CUTTING EDGE TECHNIQUES TO
MEASURE DROPLET SPECTRUM
AND CHEMICAL DEPOSITION OF
PESTICIDE SPRAY
Muhammad Farooq
US Navy Entomology Center of Excellence, Jacksonville, FL
Disclaimer
The views expressed in this presentation are
those of the author and do not necessarily
reflect the official policy or position of the
Department of the Navy, Department of
Defense, or the U. S. Government.
Spray Application
Droplet generation
Droplet Characterization
Dispersion
Flux
Transport
Deposition
Deposition Measurement
Deposition Measurement
Droplet Size
Measurement
Intrusive
Collection
Direct
Non Intrusive
Photographic
Indirect
Optical
Intrusive Methods
Coated Slides
Coated with MgO, teflon, gelatin, petroleum, resins
Impressions or stains are measured
Droplet size determined indirectly
Mainly suitable for laboratory measurements due to
handling issues
Intrusive Methods
Water Sensitive paper
Oil Sensitive paper
Coated Films
Glossy Paper
Leaf Surfaces
Liquid Media
Cascade
Impactors
Air sampled
Droplets segregated by
inertial separation
Amount on each stage
related to droplet size
Air speed increases and
droplet size decreases
Intrusive Methods
Source:www.envcoglobal.com
Intrusive Methods
Fibrous Media
Droplets captured on fibers
Droplet size measured directly
Research on ways to measure
droplets on fibers lead to
development of Army
Insecticide Measurement
System then DCIII
Source: CAB International, 1993
DCIII Portable Droplet
Counter
Enhancement of Analysis
Techniques for Intrusive Methods
• Reading slides Manually using microscope
• Drop Vision System that scans slide
in to computer that measures the
droplet sizes
Drop Vision
Slide
Microscope with digital image processor
Droplet Image Analysis software
Graphing & Reporting software
Sensitive Paper Reading
System
Cards
Scanned as Bitmap
Image analyzed with Stainalysis or with
WRK Image Analyzer
• Droplet size
• Droplet density
• Percent coverage of card surface
Reading of Collected
Droplets by Photography
Source: Aalborg University, Denmark, Website
Non-Intrusive Methods
Photographic Measurements
Holographic
Optical Array Spectrometer
Light Scattering
Laser Doppler droplet sizing
Photographic Measurements
Frozen image by
Short duration high intensity light
Mercury vapor lamp, electric spark and flash => 1 ms
duration
Laser pulses => order of ns
High speed camera
Images read by image analysis programs
Two pulses => Droplet size and velocity
Frozen Image
Photomicrography
Rathburn & Miserocchi, JEE, Feb. 1967
Laser Imaging
Source: www.oxfordlasers.com
Source: www.oxfordlasers.com
Image Analysis for Size
and Velocity
Frozen Image of fast
moving object
Source: www.oxfordlasers.com
Interferometric Mie Imaging
Fringe pattern produced by out of focus imaging
Number of fringes related to droplet size
Droplet size and 3-D Velocity
Number density
Mass Flux
Size-Velocity correlation
Source: www.LaVision.de
Shadography
High Magnification Image for visualization
Sizing by image analysis
Droplet size, shape and 2-D Velocity
Number density, Mass Flux
Size-Velocity correlation
Source: www.LaVision.de
Particle Image Velocity
6-10 ns image
100 ns time between images
Source: www.LaVision.de
Digital Image Correlation
Source: www.LaVision.de
Systems Developed
Particle Master
Size and Velocity of droplets
Spray Master
Visualization of spray
Flow Master
Study of flows
Strain master
Deformation of flows or materials under stress
Holography
The image can be reproduced with laser to measure
droplets
Optical Array Spectrometers
Principle
Number of obscured diodes related to droplet size
Source: CAB International, 1993
Light Scattering Methods
Light Intensity Technique
Forward scattering spectrometer probe (FSSP)
Laser Diffraction Technique
Malvern droplet sizing system
Sympatec droplet sizing system
Light Intensity Technique
Source: CAB International, 1993
Laser Diffraction Technique
Principle
Source: CAB International, 1993
Laser Diffraction Technique
Location of droplet in the beam does not effect the
size determination
Source: www.sympatec.com
Laser Diffraction Technique
Use He-Ne class 3, 632.8 nm laser
Spatial measurement systems
Easy to set-up and align
Provide volume distribution of droplet size
Data Rate up to 10 kHz
Size range
Malvern: 0.1 to 2000 mm with two lenses
Sympatec: 0.1 to 3500 mm with 8 lenses
Laser Doppler Droplet Sizing
Principle
Measurement /probe volume
Laser
Beam splitter
Detector 1
Measurement
volume
Detector 3
Detector 2
Laser Doppler Droplet Sizing
Principle


• Filtered signal
Doppler Signal
• Frequency of the signal related to
droplet velocity
• Phase shift related to droplet size
General Features of PDPA
•The PDPA is a flux sampling instrument (single particle
counter)
•Provides simultaneous measurement of velocity and size of
spherical particles
•Particle size between ca. 0.5 µm and several millimetres
•Can analyze many spray characteristics. The most
important are:
–Droplet number distribution
–Droplet volume distribution
–Droplet velocity distribution
–Droplet concentration and Liquid Water Content
–Turbulence intensity
–Droplet size velocity correlation
Droplet Size-Velocity Correlation
20
Vel oci ty (m /sec)
15
10
5
0
-5
0
20
40
Diameter (um)
60
80
100
Data Extraction
Dia (mm)
V (m/s)
Dia (mm)
V (m/s)
Dia (mm)
V (m/s)
0.01
5.46
0.17
8.13
0.44
5.51
0.03
10.17
0.18
7.95
0.46
9.03
0.05
4.26
0.22
8.28
0.46
3.68
0.05
7.72
0.25
6.79
0.46
7.10
0.07
7.97
0.29
6.40
0.47
6.69
0.08
5.44
0.33
1.95
0.48
7.51
0.09
8.46
0.33
8.03
0.50
7.42
0.10
6.51
0.35
4.18
0.50
3.66
0.12
7.00
0.37
6.94
0.50
1.87
0.12
8.42
0.38
3.55
0.50
1.93
0.13
11.85
0.39
4.19
0.52
8.65
0.13
3.60
0.39
1.47
0.54
6.18
0.14
5.24
0.41
4.19
0.55
2.57
0.16
6.02
0.43
9.41
0.56
3.67
Summary Data
Portable Particle Counters
Air contamination studies
Air suction system
Laser-based or centrifugal impaction
Droplet size range: 0.3 – 20.0 µm
Flow rate: Up to 100 L/min
Solid particles in gases or liquids
Looking for one to measure liquid
droplets in air
PDI Flight probe
Funded by US Navy for cloud and plane icing studies
Based on Laser Doppler sizing principle
Design being optimized
Source: Artium Technologies Inc.
Spray Application
Droplet generation
Droplet Characterization
Dispersion
Flux
Transport
Deposition
Deposition Measurement
Deposition Measurement
Why Deposition?
Fundamental part of sprayer evaluations
in agriculture
Practices in public health
Bio-assays
Droplet size characteristics
These techniques do not:
Approve or disapprove the delivery system
Elucidate the shortcomings of the equipment being tested
Lead to improvements for meeting the objective
Deposition
Measurement
Sampling
Quantification may include extraction
Amount of material extracted
Deposition 
Collection area of sampler
Samplers
Indicating Samplers
Plant species for herbicides
Sensitive Paper
Water sensitive
Oil sensitive
Samplers
Passive Samplers
Cylindrical collectors
Paper
Mylar Sheet
Plant Leaves
Cotton squares
Filter papers
Plastic tapes
Cotton ribbons
Useful for course high
volume agricultural sprays
Samplers
Active samplers
Air Samplers
Rotating samplers
Useful for sub-micron
particles and ULV space
sprays
Air Samplers
Air drawn over a filter medium
Flow rate known
Sampling time recorded
Quantity of spray determined analytically.
Result: Concentration of spray in air
Concentration is a measure of flux
Air Sampler Settings
Source: CAB International, 1993
Rotary Samplers
Rotorod Sampler
Rotary Samplers
Rotating slide samplers
Source: John W. Hoch website
Rotary Samplers
Rotating ribbon sampler
FLB sampler
Source: AMCA Vol25 page 476
Quantification of Deposition
Water/Oil soluble tracer dyes mixed in tank
Samples washed with suitable solvent
Concentration of dye in wash solution
quantified
Dye on sample surface determined
AI on sample surface determined using dye:AI
ratio in the tank mixture
Collection by Samplers
250
Water Based Single Pass Application
3 ft horizontal
6 ft horizontal
Rotating slide
Rotating ribbon
Filter on ground
200
150
Deposition (ng/cm2)
100
50
0
Oil Based Single Pass Application
200
150
100
50
AMCA Vol25
page 521-524
0
3
25
50
80
130
Distance from sprayer (ft)
215
300
Sampler Collection Efficiency
Droplet Size1
Small
Large
Small
Large
Small
Large
Collection Efficiency (%) at Wind Speed, mph
1
5
10
74.1  21.2
88.5  20.9
75.3  15.0
123.2  57.3
1461.3  447.6
1028.6  407.3
FLB
24.6  3.8
28.9  4.6
Rotating Slide
22.1  9.1
47.6  36.1
Rotating Ribbon
182.8  15.9
238.4  9.9
Modified Rotating Ribbon
Small
Large
365.5  103.3
330.1  165.0
72.9  7.8
67.6  30.7
Stationary Ribbon
17.0  4.6
23.3  3.7
18.9  9.9
67.4  32.9
123.9  32.1
194.7  32.9
65.1  1.3
73.5  11.3
Small
25.1  2.8
98.6  12.2
147.5  29.0
Large
36.1  6.3
224.7  19.0
257.6  73.6
1. Small droplet size  15 mm VMD and large droplet size  30 mm VMD
Questions?
DOD Pest Management Equipment Help Desk
http://www.afpmb.org/pubs/equipment/equipmentdesk.htm