Measurements of Net Mass Transport in Laboratory Exchange Flows Past Constrictions

Tjipto Prastowo

The effect of localised turbulent mixing on the rate of mass exchangedbetween two reservoirs of water with different densities is experimentally examined in the laboratory of steady two-layer exchange flows past a constricted channel. The exchange transport is measuredfor a set of channel geometries and shapes. The laboratory experiments strongly show that the net mass transport deviates from the maximal solution possible predicted by internal hydraulic theory and depends on the shape of the channel. For short constrictions with three different channel minimum widths, the net mass transport is 82±2% of the maximal exchange owing to mixing and friction, consistent with theoretical prediction for the upper bound on the normalised mass transport for frictionless exchange flow with mixing. For a longer constriction, however, the transport is reduced to 70±3%. The results for both cases are independent of all external parameters used in the experiments.