Natural convective heat transfer from downward-facing, heated rectangular plates to air has been investigated experimentally. Main concerns were directed to the influence of aspect ratios on the heat transfer from the plates. For the sake of this, a total of 32 rectangular plates having different width
W = 35-500 mm and aspect ratios
AR = 1, 2, 3, 5, 8, were fabricated and tested. The experiments began with the visualizations of the flow fields adjacent to the plates, then, the measurements of average Nusselt numbers followed. The flow visualizations using smoke depicted that the flows remain laminar throughout the present plates. The average Nusselt numbers
Nu_{W} measured with the plates of different aspect ratios were plotted with the Rayleigh numbers
Ra_{W}, where
Nu_{W} and
Ra_{W} are based on the short side-length of the plates. The plots showed a monotonous decrease with the aspect ratios. The above Nusselt and Rayleigh numbers were next converted to those based on the equivalent diameter
d_{e} of the plates. Then, the Nusselt numbers
Nu_{de} showed almost identical variations with the Rayleigh numbers
Ra_{de} regardless of the aspect ratios. Based on these results, empirical correlations for the average Nusselt numbers from the plates of arbitrary aspect ratios were proposed.
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