Simulation on the Conductivity of Charging Stock with Percolation Structure in the Submerged Arc Furnace

Based on the fractal geometry, a new way for selecting material burden ratio and size distribution, named physical design of burden, which is different from stoichiometric weight of carbon burden, would play a more important role in the operation of submerged arc furnace process. Cold simulation investigation was carried out to find how the fraction and size of metal balls affects the specific conductivity of charge mixture, by applying the percolation structure theory. A parameter equation, s/s=A(F-Fc)v, was suggested to calculate the specific conductivity of the charge mixture.     

Comment on “Modeling and Validation of Nanoparticle Charging Efficiency of a Single-Wire Corona Unipolar Charger”

We propose a significant correction to be applied on the modeling that appears in the article “Modeling and Validation of Nanoparticle Charging Efficiency of a Single-Wire Corona Unipolar Charger” by Chien et al., published in Aerosol Science and Technology 45(12), pages 1146–1179. It concerns the boundary condition based on Peek’s law, because the geometry of the main component of the corona charger is a needle and not a wire. The effects of adopting a more realistic modeling could be very important. Boundary conditions are a key factor in the resolution of the present problem, because they affect the results a lot. This could explain why the modeling results in that article do not fit very well the experimental ones. Our proposed modification could improve them.

Copyright 2014 American Association for Aerosol Research     

Unipolar Field and Diffusion Charging in the Transition Regime—Part I: A 2-D Limiting-Sphere Model

This work examines the unipolar charging of aerosol particles smaller than 100 nm by ions (at STP) both theoretically (Part I) and experimentally (Part II).

Among numerous well-known models for particle charging by ions a gap has been identified for the case of diffusion charging with superimposed external electric field in the transition regime. A two dimensional extension of the classical Fuchs-model Fuchs, 1963 Fuchs, N. A. 1963. On the Stationary Charge Distribution on Aerosol Particles in a Bipolar Ionic Atmosphere. Geofisica Pura e Applicata, 56: 185–193. [Crossref] , [Google Scholar]) has been developed in order to bridge this gap in the knowledge. For the first time the complete expression for the electrostatic potential between a particle and an ion has been included.

By using FEM-simulations, the quantitative influence of an external electric field on the charging process has been predicted. It is shown that an external electric field increases the average particle charge linearly. Compared to pure diffusion charging, an electric field of 10 kV/cm increases the charge on metallic particles up to 28% (30 nm particles), 55% (60 nm), and 95% (100 nm), respectively.

When compared to the Fuchs-model, the assumptions of the new model introduce additional uncertainty of less than 3%. Comparison with the simpler, but physically less reasonable continuum model by Lawless (1996) Lawless, P. A. 1996. Particle Charging Bounds, Symmetry Relations and an Analytic Rate Model for the Continuum Regime. J. Aerosol Sci., 27: 191–215. [Crossref] , [Google Scholar] shows similar charge predictions (deviations < 20% for n·t-products 10¹³ s/m³), even for 30 nm particles. So, that continuum charging model can serve as simple approximation of the more accurate charging model for the transition regime.     

Response to Comment on “Modeling and Validation of Nanoparticle Charging Efficiency of a Single-Wire Corona Unipolar Charger”

Fernández-Díaz and Domat's preceeding Letter to the Editor argued that the geometry of the discharge electrode of the charger of our previous article entitled “Modeling and Validation of Nanoparticle Charging Efficiency of a Single-Wire Corona Unipolar Charger” was a needle but not a wire. Therefore, the boundary condition for the ionic charge density at the discharge wire surface used in the simulation was suspected to be not completely correct. In the present work, the exact shape of the tip of the discharge electrode was examined and found as a hyperbolic point. The experimental onset voltage was further compared with the theoretical onset values calculated by either wire-in-tube or point-to-plane assumption. Results show that the theory of needle-type discharge electrode is also not appropriate either for the boundary condition at the tip because of higher calculated onset voltages than the experimental data.

Copyright 2014 American Association for Aerosol Research