ARTICLE IN PRESS

doi:10.1016/j.biosystemseng.2004.11.001PM—Power and Machinery

Biosystems Engineering (2005) 90 (2), 173–184

Effect of Air-jet Configuration on Spray Coverage in Vineyards

B. Panneton; B. Lacasse; M. Piché

Agriculture and Agri-Food Canada, Horticultural Research and Development Centre; 430 Boul. Gouin, St-Jean-sur-Richelieu, Qué.,Canada J3B 3E6; e-mail of corresponding author: pannetonb@agr.gc.ca

(Received 26 March 2004; accepted in revised form 15 November 2004; published online 4 February 2005)

A new type of sprayer developed for orchard is being adapted for vine spraying. The technology uses verticalair sleeves, generating a two-dimensional horizontal air jet, to distribute spray droplets within the canopy.Three different configurations were tested to determine the combination which provides the most appropriatespray distribution within the canopy along with the highest coverage on artificial cylindrical targets. Oneconfiguration (a) used a single air jet perpendicular to the row. Two other configurations used a pair of sleeves,one sleeve on each side of the row. In configuration (b), airflow rate was distributed evenly between the twosleeves. In configuration (c), the distribution of air was varied along with the angle of attack, providing aninteraction between the two airflows. Coverage on 22mm cylindrical targets covered with water-sensitivepapers was evaluated across the vine rows. These papers were processed using image analysis. Results showedthat coverage was maximised using configuration (c). The use of a pair of sleeves, in configurations (b) and (c),provided a more uniform distribution of droplets locally.Crown Copyright r 2004. All rights reserved

Published for Silsoe Research Institute by Elsevier Ltd

1. Introduction

Criticisms of pesticide use are numerous but it isexpected that farmers will continue to rely on chemicalcontrol because it is the most cost effective and rapidway of minimising crop losses due to weeds, pathogensand insects. In this context, restricting pesticides as faras possible to the actual target is fundamental to properpest management (Matthews, 2000b) and this is wherepesticide application technologies have a key role.In vineyards, a wide range of technologies is being

used for applying pesticides (Matthews, 2000b; Viret etal., 2003) manually operated sprayers, knapsack mistblowers, directed nozzle hydraulic sprayers, air blastsprayers, over-row sprayers, tunnels with or without air-assistance as well as aerial applications. While debata-ble, it is generally accepted that the sprayer shoulduniformly deposit material on the plants (Furness &Pinczewski, 1985; Pergher et al., 1997b; Stafford et al.,1970). Appropriate use of air-assistance is required toimprove the distribution of deposits and collectionefficiency of plant parts (Matthews, 2000a). At the leafscale, a better balance between coverage of the upper

1537-5110/$30.00 173

and lower surfaces requires some form of air-assistance(Viret et al., 2003). At a larger scale, spray partitionwithin the canopy is affected by airflow rate (Pergher &Gubiani, 1995) and air speed (Randall, 1971) as well asthe orientation of the airflow and the number of airoutlets used to direct the air and the spray to the canopy(Furness & Pinczewski, 1985; Gohlich, 1985; Pergheret al., 1997a; Pezzi & Rondelli, 2000).Proper use of air-assistance is not straightforward as a

too strong or a too weak air jet may cause inadequatedeposit, uneven distribution within canopy and in-creased environmental contamination (Doruchowskiet al., 1997). For the same amount of power, a higherairflow rate at a lower air speed penetrated trees betterand produced better leaf coverage than lower volumesof higher velocity air (Randall, 1971). This held trueprovided than the air speed was high enough to formopenings in the canopy for the air stream to penetrate.For Cox apple trees, a minimum air speed of 12�2m/swas sufficient. More air does not automatically implybetter coverage as on dwarf apple trees. Total depositwas better using a lower airflow rate while for a higherairflow rate, the amount of spray blown through the

Crown Copyright r 2004. All rights reserved

Published for Silsoe Research Institute by Elsevier Ltd

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Notation

A sampling surface area, mmC mean coverage, %C2 coverage that would correspond to C when the

application volume is doubled, %C_

corrected coverage, %~CCi;j deviation of the co-variable from its mean value

associated with treatment, %d droplet diameter, mmk constant depending on the spread factor of the

droplet of the sampling surfacen number of dropletsp probabilityQi effect of airflow rate for treatment i, %Qs specific airflow rate, %Qv total airflow rate through the fan, m

3/s

R airflow balance, %v travel speed, m/sV air speed, m/sVi effect of air speed for treatment i, %Vv canopy volume per unit length of row, m

3/mxc distance required for C to fall to 36�8% of its

initial value C0, mb slope of the linear regression between the co-

variable and Ci.je error termmC overall mean coverage, %

Subscripts

i treatmentj replicate

B. PANNETON ET AL.174

canopy was increased (Holownicki et al., 2002). Theseresults were reproduced when wind speed was low but inhigher wind speeds, mean deposits were lower at thelowest airflow rate (Cross et al., 2003). Leaf fluttering isenhanced by increasing turbulence in the airflow andthis could be used to increase droplet collection by thefoliage. In this regard, high air speed is detrimental as itdecreases fluttering (Matthews, 2000b). The type of fanand the shape of the resulting air jet should also beconsidered. Air speed decays more slowly from a cross-flow fan which produces a two-dimensional jet (Abra-movich, 1963) and it was demonstrated that directed airjet sprayers with a converging flow resulted in higherdeposits and lowest spray loss even when the flow ratewas decreased by a factor of three (Doruchowski et al.,1996).A new type of spray recovery sprayer, initially

developed for apple orchards (Panneton et al., 2001)is being adapted to vine spraying in our laboratory.This sprayer uses vertical air sleeves to distribute adroplet-laden airflow along the full height of the canopy.It also uses a porous air-droplet separator on theopposite side of the vine to catch the droplets notretained by the foliage. As a preliminary phase ofthe design, a series of experiments has been performedto evaluate the potential of three basic configurations:one using a single sleeve-separator unit, one using apair of sleeve-separator units mounted at 180o withrespect to each other and a last one using twosleeves and a single air-droplet separator panel. Theobjective of the study was to identify the best config-uration of air jets to optimise spray penetration insidethe canopy and spray deposition uniformity across thecanopy.

2. Materials and methods

The experimental sprayer was designed in such a waythat it could serve as a test bench for the threeconfigurations [(a), (b) and (c) configurations]. Airflowwas provided by a centrifugal fan. The fan exit was fittedwith a Y-section to divide the flow in two streams. Anadjustable internal baffle was used to choke the fanoutput to control the total airflow. Another adjustableinternal baffle was used to balance the airflow betweenthe two branches of the Y-section. The entrance port onthe fan was fitted with a tube terminated by a bell mouth[Fig. 1(a)]. The tube was 254mm in diameter and1016mm long. At 508mm from the entrance of the tubea pair of flow meters (Debimo-254, Kimo, France) wasinstalled and connected to two differential manometers(Magnehelics Series 2000) in parallel. The flow meterswere 432mm upstream from the fan housing. Distancesupstream and downstream from the flow meters were setaccording to AMCA (1990). For low airflow rates, amanometer with a 0–50�8mm H2O range was used and a0–254mm H2O range covered the higher airflow range.For all configurations, the air was brought to the

vertical air sleeves using a flexible tube, 254mm indiameter. The top of the vertical sleeve was aligned withthe top of the canopy and it extended downwards tostop at about 254mm above the ground. The cross-section of the vertical sleeves decreased linearly fromtop-to-bottom to make sure that the exit air speed wasconstant along the full height. The air exit was a slot ofconstant width extending the full length of the sleeve(1000mm). The slot geometry was defined using twotubes, 25�4mm in diameter. The distance between thetwo tubes or the slot width was adjusted to provide an

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Fig. 1. Experimental prototype: (a) one air sleeve facing one air-droplet separator; (b) two air sleeves, each one pointing to an air-droplet separator; (c) two air sleeves, one pointing towards the air-droplet separator and the other one intersecting the first airstream at the centre of the row; in (a), the long pipe extending from the fan axis is the entrance port where total airflow to the fan is

measured; (d) and (e) geometry of the air exit and location of nozzles

AIR JET CONFIGURATION SHAPES 175

independent control of airflow rate and air speed[Fig. 1(d)]. With such a sleeve design, air escapes thesleeve with a significant downward velocity (Pannetonet al., 2001). To force the exit air to move parallel to theground, a series of fixed baffles were installed immedi-ately in front of the exit slot. These were large enough tocover the range of slot width actually used during theexperiments and were 50�8mm long.The spray nozzles were installed next to the air exit

slot [Fig. 1(d)] on a wet boom. The first nozzle at thebottom of the boom was at about 381mm above theground and nozzle spacing was 254mm. Four nozzleswere used with each sleeve. The exit of the nozzle wasaligned with the exit of the flow straightening baffles[Fig. 1(e)] and at 114mm from the border of the airexit slot. The nozzles were set at an angle of 30o withrespect to the jet axis. At this angle, most, if not all thespray, penetrated and was entrained by the air jet. Thenozzles were TX-VS3 hollow cone nozzles (SprayingSystems Co, Wheaton, Il) operated at 345 kPa. Underthese conditions these nozzles generated a fine spray(ASAE, 2000) and the application rate was 25 l/ha perboom.The design of the air-droplet separator was the same

for all configurations. It was a rectangular frame,

1200mm wide by 1000mm high (inside dimensions)holding two screens, at 16mm one from the other. Eachscreen had a 66% opening area ratio.The three configurations are illustrated in Fig. 1 and

their geometric details are provided in Fig. 2. Forconfiguration (a), the lateral distance between the vineand the air sleeves or the air-droplet separator panelswas constant at 270mm. For configurations (b) and (c),the distance to the vine was 320mm on both sides.Configuration (a) used one air sleeve and one air-dropletseparator facing each other, the separator being on thesprayer side of the row. The jet axis was offset forwardto compensate for the forward motion of the sprayer. Inconfiguration (b), a symmetrical pair of air sleeve andair-droplet separator was used. The axis of the two airjets were parallel and were pointing straight at the centreof the separator panel on the other side of the row. Theexit of the two air sleeves were at a distance of 1500mmalong the row of vine. Configuration (c) used two airsleeves and a single air-droplet separator. The sleeveaway from the sprayer was pointing at the centre of theseparator panel. The sleeve on the tractor side wasinstalled in front of the separator and was pointing atthe intersection between the axis of the other jet and theaxis of the row of vine.

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Air sleeve andair jet cone

Air-droplet separator

Vine area

0.5 m

1.04 m

0.4

m0.

8 m

0.75

m

0.75

m

0.6

m

0.6

m

1.14 m

0.75

m0.

6 m

1.14 m

(a) (b) (c)

Forward direction

Fig. 2. Detailed geometry of the three configurations

Table 1Value of the independent variables

Configuration Air speed, m/s Specific flow rate, % Flow rate balance Slot width, mm

Sprayer side Far side

(a) 15�0 62�5 5015�0 125 10030�0 62�5 2530�0 125 50

Reference 22�5 94 50

(b) 15�0 62�5 50–50 28 2815�0 125 50–50 55 5530�0 62�5 50–50 14 1430�0 125 50–50 28 28

Reference 22�5 94 50–50 28 28

(c) 15�0 62�5 30–70 16 3815�0 62�5 40–60 21 3215�0 125 30–70 32 7515�0 125 40–60 43 6430�0 62�5 30–70 8 1930�0 62�5 40–60 11 1630�0 125 30–70 16 3830�0 125 40–60 21 32

Reference 22�5 94 35–65 19 35

B. PANNETON ET AL.176

For each configuration, spray penetration and cover-age were measured on water-sensitive papers (SprayingSystems, Wheaton, Il) for different combinations of airspeed and airflow rate. For configuration (c), the airflow

rate balance between the two air sleeves was also used asan independent variable. A full factorial experimentalplan was used with three replications. The experimentalscenario is summarised in Table 1. The air speed was

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Fig. 3. Water-sensitive sampling tubes; top left, insertion ofmetal clip; top right, tube geometry and location of imageanalysis windows; bottom, unrolled sequence of 9 images from asingle tube where number on the images correspond to number on

the tube drawing

AIR JET CONFIGURATION SHAPES 177

measured directly at the exit slot of the vertical sleeves.The airflow rate was expressed as a specific flow ratedefined by

Qs ¼100� Qv

V v � v(1)

where: Qs is the specific airflow rate in %; Qv is the totalairflow rate through the fan in m3/s; Vv is the canopyvolume corresponding to 1m along the row in m3/m;and v is the travel speed in m/s. To compute Vv, thetreated cross-section was considered as the space fromthe top to the bottom of the vertical sleeve (1000mm)and laterally from the air-droplet separator front surfaceto the exit slot [1�04m for configuration (a) and 1�14mfor configurations (b) and (c)]. The travel speed wasmaintained at 1�17 m/s (4�2 km/h) for all tests. A specificflow rate of 100% corresponds to a combination of fanoutput and travel speed such as to replace all the air inVv with the droplet-laden airflow from the sprayer. Theflow rate balance of configurations (b) and (c) definedthe proportions of the air volume delivered on each sideof the row. The first number is the fraction of the totalflow emitted on the sprayer side.For each configuration, a set of reference conditions

was defined (Table 1). These were used to performreference runs. The coverage data from these referenceruns were used as co-variables (Neter et al., 1990) in theanalysis of variance (Unistat, 2002). Using co-variablespermitted to account for day-to-day variations in thefield conditions (canopy development, air temperatureand humidity, etc). In addition, the amplitude of thesevariations was limited in two ways. Firstly, the experi-ment started only after the first time the canopy has beentrimmed to a known height (1�2m) and width (0�5m). InQuebec, mechanical trimming is done on a regular basis,keeping the canopy volume fairly constant over time.Secondly, experiments were not performed if the meanwind speed (5min average) recorded on site (Youngpropeller anemometer, model 5107) exceeded 3m/s. Atthe beginning of each trial day, a first reference run wasperformed. During the day, a new reference run wasperformed whenever the average wind speed changed bymore than 1m/s or the wind direction changed by morethan 451.Before each run, the slot widths were adjusted. Then

the total airflow rate was adjusted using the appropriateadjustable baffles and readings of the airflow meter. Inthe case of configuration (c), the other adjustable bafflewas set to the appropriate position to divide the flow asrequired. These adjustments were previously definedduring preliminary tests. As a final check, the air speedat the sleeve exit was measured using a Pitot tube.Adjustments were modified until air speeds were within10% of their target value.

Sampling was performed by deploying arrays ofwater-sensitive tubes (Fig. 3). Tubes were used becausesampling is not sensitive to local airflow directionprojected in the plane perpendicular to the tube axis.Tube axis was set vertical. Strips of water-sensitivepaper were wrapped around polyvinyl chloride (PVC)tubes (22mm diameter) and held in place with a metalclip near the joint (Fig. 3). Supports holding three tubeswere installed so that one tube was aligned with thecentre of the row of vine and the other two tubes wherejust at the outer limits of the vine canopy. The tube mid-point was at 600mm above ground. The joint in thesampling tubes (Fig. 3) was always oriented facing thedirection 1801 from the travel direction of the sprayer. Atotal of six tube supports were deployed at randomlocations along two adjacent rows of vine (3 per row).The two rows were sprayed travelling in oppositedirection to remove any bias from the wind direction.For each experiment, a total of 18 sampling tubes werenecessary. Great care was taken to maintain theenvironment of the tubes as dry as feasible. Tubes werealways manipulated wearing latex gloves. Except duringthe actual experiment, tubes were placed in sealed boxwith a pocket of desiccant. As a result, the contrastbetween stained areas and background of the water-sensitive paper was always excellent.Image analysis of sampling tube was performed to

extract the surface of the stained area using a proceduredeveloped previously (Panneton, 2002). A motorisedsample holder was constructed. By rotating the samplein front of a camera, a series of nine images weregrabbed for analysis (Fig. 3). Each image represented an

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B. PANNETON ET AL.178

area of 4�6mm by 9�2mm at a resolution of 28�8 mm perpixel. For each image, the percentage of the area thatwas stained by water was measured. This variable will bereferred to as the coverage in this paper. Each image iscentered in a 361 sector on the cylinder and no imagewas acquired at the joint location. Image numbers (1–9)identify a unique angular location.The application volume was 25 l/ha for configuration

(a) and 50 l/ha for configurations (b) and (c). Forcomparing configuration (a) to the others, coverage datafor configuration (a) were corrected following anapproximate extension of the equation relating coverageto the number of impacts of droplets of a knowndiameter on a surface (Spillman, 1987):

C ¼ 1� exp kd2n

A

� �� �� 100 (2)

where: C is the mean coverage in %; k is the constantdepending on the spread factor of the droplet of thesampling surface; d is the droplet diameter in mm; n isthe number of droplets; and A is the sampling surfacearea in mm2.To apply Eqn (2), two hypotheses are required: (1)

Eqn (2) applies approximately to a polydisperse sprayreplacing kd2 with a suitable constant; and (2) when theapplication volume changes, the droplet spectra remainsthe same which is our case as the doubling in theapplication volume resulted solely from doubling the

0

1

2

3

4

56

7

8

9

V = 15 m/sQs = 62.5%

V = 30 m/sQs = 62.5%

100%

10%

01

2

3

4

5

6

7

8

9

100%

10%

Fig. 4. Polar plots of coverage for configuration (a); coverage valwith Fig. 7; V, air speed; Qs, specific airflow rate;

number of nozzles. Applying these two hypotheses, Eqn(2) can be used to write

C2 ¼ 2C � C2 (3)where C2 is the coverage that would correspond to Cwhen the application volume is doubled.

3. Results and discussion

The range of meteorological conditions encounteredduring the experiments was narrow. Five minute aver-aged wind speeds were in the range from 1 to 2m/s for84% of the experiments and the maximum air speed was2�27m/s. Wind direction was more variable. It waswithin 451 from the perpendicular to the rows of vine62% of the time.Data were visualised using polar plots (Fig. 4). Each

of the four graphs in Fig. 4 presents mean coverage for aset of independent variables. Mean values were com-puted by averaging the six coverage values available foreach angular position (1–9) at a fixed lateral positionwith respect to the vine (sprayer side, centre and farside). Data for angular position 0 were computed usinga linear interpolation between mean coverage atpositions 1 and 9. Position 0 was on the joint of thewater-sensitive paper cylinder and this position wasfacing the tractor as it came towards the sampler. The

V = 15 m/sQs = 62.5%

V = 30 m/sQs = 125%

01

2

3

4

56

7

8

9

100%

10%

01

2

3

45

6

7

8

9

100%

10%

ues corrected to double application volume for visual comparison—, centre; —~—, far side; —B—, sprayer side

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0

10

20

30

15 30 15 30

62 62 125 125

Cor

rect

ed c

over

age,

%

V, m/s

Qs, %

a b

a

a

a

aa

b c

aa

c

b

a

Fig. 5. Mean coverage results for configuration (a); differentletters in chart represent significantly different corrected cover-age within a single canopy location [least significant difference(LSD), probability Po0�05]; V, air speed; Qs, specific airflow

rate; &, sprayer side; , centre; , far side

AIR JET CONFIGURATION SHAPES 179

tractor can be seen as moving from top-to-bottom andpassing on the right-hand side of the graphs. On thegraph, coverage increases with radius following alogarithmic scale. For configuration (a), it is immedi-ately visible from the graphs that increasing the airflowrate did increase coverage at all locations but mostnotably on the sprayer side (away from the air source).Increasing the air speed did not increase coverage to thesame extent. As doubling either the airflow rate or theair speed doubles the amount of energy required tomove the air, the results showed that increasing airflowrate would be a better choice than increasing air speedfor improving coverage. The profiles are slightly tilted ascould be expected since the resultant air stream wasmoving in a direction resulting from the addition of thetravel speed of the sprayer and the exit velocity of theair. This last component was decreasing rapidly withdistance from the exit due to jet diffusion. The profileamplitudes dropped rapidly on the back side of thecylinders (face not exposed to the coming airflow). Thisis an indication that the level and the scale of turbulencein the flow were not large enough to promote depositionon surfaces sheltered from the airflow.Data were transformed according to the linear model

that takes into account the effect of the co-variable. Thebasic linear model was

Ci;j ¼ mc þ Qi þ V i þ QiV i þ b ~CCi;j þ �i;j (4)

where: Ci;j is the mean coverage for treatment i andreplicate j; mC is the overall mean coverage; Qi is theeffect of airflow rate for treatment i; Vi is the effect of airspeed for treatment i; QiVi is the interaction; b is theslope of the linear regression (least-squares method) forCi,j with CCi,j as the independent variable, ~CCi;j is thedeviation of the co-variable from its mean valueassociated with treatment i; and ei,j is the error term.The mean coverage was the average of the coveragevalues from a single tube. Prior to averaging, data fromimage 5 was removed to maintain sampling symmetryaround the tube as no data was available over the jointin the sampling tube. The slope b was the slope of thelinear regression. The corrected coverage Ĉi;j wasdefined as

Ĉi;j ¼ Ci;j � b ~CCi;j ¼ mC þ Qi þ Vi þ QiV i þ �i;j (5)

Equation (5) was the basis for the analysis of variance.A plot of the corrected coverage (Fig. 5) showed thesame trends as on Fig. 4. The analysis of variancerevealed that the effect of airflow rate was significant forthe centre (probability P ¼ 0�02) and on the far sidefrom the sprayer (Po0�01). Airflow rate was lesssignificant (P ¼ 0�06) on the sprayer side. In all cases,a higher airflow rate was associated with a largercoverage. Air speed showed significant effect in the

centre (P ¼ 0�05) with a better coverage associated witha smaller air speed at high specific airflow rate.The decay in coverage with distance from the outlet

was modelled with an equation of the form:

CðxÞ ¼ C0 exp�xxc

� �(6)

The constant xc is the distance required for C to fall to36�8% of its initial value C0. At the lower flow rate(62�5%), xc was 0�24m and it was 0�39m at 125%. Thisdecay in coverage resulted from the filtering effect of thevegetation. While the decay rate was decreased withincreasing specific airflow rate, it remained significantwith configuration (a).The mean coverage computed over a single sampling

tube is a measure of the total spray flux at the samplinglocation. The coefficient of variation of the coverage(CV) computed over a single tube (image 5 excluded)was calculated as a measure of the local coverageuniformity (Fig. 6). This variable then received the samestatistical treatment as the mean coverage. The analysisof variance revealed that air speed and airflow rate didnot induced significant changes (P40�05) on CV.Polar plots of the coverage for configuration (b)

(Fig. 7) displayed more symmetrical patterns than forconfiguration (a) (Fig. 4). As expected, this effect wasmore pronounced in the centre of the row but noticeabledifferences are displayed on the sprayer and far sides.Plots are tilted by about �301 with respect to thehorizontal, an angle comparable to the 331 tilt ofthe vertical air sleeves. Having this angle reproduced inthe coverage data is an indication that there was aminimum interaction between the two air jets. Astatistical treatment similar to the one applied forconfiguration (a), showed that on the sprayer and farsides, treatment effects on the corrected coverage werenot significant (P40�05). In the centre, the airflow rate

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B. PANNETON ET AL.180

had a significant effect on corrected coverage, withbetter coverage at 125% for the higher air speed (Fig. 8).Airflow rate had a significant effect (P ¼ 0�036) oncorrected CV on the far side and the interaction betweenspeed and flow rate was significant. This was traced to asignificant reduction in CV at 30m/s (Fig. 9).For configuration (c), the symmetry in the coverage

pattern was nearly as good as for configuration (b)(Figs 10 & 7 respectively) except on the far side wherethe profile was closer to the ones observed for

0

1

2

3

4

56

7

8

9

100%

10%

01

2

3

4

56

7

8

9

100%

10%

V = 15 m/sQs = 62.5%

V = 30 m/sQs = 62.5%

Fig. 7. Polar plots of coverage for configuration (b); V, air s—B—, spr

65

75

85

95

105

115

125

15 30 15 30

62 62 125 125

Cor

rect

ed C

V, % a

a

aa

aa

a

aa

a

aa

V, m/s

Qs, %

Fig. 6. Coefficient of variation (CV) of coverage for configura-tion (a); different letters in chart represent significantlydifferent corrected CV within a single canopy location [leastsignificant difference (LSD), probability Po0�05]; V, airspeed; Qs, specific airflow rate; &, sprayer side; , centre; ,

far side

configuration (a) (Fig. 4). For configuration (c), bothairflow rate and air speed had a significant effect(Po0�05) on corrected coverage in the centre and onthe sprayer side (Fig. 11) and only air speed was asignificant factor on the far side. The airflow balancewas not a significant factor and there was no interaction.On the sprayer side, coverage increased with specificairflow rate at high air speed and with airspeed for highspecific airflow rate. In the centre, coverage increasedwith air speed at low specific airflow rate and 30–70 flowbalance and with specific airflow rate at high air speedand 40–60 flow balance. On the far side, coverage

01

2

3

4

56

7

8

9

100%10%

01

2

3

45

6

7

8

9

100%10%

V = 15 m/sQs = 125%

V = 30 m/sQs = 125%

peed; Qs, specific airflow rate; —, centre; —~—, far side;ayer side

0

10

20

30

15 30 15 30

62 62 125 125

Cor

rect

ed c

over

age,

%

a

c

a

a

a ba

a

aa

ab c

a

V, m/s

Qs, %

Fig. 8. Mean coverage results for configuration (b); differentletters in chart represent significantly different corrected cover-age within a single canopy location [least significant difference(LSD), probability Po0�05]; V, air speed; Qs, specific airflow

rate; &, sprayer side; , centre; , far side

ARTICLE IN PRESS

65

80

95

110

125

15 30 15 30

62 62 125 125

Cor

rect

ed C

V, %

a

a

a

b

a

ab

a

a

b

a

a

V, m/s

Qs, %

Fig. 9. Coefficient of variation (CV) of coverage for configura-tion (b); different letters in chart represent significantlydifferent corrected CV within a single canopy location [leastsignificant difference (LSD), probability Po0�05]; V, airspeed; Qs, specific airflow rate; &, sprayer side; , centre; ,

far side

AIR JET CONFIGURATION SHAPES 181

increased with air speed at low specific airflow rate and30–70 flow balance. When significant differences oc-curred, increasing airflow rate or air speed increasedcoverage. Coverage uniformity was improved by in-creasing specific airflow rate at high air speed on thesprayer side and on the far side by increasing air speed athigh specific airflow rate (Fig. 12).The three configurations were compared. For each

configuration, the values of the independent variablesassociated with significantly better coverage wereselected pooling the data where appropriate. Forconfiguration (a) and (b), the 125% flow rate wasretained pooling data at the two air speeds. Forconfiguration (c), the data were pooled over flowbalance at 125% flow rate and 30m/s air speed. Theresulting data set is presented in Figs 13 and 14.Configurations were compared for a fixed location usinga LSD test (Unistat, 2002). On the far side, correctedcoverage from configuration (b) was significantly lowerthan for configuration (c) and corrected coverage forconfiguration (a) was not significantly different than theone for either configuration (b) or (c). In the centre,corrected coverage for configurations (b) and (c) wassimilar and significantly higher than with configuration(a). On the sprayer side, the coverage from allconfigurations were significantly different. As expected,configuration (b) produced the more uniform coverageacross the vine but overall, configuration (c) producedhigher corrected coverage than configuration (b). In allcases, configuration (a) resulted in higher values of CV(Fig. 14). On the far side, CV for configuration (b) wassignificantly smaller than CV for configuration (a). Inthe centre, configurations (b) and (c) had similar CV,both significantly lower than for configuration (a). Onthe sprayer side, CV for configuration (c) was signifi-

cantly lower. Again, configuration (b) resulted in asymmetrical pattern of CV across the vine but config-uration (c) was slightly better.It was not expected for configuration (c) to outper-

form configuration (b). It was first thought that asymmetrical layout of the air sleeves and air-dropletseparators would yield better results. It has been pointedout that in configuration (b), the interaction between thetwo air jets was minimal. This was based on coverageresults (Fig. 7) and visual observations during theexperiments supported this conclusion. With configura-tion (c), the flow field was more complex as the two airjets interacted strongly. The resulting turbulence is themost probable explanation for the good coverage resultsthat were obtained. It was noted in the discussion ofconfiguration (a), that the surfaces facing away from thecoming flow were not well covered. These observationssupports the idea that improved coverage can only beobtained by multiplying the number of angle of attackof the flow with respect to any given target surface. Thiscould be achieved either by using multiple air jets or bycreating a turbulent flow with a characteristic lengthscale larger than the size of the target surfaces.Configuration (c) was easier to implement than

configuration (b) as only an air sleeve and a short wetboom had to be supported by the over-the-rowstructure. Observations during field experiments haverevealed that the design of the air-droplet separatorwhile adequate for configuration (a) and (b), was notsuitable for configuration (c) as a large portion of theflow did escape in the space between the vine and theseparator at the trailing edge. Shifting the separatortowards the back of the sprayer and using flaps at thetrailing edge to close the gap between the vine and theseparator would partly solve the problem.

4. Conclusion

Three configurations for a spray recovery sprayerusing air-assistance were tested on vine. In the threecases, a vertical sleeve was used to generate a two-dimensional horizontal air jet of uniform velocity profilefrom top-to-bottom. The first configuration used asingle air jet perpendicular to the row. The secondconfiguration used a pair of air jets, one on each side ofthe row. Both jet axes were parallel and angled at 331from the perpendicular to the row. The jet dimensionand initial velocity were the same. The separationbetween these two jets was large enough to avoid anysignificant interaction. In the third configuration, a firstair jet was on one side of the row with its axisperpendicular to the row and a second air jet was onthe other side of the vine with its axis intersecting the

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0

1

2

3

4

5

6

7

8

9

V = 15 m/sQs = 62.5%

R = 0.3 − 0.7

V = 30 m/sQs = 62.5%

R = 0.3 − 0.7

V = 15 m/sQs = 62.5%

R = 0.4 − 0.6

V = 30 m/sQs = 62.5%

R = 0.4 − 0.6

V = 30 m/sQs = 125%

R = 0.4 − 0.6

V = 15 m/sQs = 125%

R = 0.4 − 0.6

V = 30 m/sQs = 125%

R = 0.3 − 0.7

V =15 m/sQs = 125%

R = 0.3 − 0.7100%

10%

01

2

3

45

6

7

8

9

100%

10%

01

2

3

4

56

7

8

9

100%

01

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56

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9

100%

10%

0

1

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3

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5

6

7

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9

01

2

3

4

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7

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9

100%

10%

100%

10%

0

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6

7

8

9

100%

10%

0

1

2

3

4

56

7

8

9

100%

10%

10%

(a)

(b)

Fig. 10. Polar plots of coverage for configuration (c): (a) 0�3–0�7 flow balance; (b) 0�4–0�6 flow balance; V, air speed; Qs, specificairflow rate; R, ratio of flow balance; —, centre; —~—, far side; —B—, sprayer side

B. PANNETON ET AL.182

axis of the first jet in the centre of the row. This secondair jet delivered a lower flow rate at the same initialspeed than the first jet. Results have shown thatcoverage on artificial cylindrical targets was maximisedwith the third configuration where a strong interaction

between the two jets did occur. Furthermore, thecoverage was locally more uniform with this thirdconfiguration as with the configuration with two non-interacting jets. These experimental results showed thatinteracting air jets improved the distribution of the

ARTICLE IN PRESS

0

10

20

30

40

30 − 70 40 − 60 30 − 70 40 − 60 40 − 60 40 − 6030 − 70 30 − 70

15 30 15 30

62

15

62 62

30

62 125

15

125 125

30

125

Cor

rect

ed c

over

age,

%

R

V, m/s

Qs, %

a

a

aa

a b

c

a b

a b

b c

a b

b c

d

a b

c

a b

a b

a b

c

a b

a b

c

a b

c

a b

ca

b c

d

b cc d

c d

c

dd

Fig. 11. Mean coverage results for configuration (c); different letters in chart represent significantly different corrected coveragewithin a single canopy location [least significant difference (LSD), probability Po0�05]; V, air speed; Qs, specific airflow rate; &,

sprayer side; , centre; , far side

70

80

90

100

110

120

30 − 70 40 − 60 40 − 60 40 − 60 40 − 6030 − 70 30 − 70 30 − 70

15 15 30 30 15 15 30 30

62 62 62 62 125 125 125 125

Cor

rect

ed C

V,

%

R

V, m/s

Qs, %

a b

b a

a b

ba

b

a b

a

a b

a b

a

a b

ba

a b

a b

a

a

aa

a

aa

Fig. 12. Coefficient of variation (CV) of coverage for configuration (c); different letters in chart represent significantly differentcorrected CV within a single canopy location [least significant difference (LSD), probability Po0�05]; V, air speed; Qs, specific

airflow rate; &, sprayer side; , centre; , far side

0

10

20

30

40

Configuration

Cor

rect

ed c

over

age,

%

b

a a

abb

b

b

c

(a) (b) (c)

Fig. 13. Mean coverage results for the three configurationsunder their relative best settings; different letters in chartrepresent significantly different corrected coverage within asingle canopy location [least significant difference (LSD),probability Po0�05]; &, sprayer side; , centre; , far side

65

80

95

110

125

(a) (b) (c)

Configuration

Cor

rect

ed C

V,

% b

bc

a

a

ba b

a a

Fig. 14. Coefficient of variation (CV) of coverage for the threeconfigurations under their relative best settings; different lettersin chart represent significantly different corrected CV within asingle canopy location [least significant difference (LSD),probability Po0�05]; &, sprayer side; , centre; , far side

AIR JET CONFIGURATION SHAPES 183

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B. PANNETON ET AL.184

spray within the vine canopy. The improvement incoverage resulted mainly from having a flow comingfrom widely different directions. In addition, turbulencegenerated during interactions between air jets mighthave contributed in improving deposition uniformity onthe cylindrical targets.

Acknowledgements

This research was supported by the program PPFI ofAgriculture and Agri-Food Canada with the collabora-tors Ferme Au Pic and the vineyard l’Orpailleur. Theauthors wish to thank M. Gilles St-Laurent for hiscontribution to this work.

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Effect of Air-jet Configuration on Spray Coverage in VineyardsIntroductionMaterials and methodsResults and discussionConclusionAcknowledgementsReferences