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

Abstract

The research objective was to determine the best airflow rates and fan control methods for preventingspoilage of aerated wheat stored in round bins and large horizontal storages under tropical and subtropical climaticconditions. The best aeration strategies were determined for eight Brazilian locations based on the simulated results ofover drying costs, deterioration, and electrical energy to operate the fan using 10 years of weather data. The computermodel simulated one-dimensional forced convection using a non-equilibrium model, heat conduction in the direction ofthe airflow for periods without ventilation, and grain deterioration during the storage period. The least cost fan controlmethod for wheat aeration was a differential thermostat that operated the fan according to the difference between theaverage grain temperature and the dry bulb temperature of the outside ambient air. The best aeration conditions withgrain at 13% initial moisture content were a differential thermostat setting between 5 and 7C, a linear airflow ratebetween 1 and 3 L s1 m3, and an air temperature increment between 1 and 5C. The maximum allowable storage timesfor storing aerated wheat at 13% initial moisture content in round bins were Curitiba (12 mo), Porto Alegre (11 mo), SoPaulo (10 mo), Belo Horizonte (9 mo), Goinia (8 mo), Florianpolis (8 mo), Campo Grande (7 mo), and Cuiab (4 mo).These maximum times correlated fairly well with the annual average time that the ambient air temperature was below15C. The maximum allowable storage time was up to 3 mo shorter for horizontal grain storage structures than for roundbins.