EFFECT ON NATURAL CONVECTION HEAT TRANSFER OF NANOFLUID IN AN ENCLOSURE DUE TO UNCERTAINTIES OF VISCOSITY AND THERMAL CONDUCTIVITY

摘要

im to identify effects due to uncertainties in viscosity and thermal conductivity of nanofluid on laminar natural convection heat transfer in a square enclosure. Numerical simulations have been undertaken incorporating a homogeneous solid-liquid mixture formulation for the two-dimensional buoyancy-driven convection in the enclosure filled with alumina-water nanofluid. Two formulas from the literature are each considered for the i viscosity and thermal conductivity of the nanofluid. Simulations have been carried out for the pertinent parameters in the following ranges: the Rayleigh number, Ra_f = 10~3 ～ 10~6 and the volumetric fraction of alumina nanoparticles, Φ = 0 ～ 4%. Significant difference in the effective dynamic viscosity enhancement of the nanofluid calculated from the two adopted formulas, other than that in the thermal conductivity enhancement, was found to play as a major factor, thereby leading to contradictory results concerning the heat transfer efficacy of using nanofluid in the enclosure.