Effect of drag-reducing agents on drop breakage in stirred dispersions

Abstract

The maximum stable drop sizes, d_max, formed in turbulent stirred dispersions were found to increase significantly on addition of a drag-reducing agent (DRA) to the continuous phase. Two models have been proposed to predict the values of d_max in the presence of a DRA. The first model assumes that the presence of a DRA dampens the turbulent velocity fluctuations. The second model proposes that, during the sequential breakage of eddies, the DRA molecules elongate by absorption of energy from the eddies, thereby reducing the energy available for drop breakage. Both the models have been verified by using water containing 25 and 50 ppm polyacrylamide as the continuous phase and a number of organic liquids with widely different interfacial tensions as the dispersed phase. Both the models predict the results obtained using the 25 ppm polyacrylamide solution extremely well. There is, however, a small but systematic deviation for the 50-ppm results. This is possibly due to errors in the estimation of the reduction in the energy of eddies.