Heat-transfer enhancement in natural convection enclosure flow

The enhancement of natural convection heat transfer in an enclosure was studied experimentally in a water filled test cell at Rayleigh numbers of theta (10 to the 10th power). Surface average heat transfer, local heat transfer, and flow visualization were compared for a smooth and rough vertical heated wall. The facing cooled wall was smooth. The roughness was distributed over the entire heated wall and was of a height comparable to the velocity boundary layer thickness. Results indicate that the roughness promotes boundary layer transition giving fully turbulent behavior at overall Rayleigh numbers about half that for the smooth wall. Local increases in heat transfer of about 40% and surface averaged heat transfer increases of about 16% were observed.