Study of Laminar Convection Heat Transfer of Non-Newtonian Nanofluids in a Tube under Constant Heat Flux Using New Power-Law Relation

Abstract

In this study, thermal and rheological behavior of non-Newtonian nanofluids in a tube is studied using a new power-law relation. The tube is under a constant heat flux and the viscosity of power-law non-Newtonian nanofluids is assumed to be a function of shear rate and temperature simultaneously. Fully developed velocity and uniform velocity profiles are considered as inlet boundary condition. It is demonstrated that the viscosity along the tube is affected by temperature and shear rate for fully developed and uniform flow profiles. Local heat transfer coefficient along the tube increases with the volume fraction, however volume fraction less than 3% does not affect local heat transfer. It is demonstrated that local heat transfer and average Nusselt number are decreasing functions of Reynolds number. Contrary to the previous studies, average Nusselt number is a decreasing function of the volume fraction of nanoparticles. The Nusselt number is suggested to be a function of Peclet number when the temperature effects are considered in the power-law relation.