Experiments on natural convection in complex enclosed spaces containing either two fluids or a single fluid

Abstract Heat transfer coefficients were determined experimentally for natural convection in the enclosed space between two concentrically positioned vertical cylinders having different finite heights. The space was filled with a pair of fluid layers, one atop the other. The investigated two-fluid systems included air and water, air and hexadecane, and hexadecane and water. Experiments were also performed for the case in which the intercylinder space was filled with a single fluid—air, water, or hexadecane. Parametric variations were carried out for the height of the fluid-fluid interface and for the Rayleigh number. Comparisons were made between the experimental results and predictions obtained from numerical solutions of the problem. Very good agreement prevailed for the single-fluid cases and also for the two-fluid cases where meniscus and interfacial tension effects were either negligible or small. When these effects were more significant, as for the hexadecane-water system (the only liquid-liquid system investigated), it was found possible to achieve satisfactory agreement by making use of a relatively simple interface model. For the single-fluid results, the effect of the Prandtl number variation (between 0.71 and 40) was highlighted.