Finite element modeling of stored grain ecosystems and alternative pest control techniques

An axisymmetric finite element model was developed that takes into account the heat, mass, and momentum transfer that occurs in upright corrugated steel storage structures due to conduction, diffusion, and natural convection. Periods of aeration, dry matter loss distribution, and maize weevil density in corn were estimated. Heat and mass balances were used to calculate the temperature and relative humidity in the headspace and plenum assuming permeable grain surfaces. Two seasons of pilot bin experiments validated the model. The average standard error between the experimental and predicted temperatures was 2.4°C (1.8 to 3.1°C range) and the moisture content was 1.0 percentage point. Non-aerated, automatic ambient aeration, and automatic chilled aeration were evaluated in the replicated pilot bins as alternative methods to control insect development during summer storage. Ambient and chilled aeration reduced development of red flour beetles and maize weevils by 34% and 70% over non-aerated storage, respectively. Two locations were investigated (Indianapolis, IN and Minneapolis, MN) to demonstrate the application of the model to control insects in conventionally sized steel bins that were cooled during the fall and winter. The non-aerated and ambient aerated strategies behaved similarly until late summer when the maize weevil density increased dramatically in the non-aerated bins. Chilled aeration controlled maize weevil density at its initial population, but at an energy consumption of fourteen to sixteen times greater than ambient aeration. The simulation results indicated that automatic aeration increased the average bin temperature relative to non-aerated storage, which negated most of the benefits observed in the pilot bins. An optimal scenario includes ambient aeration during the fall, winter, and early spring with non-aerated storage during the summer. Moisture “migration” in the traditional sense did not occur in a cooled grain mass stored into the summer. Instead a more realistic theory of moisture exchange between the grain mass and headspace and plenum was developed. Permeability had a major influence on the magnitude of moisture accumulation. Moisture accumulation occurred primarily due to natural convection currents that entered and exited the headspace, which can be minimized by proper ventilation