THERMAL OPTIMIZATION OF INTERNALLY FINNED-TUBE IN NATURAL CONVECTION
The thermal performance of internally finned-tube with a vertical orientation is optimized in natural convection. The idealized configuration is obtained using analytic optimization which maximizes the rate of heat transfer under given wall-to-ambient temperature difference. For the analytic optimization, a new correlation of the thermal resistance is developed using the asymptotic method. The channels are modeled as a porous medium in fully developed limit, while the surface of a fin is considered as a vertically oriented hot wall in isolated limit. To validate our new correlation of the heat transfer coefficient, experiments are performed with finned-tubes having various configurations. With our new correlation, the three parameters of fin thickness, fin height, and channel angle are optimized at once. From the optimal configuration, it is shown that there exists optimal fin height which maximizes thermal performance of internally finned-tube in natural convection. The fins are highly populated near the center of a tube when the fin height is too large, and it causes thermally saturated region and higher flow resistance.