Micron-size particle filtration with dual wire artificial electretfibers

The authors present the construction, operation, and test results of a new type of electrostatic filter of very low pressure drop at usual flow-through velocities while providing excellent filtration for micron-size particles. The filter is constructed in the form of a thick mesh of dual wire fibers, electrically energized at approximately 200 V DC, and reversing the polarity at a very low frequency in the order of 5 mHz. While, in general, mechanical filters trap the particles on the air incoming surface, with subsequent rapid “blinding,” the new filter collects the particles inside the mesh volume thus offering a considerably longer life     

A new type of ozone generator using Taylor cones on water surfaces

Ozone has been found to be effective in many forms of water treatment. As concerns about the safety of alternate methods of water treatment increase (in particular, chlorination), ozone, which is already extensively used in Europe, offers an effective option. This paper describes a new method of ozone generation particularly suited for use in water purification. Most current industrial ozone production is based on “silent” electrical discharges in a gap between concentric electrodes separated by a glass or ceramic dielectric barrier. The authors present experimental results obtained using a parallel-plate discharge geometry. The lower electrode consists of a grounded “pool” of still water separated by a discharge gap from an upper insulated planar electrode. When the electrode is energized by an AC high voltage, a multitude of “Taylor cones” forms on the water surface. The Taylor cones form and collapse randomly and continuously, depending on the electric field. The tips of the cones provide points for electrical discharge pulses which initiate ozone generation. This method generates ozone in close proximity to the water surface. Laboratory experiments show efficiencies for gaseous ozone production as high as 110 g/kWh     

Numerical simulation of the electric field distribution intribo-powder coating of conducting cylindrical objects

The successful implementation of powder coating technology requires detailed investigation of different factors, which can improve, or disturb, the process. The two most important are the air entrainment force and the electric deposition force acting on the powder particles. The authors present a numerical model for predicting the electric field distribution between a tribe gun and a cylindrical object. It is assumed, that the particle distribution is governed primarily by the air flow and that the only source of the electric field is the space charge of the tribocharged particles. Simplified models for the field lines and design configuration have been assumed and the electric field is determined by means of the charge simulation method     

Electrostatic beneficiation of gold ores

The authors present encouraging results obtained in separation of the Doyon gold ores when using the electrostatic inverted roof apparatus described by I.I. Inculer et al. (ibid., vol.IA-9, no.3, p.318-23, 1983). The electrification phenomena through combined tribo-electric and inductive charging were studied at various relative humidities. Contrary to expectations, the experimental work showed that the best separations are achieved at relatively high humidities of ~70% or higher. One of the main cost factors in electrostatic beneficiation of minerals is that of drying the material. The lesser drying required of this gold ore may be of considerable economic importance     

Cross Current Dual Aerodynamically Shaped Atomizer Electrostatic Spray Nozzle

Experimental results of a novel method and apparatus for achieving selective deposition on the inside surfaces of an enclosure are presented. An apparatus consisting of two aerodynamically shaped air shear nozzlesa generated a charged dual cloud comprising an insecticide aerosol cloud above and a water aerosol cloud below. Through self-expansion of the cloud by mutual repulsion of the charged particles and image attraction to the wall surfaces, a significantly selective deposition was achieved on the inside surfaces in the upper and lower halves of the enclosure.     

The UWO contribution to the NIST aerodynamic database for wind loads on low buildings: Part 3. Internal pressures

Wind tunnel tests of generic low buildings have been conducted at the University of Western Ontario for contribution to the National Institute on Standards and Technology (NIST) aerodynamic database. Part 1 provided the archiving format and basic aerodynamic data. In Part 2, the data of external pressures were compared with existing wind load provisions for low buildings. This paper, Part 3, deals with an investigation of wind-induced internal pressures of low-rise buildings with realistic dominant opening and leakage scenarios. Data from one building model with four different opening sizes were compared with numerical simulations. The existing theory, using the unsteady orifice discharge equation, works well for the building models used in this study, given the external pressures near the openings, irrespective of shifts of wind direction and upstream terrain. Numerical simulations can capture the temporal variations of the internal pressure fluctuations, as well as mean values.The internal pressure fluctuations for the building with leakage (nominally sealed building) are attenuated as they pass through the openings, while mean values are consistent with spatially averaged external pressures. Internal pressure resonance occurs for the dominant opening (3.3% open ratio) with building leakage. Effects of oblique wind angles on internal pressure dynamics are not significant, at least for the openings in the centre of wall, as is the case herein. Peak internal pressures occur for a wind direction normal to the wall with a dominant opening. Measured internal pressure coefficients are compared with current wind load provisions. Some peak values were found to exceed the recommended design values for the dominant windward wall opening cases.     

ELECTROSTATIC SEPARATION OF PLASTICS FOR RECYCLING

The authors describe some successful experiments for electrostatic separation of various two-component mixtures of plastic waste. Two methods of triboelectric charging of plastics are described. One consists of a fluidized bed system with a central feeding tube. The second is a novel form of a rotating tube charger. Separation takes place in an electrostatic separation tower equipped with a set of nine sampling bins at the bottom for collection of the components. Numerous experiments have shown the feasibility of obtaining extract contents in excess of 99%. The rotating tube charger is preferred over the fluidized bed because of its simplicity and energy savings. The process has recently been adapted to an industrial scale capable of processing 1000 kg/hour and is currently being used to separate post-industrial plastic waste.     

Production and Electrostatic Precipitation of Combustion Nuclei by an Electrified Propane?Air Flame

The results are given of an investigation into the production and electrostatic precipitation of combustion nuclei by an electrified propane-air flame. The apparatus consisted of a burner with a dc potential applied which was supported inside a grounded metal combustion chamber where the generation and removal of particles could be studied. A mathematical and experimental analysis of transient combustion nuclei concentrations inside the combustion chamber was carried out to evaluate the nuclei precipitation and production rates as a function of flame potentials and air flow rates. Two new theoretical equations containing production, precipitation, and flow parameters are derived to describe these transient concentrations. The constants of the equations were determined by experiment. These lead directly to the important parameters of nuclei production and precipitation rates, which are difficult to assess individually using previously known techniques. The experiments show that the concentration of combustion nuclei in the exhaust gas can be significantly decreased by the simple electrification of the flame. For combustion processes that generate aerosols, the method has the advantage of using the flame itself to affect the removal of the particles from the exhaust gases. Since combustion nuclei are receiving increased attention as air pollutants, this study could have important practical applications.     

Spectroscopic Analysis of a Corona Space Charge in a Cylindrical System with Air-Carbon Dioxide Medium

Positive corona glow discharge was studied in a system with cylindrical geometry in air and air-carbon dioxide mixtures at normal temperature and pressure (NTP). A spatially resolved spectroscopy technique was used in an attempt to explain the previously observed anomalous charging of particles traveling through the glow region. The results corroborate the existence of the previously reported anomaly. The apparatus developed for taking the spatially resolved spectra and the methods employed may be of interest in fundamental studies of corona discharge behavior in a practical electrostatic precipitator system.