Modelling and experimental analysis of rice drying in new fluidized bed assisted hybrid infrared-microwave dryer

This study aimed to investigate how infrared (1000-2000 W) and microwave power (100-900 W), air velocity (1-5 m/s) and temperature (40-80 °C) affected the specific energy consumption, the moisture removal rate, and the product's quality (whiteness index, head rice yield, water uptake ratio, and elongation ratio) in hybrid dryer. Rising temperature, velocity and microwave power and lower temperatures resulted in improving head rice yield of paddy samples. The experiments proved that the new hybrid system significantly increased the moisture removal rate (from 100 to 700%), head rice yield (from 5 to 40 %) and decreased the specific energy consumption (from 10 to 80%) compared to the single fluidized bed dryer. The water uptake ratio and elongation ratio of the dried samples in the hybrid dryer were higher than the single dryer, however their whiteness index was not significantly different. The best drying conditions are associated with the lowest specific energy consumption and the highest moisture removal ratio and rice quality. Experimental data were fitted into empirical drying models to explain moisture ratio variations during drying. Nomhorm and verma,s model was found to be the best for moisture ratio prediction. Also, the central composite design of response surface methodology was applied to forecast outputs. A modified cubic model was observed in all responses with high R2 values (greater than0.9). The drying parameters were optimized for the specified constraints, resulting in 68 °C temperature, 5 m/s air velocity, 900 w microwave power, and 1479 w infrared power. The experimental values were found to be 0.368607 g/s for the moisture removal rate, 7.16988 MJ/kg water for the specific energy consumption, 90.6% for the head rice yield, 58 for the whiteness index, 3.63 for the water uptake ratio, and 2.28627 for the elongation ratio, at the optimum treatment conditions.