Project Number: 3020-43440-009-08-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2020
End Date: Aug 31, 2022
The objectives of this project are to: (1) develop and evaluate computational fluid dynamics (CFD) models to predict phosphine gas transfer in grain storage bunkers and (2) develop recommendations for best management practices for phosphine fumigation in bunkers to minimize the phosphine loss and reduce insect resistance to phosphine. The models will include fluid-structure interaction (FSI) effects from external flow over the tarpaulin combined with the resulting effect on internal flows of air and phosphine gas.
Bunker fumigation methods rely on diffusion and various convection currents, including the internal flows driven by movement of the covering tarpaulin due to external flow over the bunker, to distribute the gas. Phosphine, from aluminum phosphide tablets or pellets, is the most widely used fumigant to control insects in stored grain. When the gas transfer processes do not deliver lethal concentrations of phosphine throughout the treated space, some targeted insects survive resulting in fumigation failure. Computational fluid dynamics (CFD) modeling of the processes can reveal the causes of low dosage in specific locations, which are difficult or impossible to determine experimentally. The CFD model will be developed in three stages: internal flow model, external flow model, and the final model including both. The internal flow model will include: the evolution rate of phosphine from aluminum phosphide (AlP) tablets or pellets, the mathematical description of wheat as a porous medium, phosphine absorption in wheat, the change in absorption rate due to temperature, and the effects of AlP tablet location and heat transfer on the phosphine behavior. A fluid-structure interaction will be built for the external flow to include the effect of wind speed and direction on tarpaulin billowing. The final combined model will be used to optimize methods for delivering lethal concentrations everywhere in the bunker. CFD models will be verified based on the fumigant concentrations across the grain bulk and validated against published benchmarks. The outcomes of this project are anticipated to contribute to the efficacy and preservation of phosphine to control the insects in stored grain and provide a basis for accurate simulations in other grain facilities such as bins. The developed models will also serve as tools for grain storage managers in making decisions on bunker fumigation practices.