Steric-effect-induced alteration of thermal transport phenomenon for mixed electroosmotic and pressure driven flows through narrow confinements

Abstract

The present paper addresses, for the first time, the thermal transport process for mixed electroosmotic and pressure-drive flows of electrolyte solutions, through nanoscopic confinements with step-change in the wall temperature, by going beyond the prevalent simplifying assumption of non-interacting, point charge behaviour of the ions in the electrolyte solution. An attempt is made here to delineate the alterations in the heat transfer characteristics induced by the inclusion of the finite ionic size effect or the ‘steric effect’, in the electrokinetic framework, which becomes very significant for electro-hydrodynamic flows through narrow-confinements with high surface charge density. Under such situations the finite size of the ions cannot be trivially precluded from the analysis, thereby rendering the point charge assumption erroneous. The distinctive influence of the ‘steric’ effect of ions on the heat transfer characteristics is numerically investigated by delineating the variations in the local liquid temperature, local Nusselt number and the thermal entrance length for the thermally developing regime. The observed significant influences of the bulk volume fraction of ions, as represented by the steric factor, on the thermal transport phenomenon are physically explained by simultaneously highlighting their intrinsic differences with the effects of other existing parameters, like Joule heating and viscous dissipation. The utilitarian scope of the work lies in the fact that it proposes a more comprehensive methodology for analyzing the heat transfer characteristics in state-of-the-art nanoscale electromechanical devices.