A. Jaworek

Electrostatic micro- and nanoencapsulation and electroemulsification: a brief review.

Electrospraying is a method of liquid atomization that utilizes electrical forces to overcome the surface tension force. The droplets obtained by electrospraying are charged and for certain modes can be nanometers in size. The charge and size of the droplets can be controlled to some extent by liquid flow rate and the voltage applied to the nozzle. In recent years, electrospraying was tested as a ‘bottom-up’ technology for building nanostructures from elementary components obtained from fine droplets or submicron jets after solvent evaporation, such as thin films, nanoparticles or nanofibres. It was also tested as a tool for the production of micro- and nanoemulsions and micro- and nanocapsules. Research in this field was aimed at developing new drug delivery systems or medicine production and application of this technique in cosmetic and food industries. Electro-encapsulation was also used as a tool for nanocomposite materials fabrication. The paper reviews various methods based on electrospraying used for electro-emulsification and micro- and nanoencapsulation. Numerous scientific and engineering contributions in this field are presented in this paper.

Corona discharge from a multipoint electrode in flowing air

Abstract The results of the experimental investigations of the dc corona discharge in multipoint-to-plane geometry in air flowing transversely to the electric field with velocities up to 4 m/s are presented. The current-voltage characteristics of the discharge were determined and the self-generated current pulses were recorded. It was found that for positive polarity the time-averaged discharge current increases within the range of the gas velocity from 0 to 0.5 m/s, and then decreases again. The corona onset voltage and the breakdown voltage also increase by about 25% for a velocity 4 m/s, as compared to still air. In the examined range, as the gas velocity increases the pulsed current amplitude of the onset streamers decreases, but it increases in the breakdown streamers. No dependence on the chosen gas flow velocity was observed for the negative polarity discharge.

Efficiency of smoke removal by charged water droplets

The removal of fine aerosol particles such as dust or smoke by charged droplets was investigated experimentally. The droplets were sprayed by a rotary atomiser and simultaneously charged inductively. The cigarette smoke was used as a source of submicrometer dust. Smoke was charged in a specially designed corona-discharge charger. The suppression of particle concentration was determined after different time intervals of spraying of water. The electrical charging of droplets significantly increases the efficiency of removal of fine particles from air as compared to the uncharged aerosol. Further improvement was obtained after charging smoke particles. The cleaning process was up to four times better for charged smoke and droplets than that for uncharged species.

Back-corona generated plasma for decomposition of hydrocarbon gaseous contaminants

A back-corona discharge has been tested as a plasma source for decomposition of hydrocarbons . A back-corona discharge has hitherto not been applied for these purposes. The results of laboratory experiments show that the back-corona discharge can decomposite hydrocarbons, similarly to a dc or pulsed streamer corona discharge, with similar energy expense and conversion rate. However, the final concentration of after the same residence time of 60 s is lower for back-corona discharges. The back-corona also produces less CO and during the decomposition process.

Studies of the corona discharge in ehd spraying

Abstract The problems of formation and structure of the corona discharge from the surface of a conducting liquid sprayed electrohydrodynamically at the outlet of a capillary maintained at high potential are discussed. The corona discharge from the surface of conducting liquid is different from that produced by a metal electrode. This problem is also important in high voltage transmission lines, however it is hitherto not sufficiently recognized.

Numerical Simulation of Scavenging of Small Particles by Charged Droplets

The trajectories of fine aerosol particles in the vicinity of a free falling collector droplet and their deposition on it were investigated numerically by solving the equations of motion of the particle and the droplet in quiescent air. The droplet was assumed to be charged to one half of the Rayleigh limit. The Coulomb, image, Stokes, inertial, and gravitational forces acting upon the particle near the droplet were taken into consideration in the equations of motion. The equations of the droplet motion were also incorporated into the set of equations including the Coulomb and image forces on the droplet due to the particle charge. The flow field in the vicinity of the droplet was determined by numerical solution of the Navier-Stokes equations. The equations of particle motion were solved in threedimensional (3-D) space by the Runge-Kutta method of the fourth order. The collection efficiency of the particles on the droplet was determined by searching the limiting trajectory within the entire space. The results for particles charged to 10 elementary charges of the same and opposite polarity as the droplet, as well as the electrically neutral ones, were compared. The assumption on the charge of the particle was rather arbitrary. It was assumed that particles are not intentionally charged but only possess a charge generated by tribocharging due to random contacts and were independent of the particle size. Charging the collector causes the Coulomb forces between these 2 species to improve particle deposition on the droplet and in this way the aerosol is removed from the gas. For the aerosol particles charged to the same polarity as the collector, the collection efficiency is still higher than for uncharged particles due to the action of the image forces. In this case, the collection efficiency increases for smaller droplets and for particles with increasing diameter.

Smoke precipitation by charged water aerosol

Abstract Experiments on the removal of smoke particles by charged droplets were carried out. The droplets were charged inductively during their spraying by a rotary atomizer. The electrical charging of droplets significantly increases the efficiency of removal of smoke particles from air as compared to the uncharged aerosol.

Trajectories of charged aerosol particles near a spherical collector

Abstract Deposition of charged aerosol particles on a spherical object was investigated experimentally and modeled numerically. The validity of the model was confirmed by a qualitative comparison of both results. Charging both the particle and the collector increases the collection efficiency manyfolds.

Electrospray Nanocoating of Microfibres.

The paper presents experimental results of electrospray deposition of nanopowder onto microfibers. The process is designed to form fibrous filters with an enhanced collection efficiency in the submicron range by covering the fabric with a catalytic material. Polyamide fibres were coated with Al2O3, ZnO, MgO, or TiO2 nanoparticles. The structures obtained were porous at the nanometer scale which increased the total surface area of the catalyst.

Deposition efficiency of dust particles on a single, falling and charged water droplet

A numerical algorithm for simulating dust particle deposition on a charged spherical collector is presented in this paper. Trajectories of the charged dust particles are traced in three-dimensional space by solving the Newton equation, taking into account inertial, air drag, gravitational and electrostatic forces. The collector (charged droplet) falls down freely and its trajectory is also determined. A laminar viscous model is assumed for the airflow in the vicinity of the collector and modeled using the finite-element method in two-dimensional cylindrical coordinates. The deposition efficiency is defined in terms of the volume of space, from which all particles are deposited on the collector. The calculation results for different Stokes, Coulomb, and Reynolds numbers are given.