Design, construction and performance evaluation of paddy rice solar drum dryer equipped with perforated drum

A solar drum dryer was designed and constructed for paddy drying, including a fixed outer drum and inner perforated drum, which rotated at the desired rotational speed inside the outer drum. The maximum capacity of the dryer was 10 000 g. The rotational speed of the inner drum was controlled. The thermal energy required for the dryer was provided by a solar absorber plate. The dryer performance was examined at three levels of rotational speed (0.21, 0.42 and 0.84 r.p.m.), drum slope (1°, 1.5° and 2°) and air velocity (1.7, 1.8 and 1.9 m.s−1). The diameter of the drum was the geometrical parameter that affected the movement of the particles and the ratio of the particle diameter to the drum diameter changed with the change in the drum diameter. Therefore, increasing the diameter of the drum caused a reduction in the repose angle of the paddy without any effect on the filling angle. The displacement of the product along the drum increased with increasing slope and rotational speed. At the lowest air velocity, the time required to remove moisture (<13%) was less. The results showed a significant reduction in cracked brown rice for the paddy dried by the drum dryer at 43–46°C compared with those dried using a batch dryer. The highest stress-cracking index (11) was observed for the paddy with an initial moisture of 16%. The results showed that for proportional final moisture content, a longer drum should be considered to intensify the slope and rotational speed of the inner drum.