Using CFD Methods to Predict Damage of a Biological Pest Control Agent during Passage through a Hydraulic Nozzle

Abstract

Mechanized application of biological pesticides is a challenge because the organisms must remain viable during the application process to be effective. The wide variety of spray equipment components commercially available makes it impossible to test each component for compatibility with each biological agent under varying operating conditions. A unique approach to this problem is to use computational fluid dynamics (CFD) as a tool to determine equipment suitability with respect to the viability of the biological agent. FLUENT, a commercial CFD program, was used to perform numerical simulations of the internal flow within a standard flat fan nozzle (Spraying Systems XR8001VS). Aqueous suspensions of a biological pest control agent, entomopathogenic nematodes (EPNs), were passed through the nozzle within an experimental, opposed-pistons flow device at flow rates of 21.5, 28.1, 34.7, and 41.3 cm3/s. Four EPN species were evaluated: Heterorhabditis bacteriophora, H. megidis, Steinernema carpocapsae, and S. glaseri. Nematode damage was quantified by counting the number of living and dead EPNs. An empirical model relating EPN damage as a function of energy dissipation rate was developed using data from a previous study. The model parameters were calibrated for each of the EPN species. Average energy dissipation rates within the flat fan nozzle exit orifice (1.1E+8, 1.9E+8, 2.8E+8, and 4.0E+8 W/m3) were computed in FLUENT for the range of experimental conditions and were input to the mathematical model. Overall, the model was able to predict EPN damage well, in many cases within 5%. The ability to predict the damage response of the EPNs within a different system and under varying operating conditions shows the robustness of the mathematical model and the versatility of energy dissipation rate to characterize the hydrodynamic conditions responsible for the EPN damage. The results from this study show that CFD is a feasible method to evaluate the flow field conditions within an equipment component to assess its compatibility with a biological agent.