AERATION STRATEGIES FOR PREVENTING SPOILAGE OF WHEAT STORED IN TROPICAL AND SUBTROPICAL CLIMATES

The research objective was to determine the best airflow rates and fan control methods for preventing spoilage of aerated wheat stored in round bins and large horizontal storages under tropical and subtropical climatic conditions. The best aeration strategies were determined for eight Brazilian locations based on the simulated results of over drying costs, deterioration, and electrical energy to operate the fan using 10 years of weather data. The computer model simulated one-dimensional forced convection using a non-equilibrium model, heat conduction in the direction of the airflow for periods without ventilation, and grain deterioration during the storage period. The least cost fan control method for wheat aeration was a differential thermostat that operated the fan according to the difference between the average grain temperature and the dry bulb temperature of the outside ambient air. The best aeration conditions with grain at 13% initial moisture content were a differential thermostat setting between 5 and 7°C, a linear airflow rate between 1 and 3 L s–1 m–3, and an air temperature increment between 1 and 5°C. The maximum allowable storage times for storing aerated wheat at 13% initial moisture content in round bins were Curitiba (12 mo), Porto Alegre (11 mo), Sao Paulo (10 mo), Belo Horizonte (9 mo), Goiânia (8 mo), Florianopolis (8 mo), Campo Grande (7 mo), and Cuiaba (4 mo). These maximum times correlated fairly well with the annual average time that the ambient air temperature was below 15°C. The maximum allowable storage time was up to 3 mo shorter for horizontal grain storage structures than for round bins.