The Impact of Channel Shape at Surface Discharge from Rectangular and Trapezoid Sections into Stagnant and Non-stratified Water Bodies

Abstract

In recent years, with growing population and industrialization of the world, desalination techniques have developed drastically to supply the rising needs of coastal cities to fresh water. The brine is the second product of the producing fresh water process in the desalination facilities, that is usually discharged into the sea through marine outfalls (surface and submerged). The main purpose of the outfall is to enhance the dilution and reduce the impact on the local environment. In this study, in order to investigate the impact of the shape of the surface discharge channel, rectangular and trapezoidal sections with the equivalent diameter were used to discharge wastewater with negative buoyancy into stagnant and non-stratified water bodies. Experiments have been carried out in a dark room and processed using digital analysis. The location of plunge point, impact point and the dilution in this point, and the location of the ultimate point and dilution at this point were the flow characteristics studied in this research. According to the shape impact and less hydraulic conflict with the surroundings, trapezoidal section had better geometric characteristics compared to rectangular section. Results of the experiments were presented in the form of non-dimensional diagrams and equations. Finally, statistical indices such as Root Mean Square Error (RMSE) and R-Square (R2) were used to verify the accuracy of the presented dimensionless equations. The results indicated that the closer the shape of surface channel discharge is to the best hydraulic cross section (semicircular), the better geometric and mixing characteristics would be obtained for the flow along near-field area. In this way, prediction of flow characteristics and design of actual samples of these outfalls will be possible.