On the Enhancement of Heat Transfer and Reduction of Entropy Generation by Asymmetric Slip in Pressure-Driven Non-Newtonian Microflows

TL;DR

This study investigates how asymmetric slip boundary conditions influence heat transfer, entropy generation, and flow characteristics in pressure-driven non-Newtonian microflows, revealing that slip can enhance heat transfer and reduce irreversibility.

Contribution

It provides a detailed analytical and numerical analysis of asymmetric slip effects on flow, heat transfer, and entropy generation in non-Newtonian microchannel flows, which was not previously explored.

Findings

Asymmetric slip shifts velocity maximum towards the wall with larger slip.

Slip promotes uniform velocity and temperature fields, reducing irreversibility.

Different heat flux conditions lead to distinct Bejan number profiles depending on slip and fluid type.

Abstract

We study hydrodynamics, heat transfer and entropy generation in pressure-driven microchannel flow of a power-law fluid. Specifically, we address the effect of asymmetry in the slip boundary condition at the channel walls. Constant, uniform but unequal heat fluxes are imposed at the walls in this thermally developed flow. The effect of asymmetric slip on the velocity profile, on the wall shear stress, on the temperature distribution, on the Bejan number profiles, and on the average entropy generation and the Nusselt number are established through the numerical evaluation of exact analytical expressions derived. Specifically, due to asymmetric slip, the fluid momentum flux and thermal energy flux are enhanced along the wall with larger slip, which in turn shifts the location of the velocity's maximum to an off-center location closer to the said wall. Asymmetric slip is also shown to redistribute the peaks and plateaus of the Bejan number profile across the microchannel, showing a sharp transition between entropy generation due to heat transfer and due to fluid flow at an off-center-line location. In the presence of asymmetric slip, the difference in the imposed heat fluxes leads to starkly different Bejan number profiles depending on which wall is hotter, and whether the fluid is shear-thinning or shear-thickening. Overall, slip is shown to promote uniformity in both the velocity field and the temperature field, thereby reducing irreversibility in this flow.