An air-assisted electrostatic sprayer prototype suitable for coconut palms
was designed and developed. Studies on the important plant parameters, including
height of palm, canopy diameter, and angle of leaf orientation, were carried out as
the primary step in developing the prototype. The major components of the
developed unit are a High Voltage DC (HVDC) System, nozzle unit, liquid delivery
unit, and an air-assistance unit. The high-voltage DC system capable of generating
voltages in the range of 1 to 10 kV was developed using a Line Output Transformer
(LOPT 1010A) coupled with a Metal-OxideSemiconductor FieldEffect Transistor
(MOSFETIRFZ44E). Among major electrostatic spray droplet charging methods,
induction with a ring electrode (4.3 mm diameter copper wire) was chosen due to
its several advantages over the other methods. The diameter of ring electrode (40,
60, and 90 mm) and the horizontal position (5, 10, and 15 mm) of the electrode in
front of the nozzle were optimized under laboratory conditions in terms of chargeto-mass ratio (CMR) of the developed electrostatic system using a specially
designed Faraday Cage apparatus. A high-pressure hydraulic nozzle was selected
for the liquid atomization and a double-stage diaphragm pump with a cut-off
pressure of 10.5 kg‧cm2 was selected for the liquid supply unit. An Electric Ducted
Fan (EDF) was chosen for the airassistance unit.
The spray-gun comprising both the nozzle and the EDF was mounted on an
8 m long telescopic carbon fiber pole, and all other major components and control
units were arranged as a backpack unit for easy handling. Water Sensitive Papers
(WSPs) were used to study the effect of electrostatic charging on spray
characteristics. The performance evaluation of the developed prototype in terms of
deposition, droplet density, spray drift and biological efficacy was carried out under
actual field conditions and compared with a conventional sprayer (Rocker sprayer).
The field trials were conducted under optimized operating conditions viz. electrode
diameter (90 mm), electrode position (10 mm), operating pressure (5 kg‧cm2
),
VMD (156 μm), and EDF air flow velocity of 17 m‧s-1
. The results concluded that
the spray deposition of the developed sprayer has 20.69, 27.23, and 63.95 per cent
higher in the adaxial surface at the lower, middle, and upper middle canopy
respectively compared to the air-assisted spraying. And 39.05, 22.7, and 84.33 per
cent higher with respect to the conventional rocker sprayer. Moreover, electrostatic
spraying has 1.81 times more droplet density compared to rocker sprayer, and 1.2
times more than the air-assisted sprayer. The deposition efficiency was calculated
as 69.77, 43.09, and 33.86 per cent for the spraying with electrostatic sprayer, air
assisted sprayer and rocker sprayer respectively. Spraying with the developed
sprayer was able to reduce the Rugose Spiralling Whitefly (RSW) incidence,
severity and RSW live colony per leaflets by 32.76, 64.17, and 74.91 per cent
respectively. The total cost of the developed prototype was Rs. 22,120/- The
operational cost of the developed electrostatic sprayer was calculated to be ₹151
per hour, significantly lower than that of the conventional rocker sprayer, which
stood at ₹231 per hour.