The effects of property evaluation methods on the correlation of heat transfer data

An explicit consideration of the behavior of the dimensionless parameters as functions of such underlying physical variables as Delta-T or the characteristic dimension L is used to construct better correlations. Results from the temperature-dependent methods for evaluating the dimensionless parameters, including those of Sparrow (1958), Hesse (1974), mean film temperature, surface temperature, bulk temperature, surface correction exponent, integrated average value, and bulk-geometric mean temperature, were compared to data for natural convection heat transfer from a horizontal cylinder and from a horizontal wire. Good results were obtained in a treatment of the horizontal cylinder problem with the bulk-geometric mean temperature method in which beta and rho are evaluated at T sub b and c, mu, and k at T(r = 1/3). For fixed T sub b, it is suggested that Nu is an increasing function of Delta-T, implying that Ra should also be an increasing function of Delta-T.