Rosette Diffusers for Dense Effluents in Flowing Currents

Abstract

Laboratory experiments on rosette diffusers for dense concentrate disposal from seawater desalination plants into flowing currents are reported. The dimensionless parameters for riser spacing and current speed were typical of operating diffusers. Three-dimensional laser-induced fluorescence (3DLIF) was used to map tracer concentration fields from which the main geometrical and dilution parameters were obtained. As the current speed increases, dilution and impact distance increase and rise height decreases. The results were insensitive to planform orientation of the risers. The rise heights of the rosette jets were always less than that of a corresponding isolated jet in a stationary environment. Semiempirical equations were presented to predict dilution, rise height, and impact distance, and confidence levels for the predictions were estimated. The results did not become independent of riser spacing in the range tested, in contrast to studies in stationary water where the flow properties became dependent on riser spacing for sr/dF<∼2. For narrow riser spacings and relatively slow current speeds, rosette diffusers have higher dilutions than equivalent conventional multiport diffusers, i.e., diffusers with the same length and number of ports, but for higher current speeds the rosette dilutions are significantly less than for the equivalent multiport diffuser.