Dynamic characteristics of charged droplets in an electrostatic spraying process with twin capillaries

The experimental and simulated investigations on electrostatic spraying with twin capillaries are carried out. The starting electric voltage required for the cone-jet and the deposition characteristics of the droplets are measured.The whole spraying process, which includes jet and droplet motions, is simulated and the simulated results on the motions of jet and droplet are basically consistent with the experiments. According to the simulated results,the contributions of various electric forces to droplet movement are quantitatively analyzed and the droplet dynamic characteristics, especially the interaction mechanism between two sprays, are revealed. The test results on the droplet deposition characteristics partially support the simulated results on the droplet motion. The present work is useful for a better understanding on the interaction between sprays in double or multi-capillary system.

Spray Characteristics of Non-Circular Nozzle in Air-Assisted Injection System

In order to analyze the spray characteristics of non-circular nozzle holes based on the air-assisted spray system, the spray characteristics of circular and non-circular nozzles were studied under the pressure of 0.2-0.6 MPa and the spray volume of 1000-5000 mL/h. Elliptical nozzle and triangular nozzle are classified as non-circular geometries. The spray cone angle was measured by processing the spray image captured by a CCD camera. The measured spray cone angles of the circular nozzles were analyzed, and the axis switching phenomenon of minor plane of elliptical nozzle was found during the test. Among the three shapes of nozzles, the elliptical nozzle had the largest spray cone angle, and the triangular nozzle had the smallest. The velocity field obtained depended on the PIV system. The results show that for axial velocity, elliptical orifice spray has greater kinetic energy and smaller droplet size under the same working parameters. Compared with the circular and elliptical nozzles, triangular orifice reached maximum spray velocity the fastest, but its velocity decay was the fastest. For radial velocity, away from the axis, the spray velocity of the elliptical orifice was less affected by the injection parameters, and the velocity was less than that of circular orifice and triangle orifice. Increasing air pressure will weaken radial propagation. The increase of liquid spraying rate had no remarkable effect on the increase of spraying rate. The results of particle size analysis show that the particle size of the non-circular orifice is reduced compared with that of the circular orifice, which promotes the breakup of droplets to a certain extent and enhances the atomization effect.

Experimental Study and Numerical Simulation on Spray Characteristics of New-Type Air-Assist Nozzle

To investigate the spray characteristics of a new-type air-assist nozzle,three-dimensional laser phase Dopper analyzer( PDA) was used to measure the spray parameters. The external flow fields of the nozzle were simulated by means of computational fluid dynamics( CFD). The distributions of the diameter and the axial velocity for the droplets were analyzed respectively. The results indicate that,the mean diameter of the droplets fluctuates along the center axis. The distance between the measurement point and the nozzle increases,the axial velocity of the droplets decreases. The further the measurement point from the center axis is,the smaller the axial velocity of the droplets is. With the increase of the nozzle pressure drop,the axial velocity of the droplets improves while the mean diameter of the droplets is reduced,and the distribution uniformity of the droplets is better for the diameter. The simulation result agrees well with the experimental data. The average deviation ranges from 3.9% to 7.7%.

Spray Characteristics of Air-Assisted Injector Under Different Ambient Pressures

Spray atomization of liquid fuel plays an important role in droplet evaporation,combustible mixture formation and subsequent combustion process.Well-atomized liquid spray contributes to high fuel efficiency and low pollutant emissions.Gasoline direct injection(GDI)has been recognized as one of the most effective ways to improve fuel atomization.As a special direct injection method,the air-assisted direct injection utilizes high-speed flow of high-pressure air at the injector exit to assist liquid fuel injection and promote spray atomization at a low injection pressure.This injection method has excellent application potential and advantages for high performance and lightweight engines.In this study,the hollow cone spray emerging from an air-assisted injector was studied in a constant volume chamber with the ambient pressures ranging from 5 kPa to 300 kPa.External macro characteristics of spray were obtained using high speed backlit imaging.Phase Doppler particle analyzer(PDPA)was utilized to study the microcosmic spray characteristics.The results show that under the flash boiling condition,the spray will generate a strong flash boiling point which causes the cone shape spray to expand both inwards and outwards.The axisymmetric inward expansion would converge together and form a lathy aggregation area below the nozzle and the axisymmetric outward expansion greatly increases the spray width.The sauter mean diameter(SMD)of flash boiling condition can be reduced to 5μm compared to the level close to 10μm in the non-flash boiling condition.

Design and performance test of a novel UAV air-assisted electrostatic centrifugal spraying system

In order to improve the deposition and uniformity of the pesticide sprayed by the agricultural spraying drone,this study designed a novel spraying system,combining air-assisted spraying system with electrostatic technology.First,an air-assisted electrostatic centrifugal spray system was designed for agricultural spraying drones,including a shell,a diversion shell,and an electrostatic ring.Then,experiments were conducted to optimize the setting of the main parameters that affect the charge-to-mass ratio,and outdoor spraying experiments were carried out on the spraying effect of the air-assisted electrostatic centrifugal spray system.The results showed the optimum parameters were that the centrifugal rotation speed was 10000 r/min,the spray pressure was 0.3 MPa,the fan rotation speed was 14000 r/min,and the electrostatic generator voltage was 9 kV;The optimum charge-to-mass ratio of the spray system was 2.59 mC/kg.The average deposition density of droplets on the collecting platform was 366.1 particles/cm^(2) on the upper layer,345.1 particles/cm^(2) on the middle layer,and 322.5 particles/cm^(2) on the lower layer.Compared to the results of uncharged droplets on the upper,middle,and lower layers,the average deposition density was increased by 34.9%,30.4%,and 30.2%,respectively,and the uniformity of the distribution of the droplets at different collection points was better.

Precision orchard sprayer based on automatically infrared target detecting and electrostatic spraying techniques

There is an urgent need for new chemical application techniques and sprayers in Chinese orchard spraying.A new tractor-mounted automatic target detecting electrostatics,and air-assisted orchard sprayer was designed and developed to meet the demand of chemical pest control in orchards.This sprayer light weighted,highly efficient,reduces pesticide use and is friendly to the environment.The techniques of automatic target detecting,electrostatics,and air-assisted spraying were combined in this system.The electrostatically charged droplets are projected toward the target by the assistance of an air stream that increases the droplets penetration within canopy.Experimental results show that the new automatic target detecting orchard sprayer with an infrared sensor can save more than 50%to 75%of pesticides,improve the utilization rate(over 55%),control efficiency,and significantly reduce environmental pollution caused by the pesticide application.At the same time the key technological problems related to air-assisted low volume and electrostatic spraying were solved.

Development of a charge transfer space loop to improve adsorption performance in aerial electrostatic spray

In order to solve the problem of insufficient adsorption rate of droplets on the target back via aerial electrostatic spray,this study proposed a high-voltage electrostatic generator to charge the liquids in two isolated water tanks with positive and negative charges respectively.A charge transfer loop was developed in space between the aerial electrostatic spray system and the ground.This method greatly enhanced the adsorption performance under outdoor conditions that 16.7%droplets density increased on the target front,a nearly fourfold destiny increased on the target back compared with the conventional UAV spray system.The target back-to-front ratio of droplet density was improved from 6.1%to 25.7%,which validated the satisfactory performance of the developed system.

Hydrogen Gas Sensors Based on Electrostatically Spray Deposited Nickel Oxide Thin Film Structures

A simple, low-cost, and home-built electrostatic spray deposition （ESD） system with the stable cone-jet mode was used to deposit nickel oxide （NiO） thin films on glass substrates kept at temperature of 400 ℃ as the primary precursor solution of 0.1 M concentration hydrated nickel chloride was dissolved in isopropyl alcohol. Electrical measurements showed that these films were of n-type conductivity while their resistance response to hydrogen flow in air ambient was varied by 2.81% with the rise and recovery time of 48 s and 40 s, respectively.

Open channel-based microchip electrophoresis interfaced with mass spectrometry via electrostatic spray ionization

The coupling between open channel-based microchip electrophoresis and mass spectrometry via electrostatic spray ionization is proposed for in situ detection of fractionated analytes. Electrophoretic separation is performed in an open channel fabricated in a plastic substrate. The solvent of background electrolyte is evaporated from the open channel because of Joule heating during electrophoresis, leaving the dried electrophoretic bands to be directly analyzed by mass spectrometry via scanning electrostatic spray ionization. Proof-of-concept results are obtained with fluorescent dyes and antibiotics as the test samples, demonstrating an efficient on-chip detection platform based on the electrophoresis and electrostatic spray ionization mass spectrometry.

Quantification of particle separation using electrostatically charged spray mist in a dust chamber

In order to improve the efficiency of reducing fine dust emissions from diffuse sources,the commonly used water mist can be electrostatically charged.Thus,the attraction between particles and droplets increases due to electrostatic field forces.In the experimental investigations carried out,an electrostatic two-fluid nozzle was used to generate a charged spray mist according to the principle of charging by induction.In a chamber,dispersed dust was precipitated with the spray mist,while detecting the laser light attenuation.By means of comparative measurements it could be shown that faster sedimentation and separation takes place through electrostatic attraction.Parameter variations regarding the use of compressed air and water were investigated and the sedimentation time of the particle-droplet mixture in the chamber was shown.A size distribution was then calculated from the laser light attenuation,which shows that the proportion of small particles decreases with spray application.Furthermore,the influence of the polarity of droplets and solid particles on the reduction measure was determined.

Deposition Effects of Electrostatic and NonElectrostatic Aerial Spray

In this study,we compared the aerial electrostatic spray with non-electrostatic spray by helicopter R44 and fixed-wing aircraft Y5B equipped with an own-made aerial electrostatic spraying system.The results showed that the spray deposits on targets and leaves of tree crowns were notable enhanced comparing with the non-electrostatic and conventional aerial spray.The spray deposits were fine,uniform and the densities were 1.0-1.75 times higher than the non-electrostatic spray.Deposit rate of the electrostatic spray on the backs of leaves by helicopter R44 was 2.15 times of the non-electrostatic, and 3.31 times of the conventional aerial spray.The deposit rate of the electrostatic spray on the backs of leaves by the Y5B was 2.38 times of the non-electrostatic,and 3.44 times of the conventional aerial spray.

Effects of leaf response velocity on spray deposition with an air-assisted orchard sprayer

The interaction between leaves and airflow has a direct effect on the droplet deposition characteristics of the leaf canopy.In order to make clear the mechanism of droplet deposition in terms of the interaction between the droplets and leaves from the point of the leaf aerodynamic response velocity,the leaf movement under different airflow velocities and the influence of the leaf aerodynamic response on droplet coverage ratio were investigated.The effect of the aerodynamic response velocity of a leaf on the droplet deposition of the leaf surface was investigated.The aerodynamic characteristics of the leaf were analyzed theoretically.Boundary layer theory from fluid mechanics was used to develop a model of the leaf aerodynamic response velocity to nonperiodic excitations based on a convolution integral method.Target leaf aerodynamic velocities were detected using a high-speed camera,and the results indicated that the modeled leaf aerodynamic response velocity matched the measured values.At given conditions of spray liquid and leaf surface texture,the spray test showed that the droplet coverage ratio was influenced by the leaf aerodynamic response velocity,the droplet coverage ratio increased and then decreased with the leaf response velocity.Through analyze four droplets deposition state,the highest droplet deposition ratio and best deposition state on the leaf surface occur when the leaf aerodynamic response velocity was less than 0.14 m/s.According to the analysis of droplet deposition states,the uniformity of the droplet size and quantity distribution of droplets on the leaf surface related to the leaf aerodynamic response velocity.The results can provide a basis for the design and optimization of orchard air sprayers.

Preparation of polypyrrole-coated CuFe_2O_4 and their improved electrochemical performance as lithium-ion anodes

CuFe2O4 network,prepared via the electrostatic spray deposition technique,with high reversible capacity and long cycle lifetime for lithium ion battery anode material has been reported.The reversible capacity can be further enhanced by coating high electronic conductive polypyrrole（PPy）.At the current density of 100mA·g-1.Li/CuFe2O4 electrode delivers a reversible capacity of 842.9 mAh·g-1 while the reversible capacity of Li/PPy-coated CuFe2O4 electrode increases up to 1106.7 mAh-g’.A high capacity of 640.7 mAhg＂1 for the Li/PPy-coated CuFe2O4electrode is maintained in contrast of 398.9 mAh·g-1 for CuFe2O4 electrode after 60 cycles,which demonstrates good electrochemical performance of the composite due to the increase of electronic conductivity.The electrochemical impedance spectroscopy（EIS） further reveals that the Li/PPy-coated CuFe2O4 electrode has a lower charge transfer resistance than the Li/CuFe2C〉4 electrode.

Development and experiments of low frequency ultrasonic electrostatic atomizing nozzle with double resonators

Fine droplets with high adhesion can greatly improve the efficiency of atomization culture.Therefore,the development of a spray nozzle that can produce fine fog droplets with high adhesion is of great significance for aeroponics.Compared to piezoelectric ultrasonic atomizer,Hartmann resonator low-frequency ultrasonic electrostatic atomizer has the advantages of large atomization volume and constant liquid chemical structure,but the droplet size is larger.High-speed gas can generate low-frequency ultrasonic vibration sound waves in Hartmann resonator.The frequency and intensity of sound waves determine the atomization performance of supersonic atomizer nozzle.However,very few research literatures can be found on how the structure and operating parameters of Hartmann resonator affect the atomization performance.In order to improve the atomization performance of ultrasonic atomizer,a two-stage Hartmann resonator low-frequency ultrasonic electrostatic atomizer was designed.The shrinkage-type Laval tube was designed by fluid mechanics theory,and the design results were verified by fluent software.The virtual orthogonal test method was used to optimize the structure parameters of two-stage resonator and spray test was carried out.The results showed that when the included angle between the two stage resonators was 80°,the diameter was 4.86 mm,the tube length ratio was 1.0 and the gas pressure was 0.5 MPa,the droplet size could reach 22.05μm.Additionally,compared with the traditional Hartmann cavity with 90°included angle,the droplet size was decreased by 63%.The annular electrode was used as the charging electrode,and Comsol Multiphysics software was used to simulate and calculate the deformation and crushing process of electrostatic droplets and the influence of different voltage,surface tension and droplet diameter on the droplet deformation rate.The results showed that:(1)the optimum charge range of the electrode ring was within 20 mm of the axial distance along the electrode ring.(2)The higher the voltage U,the smaller the surface tensionσ;the larger the droplet diameter d and the larger the droplet deformation rate.(3)The experimental results showed that the droplet size was inversely proportional to the gas pressure P0,electrostatic voltage U and spray height h.When the gas pressure and electrostatic voltage were 0.4 MPa and 18 kV,0.4 MPa and 18 kV,respectively,the droplet sizes were 7.8μm and 43.9μm respectively,the droplet size difference between the two conditions was 82.2%.