摘要
Natural convection driven by the temperature difference of horizontal top and bottom surfaces of an enclosure containing air, Pr = 0.7, and fins of different arrangements at different lengths is studied numerically for Ra = 105 and 5 × 10^5. Evolution of heat transfer rates （Nusselt number） is illustrated along with various, steady or unsteady, cellular flow structures and temperature patterns. The effect of fin length and placement on flow regime and heat transfer is established. Different fin orientations at the walls are observed to introduce considerable unsteadiness in some cases, requiring close investigation in order to design systems for specific purposes.
