送風散布式防除機具の研究

(第5報) 散布粉剤の附着について

抄録

This study was undertaken to investigate the deposit of dusting particles on crop leaves. It was carried out under several dusting conditions, combined with various jet-speeds and discharges from the Duster.
The test was carried out in a closed room, 10 metres by 24 metres in area, and 4 metres in height. The Duster was driven on a specially designed frame, rotating at 4π/15rad/sec in angular verocity. The jet flow of air containing the dusting powders was passed once over the fixed rice leaf surfaces. After dusting, the particles deposited on the leaves were examined for size, number and the area covered.
The results of the tests are as follows:
1) The wind velocity (distribution) of the jet coming from the blower was measured with a pitot tube type, birum type and trial thermister type anemometer. In the results, the wind velocity decreased in proportion to x^-1 where x is the distance from the jet nozzle, and its distribution is approximately represented by the equation (4).
2) In the tests in which the distance exceeded 3 metres, no difference in the deposit was in evidence. When the distance was under 3 metres, the area covered decreased rapidly, according to the distance. However as the jet speed became larger, this tendency lessened. If a uniform dusting is disired, then the jet speed mast be increased according to the distance.
3) When any area was sufficiently covered-in our estimation, about 5% for an effective deposit of dust particles; we established the following figures as limit point:
at a distance of 1 to 1.5 metres for a jet speed of 20-30m/s
at a distance of 1.5 to 2 meter for a jet speed of 40m/s
at a distance of 2 to 3 meters for a jet speed 50-00m/s.
The wind velocity at all these points was 3-10m/s. Moreover, these points correspond to the minimums deposit ratio of the (dusting) particles on the leaf surfaces.
Considering the decreasing velocity of the jet stream, together with the results mentioned above, the characteristic of the jet stream can be designated by two terms: “Effective Distance of the fet Stream” i.e. the distance closest to the nozzle of the Duster wherein a satisfactory deposit can be obtained; and the “Over Distance of the Jet Stream” i.e. the distance to the farther most point for an effective dusting.
For an effective dusting, the dusting should be done within the limits of these points to secure an effective deposit. Though the deposit ratio was under 20% using 1.0 for specific weight of dust, still the Duster must be aimed at the point of maximum deposit ratio.
In using the over Distance rating, since the adhereing or dusting quality is not changed considerably either by a change in jet speeds or in alteration of discharges of dust; and since the deposits are few in number, a greater dusting efficiency as well as an improvement in results can hardly be hoped for.
4) When the slower jet speed is used for dusting, the particles deposited are large in size. and few in number, but the area covered is wide. And as the distance increases, approaching the 3 metre limit, the jet speed becomes faster, the particles decrease in size and increase in number, the area covered becomes wider. However when an excessively fast jet speed is used for dusting, the number of particles becomes fewer and the covered area decreases; in contrast with the results obtained when a suitable jet speed is employed.
When there is danger of chemical poisoning or when the distance between the nozzle and the crops is great, a faster jet speed must be used, by raising the revolutions of the blower, in this way crushing the particles of dust into smaller sizes.
As the distance between the nozzle and the crops becomes shorter, a lower revolution may be used in the blower, i.e. a slower jet speed, of course with in the prescribed range so that the size of the dust particles does not become excessively large. Consequently a wider area can