Analysis of Entropy Generation for a Power-Law Fluid in Microchannels

Abstract

Entropy generation is tied to the exergy destroyed. Hence, the amount of entropy generation is of primary concern as it is related to unavailable work. Viscous dissipation is a form of heat generation due to work done by viscous forces. Its effect on the velocity and temperature profiles would have affected the entropy generation. In this work, second law analysis is carried out on a microchannel between parallel plates for a power-law fluid. The governing energy equation for a rectangular microchannel is first solved analytically. Analytical expression is obtained for the dimensionless entropy generation and Bejan number. Dimensionless entropy generation due to fluid flow irreversibility and heat transfer irreversibility are also computed and compared. The distribution of entropy generation due to heat transfer irreversibility and fluid friction irreversibility changes as Brinkman number increases. A comparison with a previous literature on a circular pipe for the same Brinkman number reveals that the total dimensionless entropy generation in parallel plate is more than the corresponding value in circular pipe. However, the Bejan number for a parallel plate is lower than a circular pipe.