In the present work, the second law of thermodynamics analysis has been carried out for steady-state fully developed laminar gas flow in a parallel plate microchannel with asymmetrically heated walls. The rarefaction effects as well as viscous heating effects are taken into consideration. Closed-form expressions are obtained for velocity and temperature distributions and entropy generation rates. The results demonstrate that increasing values of the wall heat fluxes ratio result in greater entropy generation for positive Brinkman numbers, whereas the opposite is true for negative values of Brinkman. However, the effect of the wall heat fluxes ratio on entropy generation becomes insignificant at high values of the group parameter and Peclet number. The entropy generation decreases as Knudsen and Peclet numbers increase;however,the effect of increasing values of Brinkman number and the group parameter is to increase entropy generation. Also, it is realized that the influences of rarefaction on entropy generation are negligible for low Peclet number flows.
