| This thesis analyzes the processes in condensation drying by constructing a theoretical model. The main processes are: (1) energy delivery from the heating plate to the coating; (2) solvent movement to the surface from within a coating by diffusion; (3) solvent evaporation; (4) solvent vapor removal from the outer surfaces of a coating by diffusion and diffusion induced convection through a stagnant thin air layer; (5) solvent vapor condensing on a grooved, chilled plate; (6) solvent condensate drainage on grooved plate and recovery.; The key is the condensing plate above the coating, within a narrow gap of less than 5 mm. The plate is grooved so that the condensate is transported to end collective devices by capillary pressure with or without the help of mechanical forces. The condensate flows from the land into the near grooves, then to the collective devices; otherwise liquid builds up and instability develops, eventually "rains" off. Analyses of one-dimensional groove flow along axial direction and land flow across the groove predict the drainage capacity of a designed grooved plate, which is a strong function of geometric parameters of the grooved plate. Condensation drying; including the processes above except 6, is modeled as one-dimensional coupled heat and mass transfer in a binary polymer-solvent system. Analysis of the model yields the time courses of composition in the coating and solvent vapor saturation ratio in the upper gap. Drying performance is characterized by the drying time to a desired solvent residual, the minimum difference between coating temperature and bubble point, and the maximum saturation ratio, which are functions of parameters such as gap widths and temperatures. A drying window is a region in the space of operating parameters within which a defect-free is available. Drying windows in this thesis are surrounded by three defects: slow drying, "fogging" and "raining"---operating limits of condensation drying and groove and land flow models.; A small bench-top batch condenser dryer was designed and built for laboratory studies of condenser dryer performance and for drying polymer sample coatings under controlled conditions. Further experimental validations about the drying window are need. |
