Natural convection heat transfer of nanofluids in a vertical cavity: Effects of non-uniform particle diameter and temperature on thermal conductivity

This paper analyzes the heat transfer and fluid flow of natural convection in a cavity filled with Al2O3/water nanofluid that operates under differentially heated walls. The Navier–Stokes and energy equations are solved numerically, coupling Xu’s model (Xu et al., 2006) for calculating the effective thermal conductivity and Jang’s model (Jang et al., 2007) for determining the effective dynamic viscosity, with the slip mechanism in nanofluids. The heat transfer rates are examined for parameters of non-uniform nanoparticle size, mean nanoparticle diameter, nanoparticle volume fraction, Prandtl number, and Grashof number. Enhanced and mitigated heat transfer effects due to the presence of nanoparticles are identified and highlighted. Based on these insights, we determine the impact of fluid temperature on the heat transfer of nanofluids. Decreasing the Prandtl number results in amplifying the effects of nanoparticles due to increased effective thermal diffusivity. The results highlight the range where the heat transfer uncertainties can be affected by the size of the nanoparticles.