Variations of the optimal fin spacing according to Prandtl number in natural convection

Numerical and experimental analyses of open channel natural convection heat transfer of a finned plate were carried out. By varying the fin spacing, the heat transfer rates were calculated using FLUENT 6.3.26 for Prandtl numbers in the range 0.7 ≤ Pr ≤ 2000. Mass transfer experiments were carried out to verify the simulated data, exploiting the analogy between heat and mass transfer. The optimal fin spacing increased as the Prandtl number decreased. The calculated velocity and temperature profiles revealed the interaction between the thermal boundary layers on adjacent fins as a function of the Prandtl number. The observations of the overlap of the thermal boundary layers that develops at the corners of the fins, led the derivation of a simple heat transfer correlation that can be used to predict the heat transfer rate of a finned plate, based on an existing heat transfer correlation for a planar surface.