An experimental program was conducted to study the heat transfer characteristics of mercury in laminar natural convection flow within a vertical open-ended channel over a range of channel widths. Two sets of boundary conditions were investigated separately: (1) uniform heat flux at one wall with the other insulated, and (2) both walls symmetrically and uniformly heated. A decrease in channel width caused a decrease in channel wall temperature in the developing portion of the flow. This unexpected phenomenon persisted until the channel height-to-width ratio, Ar, reached a value greater than 18. Hence, the buoyancy induced flow of a low Prandtl number fluid in a channel is more thermally efficient than a single heated plate. Temperature data have been correlated into local Nusselt versus modified Grashof number plots, based on streamwise position, for several aspect ratios. The effect of aspect ratio on channel temperature is displayed on NuL versus Ar curves for several Gr$L*$. The infinite spacing limit is compared to previous work with temperature profiles and local heat transfer results. Expressions for local and average heat transfer correlations are presented, with suggested limits on their application. The effect of flow in from the sides of the channel was investigated by affixing plastic side plates to the channel.

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