MASS-TRANSFER AND PARTICLE MOTION IN A BARREL PLATER

This paper describes a study of mass-transfer process and particle mot ion in a plating barrel. The mass-transfer coefficient was measured wi th a diffusion-controlled metal-dissolution reaction, and the motion o f metal particles was examined with a video recording system. Three ki nds of particle motion were observed in a horizontal barrel: (i) slump ing motion at a low barrel rotational speed of 3 rpm; (ii) falling mot ion at the barrel rotational speeds of 6 to 13 rpm; and (iii) cascadin g motion at 15 to 17 rpm. When the barrel was tilted at an angle of 30 to 60 degrees from the horizontal position, the particles in the lowe r portion of the barrel rotated like a rigid body. There was no relati ve particle movement in this regime. The falling motion of particles o ccurred only near the top surface of the particle load. At a barrel ti lt angle of 90 degrees (i.e., a vertical barrel), all the particles ro tated like a rigid body, and Ilo falling layer was observed. The mass- transfer rate to the particles increased with increasing barrel rotati onal speed, and decreased with increasing tilt angle from the horizont al position. When the barrel tilt angle was less than 60 degrees, the mass-transfer rate decreased with increasing barrel loading. The effec t of barrel loading on mass transfer decreased with increasing tilt an gle; at a barrel tilt angle of 90 degrees the barrel loading had a neg ligible effect on the mass-transfer rate in the barrel. A set of empir ical equations was obtained to correlate the Sherwood number to the Re ynolds number, Schmidt number, Grashof number, barrel tilt angle, barr el loading, and barrel immersion.