VIABILITY OF A BIOLOGICAL PEST CONTROL AGENT THROUGH HYDRAULIC NOZZLES

摘要

Exposure to hydrodynamic stresses during flow through a hydraulic nozzle can cause permanent damage to biological pesticides during spray application. Aqueous suspensions of a benchmark biological pest control agent, entomopathogenic nematodes (EPNs), were passed through three different hydraulic nozzles (standard flat fan, Spraying Systems XR8001VS; hollow cone, Spraying Systems TXA8001VK; and full cone, Spraying Systems FL5-VS) within an experimental, opposed-pistons flow device. Computational fluid dynamics (CFD) was used to numerically simulate the internal flow within the XR8001VS and TXA8001VK nozzles, and important flow field parameters from the CFD simulations were compared to the observed EPN relative viability after treatment. Overall, greater reductions in EPN relative viability were observed for the flat fan (9.5%) compared to the cone type nozzles ( 2.8%). The average energy dissipation rates within the exit orifices were significantly higher for the XR8001VS flat fan compared to the TXA8001VK hollow cone, which was consistent with the greater reductions in EPN relative viability observed for the XR8001VS. These differences in EPN damage were due to the distinct characteristics of each nozzle's flow field. The reduced flow area of the narrow, elliptical exit orifice of the flat fan generates an extensional flow regime, where it was found that the tensile stresses developed were large enough to cause nematode damage. However, with the cone nozzles, the high rotational flow component did not produce hydrodynamic conditions conducive to causing nematode damage. Overall, common hydraulic nozzles were found to be acceptable for spray application of EPNs following the manufacturer's recommendations. However, it is recommended that an appropriately sized (i.e., larger than the organism) cone nozzle is more suitable for spray application than a fan nozzle to avoid damage to the biopesticide