ORO SRAUTO GREIČIO ĮTAKOS LAŠELIŲ NUNEŠIMUI VĖJO TUNELYJE TYRIMAI (Investigations of the Influence of Air Flow Speed on Droplets Drift in a Wind Tunnel)

Abstract

2020 metais VDU Žemės ūkio akademijoje Žemės ūkio mašinų technologinių procesų laboratorijoje esančiame vėjo tunelyje buvo tirtas trijų purkštukų lašelių dreifas. Buvo tirti du skirtingų gamintojų inžektoriniai purkštukai A ir B (jų: purškimo kampas – 120°, našumas – 1,82 l min^-1, purškimo slėgis – 4 bar) bei universalus (įprastinis) plokščiasrautis plyšinis purkštukas (purškimo kampas – 110°, našumas – 1,82 l min^-1, purškimo slėgis – 4 bar).

Atlikti tyrimai su įprastiniu plyšiniu universaliu purkštuku parodė, kad juo išpurkšto skysčio dreifas yra ženkliai (apie 2 kartus) didesnis nei išpurkšto su inžektoriniais purkštukais. Purškimai buvo atliekami keičiant oro srauto greitį nuo 2 m s^-1 iki 10 m s^-1, proporcingai didinant kas 2 m s^-1. Esant oro srauto greičiui (2 m s^-1) plyšiniu universaliu purkštuku buvo nunešta 20,8±0,9%, inžektoriniu A – 7,2±0,2%, o inžektoriniu B – 10,2±0,3% lašelių. Padidinus oro srauto greitį iki 10 m s^-1, plyšiniu universaliu purkštuku išpurkštų lašelių dreifas siekė 44,3±0,6%, inžektoriniu A – 27,2±0,6%, o inžektoriniu B – 27,9±0,2%. Oro srauto greičiui padidėjus nuo 2 m s^-1 iki 10 m s^-1 plyšinio universalaus purkštuko lašelių nunešimas padidėjo daugiau negu 2 kartus, o naudojant inžektorinius A ir B purkštukus, atitinkamai, beveik 3 ir 4 kartus.

Pesticides are applied to the surface of plants by agricultural sprayers, with spray nozzles which are placed in sprayer boom to spray liquid chemicals. At that moment, blowing side wind or frequent gusts of wind can blow poisonous droplets quite far away (30 m or more). Such droplet drift poses not only environmental problems but also economic ones. Drift reduction is attempted by various technical an technological means: selecting the optimal spraying speed and spraying time, choosing different nozzle types, changing pressure of spray liquid, using additives that change properties of the spray liquid, installing spray boom vibration absorbers or various technical measures to protect the flow of sprayed droplets from the influence of wind and etc.

In 2020 at the VMU Agricultural academy the Laboratory for Investigation Technological Processes of Agricultural Machinery using wind tunnel research has been carried by three different spray nozzles. It was sprayed using two air-injector nozzles A and B (spray angle – 120°, performance – 1.82 l min^-1 at pressure – 4 bar), and one universal (conventional) flat fan nozzle (spray angle – 110°, performance – 1.82 l min^-1 at pressure – 4 bar). The cross – section of wind tunnel increases from 0.9 × 0.9 m to 1 × 1 m, respectively, and its length reaches 5 m. The stand is equipped with axial air suction fan ML 1004 DT with a ten plastic blades which diameter is 1000 mm, and electric motor (power 15 kW, rated shaft speed 1465 rpm). The Delta VFD-C2000 voltage frequency converter is used to change the speed of the motor. Changing the speed of the motor and fan impeller also changes the air flow from 2 m s^-1 to 10 m s^-1 (increasing proportionally every 2 m s^-1). The spray liquid was supplied with a Pentair Hypro Shurflo Standard Table Spray 220 VAC. A nozzle was placed at a height of 50 cm above the surface of the liquid collection vessels. On both sides, in the longitudinal direction of the tunnel, the nozzle sprayed the liquid at 85 cm intervals, i.e. the area of the liquid droplets sprayed by the nozzle was 170 cm (when the air flow rate was 0 m s^-1). In this case the liquid carried further than 85 cm from the nozzle is considered as drift. The nozzle was placed to investigate the effect of side direction air flow on droplet drift – conditions were simulated when spraying in the field when the wind direction is making an angle of 90º with the direction of sprayer movement. 30 liters of liquid were sprayed during each experiment.

Studies have been performed with a conventional flat fan nozzle in such a way that the drift of the liquid sprayed with it is marked (about 2 times) more than that of the air-injector spray nozzles. At the air flow rate (2 m s^-1), 20.8±0.9% of the droplets were drifted by the conventional flat fan nozzle, 7.2±0.2% by the air-injector A and 10.2±0.3% by the air-injector B nozzles, respectively. After increasing the air flow velocity to 10 m s^-1, the drift of droplets sprayed with a conventional flat fan nozzle reached 44.3±0.6%, with an air-injector nozzle A – 27.2±0.6%, and with an air-injector nozzle B – 27.9±0.2%. The increase in airflow velocity from 2 m s^-1 to 10 m s^-1 from conventional flat fan nozzle droplet dr                 ift increased more than 2-fold, and with the use of air-injector A and B nozzles, almost 3- and 4-fold, respectively.