Combined Natural Convection and Surface Radiation Heat Transfer from Two Aligned Horizontal Cylinders in a Vented Square Enclosure

Abstract

Combined natural convection and surface radiation from two horizontally aligned cylinders at unequal surface temperatures in a vented square enclosure are solved numerically. A two-dimensional turbulent finite-volume model couples the k–ω SST closure with surface-to-surface radiation using ANSYS Fluent Software. The left cylinder is held at a constant lower temperature and the right at a higher, variable one, while a constant inlet velocity at the bottom vent keeps the flow natural-convection-dominated. The model reproduces 18 experimental cases with a mean error of  and a maximum of . Sweeps cover Rayleigh numbers from , opening ratios from , spacing ratios from , and surface emissivity from . Emissivity is the controlling parameter. Raising it from  increases the total Nusselt number by  for the left cylinder and  for the right, while the convective contribution changes by less than . Convective transfer peaks near an opening ratio of  and at the smallest spacing, whereas the total Nusselt number is highest at the tightest opening, where trapped hot air raises the radiative share. Radiation supplies  of the total at  and – at unit emissivity, so a convection-only model under-predicts by the same margins. The current arrangement is of significant interest for numerous applications in electronic housings, heat exchangers, and renewable energy fields including solar receiver cavities, flat plate solar collectors, and photovoltaic thermal solar systems.