Transient pressure-driven electrokinetic slip flow and heat transfer through a microannulus

Abstract

To guarantee the transporting efficiency of microdevices associated with fluid transportation, mixing, or separation and to promote the heat transfer performance of heat exchangers in microelectronics, the hydrodynamic behaviors at the unsteady state as well as the thermal characteristics at the steady state in a pressure-driven electrokinetic slip flow through a microannulus are studied. To present a more reliable prediction, the slip phenomenon at walls is incorporated. The Cauchy momentum equation applicable to all time scales is analytically solved by the integral transform method; thereby, the physical picture of how the flow is initiated and accelerated to the steady state is provided. The energy equation and entropy generation for the steady flow are numerically solved. Consequently, the temperature profile, heat transfer rate, and entropy generation rate are computed at different electrokinetic widths, slip lengths, Joule heating parameters, and Brinkman numbers; thereby, the coupling effect of the slip hydrodynamics, annular geometry, viscous dissipation, and Joule heating on thermal behaviors is explored. The unsteady flow takes a longer time to achieve the steady state for a smaller radius ratio. The slip length not only accelerates the flow but also alters the velocity and temperature profiles. Compared to the outer one, the inner slip length plays a more significant role on the entropy generation rate. The relevant discussion can serve as a theoretical guide for the operation and thermal management of flow actuation systems related to annular geometries.