A step-by-step prediction procedure has been developed to predict the evaporation of a sodium nitrate spray consisting of small drops moving at terminal velocity through the drying air. The procedure accounts both for the existence of radial gradients as well as radial mixing in the dryer and is selfsustaining except for values of the local air velocity.

Because the procedure can be applied only to the free-fall zone, at some distance below the nozzle, a method was developed for the indirect determination of the amount of water remaining in the partly evaporated droplets at the beginning of the free-fall zone. This procedure was then applied to experimental data on drop size distributions obtained at the beginning of this zone. Owing to uncertainties concerning the salt concentration in the drops, a number of assumptions had to be made and the procedure was only partially successful in describing the spray evaporation, although it did compute the radial spray transfer. It was possible, however, to indicate by means of a model drop distribution the general validity of the procedure.