Magnitude Of Charge Density Research Articles

An Euler-Euler model for mono-dispersed gas-particle flows incorporating electrostatic charging due to particle-wall and particle-particle collisions

A computational model for the prediction of triboelectric charging in gas-solid fluidized beds is developed in the context of the Euler-Euler two-fluid model with kinetic theory closures for the description of the particulate phase. Sub-model for charge transfer due to particle-wall collisions is obtained consistently with the boundary conditions of Johnson and Jackson (1987), and assuming the model of Matsusaka et al. (2000) for charge transfer during a single collision. Similarly, a sub-model for charge diffusion due to particle-particle collisions is developed based on the kinetic theory of granular flow of Jenkins and Savage (1983), and the aforementioned charging model. The Eulerian charging model is then coupled to the two-fluid model, with kinetic theory closures which are available in the OpenFOAM® computational toolbox for fluid dynamics. The model is tested to simulate the effect of polyethylene particle size (362, 462, 550 μm) in the electrification process, and is validated against experimental findings (Sowinski, 2012; Sowinski et al., 2012). The order of magnitude of charge densities in different regions of the bed, predicted by the model, was coherent with the experimental results. The model also predicted that particles larger than 425 μm would not stick to the column wall, which acceptably agreed with the experimental observation that particles larger than 600 μm did not adhere to the wall surface.

First-principles calculation of contact electrification and validation by experiment

Contact electrification is one of the most well-known phenomena in physics and examples arise in almost every industry. However, a scientific basis for contact charging remains unknown. Here, we present a theoretical study of contact electrification, supported by experiments, to calculate for the first time charge transfer between material surfaces from first principles physics. Electronic structure calculations and experiments are performed on single-crystal alumina (sapphire) and silicon oxide (quartz) surfaces, which have well-ordered structures that enable rigorous modeling. Both experiments and calculations show that sapphire charges positively and quartz charges negatively. The calculations cannot determine the magnitude of charge densities remaining on separated surfaces from first principles, as these are non-equilibrium effects, but our analysis is consistent with experimentally obtained charge densities of 10 μC/m2. These results indicate the possibility of quantitatively predicting and explaining contact electrification from only the molecular structure of material surfaces.

Numerical simulation of a non-equilibrium electrokinetic micro/nano fluidic mixer

In this study we numerically simulate a novel micromixer that utilizes vortex generation from the non-equilibrium electrokinetics near the micro/nanochannels interface. After mixing in combined pressure-driven and electroosmotic flows was compared with mixing in a pure pressure-driven flow, the superior mixing performance of the former was evident: for a specific case study, 90% mixing of two fluid streams for a short mixing length was achieved. The results of our numerical study were very similar to those of previously reported experiments. In this paper we explain the phenomenon occurring adjacent to the nano-junctions by plotting the electrical field components, the velocity contours and the concentration distribution in the micromixer. The vortices at the micro/nanochannel interface were obviously indicators of non-equilibrium behaviour in these regions. At the end, the mixing performance was evaluated by the investigation of different applied voltages, Reynolds numbers and surface charge densities using the mixing index parameter, and the results showed that more efficient mixing occurred when the applied voltage and surface charge density magnitude were increased and the Reynolds number was decreased.

Analysis of Hyperabrupt and Uniform Junctions in GaAs for the Application of Varactor Diode

In this study, we present a GaAs varactor diode with a hyperabrupt junction for the enhancement of breakdown voltage and capacitance variation in a reverse bias state. The hyperabrupt doping profile in the n-type active layer is prepared in a controlled nonlinear manner, with the density of the dopants increasing towards the Schottky junction. The hyperabrupt GaAs varactor diode is fabricated and characterized for breakdown voltage and capacitance over the electric field, induced by an applied reverse bias voltage. A reduced value of the electric field is observed owing to the nonlinear behavior of the electric field at the hyperabrupt junction, although the device has a larger doping density at the Schottky junction. Furthermore, the capacitance ratio of the hyperabrupt junction diode is also improved. Variation in the device capacitance is affected by variation in the depletion region across the junction. Technology CAD is used to understand the experimental phenomena by considering the magnitude of charge density as a function of the doping profile. A higher breakdown voltage and greater capacitance modulation are shown in the hyperabrupt junction diode compared to the uniform junction diode.

Water desalination by a designed nanofilter of graphene-charged carbon nanotube: A molecular dynamics study

Using molecular dynamics simulations, we show that a designed graphene-charged carbon nanotube (CNT) membrane can act as a nanofilter with the efficiency more than 90%, to separate Na+/Mg+2/Fe+3 and Cl− ions from NaCl, MgCl2 and FeCl3 solutions. It is observed that there are two significant factors in ion separation process: the magnitude of charge density which covers the surface of the CNT and the velocity of the movable wall. The ion separation is improved by increasing the magnitude of surface charge density and decreasing the velocity of the movable wall. Also, it is found that, reducing the positive surface charge of the CNT will increase the percentage of passed water molecules through the CNT.

Study of the pH effect on the properties of the hydrothermally grown V2O5

Vanadium pentoxide coatings were prepared by hydrothermal process at a temperature as low as 95°C. It was demonstrated that the structure and morphology of the coatings depend on the pH solution employed during growth. Only for pH3.5, adhesive coating growth was observed, with a substantial enhancement in the electrochemical performance in terms of charge density magnitude. The amount of lithium charge interchanged between the vanadium pentoxide and the electrolyte reached 220mCcm−2. This is a value among the best reported for low temperature growth and free of templates pentoxide with a prolonged stability up to 250 continuous charge intercalation/deintercalation scans.

Numerical simulation of the effect of lower positive charge region in thunderstorms on different types of lightning

Combined with the existing stochastic lightning parameterization scheme, a classic tripole charge structure in thunderstorms is assumed in the paper, and then 2-dimensional fine-resolution lighting discharge simulations are performed to quantitatively investigate the effect of lower positive charge (LPC) on different types of lightning. The results show: (1) The LPC plays a key role in generating negative cloud-to-ground (CG) flashes and inverted intra-cloud (IC) lightning, and with the increase of charge density or distribution range of LPC region, lightning type changes from positive polarity IC lightning to negative CG flashes and then to inverted IC lightning. (2) Relative to distribution range of charge regions, the magnitude of charge density of the LPC region plays a dominant role in lightning type. Only when the maximal charge density value of LPC region is within a certain range, can negative CG flashes occur, and the occurrence probability is relatively fixed. (3) In this range, the charge density and distribution range of LPC region jointly determine the occurrence of negative CG flashes, which has a linear boundary with the trigger condition of IC lightning. (4) The common effect of charge density and distribution range of the LPC region is to change the distribution of positive potential well of bottom part of thunderstorms, and inverted IC lightning occurs when the initial reference potential is close to 0 MV, and negative CG flashes occur when the initial reference potential is far less than 0 MV. lower positive charge, charge density, distribution range, lightning type, numerical simulation

Effect of electrostatic charges on single bubble in gas–solid fluidized beds

Electrostatic charges are well known to influence the hydrodynamics of gas–solid fluidized beds, but no detailed description is currently available showing how they can influence bubble properties such as shape and velocity. This study simulates the injection of single bubbles into a fluidized bed of charged particles. The effect of electrostatic charge is modeled by the Two Fluid Model (TFM) implemented in MFIX code, solving the governing momentum, continuity and electrical equations. This model is initially evaluated for an uncharged system by comparing the numerical predictions with the bubble shape measured by Gidaspow D., Seo, Y., Ettehadieh, B. [1983. Hydrodynamics of fluidization: Experimental and theoretical bubble sizes in a two dimensional bed with jet. Chem. Eng. Commun. 22, 253–272] and particle pressures measured by Rahman, K., Campbell, C. [2002. Particle pressures generated around bubbles in gas fluidized beds. J. Fluid Mech. 455, 103–127]. The effect of charged particles on bubble behavior is then simulated. The simulations show bubble elongation in the flow direction. As a result, bubbles rise more quickly than for the uncharged case. Analysis is performed on the magnitude of charge density and the choice of frictional model. The bubble deformation is explained based on forces on particles at the bubble periphery.

The effect of charge density in tropospheric thunderclouds on production of sprites and terrestrial gamma ray flashes

[1] We demonstrate that positive cloud-to-ground lightning flash (most often responsible for sprites) from stratiform tropospheric thundercloud leading to charge moment change iΔMq high above the sprite “threshold” 500 C km really triggers the high-altitude discharge exciting the air luminescence at sprite altitudes with brightness close to the observed brightness. Specifically, we present results for three configurations with the same charges Qcl = 200 C located at altitudes 6 and 8 km (iΔMq = 1200 C km for +Qcl at 6 km and iΔMq = 1600 C km for +Qcl at 8 km) differing by a magnitude of charge density, namely, σ = 1.86, 2.88, and 4.41 C km−2. All three configurations produce luminescence at sprite altitudes with brightness close to the observed one. In addition, the configuration with σ = 2.88 C km−2 produces observable γ emission, which can be detected in near space as terrestrial gamma-ray flashes (TGFs). The configuration with σ = 4.41 C km−2, provided it really could develop, would produce a blue fluorescence directly near the cloud top and extremely intensive γ emission not observed till now. The results obtained for smaller σ prove that too small-charge density in stratiform thunderclouds and consequently too weak electric field above them could account for the lack of Reuven Ramaty High Energy Solar Spectroscopic Imager TGFs correlated with large-charge moment change.

Aggregation and stability of 1,1′-diethyl-4,4′-cyanine dye on the surface of layered silicates with different charge densities

The aggregation and decomposition of 1,1′-diethyl-4,4′-cyanine dye (DEC) in dispersed layered silicates were studied using ultraviolet–visible (UV–VIS) spectroscopy. Series of reduced-charge montmorillonites (RCMs) and di- and trioctahedral smectites were used as silicate materials. DEC, unstable in aqueous solutions, was partially stabilized in the dispersions with layered silicates. The layer charge density significantly affected the spectral bleaching of the dye. Silicates with very low charge density suppressed dye aggregation only partially. The presence of layered silicates with moderate charge density led to dye aggregation, which stabilized the dye against decomposition. In contrast, layered silicates with very high charge densities induced very fast and irreversible decomposition of the DEC. In general, the extent of DEC decomposition was proportional to the charge density magnitude. The presence of the surfactant Triton X-100, which stabilizes the DEC in aqueous solutions, did not greatly affect dye spectral bleaching in silicate dispersions. The phenomenon of DEC bleaching and its relationship with the charge density can be used as a simple method for estimating the surface density of layered silicates and possibly other similar materials.

Electrification of Stratiform Regions in Mesoscale Convective Systems. Part I: An Observational Comparison of Symmetric and Asymmetric MCSs

Abstract The kinematic, microphysical, and electrical structures of two mesoscale convective systems (MCSs) observed during the 1991 Cooperative Oklahoma Profiler Studies (COPS91) experiment are analyzed. Profiles of the vertical electric field structure and charge density were obtained from a series of balloon-borne electric field meter (EFM) flights into each MCS. Contrasting electric field structures were found in the stratiform regions of these MCSs. In both systems, the EFM data indicate that the MCS charge structure was characterized by horizontally extensive regions of charge and charge density magnitudes on the order of what is typically observed in convective cores (⩽5 nC m−3). However, the vertical electric field profiles were each related to unique MCS precipitation and kinematic structures, with a five-layer charge profile (at T ⩽ 0°C) associated with the “symmetric” MCS and a simpler three-layer charge profile (at T ⩽ 0°C) associated with the “asymmetric” MCSs. The observational analysis iden...

Electrification of Stratiform Regions in Mesoscale Convective Systems. Part II: Two-Dimensional Numerical Model Simulations of a Symmetric MCS

Abstract Model simulations of a symmetric mesoscale convective system (MCS; observations discussed in Part I) were conducted using a 2D, time-dependent numerical model with bulk microphysics. A number of charging mechanisms were considered based on various laboratory studies. The simulations suggest that noninductive ice–ice charge transfer in the low liquid water content regime, characteristic of MCS stratiform regions, is sufficient to account for observed charge density magnitudes, and as much as 70% of the total charge in the stratiform region. The remaining 30% is contributed by charge advection from the convective region. The strong role of in situ charging is consistent with previous water budget studies, which indicate that roughly 70% of the stratiform precipitation results from condensation in the mesoscale updraft. Thus both in situ charging and charge advection (the two previously identified hypotheses) appear to be important contributors to the electrical budget of the stratiform region. The ...

Estimates of cloud charge densities in thunderstorms

The total charge density and the precipitation charge density inferred from six balloon soundings of electric field and precipitation charge are compared in order to examine the distribution of cloud charge density in small New Mexican mountain thunderstorms. Cloud charge density magnitudes were typically less than 2.0 nC m−3, and the maximum cloud charge densities were −2.1 and +6.7 nC m−3. The cloud charge density made a significant contribution to the total charge density in most of the thunderstorm depth, especially in the upper positive and upper negative charge regions, where all the charge was typically on cloud particles. The largest positive cloud charge densities were found just above the main negative charge region. In the lower part of the main negative charge region, the cloud charge density was the major contributor to the total charge density, and the precipitation charge played a minor role. The cloud charge density was often zero in lower positive charge regions but was 20–50% of the total charge density in two cases. Between the upper positive charge region and the bottom of the main negative charge region the cloud charge density changes polarity and tends to become increasingly negative with decreasing altitude.

Contact electrification and surface composition

We have studied the charge transfer to polypropylene films containing varying concentrations of amide (donor) and fluorine (acceptor) groups grafted onto the polymer backbone. Pure polypropylene charges very weakly but the addition of amide causes the charging to become strongly positive, and fluorine causes it to become strongly negative. The magnitude of charge density is similar in the two cases but is small compared to the density of donor or acceptor groups. Moreover, the charge transfer is independent of donor or acceptor density over a wide range of composition, indicating that charge transfer is limited by a feedback mechanism (such as back-tunnelling) during the separation of the metal and polymer surfaces. When gradually increasing amounts of fluorine or chlorine are added to a nylon surface (so that donors and acceptors are simultaneously present) the magnitude of the charge transfer is in general similar to that found for polypropylene with amide or fluorine groups, but depends on the relative concentrations of donors and acceptors. We show that this observation is also compatible with feedback mechanisms such as back-tunnelling. However, the precise nature of the feedback mechanism has not been ascertained.

Electrical and Kinematic Structure of the Stratiform Precipitation Region Trailing an Oklahoma Squall Line

Abstract An electric field sounding through the transition zone precipitation minimum that trailed an Oklahoma squall line on 18 June 1987 provides information about the electrical structure within a midlatitude trailing stratiform cloud. A single-Doppler radar analysis concurrent with the flight depicts a kinematic structure dominated by two mesoscale flow regimes previously identified in squall-line systems: a strong midlevel, front-to-rear flow coinciding with the stratiform cloud layer and a descending rear inflow that sloped from 6.5 km AGL at the stratiform cloud's trailing edge to 1.5 km AGL at the convective line. Electric field magnitudes as high as 113 kV m−1 were observed by the electric field sounding, which reveals an electric field structure comparable in magnitude and complexity to structures reported for convective cells of thunderstorms. The charge regions inferred with an approximation to Gauss' law have charge density magnitudes of 0.2–4.1 nC m−3 and vertical thicknesses of 130–1160 m; ...

Molecular interactions of six aromatic competitive inhibitors with bovine liver glutamate dehydrogenase

Six aromatic dicarboxylic acids (isophthalic acid, pyridine-3,5-dicarboxylic acid, and pyridine-2,6-dicarboxylic acid) and bromo-substituted aryl monocarboxylic acids (5-bromofuroic acid, m-bromobenzoic acid, and 5-bromothiophene-2-carboxylic acid) were tested with bovine liver glutamate dehydrogenase [ l-glutamate: NAD(P) + oxidoreductase (deaminating) EC 1.4.1.3] for inhibition against l-glutamate as a function of pH (6.6 to 9.0). These compounds were competitive inhibitors at all pH values tested and the inhibition remained competitive when either NADP + or NAD + was coenzyme. Maximum inhibitor potency (p K 1) for the dicarboxylic acids occurred at pH 7.8 and for the monocarboxylic acids occurred at pH 8.7. The relative inhibitor potencies were correlated with the inhibitors‘ “central atom” absolute charge densities | Q T| calculated from molecular orbital theory. This indicated that desolvation of this atom may be important for combination of inhibitor with enzyme. A high degree of solvation as indicated by the magnitude of charge density could have decreased the interaction of inhibitor with enzyme. Similar results had been obtained previously for 4 aliphatic dicarboxylic acid competitive inhibitors