Simulation of palay drying in a low cost in-bin dryer

A mathematical model was developed based on the laws of heat and mass transfer previously developed was used to simulate palay drying in the low cost in-bin drying system. Drying experiments with fixed beds of rough rice were conducted using initial moisture contents ranging from 16.4% to 19.49%. The (1) air temperatures, (2) grain temperatures and (3) moisture contents of palay at various layers (0.1 m, 0.2 m, 0.3 m, 0.4 m and 0.5 m) within the bed were measured at specified time intervals. A computer program oriented by the terms object in VISUAL Basic was developed to simulate palay drying in the low cost in-bin dryer. Simulated drying moisture content values between layers for fixed bed drying at 33 deg C were in good agreement with experimental values at 5% level of significance. The predicted and experimental values had good agreement. However, for drying experiments at 32 deg C and 38 deg C air temperatures in 0.4 m and 0.5 m (outer layers), the experimental values were significantly different from predicted. Discrepancies between experimental and predicted values may be due to: 1) product constants used in simulation were based on wheat; 2) possible that condensation could account for discrepancies; 3) lack of accuracy of thin-layer drying equation; and 4) errors in measurement of input parameters and of actual performance of the dryer. On the other hand, experimental and predicted values for both air and grain temperatures in various layers were not significantly different from each other. Relationship between moisture content, air temperature and grain temperature, and time were determined. The exponential model and Wang model were the best fit equations for moisture content while the Hoerl Function was the best fit equation for both air and grain temperature in all test condition. The Curve-Fit Equation, a computer program was also used to fit the drying equation (exponential model) to the data. Values for drying constant K was determined for different layers in all test conditions