To evaluate and improve the efficiency of liquid chemical delivery in agricultural sprays, Oxford Lasers has developed VisiSizer – a cost effective laser based analysis instrument.
VisSizer provides unique insight into three key aspects of the agricultural spray process – the break up of the spray into droplets after it leaves the nozzle, the size and velocity distribution of droplets in motion, and the adherence of droplets to leaf surfaces.
VisiSizer can characterise agricultural sprays from the initial formation of the spray through to its eventual deposition on the leaf. Cone angle, drop size and drop velocity, key parameters of the spray, are easily and accurately analysed; even non-spherical droplets may be sized – a measurement that is notoriously inaccurate with existing techniques.
Significantly, laser illumination provides a ‘cold’ light source, eliminating the problems of plant wilting under hot lamps or similar light sources.
The image below illustrates visualisation of the break up region of a flat-fan pesticide spray.
Visualisation of this region provides insights into how the nozzle parameters & chemical properties affect drop formation & sizes.
Looking further from the nozzle, and zooming in, drop sizes can be measured at up to 7680 drops per second in real time. The image below shows a suitable image for sizing.
Images are used to measure droplets of any shape or size. VisiSize is not deceived by out of focus droplet images which appear bigger than they really are. By measuring the sharpness of the image edges, VisiSizer automatically corrects for this effect.
Output (image below) takes the form of histogram of size data, statistical measures (e.g. Satuer Mean Diameter) & individual drop data for export into MS Excel.
Zooming in further, we see that the droplets from this spray, not only are non-spherical, but also include air bubbles. A unique image of this phenomenon is shown above.
Alternative measuring systems such as phase-doppler anemometers (PDA / PDPA) would measure the size of a non-spherical droplet incorrectly and would give no indication of any air inclusions.
If the laser is flashed in consecutive exposures, a pair of images can be collected. By measuring how far each droplet has moved from one exposure to the next, the system automatically calculates droplet velocities. This is illustrated below for the drops produced by a different type of agricultural spray, a micron-sprayer.
While drop size and velocity distribution information is vital in developing nozzles, it is the interaction of the droplets with the leaf, which determines the effectiveness of the delivery system.
When viewed as a movie, the sequence shows how many of the droplets simply bounce off on impact and how many adhere to the surface of the leaf.
The high speed, high magnification movies obtained by VisiSizer are so easy to understand that they can even be used as a training tool for end users.
VisiSizer systems from Oxford Lasers give quantitative details of drop-size and velocity, in much the same way as anemometry techniques, but with the benefits of: