TECHNIQUES FOR MEASUREMENT OF DROPLET SIZE AND VELOCITY DISTRIBUTIONSIN AGRICULTURAL SPRAYS

Two techniques for measuring the size and velocity of droplets in agri cultural sprays produced by hydraulic flat fan nozzles have been evalu ated for their ability to produce consistent results. These were a one -dimensional phase Doppler particle analyser (PDA) and a two-dimension al imaging probe of a Particle Measuring Systems (PMS) instrument, bot h measuring velocities in a single plane and operated in conjunction w ith a computer-controlled nozzle transporter to enable the whole spray to be sampled. The different operating principles of the instruments resulted in different droplet size and velocity distributions in relat ively dense, polydispersed sprays. PDA gave consistently lower values for the volume median diameter and higher droplet velocities than PMS. PMS gave lower percentages of spray volume in droplets less than 100 mu m in diameter, while the PDA indicated some large droplets that wer e not detected by PMS. The required sample size was smaller for PMS (3 000 droplets) than for PDA (13,000 droplets). Both instruments are use ful for measuring the characteristics of agricultural sprays, providin g that their limitations are recognized. Appropriately configured, suc h systems enable droplet size and velocity distributions, entrained ai r velocities, droplet trajectories and the spatial structure of sprays to be determined. (C) 1997 Elsevier Science Ltd.