Thermohydraulic assessment of mixing behaviors and entropy generation using pseudoplastic fluids in short microfluidic devices

Abstract

Thermal mixing fluids in chaotic microdevices have significant importance in many potential applications and have enormous utility in thermal engineering processes. In microfluidic devices, The Two-Layer with Crossing Channels Micromixer (TLCCM) emphasized its efficiency in thermally homogenizing Newtonian fluids, which inspired us to investigate its performance using pseudoplastic fluids. A numerical comparative investigation has been carried out to evaluate the thermal mixing performances of pseudoplastic fluids in laminar steady flows using four chaotic microdevices: TLCCM, L, OH and OX. Quantitative validation of pseudoplastic fluids within a complex geometry, subject to constant heat flux, has been done. Navier-Stokes, the mass conservation, energy and species transport equations have been solved numerically employing CFD code. The pseudoplastic fluids consist of carboxymethyl cellulose solutions, which are characterized using the power-law model, the flow behavior index ranging from 0.75 to 1 and the generalized Reynolds number ranging from 0.2 to 70. To quantify the thermal mixing efficiency, the effects of the fluid behavior index, the generalized Reynolds number, on the thermal mixing degree for the proposed micromixers are presented, where high thermal mixing degrees have been obtained which evolve between 0.9 and 0.99. The entropy generation due to heat transfers and fluid pressure drops has been introduced versus the generalized Reynolds numbers for different fluid behavior indexes. The Bejan number values evolve close to 1. The probability density function PDF (%) at the TLCCM micromixer exit is localized in a narrow range that refers to the ideal temperature value for mixing, which is 315 Kelvin, whatever the fluid behavior index value.