Studies on the Storage Drying of Raw Rough Rice with Vacuum Cooling

Characteristics of vacuum cooling and pressure drop for rough rice layer

Abstract

Storage drying of rough rice with vacuum
cooling was proposed as one of the processing methods for high-moisture rough rice, coping with combine hervesting. Investigation was made on the characteristics of vacuum cooling and drying of rough rice, and analysis was made on the pressure distribution in the rough rice layer during evacuation. The following results were obtained.
1) High-moisture rough rice packed in vacuum tank was cooled rapidly and dryed at the same time when the tank was evacuated.
2) Exhaust part was rather cooled than end part in the layer of rough rice. But the temperature difference of the two parts was less than one degree. Therefore, as the rough rice layer is not so deep, we can consider that the distribution of temperature and moisture content is uniform.
3) Pressure in the vacuum tank and saturated vapor pressure at the grain temperature almost agreed during vacuum cooling.
4) The pressure drop and the pressure distribution in the packed bed of raw rough rice during evacuation was aproximately expressed by the equation of diffusion. It was found from the solution that the pressure difference for the positions of the grain bed was somewhat Jarger than the measured values. To study this subject, the careful consideration should be given to the value of conductance of rough rice layer.