A new modeling approach for the prediction of yeast drying rates in fluidized beds

The mass exchange between solid particles and air during the drying of yeast in a fluidized bed is first modeled following a standard approach, using an isotherm equation and assuming that the resistance to mass transfer is localized at the external surface of the particles. The agreement between experimental laboratory results and numerical ones is poor in the drying falling rate period. A second model, where internal resistance to mass transfer is taken into account using a diffusion equation incorporating an effective diffusivity, represents substantial improvement over the first model but fails in the prediction of the total drying time. Besides, the model incorporates too many adjustable parameters. Consequently, a new mathematical model with a deep physical meaning is developed, using Fick’s law to model molecular diffusion of vapor inside the tortuous porous medium, and without employing an isotherm equation anymore. A very good comparison between numerical and experimental drying curves is now obtained.