Heat transfer correlations for free convection from upward-facing horizontal rectangular surfaces

A critical review of the heat transfer data available in the literature for free convection from upwardfacing heated rectangular plates is conducted. The review is organized in the form of a table, so as to give the reader the opportunity to compare the dimensionless correlating equations presented, and the conditions under which the heat transfer data were obtained. A comparative survey of the results that may be derived at different Rayleigh numbers from these correlations is also reported. It is shown that the discrepancy among the results, which on the whole may also amount to ±50%, decreases significantly when the data are grouped according to the working fluid and the plate geometry. The following four mean heat transfer correlating equations are porposed: Nu = 1.05Ra for square plates in air, Nu = 0.9Ra for rectangular plates in air, Nu = 0.96Ra for two-dimensional infinite strips in air, and Nu = 0.175Ra for rectangular plates in water. Key-Words: Free convection; Upward-facing horizontal plates; Heat transfer correlations; Comparative survey.