Uncharged Droplets Research Articles

Mitigation of fine hydrophobic liquid aerosols by polydispersed uncharged and charged water droplets

Mitigation of fine hydrophobic liquid aerosols by polydispersed uncharged and charged water droplets

Generalization of numerical simulation results on the electrical coalescence threshold for two conducting droplets based on non-dimensional parameters

Electrocoalescence, the physical process underlying the demulsification of a dielectric dispersion medium containing small conductive droplets (e.g., water), involves droplet merging at low electric fields and splashing at higher voltages. Understanding the physics of electrocoalescence is crucial for optimizing industrial electrocoalescers. However, mathematical modeling of these complex, multiphysics phenomena is challenging, and many published results are questionable. In this study, we utilized a previously developed reliable model for computing the threshold between electrical coalescence and non-coalescence. We investigate the applicability of dimensionless parameters, such as the Ohnesorge number and Weber electric number, to describe the coalescence threshold for uncharged droplets of equal size. Using COMSOL Multiphysics software, we analyze the dependency of the threshold electric field strength on water droplet radius and establish an equivalent dimensionless relationship. Our findings reveal that a universal Weber number quite accurately describes the threshold over a wide range of droplet radii, regardless of changes in liquid viscosity and inter-electrode gap. Direct mathematical simulations using up-to-date numerical models enable us to determine non-dimensional parameter values corresponding to the threshold electric field strength, providing generalizable results.

Constrained dynamics of DNA oligonucleotides in phase-separated droplets

Understanding the dynamics of biomolecules in complex environments is crucial for elucidating the effect of condensed and heterogeneous environments on their functional properties. A relevant environment—and one that can also be mimicked easily in vitro—is that of phase-separated droplets. While phase-separated droplet systems have been shown to compartmentalize a wide range of functional biomolecules, the effects of internal structuration of droplets on the dynamics and mobility of internalized molecules remain poorly understood. Here, we use fluorescence correlation spectroscopy to measure the dynamics of short oligonucleotides encapsulated within two representative kinds of uncharged and charged phase-separated droplets. We find that the internal structuration controls the oligonucleotide dynamics in these droplets, revealed by measuring physical parameters at high spatiotemporal resolution. By varying oligonucleotide length and salt concentrations (and thereby charge screening), we found that the dynamics are significantly affected in the noncharged droplets compared to the charged system. Our work lays the foundation for unraveling and quantifying the physical parameters governing biomolecular transport in the condensed environment.

Studies on Operational and Plant Parameters Affecting the Deposition of Charged and Uncharged Spray Droplets on Cabbage Plant Canopy

The existing method of pesticide application has resulted in wastage of chemicals and environmental pollution. Electrostatic spray charging system for impregnation of charge on spray droplets and its subsequent transfer to the precise plant target can mitigate the problems in conventional spraying. The operational parameters of spraying system and plant characteristics play an important role in deposition of spray droplets on plant canopy. In view of that, an experimental electrostatically spray charging system was developed to assess the deposition on plant surface. At electrode voltage (4kV), flow rate (250 ml/min) deposition was maximum for forward speed (1.0 km/h) and height of application (0.55 m) at charge to mass ratio of 1.53 mC/kg.

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 10 000 r/min, the spray pressure was 0.3 MPa, the fan rotation speed was 14 000 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/cm2 on the upper layer, 345.1 particles/cm2 on the middle layer, and 322.5 particles/cm2 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. Keywords: UAV spraying, droplet drift, centrifugal sprayer, air-assisted spraying, electrostatic spraying DOI: 10.25165/j.ijabe.20221505.6891 Citation: Hu H M, Kaizu Y, Huang J J, Furuhashi K, Zhang H D, Xiao X, et al. Design and performance test of a novel UAV air-assisted electrostatic centrifugal spraying system. Int J Agric & Biol Eng, 2022; 15(5): 34–40.

Quantitative analysis of droplet deposition produced by an electrostatic sprayer on a classroom table by using fluorescent tracer

Due to the ongoing COVID-19 pandemic situation, measures to mitigate the risk of transmission of the SARS-CoV-2 virus in an indoor setting are urgently needed. Among the various types of disinfectant methods, electrostatic spraying is often applied to decontamination in public places. For quantitatively characterizing electrostatic spraying, we developed the novel evaluation method by using a fluorescent tracer. By applying this method, we performed three different experiment cases (static test on a table, static test on a cylinder, and dynamic test on a table) to figure out its unique characteristics (Coulombic fission and wraparound effect) and measure its performance in various aspects. To be specific, bimodal distribution with peak sizes of ~10 and ~100 μm was found due to Coulombic fission. Otherwise, a unimodal distribution with a peak size of ~100 μm occurred for the uncharged droplets. As a result, the effective contact area increased by 40–80 % due to small progeny droplets. The wraparound effect was examined on two different cylinders: copper (Cu) and polyvinyl chloride (PVC) pipe. When the target surface was not charged (Cu 0 kV and PVC 0 kV), the average normalized concentrations on the backside of the cylinder (θ = 180°) increased by around 67 % for charged droplets. Meanwhile, when the target surface was highly charged (PVC –19 kV), the average normalized concentrations at θ = 180° were increased more than two times for charged droplets.

Nanometre-sized droplets from a gas dynamic virtual nozzle

This paper reports on improved techniques to create and characterize nanometre-sized droplets from dilute aqueous solutions by using a gas dynamic virtual nozzle (GDVN). It describes a method to measure the size distribution of uncharged droplets, using an environmental scanning electron microscope, and provides theoretical models for the droplet sizes created. The results show that droplet sizes can be tuned by adjusting the gas and liquid flow rates in the GDVN, and at the lowest liquid flow rates, the size of the water droplets peaks at about 120 nm. This droplet size is similar to droplet sizes produced by electrospray ionization but requires neither electrolytes nor charging of the solution. The results presented here identify a new operational regime for GDVNs and show that predictable droplet sizes, comparable to those obtained by electrospray ionization, can be produced by purely mechanical means in GDVNs.

Accelerated tert-butyloxycarbonyl deprotection of amines in microdroplets produced by a pneumatic spray

Protection and deprotection of organic compounds in multistep reactions using functional groups such as tert-butoxycarbonyl (Boc), is widely performed in synthetic organic chemistry. Reaction rate acceleration studies in spray-based ionization methods (electrosonic spray, paper spray, nanospray) have become increasingly common. Here, we demonstrate reaction rate acceleration of Boc deprotection using easy ambient sonic-spray ionization (EASI), a pneumatic technique which does not involve an applied voltage, in a teaching laboratory setting. The goal of this laboratory exercise was to explore acceleration in a previously unexplored spray-based reaction, while emphasizing in a pedagogic setting the importance of protecting groups for multistep synthesis. Rate acceleration factors of more than an order of magnitude were observed in the uncharged micron-sized droplets generated by EASI. The effect of reaction conditions on reaction acceleration was examined including changes in the type of acid, reagent concentration ratios and syringe pump flow rates. Student knowledge was assessed by pre-laboratory assignments, post-laboratory reports and oral interviews.

Can Accelerated Reactions in Droplets Guide Chemistry at Scale?

Mass spectrometry (MS) is used to monitor chemical reactions in droplets. In almost all cases, such reactions are accelerated relative to the corresponding reactions in bulk, even after correction for concentration effects, and they serve to predict the likely success of scaled‐up reactions performed in microfluidic systems. The particular chemical targets used in these test studies are diazepam, atropine and diphenhydramine. In addition to a yes/no prediction of whether scaled‐up reaction is possible, in some cases valuable information was obtained that helped in optimization of reaction conditions, minimization of by‐products, and choice of catalyst. In a variant on the spray‐based charged droplet experiment, the Leidenfrost effect was used to generate larger, uncharged droplets and the same reactions were studied in this medium. These reactions were also accelerated but to smaller extents than in microdroplets, and they gave results that correspond even more closely to microfluidics data. The fact that MS was also used for online reaction monitoring in the microfluidic systems further enhances the potential role of MS in exploratory organic synthesis.

Parameterization of aerosol scavenging due to atmospheric ionization

AbstractA new approach to parameterizing the modulation of aerosol scavenging by electric charges on particles and droplets gives improved accuracy and is applied over an extended range of droplet and particle radii relevant to cloud microphysical processes. The base level scavenging rates for small particles are dominated by diffusion and for large particles by intercept, weight, and flow effects. For charged particles encountering uncharged droplets, in all cases there is an increase in the scavenging rates, due to the image force. For droplets with charges of opposite sign to those of the particle charge, the rates are further increased, due to the Coulomb force, whereas for droplet with charges of the same sign, the rates are decreased. Increases above the base level (electroscavenging) predominate for the larger particles and occur in the interior of clouds even when no space charge (net charge) is present. Decreases below the base level (electroantiscavenging) occur for same‐sign charges with smaller particles. The rates for uncharged droplets are parameterized, and the effect of charges on the droplets then parameterized as a departure from those rates. The results are convenient for incorporation in models of clouds which include detailed microphysics, to model the electrically induced reductions and increases in cloud condensation nucleus and ice forming nucleus concentrations and size distributions and contact ice nucleation rates that affect coagulation and precipitation and cloud albedo. Implications for effects on weather and climate, due both to externally and internally induced variability in atmospheric ionization, are outlined.

Zero Volt Paper Spray Ionization and Its Mechanism.

The analytical performance and a suggested mechanism for zero volt paper spray using chromatography paper are presented. A spray is generated by the action of the pneumatic force of the mass spectrometer (MS) vacuum at the inlet. Positive and negative ion signals are observed, and comparisons are made with standard kV paper spray (PS) ionization and nanoelectrospray ionization (nESI). While the range of analytes to which zero volt PS is applicable is very similar to kV PS and nESI, differences in the mass spectra of mixtures are interpreted in terms of the more significant effects of analyte surface activity in the gentler zero volt experiment than in the other methods due to the significantly lower charge. The signal intensity of zero volt PS is also lower than in the other methods. A Monte Carlo simulation based on statistical fluctuation of positive and negative ions in solution has been implemented to explain the production of ions from initially uncharged droplets. Uncharged droplets first break up due to aerodynamics forces until they are in the 2-4 μm size range and then undergo Coulombic fission. A model involving statistical charge fluctuations in both phases predicts detection limits similar to those observed experimentally and explains the effects of binary mixture components on relative ionization efficiencies. The proposed mechanism may also play a role in ionization by other voltage-free methods.

Design and Performance of Inductive Electrostatic Sprayer

In order to improve spraying results, an inductive electrostatic sprayer was designed. The performance of the sprayer was then tested. The test result shows that the charge-to-mass ratio can reach 0.951 mc/Kg when electrostatic voltage is 20 KV and working pressure is 0.25 to 0.4 MPa. The particle size distribution of charged droplets are more concentrated than that of uncharged droplets, the axial velocity of charged droplets is faster than that of uncharged droplets, and the velocity distribution uniformity is also improved. The average deposition rate under charging conditions is 14% higher than that in uncharged conditions. Moreover, the deposit rate of the back of the leaf is evident.

Non‐conforming finite elements for axisymmetric charged droplet deformation dynamics and Coulomb explosions

SUMMARYThe deformations of both electrically charged and uncharged incompressible axisymmetric Newtonian viscous liquid droplets acting under the effects of surface tension (but not gravity) are studied using a non‐conforming, discontinuous Galerkin finite element procedure with moving meshes.The full Navier–Stokes equations are discretized and solved in an Eulerian manner with a simple predictor–corrector Lagrangian updating of the free boundary location coincident with the droplet surface at each solution iteration.By using linear Crouzeix–Raviart basis functions for the velocity and piecewise constant pressures, results are presented both for the simple (oscillatory) relaxation of elongated electrically charged/uncharged droplets to a sphere and for the deformation to steady state/Coulomb explosions of initially slightly oblate/prolate spheroidal droplets charged beyond/to the Rayleigh limit. Copyright © 2012 John Wiley & Sons, Ltd.

Electrospray droplet sources for thin film deposition

Electrospraying utilises electrical forces for liquid atomisation. Droplets obtained by this method are highly charged to a fraction of the Rayleigh limit. The advantage of electrospraying is that the droplets can be extremely small, down to the order of 10’s nanometres, and the charge and size of the droplets can be controlled to some extent be electrical means. Motion of the charged droplets can be controlled by electric field. The deposition efficiency of the charged spray on an object is usually higher than that for uncharged droplets. Electrospray is, or potentially can be applied to many processes in industry and in scientific instruments manufacturing. The paper reviews electrospray methods and devices, including liquid metal ion sources, used for thin film deposition. This technique is applied in modern material technologies, microelectronics, micromachining, and nanotechnology.

Pseudo‐transient processes in the numerical simulation of a water droplet in an electric field

AbstractWe solve the coupled problem of the shape of a droplet in an electric field. An artificial pseudo‐transient process leads to an iteration over the decoupled electric and mechanical sub‐problems. We discuss the numerical behaviour of the iteration and of both sub‐problems and we present new 3d results of deformed droplets. Further, the motion of uncharged droplets driven by a non‐vanishing total ponderomotoric force is approximated in a new way for a model of a realistically shaped insulator. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Utilisation of crown ethers in microemulsion electrokinetic chromatography for the separation of inorganic cations

A new method to influence the separation selectivity of inorganic cations in capillary electrophoresis is presented. This method combines the use of certain crown ethers to form complexes with a specific cation (changing its ionic radius/charge ratio and thereby its electrophoretic mobility) with partitioning of the crown ether/analyte complex between an aqueous phase and a pseudo-stationary phase, such as the oil droplet of a microemulsion. Several microemulsions, including uncharged oil droplets and oil droplets with different degrees of surface charge were tested to evaluate their ability to improve the separation of the selected analytes.

Systematic investigations of different capillary electrophoretic techniques for separation of methylquinolines

AbstractThe migration behaviour of isoquinoline, quinoline, and methyl derivatives of quinoline in different capillary electrophoretic modes has been systematically investigated. Optimised separation conditions were established by varying the key parameters (solvent, pH, temperature, surfactant concentration, core phase) for aqueous and non‐aqueous capillary zone electrophoresis (NACE), micellar electrokinetic chromatography (MEKC) with anionic or non‐ionic micelles (SDS, Brij 35), and microemulsion electrokinetic chromatography (MEEKC) with charged or uncharged microemulsion droplets. A separation of all quinolines could be achieved by MEEKC with charged droplets, by MEKC or by formamide‐based NACE. Comparing the separations with respect to separation selectivity, substantial changes in migration order could be observed between the different techniques. Regarding separation efficiency, the number of theoretical plates and limits of detection (LOD) have been compared. The best LODs were achieved using SDS as surfactant in MEKC, followed by MEEKC.

Aerodynamic effect on charged droplet train ejected from a 26 μm nozzle

The fundamental characteristics of motion of a droplet ejected from a nozzle with 26 /spl mu/m aperture have been carefully investigated. Droplets ejected are periodically charged and deflected by the deflection field. The behavior of charged and uncharged droplets in air is examined by a CCD camera, and from its images velocities and deflection distances are calculated. The results indicate that droplet train is decelerated linearly by the aerodynamic resistance, which is much smaller than the Stokes resistance for a single particle. It was found that there are two types of coalescence: one is due to Coulomb force between a charged and an uncharged droplet and the other is due to purely aerodynamic effect which is caused by the vacancy of the train. Deflected charge droplets showed complicated motion because of Coulomb and aerodynamic effects when they are proceeding in air. A factor to the Stokes resistance is shown to be between 0.5 and 0.6. Thus, the aerodynamic resistance for the train of droplets is much smaller than for the single particle.

Electrical Deflection of Polar Liquid Streams: A Misunderstood Demonstration

The electrical deflection of polar liquid streams, commonly used as a textbook illustration of the behavior of polar molecules, is shown to be due to the formation of electrically charged droplets in the polar liquid stream, induced by a nearby charged object, rather than any force exerted on molecular dipoles. Streams of water and polar organic liquids could be deflected in a uniform electric field, which could not have exerted any force on dipolar species. Water and polar organic liquid streams formed within a grounded, electrically screened region could not be deflected after exiting the screened region, demonstrating that there is no electrical force on uncharged polar liquid droplets. Induced charging was observed also in insulating polar organic liquids and is suggested to be due to ionic impurities. A weak deflection of a stream of a nonpolar liquid (tetrachloroethylene) was also observed, indicating that such impurity effects are quite general, even in nonpolar liquids.

Size distribution of the charged droplets in an axisymmetric shower

The radial distribution of the water volume and the droplet size in a charged droplets shower was estimated from the volume and size distribution of the water droplets obtained by a line-of-sight measurements with a laser particle size analyzer. The transformation method from the apparent distribution into the radial distribution was demonstrated under the assumption of an axisymmetric spray. The charged droplets shower was sprayed from an airless nozzle equipped with an induction charging electrode. The charged droplets shower spreads more widely due to electrostatic repulsion force. The difference between the radial distribution in the diameter of the charged droplets shower and that of the uncharged droplets was confirmed. The mean diameter of the charged droplets in the shower was almost constant, while that of the uncharged droplets increases with the radii.