Abstract
This study addresses a numerical analysis of heat transfer and fluid flow in a partially heated horizontal annulus filled with nanofluids. The conservation equations in cylindrical coordinates are solved using an in-house FORTRAN code based on the finite-volume method coupled with multigrid acceleration. A heat source owing constant temperature is placed along the outer cylinder of the annular region. The temperature of the inner cylinder is lower than that of the outer cylinder, while the remaining parts are kept insulated. The numerical investigation is carried out for a Rayleigh number in the range of 10(2) <= Ra <= 10(6) and for solid volume fraction of nanoparticles limited to 0 <= phi <= 0 .0 8. Four nanoparticles (Au, Cu, CuO, Al2O3) and three base fluids (water, ethylene glycol, oil) are selected to examine potential heat transfer enhancement in the annulus. In order to investigate the effects of the size and/or location of the heat source on the fluid flow and heat transfer, different configurations are considered. Results are presented in terms of streamline and isotherms plots, as well as the local and average Nusselt numbers at the heat source surface under different conditions. It is found that the average Nusselt number exhibits an increasing trend as dual functions of the Rayleigh number and the solid volume fraction of the nanoparticles. Furthermore, the results reveal that one type of nanoparticle or base fluid is a key factor for improving the heat transfer. In particular, the highest values of enhancement are obtained when using Au nanoparticles or an oil base fluid. Moreover, it is observed that the size gamma, and location, theta(p), of the heat source significantly affect the resulting convective flow. An optimum size of the heat source is manifested in which the average Nusselt number attains a minimum for a given Rayleigh number. Reliable correlations formulae expressing the average Nusselt number in terms of Ra, phi, gamma, and theta(p) are established.