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Steady-state laminar mixed convection of water-based alumina nanofluids in cylindrical enclosures with a rotating top cover has been numerically analyzed for different Reynolds numbers (500–3000), Richardson numbers (0–1) and nanoparticle volume fractions (1–5%) for an aspect ratio of unity. Two different configurations have been considered for this analysis in order to obtain physical insights into the fluid flow and heat transfer in cylindrical enclosures with a rotating end cover. In one configuration (i.e. C1 configuration), the rotating top wall is kept at a higher temperature than the bottom wall, whereas the bottom wall is heated in the second configuration (i.e. C2 configuration). The mean Nusselt number in the case of mixed convection has been found to assume higher values in the C2 configuration than in the C1 configuration for a given set of values of Reynolds number, Richardson number and nanoparticle volume fraction. It has also been found that mean Nusselt number monotonically decreases with increasing nanoparticle volume fraction regardless of Richardson number values in the C2 configuration, whereas the mean Nusselt number decreases (increases) with increasing nanoparticle volume fraction for fully forced convection (mixed convection) in the C1 configuration. The simulation data has been used to propose a correlation for the mean Nusselt number for both C1 and C2 configurations. [ABSTRACT FROM AUTHOR]

Numerical simulations have been carried out to analyze steady-state laminar natural convection of yield stress fluids obeying Bingham model in square cross-sectioned cylindrical annular enclosures with differentially heated vertical walls for both constant wall temperature and constant wall heat flux boundary conditions for active walls. The simulations have been performed under the assumption of axisymmetry for a nominal Rayleigh number range of 103 to 106 and nominal Prandtl number range of 10 to 103 for different ratio of internal cylinder radius to cylinder height range of 0.125 to 16. The mean Nusselt number on the inner periphery for the constant wall heat flux configuration has been found to be smaller than that in the case of constant wall temperature configuration for a given set of values of nominal Rayleigh and Prandtl numbers for both Newtonian and Bingham fluid cases. The mean Nusselt number normalized by the corresponding value obtained for pure conductive transport increases with increasing internal radius before approaching the corresponding mean Nusselt number for square enclosures regardless of the boundary conditions. Detailed physical explanations have been provided for the effects of the aforementioned parameters on the mean Nusselt number on the inner periphery. Finally, the new Nusselt number correlations have been proposed for laminar natural convection of both Newtonian and Bingham fluids in square cross-sectioned cylindrical annular enclosures for both constant wall temperature and constant wall heat flux boundary conditions. [ABSTRACT FROM AUTHOR]

Steady-state numerical simulations have been conducted to investigate natural convection of yield stress fluids obeying Bingham model in square cross-sectioned axisymmetric cylindrical annular enclosure with vertical walls subjected to constant heat fluxes for nominal Rayleigh number range of 103to 106, nominal Prandtl number of 10 to 103for different values of internal cylinder radius. It is found that the mean Nusselt number on the inner periphery increases (decreases) with increasing nominal Rayleigh (Bingham) number due to strengthening (weakening) of thermal advection. However, the values of the mean Nusselt number on the inner periphery obtained for Bingham fluids are smaller than that obtained for Newtonian fluids for the same set of nominal Rayleigh and Prandtl numbers. The mean Nusselt number normalized by the corresponding value obtained for pure conductive transport increases with increasing internal radius before asymptotically approaching the mean Nusselt number for a square enclosure. This suggests that the ratio of the convective to the conductive transport strengthens with increasing cylinder radius in the cylindrical annular cavity. Detailed physical explanations have been provided for the effects of the aforementioned parameters on the mean Nusselt number on the inner periphery and correlations have been proposed for the mean Nusselt number on the inner periphery for both Newtonian and Bingham fluids. [ABSTRACT FROM AUTHOR]