HEAT AND MASS-TRANSFER DURING EVAPORATION IN COATING FORMATION

A homogeneous solution of nonvolatile solute and volatile solvent is used in an industrial process of coating formation over a substrate. The loss of the volatile solvent is brought about by evaporation at the free surface. Heat may be drawn from the substrate that is kept at some temperature above the boiling point of the solvent. Heat may also be generated in the solution by various means such as radiation or chemical reaction. The rate of evaporation may also be affected by conditions over the free surface. A computer simulation model describing the coating formation is described and implemented. We simultaneously determine the distributions of the temperature and the solvent concentration in the solution, from which we can compute the rate of evaporation loss of the solvent, hence, the evolution of the film thickness. The latter is taken into consideration in the analysis, resulting in a mathematical problem involving a moving boundary. Coating formation is characterized by the depletion of the solvent from the solution, leaving a thin coating of the nonvolatile solute on the substrate. Nevertheless, some remnant solvent will remain trapped in the final coating. © 1990.