FIXED-BED BATCH DRYING OF SHRINKING PARTICLES WITH TIME-VARYING DRYING AIR CONDITIONS

The design equations for batch drying of shrinking hygroscopic materials in a fixed-bed were solved numerically for the special case of time-varying inlet air flow rate. The model presented considerable flexibility to manage the time-varying drying conditions. Almost the same drying residence times as those obtained with constant air flow rates can be achieved using a square-wave type variation of the air flow rates, depending mainly on the degree of flow rate reduction. Two important features are demonstrated theoretically as well as via numerical experiments: when the drying air flow rate is reduced, the cumulative air consumption for drying is also reduced, regardless of the controlling mass transfer process and the degree of air flow rate reduction. In addition, a minimum in the total consumption of air exists at least under external or combined internal and external control of the mass transfer process.