Experiments on Selective Withdrawal of a Codirectional Two-Layer Flow through a Line Sink

Abstract

For investigating selective withdrawal problems, laboratory experiments were conducted in a horizontal flume with a co-directional two-layer flow of different density into a line sink. Saline water was used as the fluid of the lower layer instead of sediment-laden turbid water for achieving a steady state. In this study, a trend curve was produced using the data of many runs which were taken under varying conditions from aspiration of both layers to only lower-layer aspiration. An adequate parameter for determining the critical condition was obtained from this trend curve. The critical condition is defined as the beginning or ending of aspiration for the upper layer. Suitable variables for the parameter are also discussed. A theoretical formula is suggested and verified, which is better than a traditional empirical formula for calculating the withdrawal concentration. Effects of slot elevation on the lower layer flow and the thickness of the mixing layer are also discussed.