Different Types of Dust Resistivity

Effect of dust layer in electrostatic precipitators on discharge characteristics and particle removal

This paper deals with investigations of discharge phenomena in porous materials. Experimental investigations with high-resistivity dust have been performed in a laboratory scale electrostatic precipitator. High dust resistivities in combination with a high electric field are responsible for the occurrence of discharges inside the dust layer, so called back corona. The local occurrence strongly depends on dust layer thickness and porosity which is strongly influenced by forces of the electrohydrodynamic field. The corresponding increase of the electric current density was monitored and compared for different geometric parameters and electric operation settings. This paper verifies a correlation between the electric current density, the quality of the porous material and the discharge phenomena. Furthermore a model based on percolation theory describing the initial electrical process in correlation with the porous material is presented.

In order to further improve the collection efficiency of ESP especially for high-resistivity dust and perfect electrostatic collection theory, how dust layer effects collection efficiency should be revealed more accurately. Taking dust layer as research object, the paper has theoretically analysed the charge distribution of dust layer based on basic principles of electrostatics and Ohm’s Law in order to deduce the formula of the amount of accumulated charge in dust layer. The formula of electric-field strength formed by accumulated charges in collection space was deduced according to the principle of constant voltage and the potential continuity principle of phase boundary. Then the formulas of calculating the effective collecting electric-field and the effective theory migration velocity of charged particles were obtained. The theoretical criterion of occurring back corona was proposed by theoretical analysis of distribution characteristics of electric-field strength in dust layer. Besides that, the elaboration of non-static electrostatic collection theory has enriched and developed the traditional electrostatic collection theory. The paper has player an important role in the design of structure and the selection of operating parameters of ESP, and in the direction to explore the new ways of improving collection efficiency of high-resistivity dust.

High resistivity dust is normally the major problem in electrostatic precipitation. Even though the corona current is only a fraction of a microampere per cm2 the resulting RI drop exceeds the breakdown voltage gradient of the dust layer. This breakdown or sparking through the collected dust causes the familiar back corona and premature sparkover. The Trielectrode Electrostatic Precipitator (TEP) is an effort to make precipitator performance insensitive to dust resistivity. The TEP (U. S. Patent 3,915,672) is based on the concept that the layer of collected dust behaves like capacitance and resistance in parallel so that the corona can occur in short pulses and yet maintain a moderately constant current through the dust layer. In between corona pulses the precipitating field is supplied by a third set of electrodes. Initial bench scale tests using high resistivity particulate indicate that the concept is sound. Recent testing has extended the effective operating range of the TEP for particulate resistivit...

Intermittent energization on electrostatic precipitators

The present study aims (i) to examine the association of physical fitness components (i.e., cardiorespiratory fitness, speed-agility, and muscular fitness) with brain current source density during working memory; and (ii) to examine whether fitness-related current density was associated to working memory performance and academic achievement. Eighty-five children with overweight/obesity aged 8-11years participated in this cross-sectional study. Physical fitness components were assessed using the ALPHA test battery. Electroencephalography recordings were performed during a Delayed Non-Match-to-Sample task that assessed working memory. Brain source analysis was carried out using sLORETA to estimate regional current source density differences between high and low (H-L) working memory loads. Academic achievement was measured by the Spanish version of the Woodcock-Johnson III test battery. The main results showed that higher cardiorespiratory fitness was associated with higher H-L current density differences in frontal, limbic, and occipital regions during encoding and maintenance task's phases (β≥0.412, p≤0.019). A limbic area was further related to better working memory performance (β=0.267, p=0.005). During retrieval, higher cardiorespiratory fitness was also associated with higher current density in temporal regions (β=0.265, p=0.013), whereas lower muscular fitness was associated with higher current density in frontal regions (β=-0.261, p=0.016). Our results suggest that cardiorespiratory fitness, but not speed-agility nor muscular fitness, is positively associated with brain current source density during working memory processes in children with overweight/obesity. Fitness-related current density differences in limbic regions were associated with better working memory.

Several double anodic oxidation coatings were formed on aluminum under different anodizing conditions (such as bath temperature and current density) and the effiects of anodizing conditions on surface properties and structure of coatings were studied. A hard anodized coating of excellent surface properties was obtained under a constant current density of 4Amp/dm2, in which the 1st layer (upper layer) was formed by the ordinary anodizing method (20°C, 30min.) and the 2nd layer (lower layer) was formed by the hard anodizing method (-5°C, 30min.). In particular, the coating formed by the 1st anodizing at 10°C for 30min. and the 2nd anodizing at -5°C for 30min. showed few cracks, a very plain surface, and a high wear resistance. When the bath temperature was constant at -5°C, the coating formed under a low current density in the 1st anodizing and under a high current density in the 2nd anodizing showed a wear resistance higher than that formed by the reverse order of treaments. However, the double anodic oxidation coatings under differrent current densities showed little differences in wear resistances according to the order of treatments for the 1st and 2nd processes; in contrary to the same conditions (with respect to the order of treatments) in different bath temperatures. The effect of structure of the cell on wear resistance was pursued. The coating formed under the condition for a large cell size in the 1st layer and a small cell size in the 2nd layer showed a remarkable decrease of wear resistance near the interface of the two layers. On the contrary, a high wear resistance was obtained by the reverse condition; that is, the condition for a small cell size in the 1st layer and a large cell size in the 2nd layer.

Boosting Electrocatalytic CO ₂ Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

We present a new set of analytical solutions to model the steady state structure of a protoplanetary disc with a magnetically-driven wind. Our model implements a parametrization of the stresses involved and the wind launching mechanism in terms of the plasma parameter at the disc midplane, as suggested by the results of recent, local MHD simulations. When wind mass-loss is accounted for, we find that its rate significantly reduces the disc surface density, particularly in the inner disc region. We also find that models that include wind mass-loss lead to thinner dust layers. As an astrophysical application of our models, we address the case of HL Tau, whose disc exhibits a high accretion rate and efficient dust settling at its midplane. These two observational features are not easy to reconcile with conventional accretion disc theory, where the level of turbulence needed to explain the high accretion rate would prevent a thin dust layer. Our disc model that incorporates both mass-loss and angular momentum removal by a wind is able to account for HL Tau observational constraints concerning its high accretion rate and dust layer thinness.

GaN‐based vertical transistors have demonstrated its excellent properties for high‐power and high‐frequency electronic devices. This work introduces a GaN‐based static induction transistor (SIT) which is another form of vertical GaN transistors without requiring any p‐type GaN and gate dielectrics for its operation. Processing strategy to generate the GaN SIT with a sub‐micrometer fin width involves photoresist (PR)‐assisted planarization with an understanding of dry etch parameters for the planar PR surface. The efficacy of this process is demonstrated by the device's triode‐like output characteristics with high current density (0.65 kA cm−2) and low ON resistance (1.48 mΩ cm2) at 1 V of drain voltage. In addition, the electrical properties such as current density and modulation are examined depending on the fin width of GaN SIT. The result reveals that the size reduction in the GaN SIT utilizing the sub‐micrometer fin as a channel could increase the current modulation, but it could decrease the current density because of the raised potential minima due to the depletion region overlap. It is believed that the GaN SIT demonstrating high blocking voltage and low ON resistance would present a very promising class of transistor for next‐generation high‐power and high‐frequency electronics.

Using the Green's function of the 3D heat equation, we develop an analytical account of the thermal behaviour of superconducting films subjected to electrical currents larger than their critical current in the absence of an applied magnetic field. Our model assumes homogeneity of films and current density, and besides thermal coefficients employs parameters obtained by fitting to experimental electrical field - current density characteristics at constant bath temperature. We derive both a tractable dynamic equation for the real temperature of the film up to the supercritical current density J^\ast (the lowest current density inducing transition to the normal state), and a thermal stability criterion that allows prediction of J^\ast . For two typical YBCO films, J^\ast predictions agree with observations to within 5%. These findings strongly support the hypothesis that a current-induced thermal instability is generally the origin of the breakdown of superconductivity under high electrical current densities, at least at temperatures not too far from Tc.

DC current-voltage relationships and sodium ion transport measurements for human allograft skin immersed in saline buffers have been determined using a four terminal potentiometric method and diffusion cells of our own design. About three-fourths of the skin samples were deemed suitable for study on the basis of their high resistivities and similar j-V characteristics. Most of these samples yielded sodium ion permeability coefficients less than or equal to those reported for human skin in vivo. The current-voltage relationship in these tissues was time dependent, highly nonlinear, and slightly asymmetric with respect to the sign of the applied potential. Skin resistance decreased as current or voltage increased. For current densities less than 15 microA/cm2 and exposure times of 10-20 min, this decrease was almost completely reversible; at higher current densities, both reversible and irreversible effects were observed. The overall dependence of current on voltage was nearly exponential and was satisfactorily described by an equation of the form j approximately sinh V. Diffusion potentials, sodium ion membrane transference numbers, and sodium ion flux enhancement factors during iontophoresis were measured for skin immersed both in normal saline solutions and in saline solutions of differing concentrations. The sign of the diffusion potentials and the value of the sodium ion transference number (0.51 in normal saline at pH 7.4) indicated a weak permselectivity of the skin for transport of sodium ion versus chloride. At a current density of 71 microA/cm2 and transmembrane potentials in the range of 1.1-1.6 V, the flux enhancement for sodium ion was three to five times greater than that predicted for an uncharged homogeneous membrane according to electrodiffusion theory. For transmembrane potentials less than 0.17 V, agreement of this theory with the data was better but still incomplete.

Environmental disturbances resulting from anthropogenic energy pollution are intensely growing and represent a concern for the marine environment. Benthic organisms are the significant fauna exposed to this kind of pollution; among them, foraminifera are largely used as pollution bioindicators in marine environments, but studies on the effects induced by electrical stimulation are not documented. In the present research, we evaluated the effects of short-term different electric current densities on the viability of benthic foraminiferal species Amphistegina lessonii by checking the pseudopodial activity and defined the threshold electrical density range. After 3 days of treatment, A. lessonii stimulated with a constant current showed pseudopodial activity at a lower electric current density (0.29, 0.86 μA/cm2) up to 24 h. With increasing stimulation time, the percentages of pseudopodial activity decreased. The pseudopodial activity was absent at high current densities (5.71, 8.57 μA/cm2). The viability of A. lessonii exposed to a pulsed current was higher at a low and middle electric current density (from 0.29 to 5.71 μA/cm2) than at a high electric current density (from 11.43 to 20 μA/cm2). Based on these preliminary results, the selected benthic foraminiferal species seems to better stand pulsed currents than constant ones. These first experiments might provide useful information for the definition of the appropriate electrical density threshold to avoid side effects on a part of the benthic community.

ConspectusAs the demand for a carbon-neutral society grows rapidly, research on CO2 electrolysis has become very active. Many catalysts are reported for converting CO2 into value-added products by electrochemical reactions, which have to perform at high Faradaic and energy efficiency to become commercially viable. Various types of CO2 electrolyzers have been used in this effort, such as the H-cell, flow cell, and zero-gap membrane-electrode assembly (MEA) cell. H-cell studies are conducted with electrodes immersed in CO2-saturated electrolyte and have been used to elucidate reaction pathways and kinetic parameters of electrochemical CO2 reduction on many types of catalytic surfaces. From a transport phenomenological perspective, the low solubility and diffusion of CO2 to the electrode surface severely limit the maximum attainable current density, and this metric has been shown to have significant influence on the product spectrum. Flow and MEA cells provide a solution in the form of gas-diffusion electrodes (GDEs) that enable gaseous CO2 to closely reach the catalyst layer and yield record-high current densities. Because GDEs involve a complicated interface consisting of the catalyst surface, gaseous CO2, polymer overlayers, and liquid electrolyte, catalysts with high intrinsic activity might not show high performance in these GDE-based electrolyzers. Catalysts showing low overpotentials at low current densities may suffer from poor electron conductivity and mass transfer limitations at high current densities. Furthermore, the stability of the GDE-based catalysts is often compromised as CO2 electrolysis is pursued with high activity, most notoriously by electrolyte flooding.In this Account, we introduce recent examples where the electrocatalysts were integrated in GDEs, achieving high production rates. The performance of such systems is contingent on both GDE and cell design, and various parameters that affect the cell performance are discussed. Gaseous products, such as carbon monoxide, methane, and ethylene, and liquid products, such as formate and ethanol, have been mainly reported with high partial current density using the flow or MEA cells. Different strategies to this end are described, such as controlling microenvironments by the use of polymers mixed within the catalyst layer or the functionalization of catalyst surfaces with ligands to increase local concentrations of intermediates. Unique CO2 electrolyzer designs are also treated, including the incorporation of light-responsive plasmonic catalysts in the GDE, and combining the electrolyzer with a fermenter utilizing a microbial biocatalyst to synthesize complex multicarbon products. Basic conditions which the catalyst should satisfy to be adapted in the GDEs are listed, and our perspective is provided.

Nickel-chromium alloys present high corrosion and high creep resistance. Due to the large difference between the standard potentials of the two metals, E0(Ni2+/Ni)=-230 mV and E0(Cr3+/Cr)=-760 mV, the alloy composition usually strongly depends on the current density chosen for deposition, on the nickel concentration in the electrolyte and the electrolyte temperature.The electrodeposition of chromium from the trivalent oxidation state is more challenging compared to its hexavalent state. In aqueous solutions Cr(III) ions form complexes some of which have a very low ligand exchange rate. Thus, electrochemical deposition is difficult or only possible at a very slow deposition rate. In addition to the aquo complexes, complexes can also be formed with the anion of the corresponding metal salt. Normally, complexing agents, such as carboxylic acids, are added to the electrolyte in order to increase the deposition rate.This paper will present recent results from authors’ lab on the electrodeposition of Ni-Cr alloys from aqueous electrolytes containing Cr(III) salts. The effect of formic and oxalic acids on the qualities of the deposits was investigated, as well as the influence of the deposition technique (direct or pulse plating), current density, nickel concentration in the electrolyte, temperature of the electrolyte, and the hydrodynamic conditions.We could show that the chromium content in the deposits can be easily tuned via the composition and temperature of the electrolyte, and the current density. At high current densities and low nickel concentrations, chromium-rich layers with up to 64 wt-% chromium could be deposited. An increase in the temperature led to a significant decrease in the chromium content of the deposits. The layers grow compactly and show a globular structure. The deposited films changed from a crystalline to an amorphous structure with increasing chromium content.