Dense jet modelling applied to the design of dense effluent diffusers

A model aimed at predicting the behavior of inclined dense jets in a stagnant environment was proposed. The model takes into account four jet parameters (flow rate, density, inclination and diameter) and results in a set of algebraic and ordinary differential equations, which are easily solved by simple (standard) numerical methods. Model results include information on the trajectory, spreading and dilution of the inclined dense jets. Model predictions were compared with experimental data obtained with different nozzle diameters, jet flow rates, jet densities and nozzle inclinations. Despite the wide range encompassed by the experimental data analyzed, model predictions were always found to agree very well with all other available data. The model may be therefore considered as well validated. Lastly, a sample application to the design of a dense effluent diffuser is presented.

An effective model aimed at simulating the behavior of inclined jets heavier than the environment in which they are dispersed has been developed. The main model assumptions are an entrainment flux proportional to local jet velocities and Gaussian distributions for velocity and concentration across the jet section. The model involves only one adjustable parameter (the entrainment proportionality coefficient E) and reduces to a set of three ODEs and one algebraic equation, which can be easily solved by the simplest numerical methods. Model results provide information on important geometric features (jet shape and axial trajectory geometry), as well as on the dilution levels achieved along the trajectory and on the velocity field that characterizes the jet. After best fitting the entrainment proportionality coefficient E, model predictions were compared with both in-house experimental data and data from the literature. In all cases very good agreement was observed, despite the fairly wide range of experimental conditions encompassed, therefore leading to the conclusion that the model can be regarded as being fully validated. Finally, a sample application of the model to the diffuser design for an hypothetical dense effluent was reported. It highlights how the model can be an effective tool for predicting the effects of a dense effluent disposal in a body of water.