(A) study on the mass transfer from a square cylinder and its base plate using naphthalene sublimation technique

Abstract

Naphthalene sublimation technique is employed to investigate the mass transfer processes from a square cylinder in cross flow and from the plate on which the cylinder is mounted vertically. Local mass transfer rates on the square cylinder in the two dimensional region are measured with various Reynolds numbers and at different angles of attack. Distribution of local mass transfer coefficients on each face of the cylinder changes dramatically with the angle of attack, and such variation is closely connected with the flow parameters. Average sherwood number has a minimum value at α=12˚-13˚, and has maximum at α=20˚-25˚. The dependence of Sherwood number on the Reynolds number is different from face to face. A comparison of the present mass transfer measurement with other heat transfer measurements, using the heat/mass transfer analogy, shows good agreement in average transfer rates, but slight differences in local values. Detailed distribution of mass transfer rates both on the square cylinder and on the base plate near the plate-cylinder junction region are obtained under conditions of various Reynolds numbers, boundary layer thicknesses, and angles of attack. A remarkable enhancement of mass transfer is observed due to the horseshoe vortex system. Multiple vortices, which include the primary horseshoe vortex, the corner vortex and two pairs of counterrotating vortices, are found to affect the mass transfer process. The influenced region on the cylinder extends to a height of about one side length of the cylinder, and the whole affected area on the base plate extends approximately 1.5d upstream, 1.5d to the side, and 3d downstream from the center of the protruding cylinder. Variation of either Reynolds number or initial boundary layer thickness does not significantly change the location of the peaks created by the horseshoe vortex system, but only affect the magnitude of the local mass transfer rate. As the angle of attack increases, the mass transfer peak creat...