An Unsteady Mixed Convection in a Driven Cavity Filled with Nanofluids Using an Externally Oscillating Lid

Abstract

A numerical investigation of an unsteady, periodic, laminar mixed-convection in a cavity utilized with copper-water nanofluid is presented. In this study both top and bottom walls are assumed to be isolated, meanwhile sidewalls are considered under constant temperature condition. We consider a time-dependent oscillating wall on top to fulfill a peri odic mixed-convection inside the cavity. In this type of problems both Grashof and Reynolds numbers play a great role in flow pattern and heat transfer characteristics, so we focus our study on four major parameters that can be crucial such as Grashof and Reynolds numbers, solid volume fraction and the non-dimensional lid frequency . The obtained results show that the augmentation of Reynolds number and Grashof number would enhance the average Nusselt number. It is also found that unlike steady state condi tion, at high Reynolds numbers, as lid is moving in the negative direction the average Nusselt number on the hot wall becomes higher in respect to the case that lid is moving in the positive direction due to thermal boundary layer distur bance. Lid frequency does not have a significant effect on thermal characteristics at low Reynolds numbers, meanwhile at higher Reynolds numbers, increment of lid frequency results in heat transfer reduction. Moreover, solid volume frac tion is found to have better efficiency at higher Grashof numbers.