Thermally developing combined electroosmotic and pressure-driven flow of Phan-Thien-Tanner fluids in a microchannel

We present semi-analytical solutions for the hydrodynamically developed and thermally developing flow of a non-Newtonian fluid through an isothermal rectangular microchannel. The fluid motion is actuated by the combined consequences of the electroosmotic and pressure-gradient forces. For the rheological behavior of the non-Newtonian fluid, we have used the simplified Phan-Thien-Tanner viscoelastic model. Going beyond the Debye Huckel linearization approximation, we have used the full-scale solution for the electrical double-layer potential equation to obtain the exact analytical solutions for the velocity, flow rate, and shear rate parameters. In contrast, the temperature distribution and heat transfer for the thermally developing flow have been obtained by solving the energy equation numerically considering the effects of volumetric heat generation due to Joule heating and viscous dissipation. We find that a larger value of the viscoelastic set (epsilon) over bar (W) over tildei(k) (2) contributes toward the net gain in flow rate. Both the normal and shear stress increase for increasing (epsilon) over bar (W) over tildei(k) (2), while the shear viscosity reduces with a degree of surface charging. The average shear viscosity reduces with the degree of surface charging and at higher (epsilon) over bar (W) over tildei(k) (2) values. The heat transfer is enhanced for augmenting (epsilon) over bar (W) over tildei(k) (2), although the thermal entrance region gets contracted for a pure electroosmotic flow at higher Peclet numbers. Our study reveals that the heat transfer rate can be amplified by effectively modulating the degree of surface charging and (epsilon) over bar (W) over tildei(k) (2). We have also carried out an entropy generation analysis, which shows the dominance of heat transfer irreversibility over fluid friction irreversibility. We believe that the present research will offer essential approaches for designing advanced energy-efficient microchannels appropriate to modern industrial applications using viscoelastic fluids.