Effect of Radiation on Natural Convection Heat Transfer from Heated Horizontal Cylinder in Vented Enclosure

Abstract

The natural convection heat transfer from a heated circular cylinder placed in a square vented enclosure was investigated considering the effect of the thermal radiation from cylinder using finite volume method with simple algorithm that used pressure-velocity coupling to solve Navier-Stockes and energy equations using Computational Fluid Dynamics CFD (Fluent software). The flow domain is filled with air. The enclosure width is 12.5 cm, two symmetrical openings at its lower and upper walls with size O = 2.5 cm and the cylinder diameter is 5 cm. Different rang of cylinder's surface emissivity with Rayleigh number range between 103 to 106 was applied in this study as operating condition. The effect of the Ra, cylinder radiation for vented square enclosure on the convection, radiation and total Nusselt numbers Nu and flow and thermal patterns were investigated. The numerical results for pure natural convection were compared with available experimental results, good agreement was obtained. The results revealed that the natural convection heat transfer from the cylinder in the enclosure is increased as compared with that of the unbounded cylinder without radiation effect. The results also revealed that there is a linear relationship between the heat transfer enhancement and the emissivity, there is a significant effect of the cylinder surface radiation which gives high augmentation compared with that of the free cylinder and natural convection heat transfer without radiation effect. A maximum total Nusselt number is obtained at high emissivity compared with that of natural convection heat transfer, the maximum Nu enhancement ranged between 70 to 350 % for low Ra and 25 to 125% for high Ra.