Study on Equilibrium Moisture Desorption Isotherm and Isosteric Heat of Ten Varieties of Paddy in South China

With the spread of decreasing-temperature by air-condition in the warehouses of south China region,it is necessary to study the moisture content of paddy for loading warehouse.The desorptive EMC/ERH data of ten varieties of paddy from south China were determined by gravimetric method at range of 10-35℃and RH 11.3%-96%,respectively.The parameters A,B,and C in best fitted equation MCPE,were 725.445,34.61,and 0.249,respectively.The absolutely safe storage MC of the studied paddy under 65% ERH was 14.16%,13.77%,and 13.42% wet basis (w.b.) at 15℃,20℃,and 25℃,respectively.The relatively safe storage MC of the paddy under 70% ERH was 14.91%,14.53%,14.18% w.b.at 15℃,20℃,and 25℃,respectively.The EMC of the paddy under 75% ERH was 15.78%,15.39%,and 15.04% w.b.at 15℃,20℃,and 25℃,respectively.At the same condition the EMC of both long-grain and medium-grain paddies were similar.The isosteric heat of desorption of paddy drastically decreased from 4 670 kJ/kg below 15% MC,thereafter slowly decreased to 2 500 kJ/kg with an increase in moisture content.The isosteric heat of paddy desorption approaches to the latent heat of pure water at 17% MC.These results suggest that the paddy moisture content for loading warehouse in south China region can be 15.4%-15.8% at the temperature of 15-20℃.