The present work reports the outcome of a comprehensive parametric study on mixed electroosmotically and pressure-driven flow in slit microchannels with constant wall heat fluxes. Special attention is given to disclose the applicability ranges of usual assumptions in simplified analyses. The governing equations for fully developed conditionsarefirstmadedimensionlessandthensolvedbymeansofanimplicitfinitedifferencemethod.Theresults reveal that the assumption of constant thermophysical properties does not lead to significant errors in practical applications. Although the Debye–Huckel linearization may successfully be used to evaluate velocity profiles up to the zeta potentials of 50 mV, nevertheless, the calculated Poiseuille numbers may be quite different from the exact ones, even for lower zeta potentials. It is also found that this linearization may fail at predicting accurate velocity profiles when a considerable amount of opposed pressure exists, even at very low zeta potentials. Unless a sufficiently high value of the dimensionless Debye–Huckel parameter is considered, assuming a uniform distribution for the Joule heating leads to large errors in calculating the thermal aspects for the zeta potentials of more than 25 mV. Furthermore, increasing the zeta potential leads to decreasing the viscous heating effects at lower values of the dimensionless Debye–Huckel parameter, whereas the opposite is true for higher amounts of this parameter.
