MODELING AND DESIGN OF AN INDUSTRIAL DRYER WITH CONVECTIVE AND RADIANT HEATING

Industrial equipment for drying polymeric coatings normally consists o f a series of zones, each with a controlled temperature and airflow. D rying of a polymer-solvent solution is strongly affected by the variat ion of diffusivity, solvent vapor pressure, and solvent activity with temperature and composition. The equations of mass transfer by diffusi on and of heat transfer by conduction and radiation describe changes i n composition and temperature within the shrinking coating. This syste m of equations is solved by Galerkin's method with finite element basi s functions. The boundary conditions on dryer airflow and temperature change at the entrance to each zone. In a few test cases, the predicti ons show how evaporative cooling can slow drying in early zones where the coating temperature drops below the dryer temperature, whereas in later zones the coating temperature rapidly approaches the dryer tempe rature. Infrared heating can be used to reduce the extent of evaporati ve cooling. In the test cases and experiments, ''blistering'' occurs i n later zones where high oven temperature causes the solvent partial p ressure to rise; dryer parameters can be chosen to maintain solvent pa rtial pressure just below ambient pressure in order to avoid ''blister ing'' with least sacrifice of process speed. (C) 1995 John Wiley & Son s, Inc.