Unipolar Ions Research Articles

Electric fields in stationary ion flows in symmetric geometries.

A method is presented that yields exact closed-form solutions in curvilinear coordinates for the partial differential equations determining the electric field in a stationary flow of unipolar ions with constant mobility. The method is applied to the parabolic cylindrical, elliptic cylindrical, bipolar, parabolic, and spheroidal coordinates. The new solutions approach infinity roughly in the manner of the classical parallel-plate solution. They are expected to apply to analyses of non-self-sustained ion flows.

Aerosol Charger Using Sinusoidally Driven Ion Current from a Corona Discharge

Construction and testing of an aerosol charger capable of charging initially neutral 0.913–μm diameter plastic spheres to 200 elementary charge units in 20 ms is described. The charger utilizes a continuous corona discharge from fine wires located in cylindrical cavities in opposite walls of a rectangular aerosol flow channel of dimensions 1.00 × 5.56 × 2.54 cm. A 3000-Hz AC voltage with maximum amplitude of 10 kV is applied across the 1.00-cm channel gap to produce an ion current which reverses direction with the cycling of the electric field. Aerosol particles moving through the channel are impacted by unipolar ions from first one side and then the other. Lateral motion of charged particles is oscillatory at the frequency of the applied electric field. This serves to minimize loss of charged particles due to wall deposition. A method for calculating the acquired particle charge based on field charging theory is presented. Particle charge levels calculated are in satisfactory agreement with measured part...

The influence of the statistical nature of the charging parameters on the particle charge

The charging of aerosol particles by unipolar ions in a gaseous medium has been analyzed and described in different theories. The theoretical description of the experimental setup must keep abreast of the improvement of the theoretical description of the physical phenomenon. One of the basic charging parameters is the charging time T which is given by the particle velocity and the geometry of the charging region. Due to the flow profile in the charging region the charging time is not uniform for all particles. Therefore the charging time can be considered as a random variable. The consequences of this statistical approach are presented.

Performance of a Long-Term Unattended Station for Measuring DC Fields and Air Ions from an Operating HVDC Line

The authors describe the experience of the Bonneville Power Administration in building and operating a long-term, unattended station to measure electric fields and air ions from the Pacific NW/SW HVDC (northwest/southwest high-voltage direct current) Intertie. The major emphasis is on the performance of the unipolar ion counters, as these have been the most difficult type of instrument to incorporate in an outdoor measurement station. Based on this experience, if heat is properly applied to the ion counter and good procedures are used for regular calibration and maintenance of all the instrumentation, then electric field and air ion instrumentation can be operated unattended in an outdoor environment. >

Electrical Environment of the Uprated Pacific NW/SW HVDC Intertie

The authors summarize the results of a research effort to characterize the electrical environment of the Pacific NW/SW HVDC (northwest/southwest high voltage direct current) Intertie. Forty channels of data were collected simultaneously at 10 test locations, including electric field, ion current density, unipolar ion density, net space charge density, audible noise, radio noise, and important weather parameters. The significant results of the analysis of one year of data collection are that the fields and ions on the negative side of the line are 2-3 times higher than those on the positive side and that all air ion parameters increase with perpendicular wind speed up to 11 m/s at distances from 29 m to 610 m from the line. >

Unipolar A.C. field charging

We derive an expression for the total charging current of a sphere exposed to unipolar ions in an a.c. field. If the frequency of the field variation is larger than a certain limiting frequency the charging current becomes independent of the frequency itself. It is given by a unique expression which only depends on the relative charge on the particle. The a.c. case is compared with the classical d.c. case. It will be shown that the saturation charge is the same in both cases but the rate of charging is slower in the a.c. case.

A novel technique for drying soil samples

Abstract Evaporation rates and drying times of soil samples exposed to high fluxes of unipolar air ions of either polarity, produced by corona electrodes, were studied with a beta‐ray gauge. Ion‐treated soils dried more than three times faster than the control samples under the same laboratory conditions. An analysis of the experimental curves on Rideau clay showed evaporation rates of 2.96 x 10‐4and 8.84 x 10‐4g cm‐2min‐1for control and treated samples, respectively, when exposed to 4.39 x 1012negative air ions cm‐2s‐1. An objective criterion was defined for a state of soil dryness when the sample acquired a steady‐state value of transmission of beta particles with time. Electric wind caused by the ionic drag is proposed as the principal driving force for the enhancement of evaporation rates from soil samples used.

Impact of air ions on mass transfer from liquids

Evaporation rates and drying times of liquids exposed to relatively high fluxes of unipolar air ions of either sign, produced by corona electrodes, were studied with a beta-ray gauge apparatus. Liquids of constant volume, exposed to air ions, dried 1.72 to 4.80 times faster than the corresponding control liquids under the same laboratory conditions. An analysis of the time-transmission curves from the beta-ray gauge showed mass transfer rates of 1.90 × 10 −3 and 8.5 × 10 −3 g min −1 for control and treated (2.44 × 10 12 positive ions cm −2 s −1) water, respectively. Air ions were observed to cause circulatory and vibrational movements in the treated liquids. These movements contributed to the enhancement in the mass transfer rates from organic and inorganic liquids studied. Polarity of the molecules may also determine the rapidity at which a liquid will evaporate when exposed to a high flux of air ions.

Unipolar Diffusion Charging of Ultrafine Aerosols

Experimental data are reported for unipolar diffusion charging of NaCl and Ag aerosols in the 0.004- to 0.075-μm-diameter range. Monodisperse, uncharged particles were exposed to unipolar positive ions produced by a corona discharge. The nt product was varied between 3 × 106 and 1 × 107 (ions/cm3) (s), where n is the unipolar ion concentration and t is the charging time. The resulting aerosol charged fraction was measured by using a single-particle-counting condensation nucleus counter in conjunction with an electrostatic condenser. From the measured charged fraction and the known charging parameters, the combination coefficient between the neutral particles and the positive ions are obtained. Measurements are then compared with the available charging theories. It is found that the theory of Marlow and Brock best predicts charging rates in the ultrafine particle size range. Above 10 nm, the data approach the theory of Fuchs consistent with the experimental observation of Adachi et al. *Presented at Semina...

Continuum field-diffusion charging of particles possessing non-zero initial charge

Experiments were performed to determine the charging of continuum regime aerosols possessing non-zero initial charge. Highly monodisperse poystyrene aerosols of 0.31, 0.50, 0.76, and 1.09 μm diameter were pre-charged to various levels and then exposed to unipolar and bipolar ions in the presence of an external electric field. For a given bipolar conductivity ratio, charge was found to approach a single steady-state level, regardless of initial charge. For unipolar ions, charge either increased or, in the case of very high initial charge, remained constant. Predictions of charge based on continuum field-diffusion theory were found to show good agreement with experimental data, generally differing by no more than 10–20% with one major exception. This was for highly negative initial charge at small times, where theoretical predictions were significantly above measurements. It is not known if the differences are due to a fundamental limitation of the theory or are an experimental artifact.

棒対平板ギャップの単極性イオン流場における相似則

棒対平板ギャップの単極性イオン流場における相似則

Unipolar and bipolar diffusion charging of ultrafine aerosol particles

Unipolar and bipolar diffusion charging of monodisperse aerosol particles of 4–100 nm in diameter has been studied experimentally and theoretically. Particles are charged by unipolar or bipolar ions produced by α rays from Am-241. They are enlarged by condensation of DBP vapor on them using the particle size magnifier and the enlarged particles are admitted into an observation cell having parallel d.c. electrodes to distinguish charged particles from uncharged particles by TV camera. In the case of unipolar charging, the ratios of charged particles to total particles at various values of the ion concentration and charging time are found in quite good agreement with the solution of equations based on the Fuchs' formula for the combination probability of ion with particle and introducing ion properties reported in previous papers. From these results, the necessary conditions to bring uncharged particles to a desired charge distribution are clarified for various particle sizes. In the case of bipolar charging, the number ratios of charged particles to total particles in a steady-state are again found in quite good agreement with the solution of basic equations similar to those of unipolar charging using the Fuchs' theory for the combination probability and the same ion properties as those used for unipolar charging. The ratio of positively to negatively charged particles is found to be approximately 0.35:0.65, which is explained by the difference in physical properties between positive and negative ions.

Cost Evaluation of Control Measures for Indoor Radon Progeny

Based on assumed conditions within a typical U.S. home, annualized costs for reducing indoor airborne radon progeny concentrations have been calculated for a variety of methods of control. These analyses were limited to methods for control in existing homes. Control through modified construction techniques was not evaluated. Methods assessed included increased air circulation, increased ventilation, particle removal using electrostatic precipitation and unipolar ion generation, and the application of sealants to room surfaces. Although surface sealants proved to be reasonably cost-effective per person- sievert dose reduction, such sealants are prone to cracking and the durability of their effectiveness is questionable. Use of ceiling fans for increased air circulation and particle deposition appears to be least cost-effective, but this method may be attractive in some cases for reasons of comfort. The use of unipolar ion generators appears to be the best approach from the standpoint of cost effectiveness. These devices are also easy to install and are esthetically readily acceptable.

Tracer experiments with turbulently dispersed air ions

Unipolar air ions released into the wind constitute a tracer which can be measured with high resolution. An ion source produces a cloud with homogeneous charge density, insensitive to source strength, dependent on time since formation only. It is well suited for tracing concentration changes due to turbulence, less suited for cloud size tracing.

General field charging theory for aerosol particle charging and neutralizing in unipolar and bipolar ion fields

The field charging process of aerosol particles in a bipolar ion field is examined. Equations to explain and predict both saturation charge and time-limited charge in bipolar as well as unipolar ion fields are derived. A small α-ionization electrostatic precipitator is prepared to experimentally test the derived theoretical equations. Actual particle tracks are photographed and the results show no disagreement with the derived equations. α-Ionization, instead of corona discharge, and the use of bipolar charging fields, may provide advantages in applications of particle sizing and research on electrostatic charging parameters.

Chaotic Behavior of Instability Due to Unipolar Ion Injection in a Dielectric Liquid

The chaotic regime encountered in electrohydrodynamic instability of an insulating liquid subjected to space-charge-limited unipolar injection has been investigated experimentally. Two types of behavior of the power spectra of the intensity fluctuations have been characterized: an exponential decay obtained when viscous terms are dominant and a power-law decay obtained when inertial terms are dominant. Emphasis is put on the quasiuniversality of these behaviors and this is discussed in relation to the phenomenon of smallscale intermittency.

Simple approximate treatment of unipolar space-charge-dominated coronas: The Warburg law and the saturation current

Unipolar space-charge distribution ρ(t) drifting with constant ion mobility μ in gas under time and space dependent electric fields will evolve according to the unipolar charge drift formula [1/ρ(t)]−[1/ρ(t0)] = (μ/ε0)(t−t0), neglecting diffusion effects. This general formula is especially useful as a starting point for approximate treatment of space-charge effects, both in ion drift and diffusion experiments, and in electrical coronas. A first simple derivation of an equivalent of the Warburg cos5ϑ current-density distribution for point-to-plane coronas is given, together with a formula for the maximum possible unipolar ion current (the unipolar saturation current) Is ≊2με0 V2/d, for a given corona voltage V and point-to-plane distance d. It is demonstrated that corona currents in excess of this limit always involve free electron or bipolar conduction phenomena, like streamers.

On the transient space-charge-limited current problem—a solution in Lagrangian mass variables

Using a one-dimensional unipolar ion conduction model of the type originally studied by Many and Rakavy, the transient behavior of the electric field and space-charge distribution is studied in planar, cylindrical, and spherical geometries. A general solution in Lagrangian mass variables is obtained. We are able to recover the recent results of Hensen in planar geometry.

Field‐controlled ionic charging of ice crystals

The charging curves and the saturation values of both charge and potential have been determined for six metal models with typical ice crystal shapes (bullet, columns, needle, plate, and dendrite) with different orientations in a unipolar ion current, in conditions that make the charging process field controlled. Metal spheres of several sizes were also used, as a reference. It was found that the theory of field‐controlled charging for spheres adequately describes the process for ice shapes, provided the variable (charge or potential) is multiplied by a factor depending on shape and orientation. Thus the saturation charge per unit cross section exposed to the ion current varied from 0.4 to 15 times that for a sphere, for the models used. The results are relevant to the formation of shielding layers at the upper level of thunderclouds. The measurements also provide estimates of a parameter (numerically equal to capacitance) that controls the rate of growth by sublimation.

Diffusion charging of submicrometer aerosol particles by unipolar ions

Experimental investigation of submicrometer particle diffusion charging by unipolar ions was made in the presence of vapors of various liquids. It was found that at a constant value of ion conductivity in the charger the presence of various vapors and the change of polarity affected the mobility of the ions but did not affect the particle charging. It was shown that the mean charge value of particles of 0.06–2.0 μm dia. was in good agreement with Fuchs' theory.