The present investigation is devoted to the second law of thermodynamics analysis of steady state hydrodynamically and thermally fully developed laminar gas flow in a microannulus with constant but different wall heat fluxes. Slip velocity and temperature jump boundary conditions are used to describe rarefaction effects. Viscous heating is also included for both the wall cooling and heating cases. Using already available velocity profile, closed form expressions are obtained for the transverse distribution of temperature and entropy generation rates. The results demonstrate that the effect of the wall heat fluxes ratio on entropy generation is negligible at large values of the group parameter and Peclet number, while the effect of increasing values of the annulus geometrical aspect ratio is to severely increase entropy generation. The entropy generation decreases as Knudsen and Peclet numbers increase, however the effect of increasing Brinkman number and the group parameter is to increase entropy generation. Furthermore, it is realized that the influences of rarefaction on entropy generation are slighter for low Peclet number flows.
