An experimental investigation of heat transfer from round air jet impinging normally from below on flat square plates was performed. Smooth and rough plates were used to collect heat transfer data as well as velocity and turbulence intensity profiles. The heat transfer data have been collected for Reynolds numbers ranging from 6500 to 19000. The nozzle-to-plate distances ranged from 0.05 to 15 to cover both the potential core of the jet and the far region. The study was made to investigate the effect of roughness on the local and average heat transfer values and on the fluid characteristics. The roughness was composed of cubes of 1mm dimension distributed uniformly along the plate. The local and average Nusselt numbers for the rough plate showed an increase ranging from 8.9% to 28 % over those obtained for the smooth plate. Roughness was seen to have a strong effect on the flow characteristics, it affected the mean velocity as well as the turbulence intensity of the flow. The mean velocity profiles for the smooth case at r/D = 1 and r/D = 2.5 had steeper near-wall velocity gradient compared with the rough case. Roughness caused an increase in the turbulence intensity of the flow.

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