DROPLET EVAPORATION AND SOLUTE PRECIPITATION DURING SPRAY-PYROLYSIS

The process of spray pyrolysis was investigated theoretically using a model that describes the evolution of the droplet size, solvent vapor concentration in the carrier gas, and both droplet and gas temperature s along the reactor axis. The model also accounts for solute concentra tion profiles and solute precipitation in the solution droplets. The m odel was used to describe the evaporation of sodium chloride aqueous s olution droplets in diffusion dryers and hot-wall reactors as a functi on of reactor residence time, droplet size (a few microns), solution m olality (up to 2 M), droplet concentration (10(6)-10(7) cm-3), relativ e humidity of the carrier gas (0-50%) and reactor wall conditions. Dec reasing initial droplet size and solution molality accelerated droplet evaporation and resulted in smaller droplets at the onset of solute n ucleation. Decreasing droplet concentration and carrier gas inlet rela tive humidity as well as increasing wall temperature (up to 350-degree s-C) or axial wall temperature gradient (up to 100-degrees-C cm -1) in creased the droplet evaporation rate, but did not change appreciably t he droplet size at the point of precipitation for a given droplet size and solute concentration. Thus, control of droplet size at the onset of solute nucleation by varying process parameters other than the solu tion concentration and initial droplet size is limited.