Heat and mass transfer in batch fluidized-bed drying of porous particles

A coupled heat and mass transfer model is developed for batch fluidized-bed drying of moist porous particles considering the temperature, moisture saturation and pressure distributions in the particle. The model equations are solved numerically based on physical properties of apple. The heat and mass transfer mechanisms in the fluidized-bed process are analyzed. The results show that capillary flow and vapor diffusion play different roles in moisture transfer in the particle during different drying periods. The internal heat transfer can greatly affect the drying process while the effect of gas pressure distribution is insignificant. Due to the coupled effects between gas and particles, the state of gas in the fluidized-bed changes substantially along the bed height and affects the heat and mass transfer in the particle significantly. A new parameter called bed area factor is derived and analyzed. It is important in determining the drying efficiency in the design and operation of fluidized-bed dryers. The effects of particle parameter and inlet gas conditions on heat and mass transfer in the fluidized-bed drying process are discussed through the analyses of drying characteristics.