Abstract
The increase of heat transfer coefficient due to roughness on a heat transfer surface is well-known, and several researches on the effect of roughness size, shape and its arrangement have been reported. This paper purports to clarify the cause of this increase of heat transfer coefficient by roughness. An experiment was carried out in a rectangular duct 37×77 mm2 with a cylinder 5.66 mmφ as a two-dimensional roughness. Measurement was made about static pressure distribution, time averaged mean velocity profile, turbulence intensity in the flow and near the wall and the distribution of heat transfer coefficient in the flow direction. It is shown that the distribution of heat transfer coefficient is closely similar to that of turbulence near the wall and the increase of heat transfer is considered to be caused by the change of mean velocity and temperature distributions due to intense turbulence near the wall.
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