Modeling and simulation of droplet-to-particle formation during spray pyrolysis

Abstract

This study examined the drop-to-particle formation process during spray pyrolysis by developing a model to describe the key processes of multi-component transport, droplet evaporation, precursor precipitation, and thermal decomposition. Results suggest that the precipitation of precursor significantly hinders droplet evaporation and reduces the overall evaporation rate. The decrease in the evaporation rate further results in a rapid increase in droplet temperature, which triggers the subsequent thermal decomposition of precursor. The study also investigated the impact of experimental variables of ambient temperature and initial precursor concentration as well as the physical properties of the precursor saturation concentration and the decomposition temperature on the droplet-to-particle formation process. Results suggested that increasing the ambient temperature promotes the evaporation rate, and advances both the precipitation and decomposition processes in time. An increase in the initial precursor and a decrease in the saturation level led to the advancement of the precipitation process and increased decomposition reaction due to the temperature rise. Lowering the decomposition temperature promotes the thermal decomposition process but has little effect on the precipitation and evaporation processes. The thermal decomposition plays a noticeable role in the solid volume fraction gradient structure within the synthesized final particles. The liquid precursor inside the droplet can be directly transformed into a solid by thermal decomposition and retained inside the droplet, increasing the solid volume fraction within the droplet. On the other hand, among all investigated parameters, the synthesized particle exhibits a high gradient shell in term of the solid volume fraction with a typical thickness around 0.1r0. The results indicate that the initial precursor concentration has the greatest impact on the final particle size which is found to be primarily controlled by the precipitation process. This work provides insights into the droplet-to-particle formation process, and can be used as a numerical tool for the tailed design of particle generation from spray pyrolysis.