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 µm drops

Droplet Volume in the Spray Cloud 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: V (V 200 )+ 64(V 100 ) V 400 = 64 x V 100 = 8 x V 200

We have a total Volume V. V *V *V 100 = V Why Volume vs Count? Count Distribution We have a total of 73 drops 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 D V10 or D V0.1 D V50 or D V0.5 or VMD D V90 or D V0.9 %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 D V10, D V50 or VMD, D V90 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 D V10

Review 100% 50% This diameter is the VMD D

150 µm370 µm634 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 D V µm D V µm D V µm D V µm D V10 90 µm D V 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 –D V10, D V50 (VMD), D V90, 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 SMALL MEDIUM LARGE While Numerical Diameters may differ, Relative Size will be consistent

Reference Sprays Establish Reference Nozzles/Sprays VF/FF/MM/CC/VCVC/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 MEDIUM

2 MEDIUM Sprays Medium #1 8°, 60 psi and 150 mph D V10 = 184 VMD = 322 D V90 = 543 %<100um = 2.7% Medium #2 38°, 60 psi and 150 mph D V10 = 146 VMD = 282 D V90 = 433 %<100um = 5.6% CP11TT with 4015 FF

2 MEDIUM Sprays MEDIUM

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