Heat transport coefficients for constant energy flux models of broad leaves

Experimental determinations of the local heat transfer by forced convection from model leaves heated by a constant energy flux were made in the laboratory under laminar and turbulent flow conditions. The results are expressed in a logarithmic dimensionless plot of the local Nusselt number, Nu d , against the local Reynolds number, Re d . For the laminar case, Nu d was only a linear function of Re d 1/2 downwind from the leading edge regions, although this relationship departed from that predicted theoretically due to the finite size and thickness of the model. For the turbulent case, a simple relationship between Nu d and Re d was found over a wide range of Reynolds numbers. The enhancement of heat transfer in the turbulent case depends primarily on the scale of turbulence rather than on the turbulent intensity. Past workers have discussed their results in relation to a factor β, defined as the ratio between the heat transfer predicted by the Polhausen equation, and that measured. The results suggest that β is not a unique parameter and may not be useful in describing the overall turbulent transfer process.