A THIN FILM DRYER APPROACH FOR THE DETERMINATION OF WATER DIFFUSSION COEFFICIENTS IN VISCOUS PRODUCTS

摘要

A thin film dryer device has been used to study the drying behavior of viscous productsrnand their water diffusivities. The thin product film was dried convectively usingrndifferent air velocities, air temperatures, air humidities, initial solid concentrations,rninitial film thicknesses and optional addition of agar.rnA mathematical model was developed based on the external and internal heat and massrntransfer with ideal shrinkage. A coordinate system attached to the solids was used andrnlater transformed to the initial height to facilitate the numerical implementation. Therndiffusion coefficient of the product was expressed as a function of water content andrntemperature by fitting the model to the experimental drying kinetics (for differentrnconditions) obtained for a given product. The diffusion coefficients obtained forrnmaltodextrin and PVP show good agreement with literature. They are significantlyrnreduced when the material changes from the rubbery to the glassy state and can be wellrnexpressed by the Williams-Landel-Ferry (WLF) equation.