Transcript Spray Droplet Sizing

Spray Droplet Sizing –
Understanding the Basics
Brad Fritz
USDA ARS
Aerial Application Technology
Research Unit
College Station, Texas
Droplet Diameter
D
D = droplet diameter
V = droplet volume
At equal volume with droplets of ½ diameter
8X the # Droplets
Droplet Volume in the Spray Cloud
One 400 µm drop
Droplet Volume in the Spray Cloud
8 - 200 µm drops
Droplet Volume in the Spray Cloud
64 - 100 µm
drops
Total Spray Volume
Characteristics
of total spray
volume.
Number
Distribution
Or
Volume
Distribution
Volume vs Number
8X
200µm
1X
400µm
V400
=
8 x V200 =
64X
100µm
64 x V100
Total Spray Volume of:
V400 + 8(V200)+ 64(V100)
Why Volume vs Count?
Count Distribution
We have a total of 73 drops.
1 + 8 + 64
Volume Distribution
We have a total Volume V.
V400 + 8*V200 + 64*V100 = V
Amount of active
product:
400 µm
=
Volume of spray droplets
NOT
200 µm =
200 µm =
Number of droplets
400 µm =
100 µm =
100 µm =
Volume Distribution
•
•
•
•
•
DV10 or DV0.1
DV50 or DV0.5 or VMD
DV90 or DV0.9
%Vol<100µm
%Vol<200µm
• How do we get to the numbers we typically
deal with?
• Using some measurement system, the
percentage of the total spray volume
that is in each droplet size range is
determined.
Review
• DV10, DV50 or VMD, DV90
• The diameter for which 10% of the total spray volume
is made up of droplets of equal or lesser diameter.
100%
D
10%
This diameter
is the DV10
Review
100%
50%
D
This diameter
is the VMD
150 µm
370 µm
634 µm
17.2%
4.7%
Relative Span
An indicator of the
width of distribution.
VMD = 300µm
RS = 0.67
RS = 1.4
RS = 2.2
DV10
90 µm
DV10 DV10
200 µm
165 µm
DV90 D
V90
400 µm
435 µm
DV90
510 µm
Take Home
• At equal volume:
– Halving the diameter creates 8X droplets
– Quartering creates 64X droplets
• The smaller the diameter, the greater the number
of droplets, and the less control you have over
them.
• Volume Distribution corresponds to
available product and efficacy
– DV10, DV50 (VMD), DV90, RS, %<100µm, etc…
Spray Measurement
Measurement
Groundspeed?
It’s All About How You Measure…
Likely Will Get
Different Exact
Numbers
It’s All Relative
Slowest
Fastest
Same Concept
While Numerical Diameters may
differ, Relative Size will be consistent
SMALL
MEDIUM
LARGE
Reference Sprays
• Establish Reference Nozzles/Sprays
VF/F
F/M
M/C
C/VC
VC/XC
Reference Nozzle Curves
MEDIUM Spray
DV10: 80 to 110 um
DV50: 190 to 280 um
MEDIUM Spray
DV10: 105 to 155 um
DV50: 230 to 350 um
Be Cautious with Numbers
ASABE S572 Standard
Labels – Beware of Conflict
Take Home
• Droplet Size Number can vary from lab to
lab, company to company….
• BUT
• Droplet Size Classification is consistent.
Differences Within a Class
MEDIUM Spray – USDA ARS Current Nozzle Models
429
280
180
141
2 MEDIUM Sprays
Medium #1
8°, 60 psi and 150 mph
DV10 = 184
VMD = 322
DV90 = 543
%<100um = 2.7%
CP11TT with 4015 FF
Medium #2
38°, 60 psi and 150 mph
DV10 = 146
VMD = 282
DV90 = 433
%<100um = 5.6%
2 MEDIUM Sprays
429
280
180
141
What Happens in the Field?
Downwind Drift
Medium #1
1.6%
Medium #2
2.4%
AGDISP
Take Home
Consider Size Class first.
Then
Optimize setups to decrease fines.
Remember
Not all MEDIUM or COARSE sprays are equal