Miller Magazine Issue 108 / December 2018

78 MILLER / DECEMBER 2018 “Utilizing the capabilities of fumigation modeling, the phosphine concentration could then be determined for every location inside the storage volume and at any given time, thus a prediction method for fumigation duration and success could be enabled. Additionally, as the CFD model correlates phosphine exposure with insect mortality, a methodology for planning precision fumigations can now be established.” THE CHALLENGING NATURE OF PHOSPHINE FUMIGATIONS Phosphine (PH3) has been used for decades in various fields of pest control, and particularly for disinfestation of grains in bags or bulk. Howe- ver, there are several factors that occasionally affect the toxicity of the fumigant and prevent treatments to be successful: • leaky storage structures • outdated monitoring procedures • non-constant degassing rates • unfavorable weather conditions • sorption of phosphine by the grain • poor correlation between PH3 concentrati- on duration with insect mortality Improper use leaves the treated commodity susceptible to insects, increasing the possibility of spoilage, but is also known to lead to tolerant strains among key stored product insects throu- ghout the world. PRECISION FUMIGATION METHOD In view of the above, it is important to bolster the effectiveness of phosphine fumigation pro- cesses and ensure the ecosystem can continue to rely on this important fumigant. To achieve this, an in-depth knowledge and understanding of fumigant behavior is crucial. An efficient met- hod for tackling this is through the combination of field experiments and computer simulation based on Computational Fluid Dynamics (CFD) models. CFD is a branch of fluid mechanics that uses numerical analysis and data structures to solve and analyze problems that involve fluid flows. Fast computers (typically on the cloud) are used to perform the calculations required to simulate the interaction of liquids and gases with surfaces defined by boundary conditions. Utilizing the capabilities of fumigation mode- ling, the phosphine concentration could then be determined for every location inside the storage volume and at any given time, thus a predicti- on method for fumigation duration and success could be enabled. Additionally, as the CFD mo- del correlates phosphine exposure with insect mortality, a methodology for planning precision fumigations can now be established. APPLICATION EXAMPLE To illustrate the capabilities of the model and the way it addresses all the challenges described Predicting the distribution of phosphine Dr. Efstathios Kaloudis Phycist with PhD on Computational Fluid Dynamics Centaur Analytics, Inc.