Effect of sinusoidal heated blocks on electroosmotic flow mixing in a microchannel with modified topology

Abstract

The present study is focused on micromixing enhancement techniques for electroosmotic flows in a modulated microchannel with a modified topology by utilizing heated blocks on the surface of the microchannel. The heated blocks carry higher temperatures as compared to the other portions of the channel wall, resulting in a sharp variation in the temperature of the fluid. The species transport is governed by the Nernst–Planck equation in a modified form by adding a thermo-electrochemical migration term due to the temperature variation in the ions, justifying the electrochemical equilibrium conditions. The fluid considered for the study is non-Newtonian and is governed by a power-law model. The Navier–Stokes equations, along with the thermal energy equation, are simulated numerically in a coupled form utilizing a finite volume-based semi-implicit method for the pressure-linked equation algorithm to interpret the behavior of the electric potential distribution, the external electric field, the flow field, the temperature distribution, and the species concentration, which are the major contributors for the mixing efficiency. The numerically simulated results are varied with the analytical results for the simple electroosmotic flow in the microchannel, indicating that the mixing efficiency can be enhanced by increasing the temperature of the heated blocks. Due to the thermo-electrochemical migration, ions are redistributed along the heated blocks, oscillating the flow velocity by creating vortices, resulting in the mixing enhancement. The effects of the geometrical parameters, the Debye–Hückel parameter, the temperature gradient, the power-law index, and the Nusselt number are elaborated for the effective flow rate and micromixing. The mixing efficiency is found to be optimum for higher temperature gradients and higher power-law indices. The net throughput analysis that combines the geometrical modulation and wall temperature variation will aid in improving the design and fabrication of microfluidic mixers.