Equilibrium moisture and drying of wheat at embient conditions in Manitoba

Abstract

The need to conserve energy has created interest in improving the performance of grain drying systems and in studying the potential of ambient or low temperature drying systems. Equilibrium moisture content data are required to analyze the low temperature drying systems. Due to lack of equilibrium moisture content data below 20o C, the main objective of this study was to determine equilibrium moisture contents of wheat below 20o C. Equilibrium moisture contents of wheat were determined at five temperatures ranging from -21o to 22o C. Desired relative humidities (in the range of 12 to 90%) were maintained in wooded cabinets by using saturated salt solutions. Temperatures in the test cabinets were controlled by placing the cabinets inside an environmental chamber. Wheat samples with three different moisture contents were placed in the test cabinet until constant mass was indicated. Moisture contents were determined by heating the samples in an air oven at 130o C for 19 h. Equilibrium was attained within 6 to 14 days... Using the equilibrium moisture content data, theoretical calculations were performed to predict the energy consumption in low temperature drying, for various grain and weather conditions. A rise in air temperature of 1o C due to fan heat can save a maximum of 33% of the energy in low temperature drying. Adding more than 1o C supplemental heat to the drying air caused energy consumption to increase sharply. Drying with winter air at -20o C and 75% relative humidity can increase the energy consumption by 150% above that used in drying at 0o C and 70% relative humidity. It appears that before the spoilage of high moisture grain can occur, the most suitable time for low temperature drying with minimum energy requirement is in the spring.