Predicting drying in multiple-zone ovens

In the-coating industry, the drying of solvent-coated polymeric films takes place in convected heated dryers, which usually consist of a series of zon es. The operating conditions of airflow solvent partial pressure(s), and te mperature at the entrance of each zone are chosen to minimize the drying ti me while maintaining an acceptable product quality. In this work, the dryin g behavior of polymer solutions in such oven configurations is predicted fr om binary and multicomponent drying models. Both models involve coupled hea t- and mass-transfer equations that describe the changes in the concentrati on Of each solvent, the temperature, and the thickness of the film througho ut the drying. The-model equations become highly nonlinear because of the s trong and complicated concentration and temperature dependencies of the the rmodynamic and transport properties of polymer solutions. These nonlinear e quations are solved numerically using the finite difference approximation. The solutions show that multiple-zone ovens can be used to eliminate bubble formation and to minimize the residual solvent content by controlling the operating conditions individuality or simultaneously.