Free-stream Turbulence Effects on Heat and Mass Transfer from Spheres : 2nd Report, Local Transfer Coefficients

Abstract

The effects of free-stream turbulence on the local mass transfer coefficients of a single sphere situated in air flow were studied with naphthalene spheres. The flow conditions covered Reynolds numbers between 3.5×10³ and 1.4×10⁵ and the turbulence intensities from below 0.3% to 8.5%. The influence of freestream turbulence was found to be much more remarkable on the mass transfer from the rear hemisphere, the mechanism of which was investigated by means of flow visualization, measurements of velocity fluctuations and wall-pressure distributions around the spheres. The appearance of a peak in the local Sherwood number distribution at the rear hemisphere with the increase of Reynolds number and of turbulence intensity was attributed to the intermittent reattachment of a separated free shear flow.