Rosette Diffusers for Dense Effluents

Abstract

Laboratory experiments on rosette diffusers for dense concentrate disposal from seawater desalination plants are reported. The rosettes each had four nozzles pointing upwards at 60° and arranged 90° apart in planform. Single and multiple risers in two planform orientations in stationary environments were tested for various riser spacing. Three-dimensional laser-induced fluorescence (3DLIF) was used to map tracer concentration fields from which the dilution, length, and thickness at the end of the near field were obtained. The effect of riser spacing depends on the dimensionless parameter sr/dF, where sr is the riser spacing, d the nozzle diameter, and F the jet densimetric Froude number. For sr/dF>∼2, the results were independent of riser spacing but the near-field dilution was approximately 27% lower than it is for a single jet. For sr/dF<∼2 the dilution, near-field length decrease, and empirical equations for their dependence on spacing were proposed. Dilution is less dependent on riser spacing than might be expected based on multiport diffuser results. This is because the jets from a rosette diffuser do not readily merge and block penetration of entrained diluting water, so the diffuser can be shorter for the same dilution.