ABSTRACT:
Natural convection of non-Newtonian power-law fluids around curved surfaces is a ubiquitous phenomenon in industrial applications and research. In this context, the importance of temperature-dependent properties combined with the power-law behavior of the fluid was studied numerically to elucidate the extent and significance of non-Boussinesq effects. An order-of-magnitude-analysis (OMA) indicated that both the thermal expansion coefficient and consistency index had significant temperature dependencies for the class of fluids considered. These dependencies were incorporated in the governing equations applicable over practical temperature ranges. It was found that the effect of curvature on the local shear rate distribution for flow around the object lends additional significance to the non-Oberbeck-Boussinesq (NOB) effects augmented or diminished by power-law behavior. The importance of using actual temperature differences in the analysis because of a complete reversal of trends at very low temperatures was demonstrated. The influence of NOB effects in studies where the fluid and geometrical parameters are optimized was found to be significant. Comprehensive numerical studies to estimate the extent of NOB effects due to the inadequacy of OMA were found necessary. The solutions provided additional insight to the relative importance of thermo-dependent viscosity and thermal expansion coefficient for the class of power-law fluids considered.
