A REVERSE VENTURI ATOMIZATION CHAMBER
by
Russ
Stocker
Contact: Russ Stocker
Bob's Flying Service
3412
Laguna Avenue
Davis, CA 95616
email: rlstocker@earthlink.net
Summary: Spray drift is one of the most significant issues
facing aerial applicators. Material not
applied to the target is a financial loss for the farmer and a potential
liability for the applicator. Off-site
drift also represents an environmental liability, particularly as habitat,
water quality and urban encroachment concerns demand greater attention to
larger buffer and/or no-spray zones. During conventional aerial applications,
fluid leaving the nozzle is subjected to air shear resulting in an atomization profile
(bell curve) with a portion of very small droplets (driftable
fines). Increased airspeeds produce more driftable
fines, increasing the potential for undesired off-site movement. Controlling
the environment where atomization occurs reduces driftable
fine production thereby reducing the potential undesired off-site movement of
spray material. Control of the nozzle
environment is accomplished using the Reverse Venturi
Atomization Chamber (RVA). The RVA has
three sections. Air enters the first section (diffuser), with a restricted
opening, and flows into a larger area (settling chamber) where air velocities
are reduced, the nozzle is located, and where atomization occurs. The atomized spray and air then travel together
through the third chamber (constrictor) where they are accelerated to match the
aircraft’s air speed. By reducing the air speed where atomization occurs, the
atomization profile demonstrated by the RVA system produces fewer fines,
resulting in less drift. The RVA chamber has demonstrated up to a 93% reduction
in fines at 100 mph and 78% reduction in fines at 150 mph airspeed in wind
tunnel testing. Actual drift testing with the RVA system on the testing
aircraft at 150 mph in the field demonstrated a 40 percent reduction in drift
at 50 meters downwind compared to a conventional spray system.
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