Studies on Cooling and Cold Air Drying for Grain Storage (I)

On the Fundamental Experiments of Cooling and Cold Air Drying of Unhulled Rice

Abstract

In general, the heat-drying method of grain has some disadvantages results in deterioration.
These studies have been tried to prevent such faults and to investigate experimentally on dehydrofrigidation method for storage of grain. Based on allowable storage time which was dependent on moisture content and temperature of grain, this paper presented the cooling and drying process of deep bed grain.
1. The temperature of 5-6±1°C and moisture content of 20% was adopted as most applieable storage condition.
2. The time required for the unhulled rice (about 300kg) of the initial grain temperature of 15°C and the moisture content of 25-30% to reach the above condition was 4 to 20 hours in cooling and 40 to 275 hours in drying, under air temperature of 5-6±1°C, relative humidity of 70-90±5%, and air flow rate of 0.5-8m³/min.
3. The reductions of moisture content and temperature in drying and cooling process of deep bed grain were expressed by equations (1) and (5). Constant numbers k and h were shown by following equations.
k=0.0018U^0.638 to 0.0054U^0.638
(R. H: 90 to 70±5%)
h=0.18U^0.84
(air velocity: 0.55 to 8.8m/min)
4. Drying rate was influenced by air velocity and relative humidity, particularly the latter is more effective.
5. Cooling rate was increased by increasing air velocity and relative humidity.
6. The time lag of cooling in each layer varied inversely with the increase of air flow and was in direct proportion to the increase of relative humidity. At the beginning period of cooling, temperature rise was seen in the upper layer for a short time, but soon each layer was cooled at the identical rate.