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.
Highlights
The results 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
The results of the present work for the natural convection from heated cylinder placed in a cold square enclosure with lower and upper openings are presenting
The radiation Nu is approximately constant with the increase of Rayleigh number (Ra) because the natural convection flow has no effect on the radiation Nu value for low emissivity values (0.2-0.4)
Summary
(Wang et al, 2011) investigated the combined effect of the natural convection-conduction and surface radiation in an open cavity with constant heat flux in a laminar region. There are many studies considered the enhancement of natural convection from a heated horizontal cylinder using different methods to transfer the heat. The radiation effect from the cylinder’s surface on the natural convection still needs more investigation using different range of enclosure size and dimension. This paper investigates the effect of the natural convection mixed with radiation on the heat transfer from a horizontal cylinder in a symmetrical vented square enclosure using finite volume numerical method that based on simple algorithm with employment of Fluent software. Wide range of Rayleigh number, outer cylinder emissivity and constant enclosure width and opening size were applied. The study predicts the thermal behavior for Nusselt number, fluid temperature inside the enclosure, streamlines and isotherms
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