An experimental investigation was conducted to determine the dilution characteristics of single and multiple port buoyant discharges typical of modern natural and mechanical draft cooling towers. Simultaneous measurements of velocity and tracer concentration profiles were taken at various downstream locations in the three-dimensional plumes discharged into a stagnant ambient using a hot film anemometer and conductivity probe. The number of discharge ports was varied from one to seven. Discharge densimetric Froude numbers were varied from 1.5 to infinity. Numerical integration of the profiles gave dilution, tracer conservation, and momentum fluxes. The effect of reducing Froude number was to increase entrainment considerably. Increasing the number of discharge ports reduced the rate of entrainment. In multiple port discharges the shape of the plume changed from an elongated configuration to nearly axisymmetric within the first 20–30 diameters of discharge.

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