Analysing deep-bed drying based on enthalpy¯water content diagrams for air and grain

The enthalpy¯water content diagram for moist wheat was combined with the enthalpy¯water content diagram for humid air for the case of deep-bed drying at constant inlet air conditions. Referring to the mean moisture content of the grain, the driving forces of mass transfer within the drying zone were computed directly and definitely from the combined diagram and then related to the measured time course of temperature respectively to the drying rate of the grain. The method led to a thin-layer equation for wheat basing exactly on the thermodynamic relationships between the air and the grain that appear in the drying zone at certain drying conditions. The thin-layer equation was integrated into a mathematical model developed to analyse solar assisted drying of hygroscopic bulk materials and short-time storage of lowtemperature heat. The deep-bed drying model was validated for wheat with a good agreement between experimental and simulation results including varying inlet air conditions.