COMPARATIVE ANALYSIS OF DIFFERENT THERMAL CONDUCTIVITY MODELS FOR NANOFLUIDS IN A SQUARE ENCLOSURE UNDER NATURAL CONVECTION CONDITIONS

摘要

Previous investigations have revealed that addition of nanoparticles dispersed in conventional fluids such as water or ethylene glycol result in a new class of coolant which has anomalously high thermal conductivity under stagnation conditions. Few theoretical models have been proposed to resolve this abnormal behavior of nanofluids. This study focuses on the comparative study of some of these models namely, Wasp's model, Choi's modified Maxwell model, Bruggeman model and Xue's model for complex nanoparticles. Row in a cavity has been considered with insulated horizontal walls and vertical walls at different uniform temperatures under Boussinesq's approximation. Results obtained are presented in form of plots of streamlines, isotherms and Nusselt number. Steady state solutions have been obtained for natural convection in a square cavity partially filled with copper-water. Parameters considered are Grashof number (10~3 to 10~5) and particle concentration (φ=0%-20%). The results validate the stand that nanofluids are better coolants under dynamic conditions than conventional fluids. The flow properties have been found to be dependent upon the choice of thermal conductivity models chosen. The flow patterns predicted by various models have been found to be in close agreement with each other; however substantial variance has been found to exist in Nusselt numbers predicted by these models.