Thermal transport characteristics of AC electrokinetic flow in a micro-annulus

Abstract

Alternating current electroosmotic flow and associated heat transfer under constant surface heat flux conditions are numerically examined in a micro-annular channel. The channel surfaces are arbitrarily heated and/or cooled, while the resultant heating is normally transferred downstream by the advection mechanism. An important feature of time-periodic electrokinetic flow is that there is not any preferential axial direction. If the excitation frequency is sufficiently small and/or the liquid kinematic viscosity is sufficiently large, momentum diffuses far into the bulk fluid and thus the advection mechanism is intensified. The reverse is true for relatively large frequency and small kinematic viscosity values. Mean Nusselt number fluctuates over a period of time; its time-averaged magnitude is dependent on the electrokinetic diameter and the dimensionless frequency. This quantity approaches a specific value regardless of the thermal scale and the wall heat flux ratios. The system may attain optimal effectiveness for particular magnitudes of the frequency and electrokinetic diameter. An interesting case may exist in the cooling mode where the axial variation of the mean fluid temperature vanishes temporarily while the state of constant surface temperature is instantly satisfied; at the particular points in time, the advection mechanism does not contribute to the development of the liquid temperature field.