Effect of air flow rate and air temperature on milling characteristics and drying time of three paddy varieties in closed cycle fluidized bed dryer

In this research, the effect of air temperature and and air flow rate was investigated on the broken grains percent, milling recovery and paddy drying time of three rice varieties dried in fluidized bed dryer. The experiment was carried out as factorial in completely randomized design with three replications and the experimental factors were including air temperature at four levels (45, 50, 55 and 60 °C), air flow rate at three levels (0.12, 0.14 and 0.16 m3.s-1) and three rice varieties (Tarom, Fajr and Shirudi). Results indicated that increasing temperature from 55 to 60°C increased the broken grains percent of Shirudi, Fajr and Tarom from 19.10 to 35.97%, 43.30 to 51.36% and 19.82 to 29.06%, respectively. The lowest broken percent (17.17%) was obtained from the air rate 0.12 m3.s-1 and the temperature 45°C and the highest broken percent (40.54%) was registered from the rate 0.16 m3.s-1 and the temperature 60°C. The milling recovery of Shirudi variety at the air rate 0.12 to 0.16 m3.s-1 decreased from 72.37% to 71.74%, but in Fajr and Tarom varieties was not observed significant variation in the milling recovery. Increasing the air temperature from 45 to 60°C at the rate 0.16 m3.s-1 reduced drying time from 13.45 to 5.37 h, respectively, however increasing the air rate from 0.12 to 0.16 m3.s-1 at the air temperature 60°C reduced drying time only from 6.37 to 5.37 h.