Abstract
Most studies of buoyant jet phenomena have been conducted with the outfall pipe remote from the bed. This situation idealises the practical case because, over a period of time, it is likely that the diffuser pipeline will settle some way into the bed due to the scour action of prevailing currents. Thus, the dilution achieved in the rising jet may be affected to some extent by the proximity of the ocean bed.
This paper describes an experimental study conducted to determine the effect of a bed immediately below the outfall mozzle. The results indicated generally that the effect of the floor was to considerably increase the surface dilution above the value predicted by current theories and other experiments, in which the nozzle is remote from the floor. The magnitude of the increase varied but could be as high as 1000%.
Although no analytical studies were undertaken visual observations indicated some reasons for the increase of dilution. As the jet was discharged shear stresses between the floor and the jet caused the effluent to cling to the floor in a manner somewhat similar to that of a wall jet. This caused greater momentum exchange at the interface between the jet and receiving fluid and thereby increased dilution beyond that obtained with a free jet.
It has been known for some time that studies of buoyant jets undertaken in quiescent homogeneous receiving fluid considerably underestimate the dilution which will be achieved in practice because of prevailing currents at the outfall site and the possibility of stratification in the receiving fluid. This study indicates that existing theories for buoyant jet dilution may be even more conservative than was previously thought.
AN EXPERIMENTAL STUDY ON TEMPERATUER DIFFUSION OF NEGATIVELY BUOYANT JETS ON THE BED FLOOR