Investigation of batch fluidized-bed drying by mathematical modeling, CFD simulation and ECT measurement

Mathematical modeling, computational fluid dynamics (CFD) analysis and electrical capacitance tomography (ECT) is used to develop an understanding of batch fluidized-bed drying, which is a complex air-solids, multiphase process. The mathematical model is based on a three-phase theory that describes the mass-and heat-transfer between the air and solids phases. The CFD model is based on a two-fluid model (TFM) approach, in which both phases are considered to be continuous and fully interpenetrating. The hydrodynamic parameters used to model the heat-and mass-transfer between the two phases are determined by a correlation approach, and the estimated parameters are incorporated into a user defined function (UDF) in FLUENT. The moisture diffusion in the air and solids phases is simulated using the user defined scalar (UDS) transport equation in the software package. ECT is used for the online solids concentration and moisture measurement, based on dynamic calibration. Comprehensive comparisons between results from mathematical modeling, CFD simulation and ECT measurement are presented, and are validated using experiment results. Online measurement of moisture content is compared with a static calibration. The mathematical model, CFD and ECT presented are being integrated into an online process control system for a batch fluidized-bed drying application in the pharmaceutical industry.