An approximate fully three-dimensional numerical model for predicting the detailed flow and thermal characteristics of spray units is presented. The new model differs from all previous analyses of spray cooling systems in that it determines the local variation in the dry-bulb temperature, absolute humidity and the air streamlines throughout the flow field encompassing the spray umbrella and the effect of this local variation on drop cooling. The conservation equations to determine the local absolute humidity, velocity and dry-bulb temperature of the air-vapor phase are written in Lagrangian form where the droplets are treated as spatially varying sources of mass, momentum and energy. The analysis takes into consideration stable and unstable meteorological conditions, turbulent mixing in the atmospheric surface layer and nonuniform upwind and local air-velocity profiles. The numerical model is of intrinsic interest because it demonstrates the feasibility of computing a three-dimensional, two-phase flow field without the use of excessive computer time. Model predictions of droplet return temperature along the spray centerline were compared with data for the Spraco 1751 nozzle. Good agreement was observed.

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