Conversion Factors on Heat Transfer of Nanofluid’s Natural Convection

Abstract

The concept of conversion factors on heat transfer of nanofluid’s natural convection are proposed. The conversion factors on heat transfer coefficient, and local and total heat transfer rates of nanofluid’s natural convection are equal, and proportional to the thermal conductivity ratio at wall temperature, Grashof number ratio and wall temperature gradient ratio of the nanofluid’s natural convection, respectively. Through further formula analysis, the predictive formulae of the wall temperature gradient ratio at wall temperature, Grashof number ratio and wall temperature gradient ratio are respectively obtained. Then, the predictive formulae of the conversion factors on heat transfer coefficient, local and total heat transfer rates, as well as Nusselt number are developed for Al2O3-water nanofluid’s natural convection. These predictive formulae are actually based on comprehensive consideration of nanofluid’s variable thermophysical properties, nanoparticle’s shape factor and concentration, and fluid’s boundary temperatures, they have reliable theoretical and practical value for heat transfer application.