J.J.C. Picot
Dept. of Chemical Engineering,University of New Brunswick,Fredericton, N.B., Canada

SERG Project #2002/05
Year of Project: 2002
Report Received: 2003


Technical Note

This is a description of the method used to measure the flux-based(temporal) droplet size distribution for atomizers used in the aerial application of pesticides in agriculture and forestry. Figure 1 shows a sketch of the circular cross-section wind tunnel (1.02 m in diameter)used for this. The Malvern 2605C laser Fraunhofer diffraction instrument is installed so that the laser beam crosses the wind tunnel horizontally (through apertures in the wall) on a diameter of the tunnel cross-section, with transmitting and receiving modules fixed on pylons independent of the tunnel structure. Atomizers are fixed on a vertical boom which is located on a diameter of the tunnel cross-section upstream of the laser beam. Testing is conducted by releasing the liquid stream through the atomiser into air flowing through the tunnel. Air velocity in the tunnel exhibits a square profile upstream and a short distance downstream of the atomizer, and is set at a value equal to aircraft airspeed.

A total spray plume traverse is done by making measurements at each of a series of laser beam transects (along a chord) across the plume, separated by a vertical spacing of 1 or 2 inches (2.5 or 5.1 cms), depending on the size of the plume, from upper to lower plume edges. For axially symmetric plumes (e.g. from rotary atomizers), it is sufficient to carry the sampling from the center of the plume to one edge.