NATURAL-CONVECTION BETWEEN 2 HORIZONTAL CYLINDERS INSIDE A CIRCULAR ENCLOSURE SUBJECTED TO EXTERNAL CONVECTION

This paper presents a numerical study, supplemented with experiments o f flow visualization and holographic interferometric measurement, conc erning the buoyancy-induced fluid flow and heat transfer between two h orizontal, differentially heated cylinders inside a circular, air-fill ed enclosure subjected to external convection, Numerical simulations v ia a finite-difference method have been conducted mainly to investigat e the effect of insulation (namely, the external convection boundary c ondition) at the circular enclosure wall on the buoyant air flow struc ture and heat transfer characteristics among the horizontal cylinders and the circular enclosure wall. The results are displayed graphically to emphasize the effects of the Rayleigh number (Ra = 10(4) approxima tely 10(7)), the inclination angle of the enclosure with respect to gr avity (phi(g) = 30, 60, 90-degrees) and the gap width between the hori zontal cylinders (s/d = 0.7, 0.8333, 1.0) in the presence of external convection. The external convection at the circular enclosure wall was found to further promote buoyant convection flow and a markedly enhan ced heat transfer between the cylinders accordingly results. In additi on, the simulation taking account for the external convection at the e nclosure wall was found to compare favorably with the experimental res ults of flow visualization and temperature distribution in a test cell with imperfect thermal insulation.