Near-Optimization of Operating Conditions and Residence Times in Multizone Dryers for Polymer Coatings
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Several polymeric coatings are dried by blowing jets of hot air on them from the top and bottom sides in multizone dryers. The goal of quickly removing solvent from a coating by manipulating air flow and temperature, together called operating conditions in this work, conflicts with the goal of producing blister-free coatings. Optimum operating conditions ensure both minimum residual solvent and no defects. Determining optimum conditions for multizone dryers is a difficult task with severe convergence problems. In this work, an easy method is developed to determine near-optimum operating conditions and residence times. The results indicate that the air flow on the top side should always be lower than or equal to that on the bottom side; the minimum residence time in first zone should be such that, toward the end, the solvent concentration starts to fall at the bottom. As long as the residence times are reasonably long, several different combinations of residence times in the second and subsequent zones nearly minimize residual solvent.
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