To justification of parameters of ultra-low-volume spraying with pneumatic slot sprayers

. Intensive potato production technology provides for improving the process of planting tubers with a potato planter with simultaneous treatment with protective and stimulating liquids. To this end, the design of the device was developed, and the parameters of pneumatic slot sprayers recommended for treated tubers with working fluids were optimized.

At the same time, it is possible to use the inflow principle when the working fluid enters from a container located at a higher level relative to the jet nozzle ( Figure 1). The use of these methods allows to create a more economical scheme of the technological process of forming an air-drop jet that treats plants, since there is no need to use sufficiently complex technical means, in the form of pumping devices and controlling and regulating units A special feature of the pneumatic slot sprayer design is the creation of air jets by using slot nozzles of different designs.
For the formation of air jets in a jet generator, a pear-shaped nozzle or a "Vitoshinsky" type nozzle with different geometric parameters and operating in different modes are used, thanks to which the certain shape of the jet from the nozzle, the size of the spray torch, the size of drops on the surface of plants and the coating density of the treated objects are provided. The technological process of the sprayer with a pneumatic slot sprayer is shown in Figure 3.

Fig. 3.
Flow diagram of the spraying process:1 -tank; 2-tap; 3-equalizing tank; 4-distributor; 5supplying tube; 6-sprayer; 7-compressor; 8-receiver; 9-tap; 10-pressure regulator; 11-air collector; 12-compressed air supply tube To determine the parameters of a pneumatic slot sprayer, we use the Bernoulli equation, which is the equation of operation, that is, energy, where each of its items characterizes air energy, attributed to a unit of mass (J/kg) or specific energy.
The Bernoulli equation is the following: (1) where -specific energy of pressure; -specific kinematic energy; -energy losses under movement in a jet-forming slot sprayer; , -at turn energy losses occur at the transition of air jet from the inlet tube into the pear-shaped slot nozzle under the angle 0º, in our case under the angle 90º; -energy losses under the movement in a confuser; (2) where -pressure losses at turn defined from the equation: , This dependence is obtained by considering the solution of a right triangle ( Figure 4).
After the transformation, the regression equation takes the form: . (5) Pressure generated by the air jet: , where -air pressure in the inlet, in the nozzle; -air pressure in the outlet from the nozzle; p -air density плотность.
Substituting in the expression (7), according to the law of mass conservation: where Q -air consumption entering the jet nozzle, we get under pressure: .
Thus, the coefficient of resistance for the air flow when moving in the jet generator will be: , . ( The coefficient at the outlet of the flow into the atmosphere depends, respectively, on the dynamic pressure at the inlet to the nozzle and the narrow cross-section of the confuser: , where -air compaction.
Since, according to the design features , where -nozzle cross-sectional area at the inlet; а -inlet nozzle thickness; b -inlet nozzle width.
So, the resistance coefficient of the jet-forming nozzle: . (12) The general formula of the gas mass flow rate is the following: , where -the flow consumption coefficient for the case of the compressible liquid flow, where for air; -the compression ratio; -the velocity ratio which can be determined by the following dependence: , wherte -the Carliolis coefficient; -the resistance ratio.

Taking
; (12) for our case, we have , and the coefficient of the consumption is . Along with theoretical studies, experimental studies of air flow by pneumatic slot sprayers were carried out.
The sprayer was connected to a pneumatic line, into which air was supplied from the compressor, and a flow meter was installed before entering the slot nozzle to determine the air flow through the slot nozzle of the jet generator, which has a size of 0.3 mm × 5 mm at the outlet.
The pressure regulator sets the pressure from 0.05 to 0.3 MPa with an interval of 0.05 MPa. The flow meter showed the air flow rate in m 3 /h.
The results of the studies were entered in the table, analyzing the flow parameters using sprayers with different slot nozzle shapes (one nozzle had a pear-shaped shape, the second "Vitoshinsky" nozzle with a mleniscate conjugation of generators), Figure 6. The following results were obtained: the maximum flow rate of the "Vitoshinsky" nozzle was 1.0 l/min, and from the pear-shaped nozzle 0.700 l/min at air pressure in the system of 0.3 MPa, and respectively 0.500 and 0.400 l/min at pressure of 0.05 MPa ( Figure  6). This is due to the speed characteristics of nozzles. Higher values are typical for the "Vitoshinsky" nozzle, which determines the selection of the nozzle type for corresponding object processing tasks.
To reduce the energy consumption pneumatic slot sprayers, aggregated by tractors, and simplification of the design, it is recommended to use a compressor of a tractor to create air-drop jets of working fluids. The air consumption of the MTZ-80 type tractor compressors is 110-145 l/min.
It is possible to provide air from 6 to 12 pneumatic slot sprayers, depending on the shape of the air nozzles of the jet generators taking into account the losses of the working pressure created by the tractor's compressor when moving in pneumatic ducts and other elements of the sprayer.