range of 0.1-1, and for D_S in the range of 0.5-0.9, at fixed Reynolds and Peclet numbers of Re=1 and Pe=10000. Results indicated that ε_out increases with D_S, and especially with K, while it displays a non-monotonic behavior with U_S. Furthermore, U_ave and mec decrease with increasing D_S and K. However, U_ave is not influenced by U_S variations, but mec shows a decrease-increase trend with increasing〖 U〗_S. The pec increases with increasing of all three parameters. Finally, the optimization results indicated that non-dimensional values of 0.5, 0.702, and 1 respectively for D_s, U_s and K are the optimum values for the simultaneous optimization of all four (ε_out,U_ave,mec and pec) responses.

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