Hydrodynamic and thermal analysis of a fluidized bed drying system

Characteristics of the drying process of granular materials in the fluidized bed system has been studied. Experimental and theoretical approaches are used to undertake the study. Experiments are conducted in the laboratory scale fluidized bed to investigate the effect of the swirling outlet of air from the distributor plate, and the effect of initial moisture content of materials on the hydrodynamics of fluidized bed.;Digital signal processing of pressure fluctuations is used to understand and analyze the effect of swirling induced distributor plate on the hydrodynamics of the bed. The results obtained from the power spectral density function, autocorrelation, and probability density function analyses of pressure fluctuation signals show that the swirling induced distributor plate may significantly improve the contact efficiency of the fluidized bed by reducing the bubble size, in the case of shallow bed or low density materials in the bed.;Experimental investigations on the fluidization of moist material reveal that the moisture content of the bed material is directly proportional to the bed pressure drop. The pressure drop vs. velocity curve for wet particles exhibits a different pattern from that of the dry particles case.;In the theoretical section, a comprehensive mathematical model for simulation of simultaneous heat and mass transfer in fluidized bed drying is developed. The model considers the presence of different phases inside the bed, and their physical variation along the bed. A set of coupled non-linear partial differential equations is employed to accurately model the drying process without using any adjustable parameters. A numerical code is developed to solve the governing partial differential equations using a control volume based discretization approach.;Results of the model predictions show very good agreement with a large number of experimental data obtained in the drying of two types of grains (wheat and corn).;It is found that the drying of grain materials is usually controlled by internal mass transfer parameters. The inlet air temperature has an important effect on the magnitude of drying rate while the gas velocity and bed hold up do not show significant contribution on the drying rate. The initial moisture content of the bed materials can have an important effect on the drying rate depending on the physical properties of bed materials.;Different schemes for increasing the thermal efficiency of fluidized bed drying are introduced in the mathematical model including the recycling and intermittent schemes. It is found that the recycling scheme may increase the thermal efficiency of fluidized bed system substantially without considerable increase in the drying time. (Abstract shortened by UMI.)...