Post on 03-Jan-2016
transcript
Spray Droplet Sizing –Understanding the Basics
Brad FritzUSDA ARS
Aerial Application Technology
Research Unit
College Station, Texas
Droplet Diameter
DD = droplet diameterV = 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
1X 400µm
8X 200µm
64X 100µm
Total Spray Volume of:V400 + 8(V200)+ 64(V100)
V400 = 64 x V100= 8 x V200
We have a total Volume V.
V400 + 8*V200 + 64*V100 = V
Why Volume vs Count?Count Distribution
We have a total of 73 drops.
1 + 8 + 64
400 µm =
200 µm =
100 µm =
Volume Distribution
400 µm =
200 µm =
100 µm =
Amount of active product:Volume of spray droplets
NOT Number of droplets
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.
300 µm10%
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% 10%D
This diameter is the DV10
Review
100%50%
This diameter is the VMD
D
150 µm 370 µm 634 µm
4.7%
17.2%
Relative Span
An indicator of the width of distribution.
RS = 0.67
RS = 1.4
RS = 2.2
VMD = 300µm
DV10
200 µm
DV90
400 µmDV10
165 µmDV90
435 µm
DV10
90 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 RelativeSlowest
Fastest
Same Concept
SMALL
MEDIUM
LARGE
While Numerical Diameters may differ, Relative Size will be consistent
Reference Sprays• Establish Reference Nozzles/Sprays
VF/F F/M M/C C/VC VC/XC
Reference Nozzle Curves
VERY FINE
FINE
MEDIUM
COARSE
VERY COARSE EXTREMELY
COARSE
MEDIUM SprayDV10: 80 to 110 um
DV50: 190 to 280 um
MEDIUM SprayDV10: 105 to 155 umDV50: 230 to 350 um
Be Cautious with NumbersASABE S572 Standard
Labels – Beware of Conflict
Better to go by Class than Size
Take Home
• Droplet Size Number can vary from lab to lab, company to company….
• BUT
• Droplet Size Classification is consistent.
Differences Within a ClassMEDIUM Spray – USDA ARS Current Nozzle Models
141
180
280
429
MEDIUM
2 MEDIUM SpraysMedium #18°, 60 psi and 150 mphDV10 = 184VMD = 322DV90 = 543%<100um = 2.7%
Medium #238°, 60 psi and 150 mphDV10 = 146VMD = 282DV90 = 433%<100um = 5.6%
CP11TT with 4015 FF
2 MEDIUM Sprays
141
180
280
429
MEDIUM
MED#1
MED#1
What Happens in the Field?
Downwind Drift
Medium #11.6%
Medium #2 2.4%
AGDISP
Take Home
Consider Size Class first.
Then
Optimize setups to decrease fines.
RememberNot all MEDIUM or COARSE sprays are equal