Numerical simulation of pyrethrin aerosol deposition

Authors: ASUNCION, F. XYZA - Kansas State University; Casada, Mark; MAGHIRANG, RONALDO - University Of Illinois; SCHUMACHER, K. - Mri Global; ELSAYED, SHERIF - Kansas State University; Brabec, Daniel - Dan; ARTHUR, FRANKLIN - Retired ARS Employee; Campbell, James - Jim; ZHU, KUN YAN - Kansas State University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Aerosol insecticides, such as pyrethrin, are widely used to control stored product insects by spraying inside food facilities. Optimization of aerosol application is important for effective control of the insects. A previous series of laboratory experiments reported 100% knockdown of insects (adult confused flour beetles, Tribolium confusum), held in Petri dishes, with large (16 µm) aerosol droplets and 10% or less knockdown with small (2 µm) droplets in a test chamber. As a follow-up to this previous study, we used a standard computer modeling technique, called computational flow dynamics (CFD), to simulate the motion of individual aerosol droplets and evaluate how the droplets impacted the insects and dishes under different airflow rates. Predicted deposition of pyrethrin increased with increasing droplet size. Larger droplets tended to settle quickly while smaller droplets tended to continually flow with the air without settling out. Large droplets settled in the dish 92% of the time, while 12% of the small droplets settled in the dish. In addition, deposition also increased under low airflow rates. These results, with droplet deposition varying with droplet size, showed how the previous experimental results—greater insect knockdown with large versus small droplets—was caused by more insecticide reaching the insects in the dishes when droplets were larger. The model can also be extended and used for developing improved aerosol application methods in other types of facilities.

Technical Abstract: Aerosol insecticides (e.g., pyrethrin) are widely used for control of stored product insects inside food facilities. To optimize pyrethrin aerosol application, computational fluid dynamics (CFD) was used to predict airflow and aerosol transport inside a vertical flow aerosol exposure chamber, operated under laminar flow conditions. A discrete phase model was developed in ANSYS FLUENT 2021 R1 and simulations were conducted to track pyrethrin droplets of various diameters (0.1 to 20 µm) and determine their deposition on Petri dishes located near the center of the chamber. Deposition efficiency of the different aerosol droplet sizes and the effect of two flow rates (5.0 × 10-4 m3 s-1 and 4.0 × 10-4 m3 s-1) on deposition efficiency were determined. Results showed that the predicted deposition of pyrethrin aerosol increased with increasing droplet size largely due to inertial and gravitational effects. Deposition efficiencies decreased with the higher flow rate—with 0.1% to 96.6% predicted deposition efficiencies for the low flow rate and 0.1% to 93.8% for the high flow rate. Results of this study can be used for improving aerosol application methods for stored product insect control.