A dimensionless study of the evaporation and drying stages in spray pyrolysis

An original dimensionless study of the pure evaporation and precipitation stages of a spray pyrolysis process has been performed. An estimation of he evaporation time is proposed and the influence of the main processing parameters has been investigated. For operating conditions corresponding o industrial requirements, the main limiting step of the evaporation stage is thermal transfer from the column walls to the gas, not mass or thermal ransfer at the droplet surface. Therefore, gas and liquid temperatures remain equal and constitutive equations can be greatly simplified. Moreover, n these conditions, neither solute concentration nor temperature gradients exist inside micronic droplets. Some data from the literature have een modelled and show the large range of validity of the equations and explanations proposed. Finally, with the assumptions made here, the imensionless study of the precipitation stage shows that the presence of a crust can increase the drying time four-fold. However, a filled particle an still be formed.