Modeling of precipitate formation in precursor droplets injected axially into an oxygen/acetylene combustion flame

A computational heat and mass transfer model of ceramic precursor solution containing droplets injected into a combustion flame is presented. Upon heat-up and vaporization, the precursor in droplets precipitate and ultimately form the ceramic material. Temperature and solute concentration distributions were computed to estimate the precipitation zones within droplets based on a simple homogeneous nucleation hypothesis. Effects of droplet size, injection velocity and injection angle were studied parametrically. High relative velocity between the droplets and the hot gas medium results in rapid heat-up and vaporization rates. Consequently, the solute concentration near the droplet surface increases rapidly. It is predicted that small droplets form nearly solid spherical particulates whereas larger droplets form shells and interconnected ceno-spheres. Predicted morphologies are supported by experimental evidence of shell-type structures and spherical particles in the combustion flame experiments performed earlier.