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Recent Submissions

Now showing 1 - 5 of 81
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    Comparison of the mechanistic AGDISP ground boom spray model with experimental data
    (The New Zealand Plant Protection Society Inc., 2012) Connell, Robert J.; Schou, W. C.; Nuyttens, D.; Wolf, T.; Praat, J.-P.
    Since work reported in 2008, developments on the AGDISP ground boom model have improved results against New Zealand field trial drift data and also compare better with ground boom drift data sets from Belgium and Canada. The model still predicts more drift than the experimental data in most cases, especially for smaller droplet sizes, but does predict less drift for larger droplets at large distances downwind. The original AGDISP ground model was calibrated from Spray Drift Task Force data from the United States. The experimental methods need to be developed to improve collection efficiency and mass balance. The physics behind the model are discussed and proposed methods for improvement are suggested, including air velocities in the spray jet below the nozzle, the dispersion of the spray plume cloud at ground level due to atmospheric turbulence and wakes from the spraying equipment. © 2012 New Zealand Plant Protection Society (Inc.).
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    Evaluation of the AGDISP ground boom spray drift model
    (The New Zealand Plant Protection Society Inc., 2008) Woodward, Simon; Connell, Robert J.; Zabkiewicz, J. A.; Steele, K. D.; Praat, John-Paul
    AGDISP is a well-established spray drift model that has been validated for aerial spraying of forests. Recently a prototypical ground boom option has been added to AGDISP. This was evaluated in the current study by collecting data from spray trials over a grass sward using a ground boom sprayer and representative application parameters. Spray solutions were made up of water, sticker adjuvant and a metal cation, which was changed for each spray application. Deposition from spray drift was measured by analyses of the cation deposits on artificial targets (plastic tapes) placed on the grass surface. Measured deposition was compared with profiles calculated using AGDISP. AGDISP overpredicted deposition from spray drift by a factor of 3.5-100 outside the spray block. Possible reasons for these discrepancies are given. Options are to improve measured deposition and the algorithms for the deposition on the downwind swath of the spray block and evaporation of droplets.
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    The Lektraspray Nozzle: A novel ultra low volume spray applicator for the greenhouse industry
    (Lincoln University, 1995) May, William A.
    A novel electrostatic spray nozzle, termed the Lektraspray Nozzle, was evaluated to assess its suitability for pesticide application in the greenhouse industry. The nozzle is based on the vortical nozzle principle, releasing the spray liquid into a low pressure/high volume airstream through a flexible emitter tube. The encompassing airstream shatters the liquid into small droplets and transports them to the target. The experimental work identified that the nozzle could deliver a droplet spectra with a Volume Median Diameter (VMD) of approximately 75 μm for a range of liquids and viscosities. Charging the droplets had a minor effect on the VMD, although typically improved the droplet spectra. The nozzle could be operated satisfactorily with or without electrostatically charging the droplets. The VMD could be changed simply by increasing/decreasing the liquid flow rate and/or adjusting the air pressure of the encompassing airstream. Small adjustments to the air pressure (4.5 to 14 kPa) will allow the production of an acceptable droplet spectra over a large range of liquid flow rates (30 to 1000 ml/min). The results of a limited number of tests using the Lektraspray nozzle on plants indicated that electrostatic charging could significantly influence the deposition of droplets on the underside of the leaves, providing the foliage was not "dense". However no significant increase in the total amount deposited on the plant was noted when the droplets were charged. The results from spraying a "dense" foliage plant (Pittosporum eugenioides) indicated the need to adjust the charge/air pressure relationship of the spray nozzle to increase underleaf deposition and improve droplet penetration into the plant canopy. After evaluating the experimental work on the Lektraspray nozzle, and considering the simplicity and ruggedness of the nozzle, the conclusion was that it should be seriously considered as an alternative spray application technique for use where controlled environment spraying is required. In particular - the greenhouse industry.
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    Optimising MICREDOX to accurately report the BOD of sewage samples
    (Lincoln University. Lincoln Ventures., 2004) Webber, Judith; Hay, Joanne; Noonan, M.; Pasco, Neil
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    Scale-dependent dispersivity: a velocity fluctuation model
    (Modelling and Simulation Society of Australia and New Zealand, 2003-07) Verwoerd, WS; Post, DA
    In the previous paper, it was shown that the cumulative effect of multiple one-dimensional velocity fluctuations can explain qualitative features of the observed scale dependent dispersivity in natural aquifers, but not the magnitude of the effect. It is plausible that in real systems the enhancement of dispersion caused by a single fluctuation may be larger than that derived for the 1-dimensional stepped fluctuation, because for example there are additional enhancement mechanisms in 2- and 3-dimensional systems. However this paper shows that to achieve the observed magnitude, it is not enough to increase the size of enhancement factor but in addition the rate at which the effect of a single fluctuation changes with fluctuation length and with position along the fluctuation sequence need to be modified. Several variations are explored. Simple assumptions are shown to lead to dispersivity formulas in terms of purely algebraic power laws, while more elaborate assumptions yield expressions that are still analytic but contain non-elementary functions. In either case it is possible to find the required variation of the dispersivity over 3 or more orders of magnitude and with curve shapes that are consistent with historical observations Moreover, this is achieved with plausible parameter values, leading for example to the conjecture that in the observed systems the porous medium could not have been homogeneous on a scale of more than centimeters. The model presented is schematic in the sense that it contains some detail assumptions not derived from first principles, but is believed to capture the essentials of the mechanism that causes scale dependent dispersivity. It sets some boundaries for viable detail models, but within those boundaries the final predictions are not very sensitive to the detail assumptions. A key merit of the treatment is that it identifies crucial variables that need to be measured or controlled in experimental studies.