Simultaneous effects of free-stream turbulent intensity and integral length scale on mass transfer about a cylinder

Abstract

The purpose of the present study is to investigate the simultaneous effects of crossflow turbulence intensity and length scale in a subcritical flow regime on mass transfer from a cylinder surface. Efforts are made to find a parameter which combines both effects on Sherwood number. Turbulent quantities are measured by a hot wire anemometer. About 40 k word data are time averaged to obtain turbulent intensity and length scale at a measuring point. Measurements were performed for turbulence intensities ranging from 0.5 % to 10 %, and integral length scales from 4 mm to 23 mm at a free-stream mean velocity of 10 m/s, which yields a Reynolds number based on the cylinder diameter of about 49,000. Turbulence levels were generated by various grids and by adjusting distance from the grid to the cylinder. Circumferential distributions of the local Sherwood number were measured by using a naphthalene sublimation technique for turbulent conditions given above. In the cases of lower turbulent intensities, the general trend of the local Sherwood number distribution is typical of the subcritical Reynolds number flow with no turbulence except for its magnitude. In contrast to that, higher turbulence leads to change in the distribution with two minima which exhibits a tendency to one found in the supercritical flow regime. Moreover, it has been found that the Sherwood number at the front stagnation point is well fitted linearly in terms of a parameter, (u/U0)2/(Lx/D).