Numerical study of unsteady natural convection heat transfer of Newtonian and non-Newtonian fluids in a square enclosure under oscillating heat flux

摘要

This paper presents a numerical study on the unsteady natural convective flow of Newtonian and non-Newtonian fluids in a square enclosure. A heat source with oscillating heat flux is located on the bottom wall of the enclosure. The top wall is thermally insulated and the other walls are at a relatively low temperature. The continuity, momentum, and energy equations for a computational domain encompassing the enclosure are solved numerically using the SIMPLE algorithm. The flow and temperature fields and the heat transfer performance are examined for different non-Newtonian fluids and heat source locations. The results are presented for different values of power-law index, Rayleigh number, and fluctuation period. It is found that the flow and temperature fields vary as the oscillating heat flux is changed. The pseudoplastic non-Newtonian fluid (n<1) is associated with a higher heat transfer, and the dilatant non-Newtonian fluid (n>1) is associated with a lower heat transfer with respect to the Newtonian fluid. The heat source oscillation period significantly affects the maximum flow temperature in the enclosure. This study provides useful information for the designers of electronic cooling systems using non-Newtonian fluids.