Internal Hydraulics of a Chlorine Jet Diffuser

Abstract

Multiport diffusers are used in many environmental applications to distribute a discharge flow uniformly through a number of jet nozzles into the same or another fluid. For example, a sewage diffuser can be designed to achieve approximately equal port discharges along the diffuser to maximize environmental benefit, i.e., approximately the same port discharge to achieve similar dilutions for all ports. When the effluent density is smaller than that of the ambient receiving water (i.e., positively buoyant), the energy head increases with elevation (in the inshore direction); as the total diffuser flow varies, the relative port discharge distribution remains similar. However, for dense (negatively buoyant) discharges, this may not be the case. This paper presents an experimental and theoretical study of the internal hydraulics of a diffuser used for dosing sodium hypochlorite solution (specific gravity 1.2) for sewage disinfection. Because of the significant density difference, the jet discharge undergoes a flow switching (reversal of relative discharge distribution) as the total discharge decreases. The predictions were validated with full scale experiments carried out with water jets into air; the design implications for plant operation are discussed. The findings are of general interest to the design of diffuser manifolds for dense effluents.