Determination of coverage area

This parameter can indicate the efficiency of the method of application. The best method can be judged as that which gives a high coverage area on the intended target and relatively less drift to the environment or on the ground. For this reason coverage is used to compare the methods or ways of application. To test the ability of the novel induction nozzle to cover the target (insect), evaluation of the coverage area was deemed necessary. Figures 6.20 and 6.21 illustrate the preparation of the artificial plants and experimental setup. The front and back surfaces of the leaves of the plants were covered with WSP so as to facilitate calculation of the coverage area of both surfaces (front and back of the leaf). The other reason for using WSP was to capture the droplet size distribution, with and without charging.

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Figure 6.21: The experimental setup for controlling the insects and measuring the coverage area: robot (1); computer (2); high voltage supply (3); induction nozzle (4) and insect targets (5, 6 and 7).

The level of induction voltage used in these experiments was 800 volts as it was found to be the best in the experiments conducted previously. From Figure 6.22, it can be seen that the induction nozzle can deal with the targets when they are arranged individually or in groups with different positions. A change in the colour of the WSP from yellow to blue indicated the ability of the nozzle to deal with the intended target.

Figure 6.22: Induction nozzle dealing with the individual and group targets.

The values of depositions on the back surface of each leaf were captured both for with and without charging (see Figure 6.23).

Figure 6.23: The coverage area on the back of the leaf target under the charged (left) and uncharged condition (right).

Figure 6.24 shows the induction nozzle operating with different targets, before, during and after the procedure.

Figure 6.24: The induction nozzle working on the targets.

In order to compare the results of the samples that were collected, microscopic pictures were prepared from the samples and a digital microscopic device, the model HD colour CMOS Sensor, High-Speed DSP was used for this task. The unit area captured for all the samples was 0.5cm2 which is equivalent to 640x480 pixels. The images presented in Figure 6.25 below represent the nature of the coverage area under the charged condition. These pictures are for both the top and bottom surfaces of the leaves. Furthermore, Figure 6.26 presents the nature of the coverage without charging for the top and bottom surfaces of the leaves. The results obtained for these two cases indicate that the coverage area when charging is more

than when without. Moreover, the top surface has greater coverage than the bottom in both cases.

Figure 6.25: The coverage area under the charged condition on the top surface (top samples) and the charged condition on the back surface (bottom samples) of the leaves.

Figure 6.26: The coverage area for the uncharged condition on the front surface (top samples) and the uncharged condition on the back surface (bottom samples) of the leaves.

In order to measure the coverage area for the two cases, a simple program created with Matlab software was used. This program calculates the percentages of coverage area of all the droplets in one unit to the area of the original sample. The results obtained from this program for all the microscopic pictures were plotted and are presented in Figures 6.27, 6.28 and 6.29. These show that the areas of efficient coverage for the two cases, i.e. with and without charging as well as for the two leaf surfaces, front and back, are different. The percentage of coverage area for the front surface under the charging condition is three to fourfold more when compared to that for the same surface in the uncharged condition (see Figure 6.27). Moreover, in the charged condition on the back surface the value is two to three times more compared to the back surface under the uncharged condition (see Figure 6.28). These results are in good agreement with those of Maski and Durairaj, indicating that the adaxial (upper) surfaces received greater deposition than the abaxial (bottom) ones [41], also being consistent with findings by Chao et al [109]. In addition, the results that are obtained

from this study agree with the range of values obtained by Law 1980, which fell between 1.8 fold to seven-fold for the charged versus uncharged scenarios. Moreover, when comparing the charged value and the value of conventional deposition the range was 1.9 fold to 4.4 fold [12]. However, the results of the current study recorded greater increases than those reported by Cooper and Law [66], who recorded values of 1.5 and 1.8 fold increases when the current spray was positive and when it was negative, respectively [24].

Figure 6.27: The coverage area of the front surface for the charged and uncharged conditions.

Figure 6.28: The coverage area of the back surface for the charged and uncharged conditions.

In general, the coverage area is reduced in the uncharged condition and the under surface receives less deposit than the upper regardless of whether the spray is charged or not (see Figure 6.29).

Figure 6.29: The coverage area for all the results.