Browsing by Author "Parkin, C. S."

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    Atomisers for the Aerial Application of Pesticides in Tsetse (Glossina sp) and Armyworm (Spodoptera exempta) Control
    (Cranfield University, 1992-07) Kinnersley, Robert P.; Parkin, C. S.
    Aerial application of insecticides is likely to remain an important component in realistically-costed vector and migratory pest control operations for the foreseeable future. The objective of this work was to identify or design improved atomisers for use in two such operations, tsetse (Glossina sp. ) and African armyworm (Spodoptera exempta) control, the former requiring an insecticide aerosol ýx'ith a VMD of 20 to 30ýim at rates upto 0.5 litres/minute and the latter a fine spray with a VMD of 80 to 120ýtm at rates around 16 litres/minute. In both cases rotary atomisation was confirmed as the most appropriate technique. Assessments were made of seven commerciall%, available atomisers and two existinc, prototypes, on the basis of existing reports and new data generated under simulated flight conditions in a wind tunnel. Droplet sizing was carried out using an optical array probe set to give a resolution of 54m over a range of 3.6 -3) 12.54m. None of the atomisers tested met the specification for tsetse-spraying, the limiting factors being rotation speed and inability to distribute low volumes of liquid across their full atomising surface. The Micronair AU4000 and AU5000 and the Micron X-I were found to be suitable for armyworm control, the Micron X-1 having the additional ability to produce spray with VMDs down to 40ýim. A review of rotary atomiser literature provided design guidelines for the design of an atomiser capable of meeting tsetse specifications. The principle effect of liquid flow 4D within the atomiser was found to be on the uniformity of fluid distribution. Premature ligament formation and formation of cross-flow vortices were identified as factors which could adversely influence fluid distribution under some conditions. Ligzan ment seperation from disks can be aided byI slender teeth, providing that these have a spaciniz similar to the natural spacing of ligaments predicted by Taylor instability theoInry . The effect of rotation speed and atomiser diameter on droIp let diameter is determined by the degree of stretching of the ligament due to its acceleration relative to the atomiser, implying that a finer spray would be achieved using a smaller rotating diameter disc than a larger diameter disc with the same peripheral speed. A series of experimental studies was carried out usinrgD higZDh speed photogZ_r_a phy in conjunction with the droplet sizinaprobe. Disturbancesh a,,i,n, g the forrn predicted for C cross-flow vortices were observed in liquid on a plain spinning disc. A sin(-)'Ieligament generator was constructed. With increasing rotation speed this rt\'taled a series of increasingly unstable ligament disintegration modes in which interaction with the surroundin4g15 air became a controlling-- factor. Complete shattering of the ligament occured at a Weber number of between 4 and 5, similar to reported values for liquid jets in a cross flo%v of cyas. Droplet sizing indicated that the specified performance for tsetse operations could be obtained from 50mm diameter atomisers with a total of around _'30000is suing points at a rotation speed of 26000 RPNI. This Zý sucy(yestecdN l,i ndcr rather than disc-based atomisers. A slit was found to be impractical as a means of distributing liquid unifom-ily at high rotation speeds but distribution was sucýe: ssfully achieved using a porous flow resistor. Prototype wind- and electi-ically-driven atornisers were constructed using rotating porous cylinders fed internally by spray bars designed with the help of finite element methods. Ligament formation was found to occur from a film of liquid on the outer surface of the cylinder, the variation in spacing with feedrate and rotation speed suggesting Taylor instability to be the controlling factor. The prototype atomisers achieved a performance suitable for tsetse control operations. This was not enhanced by the provision of discrete issuing points.
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    Fluid driven rotary atomiser for controlled droplet application of herbicides.
    (1991-04) Craig, I. P. S.; Parkin, C. S.
    Handheld electrically driven spinning disc atomisers are capable of applying pesticides more efficiently than with hydraulic nozzles, because the narrower droplet spectra they produce leads to reduced drift and wastage of chemical. Despite these savings however, farmers are frequently reluctant to use such methods because of poor reliability, and high maintenance costs of the electrical drive systems. This research has therefore examined an alternative drive system using a jet of the pesticide fluid to power the atomiser. Experiments have been carried out to increase understanding of the processes involved, with the aim of producing an optimum design suitable for mounting to a knapsack sprayer. The fluid drive mechanism is comparable to that of a Pelton Wheel; driving torque arises from a change in momentum of a fluid jet as it strikes the inside of a cup causing it to rotate. The fluid is emitted from grooves and teeth to form ligaments which produce uniform droplets. Peripheral distribution of fluid is made uniform by a series of slotted weirs on the inside wall of the cup. Form and size of various components including the nozzle, bearing, cup and atomising disc have been investigated. The requirement for low flowrate necessitates the use of a small nozzle with filter. Supply pressure available from hand- pressurised knapsack sprayers is also restricted. Available input energy is therefore limited, requiring that all the processes leading up to atomisation are as efficient as possible. Rotational speed is a function of jet velocity, mass flowrate, inner and outer cup radius, and bearing frictional torque. A simple computer model has been developed to predict the effects of changing these parameters. Radial exit velocity of the fluid has been derived from a consideration of the viscous forces to which thin fluid layers are subject during centrifugal acceleration upon rotating surfaces. This has enabled undisturbed ligament radius to be calculated, and has therefore provided a satisfactory method for the prediction of dropsize. Spectral and deposit characteristics are satisfactory for CDA herbicide application with water based formulations, although antifoam agent is required for formulations containing surfactant. Typical average droplet size for an operating pressure of 3 bar is 250μm, and optimum swath width is 1.2m for an intended application rate of 30 to 40 litres per hectare.
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    Mathematical modelling and simulation of irrigation sprinklers
    (Cranfield University, 1999-10-16) Grose, Daniel J.; Parkin, C. S.
    A set of equations suitable for describing the dynamics of a liquid droplet - gas mixture (spray) have been developed. The equations are arrived at by considering the spray as a multiphase continuum within which the gas and droplets of different sizes constitute individual phases. By ignoring droplet-droplet interactions and considering the gas phase as an inviscid fluid a simplified form of the equations of motion has been arrived at. The equations are considered in one dimension and used to describe the dynamics of the interior of spray produced by a large or medium scale irrigation sprinkler. When combined with data representing the distribution of droplet diameters within the spray this model can be used to predict the water application produced by a sprinkler operating in windy conditions. Such simulations have been undertaken to predict the water application from static sprinklers and the results validated by comparison with data obtained experimentally. A simulation methodology is used to determine the uniformity of water application produced by a travelling sprinkler. By considering the results of large number of simulations produced using meteorological data spanning several years the manner in which the simulation can be used for determining optimum irrigation practice is demonstrated. A simple model has been developed for predicting the water application from a travelling sprinkler operating in still air. The model can be used for obtaining first approximations to optimum operating conditions and provides a means for easily quantifying the performance of a given sprinkler. Further use of the model may be made for aiding in the design and control of irrigation sprinklers.