Comparison of heat transfer from single- and double-sided heated horizontal plate under free convection in air with constant heat flux condition

This paper presents the results of an experimental and numerical study of convective heat transfer from a newly designed double-sided heated horizontal plate in air. To ensure equal heat transfer from both surfaces, the plate was equipped with two independently supplied electric heaters and resistance thermometers on each side. Minimizing the plate's thickness reduced lateral heat loss and improved measurement accuracy. The study used the balance method for convective heat transfer analysis, and results were validated through standard numerical calculations for q = const. Additionally, results were compared with experimental literature for intermediate cases, such as a cuboid, where convection occurs from both horizontal and vertical sides. Experimental results for the plate showed a 15.5–18.0% difference from numerical ones and a 24.7–29.3% difference from average extreme cases. These findings, presented as the Nusselt-Rayleigh relationship, were positively verified by numerical calculations, confirming their reliability. This advancement enables separate studies of free convection from the upper and lower parts of horizontal plates.