Local heat transfer characteristics of a slot nozzle array for batch drying of thin films under industrial process conditions
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For optimizing the drying process of thin functional films, knowledge of the relevant influencing parameters is needed. One paramount parameter for design of experimental conditions and the accurate interpretation of experimental data is the heat transfer coefficient inside a dryer. Information on the heat transfer in a dryer also facilitates a reliable transfer of results obtained in laboratory set-ups to industrial production. In this work, the heat transfer in a batch drying set-up with an array of slot nozzles is investigated. The measurement arrangement consists of a heat flux sensor mounted on the surface of a temperature-controlled plate. For validation of this arrangement, heat transfer measurements with a single round nozzle were compared to transient heat transfer experiments using thermochromic liquid crystals. The data measured in the batch drying set-up show a periodically homogenous distribution of heat transfer coefficients for the investigated 16 nozzles. This gives the possibility to dry thin films with a coating length of up to 800 mm in the set-up at constant conditions along the coating length. A prerequisite is a periodical movement with an amplitude of at least one nozzle-to-nozzle spacing.
KeywordsHeat transfer Mass transfer Drying Coating Impingement dryer
The present work was supported by the German Research Foundation (DFG, research Grant SCHA 1266/9-1) and the European Union (FP7-NMP, Grant agreement 608931). Determination of the TLC data used for validation of the measurement arrangement was funded by the German Research Foundation (DFG, research Grant SCHA 1266/8-1). The authors would like to thank M. Zimmermann, S. Schneider, and T. Schick for their help with the experimental work and the Project Competence E at KIT for support.
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