| Author | Dante, Edgar Trinidad |
| Call Number | AIT Diss. no.AE-96-01 |
| Subject(s) | Spraying and dusting in agriculture
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| Note | A dissertation submitted in partial fulfillment of the requirement for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. AE-96-01 |
| Abstract | Pesticide spray drift may damage neighboring crops and is hazardous to human and the environment. Despite numerous methods of control, such as air-assistance, spray shielding, use of anti-drift additives, and electrostatic charging, drift is still a main problem and remains the main focus of current research. This study examined previously reported drift-reduction technique based on heating with a flame of hot gas of liquid spray sheet from hydraulic nozzle. In view of the limited information on the mechanism of atomization of heated spray sheet, the effects of heating on droplet size distribution under various nozzle operating conditions, such as nozzle type. liquid pressure, liquid flow rate, spray angle. liquid surface tension, and liquid viscosity, were investigated. Also the influence of heat application methods using heated air from electric heater and hot spray liquid on atomization was studied. Finally, an attempt was made to understand the mechanics of heated spray atomization and actual drift reduction due to heal application. All experiments were carried out at the Long Ashton Research Station, Department of Agricultural Sciences. University of Bristiol, United Kingdom. Measurements of droplet spectra were made using a laser-based Phase Doppler Particle Analyzer (PDPA) by Aerometric, Inc., USA. Hollow cone and fan nozzles of different orifice sizes and spray angles were used to spray tap water at various liquid pressures and heat application methods. Spray additives such as Agral, Silwet, Propanol and Target were used to vary surface tension and viscosity of the spray liquid. Drift experiments were carried using a single hollow cone nozzle spraying 0.025% w/v sodium fluorescein in tap water in an enclosed spray chamber. Six Horizontal strings spaced 7.6 cm apart with the bottom string 40 cm below and 2 m downwind of the nozzle were used to collect spray drift. A limited high-speed photographic work was carried out to analyze the effect of heating on the mechanism of liquid atomization. Heating of liquid sheet by flame or electric heater resulted in the formation of perforations on the sheet. causing it to break-up prematurely and producing a modified droplet size distribution. It increased the droplet volume median diameter (VMD) by 30% and reduced the spray volume below 100 um by an average of 42% in hollow cone and 66% in fan nozzles. This clearly affirmed the drift reduction potential of heating. However, the observed reduction in volume of fine drops was accompanied by an increase in volume of coarser drops. As a result of heating, the range of the droplet size distribution of hollow cone spray was increased by about 14%. Heating the liquid sheet by electric heater reduced the mean droplet velocity by half in hollow cone spray and increased droplet velocity by one-fourth in fan spray. The effect of heating on droplet size distribution tended to diminish slightly with increase in liquid pressure or flow rate. In general, heating had very little effect on the dropet size distribution of spray liquid added with surfactant or drift reducing agent. Actual drift reduction due to heating in hollow cone nozzle was about 28% Heat application in the form of hot air from a hair dryer or electrically heated element positioned near the base of the nozzle could modify spray atomization in hollow cone and fan nozzles and was similar to the pattern observed in flame or hot gas application. The former method involved much lower temperature (150°C) than the latter (about 1000°C). However, the hypothesis of previous researchers that ionized particles in hot gas cause premature break-up of the sheet could not be verified independently though it is likely that the heated air at relatively low temperature also contains ionized particles. This study concluded that the spray atomization observed with heat application could not be achieved simply by using a hot spray liquid. However, certain concentrations of surfactant solutions were observed to modify spray atomization without heat application. Mathematical models relating VMD with nozzle parameters were developed using direct regression and dimensional analysis. A linear model provided the best correlation (R² = 0.97) with the experimental data. It showed that in heated atomization only the orifice diameter and liquid pressure significantly influenced the VMD of droplets. |
| Year | 1996 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AE-96-01 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Chandra P. Gupta; |
| Examination Committee(s) | Vind K. Jindal,;Prbert H.B. Exall; |
| Scholarship Donor(s) | The Government of Australia; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1996 |