New technique for electrostatic charge measurement in gas–solid fluidized beds

Electrostatic charge generation within gas–solid fluidized bed reactors has been a concern to industry for many years. Over the years, numerous methods for measuring this phenomenon within a fluidization column have been proposed. This paper focuses on the design of a new method that minimizes effects such as extra charging due to particle handling and bed hydrodynamic disruption due to the location of the measurement device. In addition, the new method provides the bulk charge of the bed particles rather than a local measurement. The device is flexible and can be adapted to a range of fluidization columns. The new method developed consisted of a Faraday cup placed within the windbox of a fluidization column. The distributor plate was designed in such a way that it can be automatically opened to drop the charged fluidizing particles into the Faraday cup below. The new measurement technique was validated by conducting fluidization experiments in a system consisting of a 0.10 m in diameter carbon steel column with glass beads as the fluidizing particles. The technique was proven to be suitable for measuring the total net electrostatic charges in gas–solid fluidized beds.     

Electrostatic charging behaviour of dielectric particles in a pressurized gas–solid fluidized bed

The charging behaviour of insulating particles in pressurized fluidized beds was investigated by fluidizing five polyethylene resins in a column of 150 mm inner diameter and 2.0 m height. Seven collision ball probes at different levels and radial positions monitored the electrostatic charge generation in the bed. The influences of operating pressure and superficial gas velocity on the degree of electrification were studied. For each polyethylene resin, the electrostatic charges of the particles in the upper part of the bed gained a polarity which differed from the particles in the lower part of the bed due to bipolar charging and particle segregation. The hydrodynamics in the fluidized bed significantly influenced the particle electrification. Due to increased bubble size and rise velocity, electrostatic charge generation was enhanced as the superficial gas velocity increased. However, it was difficult to predict the influence of elevated pressure on the charging behaviour of each resin as a result of the complex impacts of pressurization on the hydrodynamics and electrification.     

Comparison of influence of fluidization time on electrostatic charge build-up in the bubbling vs. slugging flow regimes in gas–solid fluidized beds

Electrostatic charge generation poses significant problems in some commercial gas–solid fluidized bed reactors such as those in gas-phase polyolefin production. Understanding the contributing factors to charge generation is important in determining the charge generation mechanisms, leading to the development of methods to reduce or prevent this phenomenon. This work focused on determining the effect of fluidization time on particle charging and the amount of particle adhesion on the fluidization column wall in both the bubbling and slugging flow regimes. The charging effect was investigated for particles in three regions of the fluidized bed: elutriated fines, bulk particles inside the bed, and particles adhered to the column wall. The particles size distribution, mass and charge were measured for all three regions. Fluidization was carried out with polyethylene resins from an industrial reactor; times of 15, 30, 60, 120, 180, and 360 min were evaluated. Increased fluidization time decreased the amount of particles mass collected in the bulk region and increased those adhered to the column wall during the velocities tested in the bubbling flow regime. Whereas the quantity of particles in each region was not affected by fluidization time for the velocities examined in the slugging flow regime. Bipolar charging was observed with relatively smaller particles becoming predominately positively charged and larger particles becoming predominately negatively charged. Each region of the bed affected the magnitude of net q/m, with elutriated fines having the largest magnitude, followed by those adhered to the column wall, and finally those in the bulk of the bed. Charge saturation was attained for fluidization times greater than 60 min for particles in the bulk and along the column wall for all gas velocities. However, extended fluidization times were required with the entrained fines in bubbling flow; whereas charge saturation of fines in slugging flow occurred shortly after the onset of fluidization. Mean particle diameter for each measurement region was not impacted by the fluidization time for any of the gas velocities tested. The bed hydrodynamics was found to definitely have an impact on the particle–wall fouling where the particle layer continued to develop on the inner column wall as fluidization time increased for those velocities in the bubbling regime while comparatively less impact on particle layer growth was observed in the slugging flow regime. In addition, the bubbling flow regime resulted in particle layers formed on the column wall to be longer and thinner whereas those formed in the slugging flow regime were shorter and thicker.     

Investigation of electrostatic charge distribution within the reactor wall fouling and bulk regions of a gas–solid fluidized bed

The distribution of charge within the wall fouling region and bulk of a fluidized bed reactor was investigated. Experiments were conducted in a 0.1 m in diameter carbon steel fluidization column under atmospheric conditions. Polyethylene particles were fluidized with extra dry air at 1.5 the minimum fluidization velocity (bubbling flow regime) for 1 h. Using an online Faraday cup measurement technique, the net charge-to-mass ratio (q/m), as well as the size distribution of all particles adhered to the column wall and those in the bulk of the bed was determined. The wall particles were found to be predominantly negatively charged while those which did not adhere to the wall were predominantly positively charged. The charge distribution within each region was then investigated by a custom made charged particle separator that separated the particles according to their charge magnitude and polarity. It was determined that although the net charge of the wall layer particles was negative, a significant amount of positively charged particles existed within each sample and therefore the entire wall particle layer. This suggests that the wall layer was formed through layering between positively and negatively charged particles. Particles in the bulk of the bed also consisted of bipolarly charged particles.     

Fermions in the background of mixed vector–scalar–pseudoscalar square potentials

The general Dirac equation in 1+1$1+1$ dimensions with a potential with a completely general Lorentz structure is studied. Considering mixed vector–scalar–pseudoscalar square potentials, the states of relativistic fermions are investigated. This relativistic problem can be mapped into a effective Schrödinger equation for a square potential with repulsive and attractive delta-functions situated at the borders. An oscillatory transmission coefficient is found and resonant state energies are obtained. In a special case, the same bound energy spectrum for spinless particles is obtained, confirming the predictions of literature. We showed that existence of bound-state solutions is conditioned by the intensity of the pseudoscalar potential, which possess a critical value.     

Pion-Nucleus potentials in the energy range of 0–80 MeV

Data for the elastic scattering of 30–80 MeV positive and negative pions by a wide range of nuclei is analysed with an Ericson-Ericson MSU type optical potential. By use of consistent sets of data for π⁺ and π⁻ and of experimental results for total reaction cross sections we obtain for the first time optical potentials that describe well all the data without the need of introducing non-standard charge-dependent effects.     

Electrophoretic mobility without charge driven by polarisation of the nanoparticle–water interface

Polarisation of the interface, spontaneously occurring when water is in contact with hydrophobic solutes or air, couples with the uniform external field to produce a non-zero force acting on a suspended particle. This force exists even in the absence of a net particle charge, and its direction is affected by the first-order, dipolar and the second-order, qudrupolar orientational order parameters of the interfacial water. The quadrupolar polarisation gives rise to an effectively negative charge. The corresponding surface charge density is inversely proportional to the area of the shear surface. As a result, the overall contribution from the quadrupolar polarisation to the particle mobility becomes negligible compared to experimentally reported values for particles exceeding a few nanometres in size. In contrast, the contribution of the dipolar order of the interface to the effective surface charge scales inversely with the particle size and dominates the zero-charge mobility of submicron particles. The corresponding electrokinetic charge is determined by the preferential orientation of interfacial dipoles relative to the surface normal.     

Formation of freak waves in a soliton gas described by the modified Korteweg–de Vries equation

The nonlinear dynamics of multisoliton, differently polar fields is investigated within the framework of the modified Korteweg–de Vries equation. It is shown that the occurrence of abnormally large waves (freak waves) is possible in similar fields, which is associated with the modulation instability of cnoidal waves. The statistical moments of wave fields are investigated. It is shown that an increase in the coefficient of excess due to the interaction of solitons correlates with an increase in the probability of occurrence of freak waves. It is shown that the nonlinear interaction of differently polar solitons results in variation of the distribution functions of peak characteristics: the fraction of low-amplitude waves decreases, while that of the waves with large amplitudes increases. The dependence of the intensity of the density of the characteristics of the soliton gas is shown.     

Transferred charge of brush discharges in explosive gas atmospheres – A verification of the ignition threshold limits

A wide series of experiments has been performed to check the incentivity of hydrogen/air, ethene/air and propane/air mixtures due to brush discharges. Thereby, the transferred charge as a criterion to judge the ignition potential is determined to verify the thresholds of transferred charge given in the standards IEC 60079-0 and in EN 13463-1. These thresholds have never been examined directly in an experiment before. It is stated that the thresholds for explosion group IIA, IIB and IIC represent different levels of safety. Using adequate thresholds the criterion of transferred charge is suitable for a judgement of potential electrostatic ignition sources.     

Improvement of spectral resolution by using the excitation dependence of dipole–dipole interaction in a dense atomic gas

We have studied the selective reflection from the interface between a dense rubidium (Rb) atomic vapor and a transparent dielectric. A remarkable narrowing of the spectrum, which can be used to improve the resolution of spectroscopy of dense media, has been demonstrated. This narrowing results from the reduction of the dipole–dipole interaction between atoms when the Rb vapor is excited by a strong pump laser. By using this technique, we have resolved the hyperfine structure of the Rb D₂ line, which is hidden by collisional broadening. PACS 32.70.Jz; 42.50.Ct; 34.80.Dp     

Isotopic effect in the solid–liquid phase diagram of quantum clusters

Applying the Fourier path integral formalism to the isothermal-isobaric ensemble, the solid–liquid transition for 13-atom pure Lennard–Jones clusters was characterized. The masses of the clusters were taken as the masses of hydrogen, deuterium and tritium, hence isotopic effects of quantum clusters were considered. The parallel tempering Monte Carlo algorithm was used to solve all multidimensional integral in the FPI method. The volume of the system was defined with respect to the centroids of the quantum particles and a variable constraining potential was used to restrict undesirable thermodynamic events. The maximum value of the constant pressure heat capacity at a given temperature was used to identify the melting temperature. Pressure versus temperature phase diagrams were constructed for these systems with and without the inclusion of quantum effects. A significant difference in the melting temperature was encountered for the different isotopes due to quantum contribution.     

Prediction of the solid–liquid–liquid equilibria of linear and branched semi-crystalline poly-ethylene in solutions of diphenyl ether by Lattice Cluster Theory

ABSTRACT

Recently, Lattice Cluster Theory has been applied to predict liquid–liquid equilibria and solid–liquid equilibria of low and high molecular weight mixtures taking into account the molecular architecture and the nature of crystallinity of the respective component. Herein, an LCT-based theory is applied to calculate solid–liquid–liquid equilibrium of a polyethylene + diphenyl ether system, depending on branching and degree of crystallinity of the polymeric component. Understanding the role that branching number, branching type and degree of polymer crystallinity play in the behaviour of triple and triple critical points is focused on. Insight is given here into constitution and properties of triple and triple critical points in binary polymer solvent systems depending on the molecular architecture of both components, polymer and solvent respectively, and the semi-crystalline nature of the polymer.     

Numerical investigations on the current conduction in bilayer organic light-emitting devices with ohmic injection of charge carriers

A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trapped charge limited conduction. The dependences of the current density on the operation voltage, the thickness and trap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure anode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trap depth, total trap density, and cv~rrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL to the sum of HTL and EML, by which a maximal current density, and hence maximal quantum efficiency and luminance,can be achieved. The current density decreases quickly with the mean trap density, and decreases nearly exponentially with the mean reduced trap depth.     

Analysis of Electrostatic Interactions of Amino Acid Residues by the Example of Formation of a Nap1–Nap1 Dimer

Technical Physics - A new method, which analyzes the potential energy of electrostatic interaction of protein complexes at point replacements of amino acid residues assuming a three-dimensional...     

Electrical contact properties of Cu2S nanowires grown vertically on Cu foil by gas–solid reaction

We grew Cu₂S nanowires vertically on Cu foil by gas–solid reaction with a gas mixture of O₂ and H₂S. The electrical contact properties between the Cu₂S nanowires and Cu foil were investigated using a modified current–voltage–temperature plot. The Cu/Cu₂S layer exhibited the characteristics of a Schottky barrier with a barrier height of ∼0.72 eV, which was closer to the value for Cu/Cu₂O than to Cu/Cu₂S. Energy dispersive spectroscopy results showed the presence of Cu-oxide between the Cu₂S nanowires and Cu foil. The overall structure was Cu/Cu-oxide/Cu₂S and the electrical properties were controlled by the Cu/Cu-oxide.     

Neutron diffraction study of the nano-inhomogeneities of the sphalerite crystal structure induced by magnetoactive 3d ions in II–VI solid solutions

It is shown by means of the thermal neutron diffraction method that, during the doping of Zn-chalcogenide semiconductor crystals with 3d ions, elongated distortions whose spatial topology depends on the type of impurity can be formed in the sphalerite modification based on the initial crystal structure. Experimental results are discussed using the concept of vibronic interaction induced by foreign ions with partially filled outer electron shells in the cubic crystal field.     

Self-focusing of acoustical beam in solid by time-reversal processing

1 IntroductionTime reversal is a unique self-adaptive focusing technique, it can realize the acollsticalbeam focusing and ultrasonic testing in the inhomogeneous mediatl], and the inhomogeneityof the media always causes curve of sound ray, distortion of wavefront, aberrance and blur ofimage. It is difficult or impossible to know the acoustical inhomogeneity of the media, such asocean or interior of solid. The greatest advantage of TR is that it can realize the self-adaptivefocusing without pr…     

Sonoluminescence and acoustically driven optical phenomena in solids and solid–gas interfaces

During the last decade, significant progress has been achieved in our understanding of the generation of light in acoustic fields, a research area which is known as sonoluminescence (SL). Some of the data obtained, including SL effects in water, have previously been reviewed in the literature. This article takes a broader view and reports on experimental evidence of SL phenomena in solids and solid–gas interfaces as well as on interpretations and potential applications. It is shown that the understanding of SL is facilitated when couched in the language of moving dislocations which produce vacancy–interstitial pairs of host atoms. Radiative transitions in defect pairs would then constitute the SL effect in solids. It is further shown that the occurrence of electric fields due to the generated point defects and charged dislocations produces a number of interesting phenomena. These fields are particularly important for the occurrence of SL at solid–gas interfaces which has been suggested to be initiated by gas discharges due to strong electric fields of charged dislocations. The appearance of acoustically driven internal electric fields is shown to lead to remarkable effects with regard to exciton lifetimes. The storage of photogenerated electron–hole pairs in the moving piezoelectric potential of acoustic waves allows prolonged exciton recombination times of μs in InGaAs/GaAs quantum well structures. The intertwining of acoustically driven long-range electric fields and microfields occurring at the exciton sites turns out to be a prerequisite for attaining the lifetime tuning of the bound excitons in CdS crystals. The review is concluded by discussing sonoluminescence effects in granular systems. Implications for the relevance of this effect to the dynamical behavior of granular media are outlined.     

Interaction between phases in the liquid–gas system

This work analyzes the equilibrium between a liquid and a gas over this liquid separated by an interface. Various gas forms exist inside the liquid: dissolved gas molecules attached to solvent molecules, free gas molecules, and gaseous bubbles. Thermodynamic equilibrium is maintained between two phases; the first phase is the liquid containing dissolved and free molecules, and the second phase is the gas over the liquid and bubbles inside it. Kinetics of gas transition between the internal and external gas proceeds through bubbles and includes the processes of bubbles floating up and bubble growth as a result of association due to the Smoluchowski mechanism. Evolution of a gas in the liquid is considered using the example of oxygen in water, and numerical parameters of this system are given. In the regime under consideration for an oxygen–water system, transport of oxygen into the surrounding air proceeds through micron-size bubbles with lifetimes of hours. This regime is realized if the total number of oxygen molecules in water is small compared with the numbers of solvated and free molecules in the liquid.