Numerical simulation of phosphine movement in bulk-stored grain

Bunker storage is an inexpensive and, thus, popular method for medium-and long-term storage of wheat. To control insect infestations in bunker storage, phosphine (PH3) fumigant, released from aluminum phosphide (AlP) tablets, is commonly used, especially in Australia. For fumigation to be effective, a lethal concentration of PH3 throughout the bunker must be ensured. Because bunkers are exposed to ambient conditions, temperature gradients are created throughout the bunker, resulting in natural convection currents that move PH3 from areas around the fumigation points to the entire bunker. This research used computational fluid dynamics (CFD) simulation to investigate the effect of natural convection on fumigation in bunkers. The model was validated against published benchmarks and a field experiment with a full-scale bin with sorption and leakage. The effects of PH3 release points location, bunker shape, bunker orientation, leakage, sorp-tion, ambient temperature fluctuation, and PH3 motion in 3D were studied. Results agreed well with the experimental data and provided various recommendations for best management practices for PH3 fumigations in bunkers. Results showed that diffusion and natural convection solely are insufficient in spreading out PH3 within bunkers. Further research is needed on the effects of tarpaulin billowing in relation to PH3 behavior.