Abstract
In this study, mixed convection in an annulus formed by two horizontal isothermal cylinder surfaces and filled with hybrid nanofluids was examined with Galerkin weighted residual finite element method. The outer cylinder is rotating and inner cylinder is stationary. Influence of Rayleigh number, angular rotational speed of the outer cylinder, eccentricity of the inner cylinder, solid volume fractions of different nanoparticles (alumina, copper, hybrid particles between 0 and 0.02) on the fluid flow and heat transfer characteristics were analyzed. It was observed that average heat transfer enhances with Rayleigh number, solid volume fractions of nanoparticles and eccentricity ratio and reduces as the angular rotational speed of the outer cylinder increases. Adding nanoparticles was found to be advantageous for lower values of Rayleigh number and higher values of angular rotational speed. At the highest volume fraction of Cu nanoparticles, average Nusselt number increases by 31.75 % when the inner cylinder center moves in +y direction. Nanofluid with hybrid nanoparticles gives heat transfer rates which are higher than that of with alumina and lower than that of with copper nanoparticles for the same volume fraction.
Highlights
Free convection within the annulus of horizontal cylinders was studied by many researchers due to its importance in various engineering applications such as thermal energy storage, solar power, heat exchangers and many others
In this numerical simulation study, mixed convection of hybrid nanofluids in an annulus formed by two isothermal horizontal surfaces with the outer cylinder surface rotating is investigated
Effects of Rayleigh number, angular rotational speed of the outer cylinder, eccentricity of the inner cylinder, solid nanoparticle volume fractions of different particles on the fluid flow and heat transfer characteristics were studied in detail
Summary
Free convection within the annulus of horizontal cylinders was studied by many researchers due to its importance in various engineering applications such as thermal energy storage, solar power, heat exchangers and many others. In the numerical study by El-Maghlany and Elazm [30], mixed convection in an eccentric horizontal annulus filled with water and Cu, TiO2 and Al2O3 nanoparticles were analyzed. The inner cylinder rotates and the two cylinder surfaces were kept at constant temperatures They noted that use of nanoparticles is only effective for the mixed and natural convection regions. Mehrizi et al [31] performed a numerical study of mixed convection in micro-annuli filled with electrically conductive nanofluids under the effect of magnetic field. They showed that taking into account the temperature dependent thermophysical properties does not change the flow fields and heat transfer behavior. Matin and Pop [32] performed
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