Near and intermediate field evolution of a negatively buoyant jet. Laboratory experiments and mathematical modeling

Abstract: The purpose of this study is to explore the behavior of a dense jet and bottom plume, composed of brine water, discharged into a receiving body of lighter fresh water. This situation is common in connection with freshwater production from sea water (desalination), which produces a brine waste stream, usually discharged into sea water. The increasing interest in desalination processes requires investigations on how to reduce the negative impacts deriving from the brine discharge, appearing as a negatively buoyant jet. In this study a mathematical model was developed to simulate the jet and plume behavior in order to determine the optimum discharge conditions for different scenarios. The model was divided into two sub-models, describing respectively the near and intermediate field properties of the discharge. Equations utilized are mass and momentum conservation, and several assumptions were made in order to simplify the mathematical description. The predictions of the model were compared with data collected at the Water Resources Engineering (TVRL) laboratory as well as results obtained with a commercial software simulation package (CORMIX®). After the calibration of the main parameters, the model satisfactorily reproduced the experimental data, although the simulations are not able to adequately describe the effects of one important parameter, that is, the bottom slope. To overcome this problem separate calibrations are done with and without the bottom slope. The main conclusions of this work are that the model produces results in acceptable agreement with data and observations, even though some improvements should be made in order to give the correct weight to the bottom slope parameter and to reduce the need for user calibration. An overall assessment of the CORMIX® software behavior cannot be made; in our case (i.e. small scale) the software was not giving simulation results that reproduced the data.