In the present study, the first and second law analyses associated with combined pressure-driven and electroosmotic flow of power-law liquids through a uniform microannulus are performed numerically. In the first law analysis, the Poisson-Boltzmann and incompressible Navier-Stokes-Fourier (NSF) equations in the cylindrical polar coordinate reference frame as the governing equations are numerically solved using a finite difference method. The obtained velocity and temperature distributions are then employed to evaluate the associated Nusselt number, while simultaneous effects of viscous dissipation and Joule heating are taken into consideration. In the second law analysis, the relevant general expression for the entropy generation process is derived and the contributions of thermal diffusion, fluid friction and Joule heating irreversibility to the total entropy generation in the micro domain are examined. Finally, the variations of the aforementioned major variables with influential parameters such as the aspect ratio of the annuli, flow behavior index, dimensionless Debye-Huckel parameter, forcing ratio, dimensionless viscous heating parameter, and dimensionless Joule heating parameter are investigated. (C) 2012 Elsevier Ltd. All rights reserved.