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Drop size distribution measurement of ISO nozzles by shadowgraphy method

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Academic year: 2021

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(1)

by shadowgraphy method

Nicolas De Cock, Mathieu Massinon, Sofiene Ouled

Taleb Salah, Benoît Mercatoris, Frédéric Lebeau

(2)

Agricultural spray application

𝑊𝑒 =

𝜌 𝒗

2

𝒍

𝜎

Deposition

From the nozzle to the plant  Effect of the size on droplets

driftability

Retention

Droplet impacts on the plant surface

 Effect of the droplets energy on the retention

(3)

Spray characterization techniques

Laser diffraction spectrometry (LDS)

Droplet size

Phase Doppler Anemometry (PDA)

Droplet size and speed

Particle/Drop Image Analysis (PDIA)

Based on image analysis

Droplet size and speed

Need coherent light (laser)  High cost Based on optic theory  Require liquid optical properties

(4)

Validation of a versatile, low cost and accurate spray

characterization tool based on high speed imaging

Objective

Method

Assess the method capability to segregate nozzle class

boundaries (VF/F, F/M, …)

(5)

Image acquisition set-up

8-bit PIV camera

72 W LED panel

Acquisition of picture

in PIV mode (double

frame)

(6)

Image processing method

Diameter

Velocity (x,y)

Overall spray characteristics is set by summing each droplet characteristic

(7)

Drops localization

Average background subtraction Gradient computation

Localization of the drop boundaries by applying a Canny filter

(8)

Out of focus drops rejection

Drop shadow boundaries present various levels of sharpness

3

𝑆ℎ𝑎𝑟𝑝𝑛𝑒𝑠𝑠 ∝ 𝐺𝑟𝑎𝑑𝑖𝑒𝑛𝑡 𝑖𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦 𝑎𝑡 𝑡ℎ𝑒 𝑏𝑜𝑢𝑛𝑑𝑎𝑟𝑦

Pixel intensities accross droplet shadows 4

2

(9)

Determination of focus parameter threshold

Out of focus drops rejection

𝐹𝑜𝑐𝑢𝑠 𝑝𝑎𝑟𝑎𝑚𝑒𝑡𝑒𝑟 = 𝑔𝑟𝑎𝑑𝑏𝑜𝑢𝑛𝑑 𝐼𝑜𝑏𝑗𝑒𝑐𝑡 − 𝐼𝑏𝑎𝑐𝑘 Oblique stream of monosized drops

Relative error on drop diameter measurements

(10)

Droplet tracking based on:

 Droplet size

 Most probable displacement

Velocity measurement

𝐷𝑚𝑎𝑥 = 𝑣𝑚𝑎𝑥 Δ𝑡

(11)

Sampling probality

Residential time Size of the probe volume

(12)

Correction of the drop size distribution

𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟 =

𝑣

(𝐹𝑂𝑉

𝑐𝑜𝑟

𝐷𝑂𝐹)

𝑆𝑎𝑚𝑝𝑙𝑖𝑛𝑔 𝑝𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 ∝

𝑃𝑉

𝑠𝑖𝑧𝑒

𝑣

𝑑 Correction

(13)

Measurements

Scan of 6 nozzles defining the

droplet size class boundaries

Class boundary Nozzle type Pressure (bar)

VF/F TeeJet TP 110 01 4.5 F/M TeeJet TP 110 03 3.5 M/C TeeJet TP 110 06 2.5 C/VC TeeJet TP 80 08 2.5 VC/XC TeeJet TP 65 10 1.5 XC/UC TeeJet TP 65 15 1.5

(14)

Droplet density

110 03 @ 3 Bars

Droplet/cm²

Spatial distribution of the droplets

• Highest droplet density at the spray center • Ellipsoidal shape (~1-10 for the 110 03)

(15)

Spatial distribution of the droplets

• Linear decrease of the droplet density with the distance to the spray center

• Weak effect of the nozzle

• Less than 5% of the droplet measured in the last scanning line

(16)

Cumulative drop size distribution

Droplet size class boundary

Class Boundary Dv10 (µm) Dv50 (µm) Dv90 (µm) Droplet count VF/F 107 154 232 95398 F/M 158 239 414 46756 M/C 186 304 532 39947 C/VC 225 375 612 28817 VC/XC 274 479 786 15552 XC/UC 305 532 927 20084 VF F M C VC XC UC

(17)

An image processing method has been presented

The spatial analysis of the data showed that the

scanning method is appropriate for flat fan sprays

The imaging method is able to segregate the

droplet size class boundaries

Further work

Computation of the flow rate by integrating the

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