Effect of constricted flow on the viability of a biological pest control agent.
Authors:
Fife, J.P. Derksen, R.C. Ozkan, H.E. USDA, ARS
Source:
Paper. 2002, no. 021025, 20 p.
NALT Subjects:
biological control spraying application equipment entomopathogenic nematodes biological control agents equipment design viability mortality equipment performance Steinernema carpocapsae Heterorhabditis bacteriophora Heterorhabditis megidis scanning electron microscopy computer software shear stress
Issue Date:
2002
Abstract:
Delivered through conventional spray equipment, biological pest control agents must pass through various components and passageways that could reduce their viability. The objective of the study was to evaluate the effect of flow through a constriction on a benchmark biological pest control agent, entomopathogenic nematodes (EPNs). An opposed-pistons constricted flow device generated flow rates ranging between 8.3 and 41.3 cm3/s through a 0.635-mm orifice. Three EPN species were evaluated: Steinernema carpocapsae, Heterorhabditis bacteriophora, and Heterorhabditis megidis. Organism damage was quantified by counting the number of living and dead EPNs. The experimental flow field was modeled using FLUENT, a computational fluid dynamics program. The type and extent of damage varied between the three EPN species. Significant damage was observed at lower flow rates for H. bacteriophora and H. megidis (21.48 cm3/s) compared to S. carpocapsae (31.39 cm3/s). Damaged H. bacteriophora and H. megidis nematodes remained whole with an internal rupture and necking region located near the center of the body. S. carpocapsae nematodes were broken into pieces. The fast-transient stress field generated near the entrance to the constriction caused a rapid tensile loading and then relaxation that damaged the EPNs. The tensile stresses became large enough at high flow rates to break the EPNs. Comparison of the maximum energy dissipation along the centerline with observed relative damage of the EPNs indicates that to maintain viability of the EPNs, energy dissipation rates within equipment components should be kept below 8E7 W/m3 to avoid hydrodynamic related damage.
