Modelling heat and mass transfer in batch, top-spray fluidised bed coating processes

The objective of this study was the development of a new process model for the different heat and mass transfer phenomena during fluidised bed coating processes. The model is based on the discretisation of the bed into horizontal control volumes, in which the heat and mass balances for air, water vapour, droplets, particles and coating material were established. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions which were measured in a fluidised bed pilot reactor using a scanning probe. A sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidisation air and atomisation air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on this sensitivity study, it was concluded that nozzle parameters are as important as the fluidisation air properties for coating growth rate uniformity and process yield.