Diffusion coefficient modelling of thin-layer drying of paddy using spouted free fall bed dryer

Abstract

This research developed a new model to determine the moisture diffusion coefficient for the thin-layer paddy drying with the spouted free-fall bed dryer. The design and construction of the dryer was done to experiment with the drying kinetics. The experiment has studied under conditions of hot air temperature of 60-150 °C, the initial paddy mass of 5 - 15 kg and hot air velocity of 19 m/s. The results showed that the higher hot air temperature and the lower initial paddy mass resulted in a significant reduction in drying time. The experimental results were used to calibrate 12 of the most popular thin-layer drying models to find a suitable one, considering based on the root mean square error (RMSE), chi-squared value (χ2) and the correlation coefficient (r). It was found that the popular thin layer drying model was able to accurately predict the effect of the moisture ratio, considering both the influence of hot air temperature and the initial paddy mass, in linear models. The highest accuracy was RMSE = 0.0279, χ2 = 0.00084 and r = 0.9938. In addition, the experimental results have been used to synthesize the new diffusion moisture coefficient, which is a function of initial paddy mass, temperature and drying time. This developed model was based on an exponential function with only 7 model constants. The simulated results observed that the new model achieved the average error only 1.8 percent compared with the best model that uses up to 24 model constants.