Dynamic characteristics of natural convection from horizontal rectangular fin arrays

This work numerically analyzes the dynamic behavior of natural convection from horizontal rectangular fin arrays. Unsteady simulations are conducted for different fin lengths of L = 56-500 mm with fin heights of H = 6.4 and 38 mm and a fixed fin spacing of 6.4 mm. With a decreasing H/L ratio, the flow pattern evolves from a steady single-chimney to an oscillating sliding-chimney flow in which cold air is drawn downward from the upper ambience. For both fin heights, the average convection heat transfer coefficient decreases with increasing fin length. It first drops steeply and then decreases mildly beyond a certain length when the sliding-chimney flow occurs. The effect of the downward flow on heat transfer is weaker for high fins because the penetration depths are limited by the thicker boundary layers developed in the high channels. The predicted average Nusselt numbers agree well with the experimental data in the literature. For an intense sliding-chimney flow pattern from long and low fin arrays, an unsteady simulation yields higher average convection heat transfer coefficients than those using a steady-state simulation. (C) 2012 Elsevier Ltd. All rights reserved.