Natural convection heat transfer from horizontal flat plates cooled on both upper and lower surfaces

Expressions found in standard textbooks (1), (2), (3), (4), and (5) which correlate the heat transfer rates from finite horizontal plane surfaces by natural convection are inconsistent. Discrepancies exist for the assigned value of the constant found in the expressions although most authors agree on the power variation. A literature search indicates the equations were based on a very limited amount of experimental data; and consequently, inconsistencies should be expected. Studies performed more recently (6), (7), (8), and (9) suggest the relationships may be in error by as much as a factor of two with perhaps even an incorrect power variation. The controversy which exists among investigators concerning the relationships which predict natural convection heat transfer rates from horizontal flat plates, indicates a need for further experimental study to establish more reliable expressions.