Effect of Fluid Flow on Convective Transport in Small Cavities

Mass transfer between the interior surface of small rectangular cavities and the solution flowing past the cavity opening, was investigated by both theoretical and experimental techniques. The boundary integral method was used to calculate the viscous shear stress along the cavity surface under the assumption of Stokes flow for aspect ratios (width:depth) between 0.75:1 and 10:1. It was found that the separation streamline became reattached to the bottom surface of the cavity when the aspect ratio exceeded about 3:1. The Lighthill integral method was used to calculate the local mass transfer rate along the cavity surface and the separation streamline(s). Experimental measurements of the average mass transfer coefficients were made by an electrochemical method in which the Cu test specimen was an anode and formed a soluble surface film of dissolution products in . Predictions of the average mass transfer rate along the interior surface agreed with experimental data to within 2.6% for the 1:1 cavity, and to within 14% for the 5:1 geometry. The results are discussed with respect to processing of printed circuit boards to form lines by pattern etching.