Natural Convection Correlations for Vertical Surfaces Including Influences of Variable Properties

Abstract

New correlations are presented for natural convective heat transfer from vertical isothermal surfaces in gases. The influences of variable properties are accounted for by using empirical equations which are of the general form Nu = g(Ra) • f(Ra, Tw/T∞). The influence of the reference temperature at which the thermal properties are evaluated is also established. Comparisons with available data are made over a Rayleigh number range 104 < Ra < 1012 and a range in the surface-to-ambient temperature ratio of 1 < Tw/T∞ < 2.6. Five data sets, which represent over 200 test points, are examined.