Electrohydrodynamic flow patterns in a narrow electrostatic precipitator with longitudinal or transverse wire electrode

Results of 2- and 3-dimensional Particle Image Velocimetry (PIV) measurements of the flow velocity fields in narrow electrostatic precipitators (ESPs) with either a longitudinal or transverse wire electrode are presented in this work. The obtained results confirmed that the particle flow in the ESP have a strongly 3D character mainly due to applied voltage and narrow cross section of the ESP duct. It was found that several vortices were formed along and across the ESP duct. The complex character of the flow in both ESP may considerably affect the particle collection efficiency of the ESP. This issue is under investigation.     

Electrohydrodynamic flow patterns and collection efficiency in narrow wire-cylinder type electrostatic precipitator

Recently, narrow electrostatic precipitators (ESPs) have become a subject of interest because of their possible application for the cleaning of the exhaust gases emitted by diesel engines. Diesel engines emit fine particles, which are harmful to human and animal health. There are several methods for decrease particulate emission from a diesel engines, but up to now, these methods are not enough effective or very expensive. Therefore, an electrostatic precipitation was proposed as an alternative method for control of a diesel particulate emission.In this work, results of electrohydrodynamic (EHD) secondary flow and particle collection efficiency measurements in a narrow wire-cylinder type ESP are presented. The ESP was a glass cylinder (300 mm × 29 mm) equipped with a wire discharge electrode and two collecting cylinder-electrodes. A 0.23 mm in diameter and 100 mm long stainless-steel discharge wire electrode was mounted in the center of the cylinder, parallel to the main flow direction. The collecting electrodes were made of stainless steel cylinders, each with a length of 100 mm and inner diameter of 25.5 mm. An air flow seeded with a cigarette smoke was blown along the ESP duct with an average velocity of 0.9 m/s.The EHD secondary flow was measured using 2-dimensional particle image velocimetry (PIV) method. The PIV measurements were carried out in the wire electrode mid-plane, perpendicularly to the wire and the collecting electrodes. The results show similarities and differences of the particle flow in the wire-cylinder type ESP for a negative and a positive DC voltage polarity.The collection efficiency was calculated from the fractional particle concentration. The fractional particle concentration was measured using the optical aerosol spectrometer. The results of the fractional collection efficiency confirmed the common view that the collection efficiency of fine particles in the ESP increases with increasing voltage and it is higher for negative voltage polarity and decreases when decreasing particle diameter.     

Electrohydrodynamic flow in a wire-plate non-thermal plasma reactor measured by 3D PIV method

This work was aimed at measurements of the electrohydrodynamic (EHD) secondary flow in a non-thermal plasma reactor using three-dimensional particle image velocimetry (3D PIV) method. The wide-type non-thermal plasma reactor used in this work was an acrylic box with a wire discharge electrode and two plate collecting electrodes. The positive DC voltage was applied to the wire electrode through a 10 MΩ resistor. The collecting electrodes were grounded. The voltage applied to the wire electrode was 28 kV. Air flow seeded with a cigarette smoke was blown along the reactor duct with an average velocity of 0.6 m/s. The 3D PIV velocity fields measurements were carried out in four parallel planes stretched along the reactor duct, perpendicularly to the wire electrode and plate electrodes. The measured flow velocity fields illustrate complex nature of the EHD induced secondary flow in the non-thermal plasma reactor.     

Laser flow visualization and velocity fields by particle image velocimetry in an electrostatic precipitator model

Although improving electrostatic precipitator (ESP) collection of fine particles (micron and submicron sizes) remains of interest, it is not yet clear whether the turbulent flow patterns caused by the presence of electric field and charge in ESPs advance or deteriorate fine particle precipitation process. In this paper, results of the laser flow visualization and Particle Image Velocimetry (PIV) measurements of the particle flow velocity fields in a wire-to-plate type ESP model with seven wire electrodes are presented. Both experiments were carried out for negative and positive polarity of the wire electrodes. The laser flow visualization and PIV measurements clearly confirmed formation of the secondary flow (velocity of several tens of cm/s) in the ESP model, which interacts with the primary flow. The particle flow pattern changes caused by the strong interaction between the primary and secondary flows are more pronounced for higher operating voltages (higher electrohydrodynamic numbernehd) and lower primary flow velocities (lower Reynolds number Re). The particle flow patterns for the positive voltage polarity of the wire electrodes are more stable and regular than those for the negative voltage polarity due to the nonuniformity of the negative corona along the wire electrodes (tufts).     

Kinematic structure of electrohydrodynamic flow in “wire-wire” and “wire over plane” electrode systems placed in a liquid

A specially designed program package is used for the visualization of experimental data for 2D electrohydrodynamic flows in geometrically symmetric (wire-wire) and asymmetric (wire over plane) electrode systems. The velocity and acceleration distributions in the flows are obtained. The influence of the passive electrode on the kinematic and dynamic structures of the electrodynamic flows is revealed by comparing the results obtained for both electrode systems. A recombination zone is separated and studied.     

PIV and LDV evidence of hydrodynamic instability over a liner in a duct with flow

The acoustical behavior and the flow in a rectangular lined channel with grazing flow have been investigated. The liner consists of a ceramic structure of parallel square channels and is locally reacting. In the absence of flow, the liner has a classical behavior: the acoustic transmission coefficient has a minimum at the resonance frequency of the resonators. When the Mach number of the grazing flow increases, the material behavior becomes unclassical in the sense that its acoustic transmission increases strongly around the resonance frequency. To connect this behavior with flow features, the flow itself in the vicinity of a liner has been measured by means of laser velocimetry. Periodic structures have been observed along the liner that are phase-locked with the incident sound wave. The axial and transverse velocity of these structures bear the typical features of an instability. In particular, the wavelength, convection speed, and growth rate are given. This is the first time that an aeroacoustic instability resulting from the interaction of flow and sound over a liner is measured.     

3-D numerical analysis of EHD turbulent flow and mono-disperse charged particle transport and collection in a wire-plate ESP

The present study attempts to develop a detailed numerical approach and a simulation procedure to predict the motion of gas, ions and particles inside a simple parallel plate channel containing a single corona wire. A hybrid Finite Element (FEM)-Flux Corrected Transport (FCT)-Finite Volume (FVM) method is used: the FEM–FCT numerical algorithm is applied for modeling the steady-state corona discharge, while the turbulent gas flow and the particle motion under electrostatic forces are modeled using the commercial CFD code FLUENT. Calculations for the gas flow are carried out by solving the Reynolds-averaged Navier–Stokes equations and turbulence is modeled using the k–? turbulence model. An additional source term is added to the gas flow equation to include the effect of the electric field, obtained by solving a coupled system of the electric field and charge transport equations using User-Defined Functions (UDFs). The particle phase is simulated based on the Lagrangian approach, where a large number of particles is traced with their motion affected by the gas flow and electrostatic forces using the Discrete Phase Model (DPM) in FLUENT. The developed model is useful to gain insight into the particle collection phenomena that take place inside an ESP.     

Crystal plasticity study on stress and strain partitioning in a measured 3D dual phase steel microstructure

Dual phase steels are advanced high strength alloys typically used for structural parts and reinforcements in car bodies. Their good combination of strength and ductility and their lean composition render them an economically competitive option for realizing multiple lightweight design options in automotive engineering. The mechanical response of dual phase steels is the result of the strain and stress partitioning among the ferritic and martensitic phases and the individual crystallographic grains and subgrains of these phases. Therefore, understanding how these microstructural features influence the global and local mechanical properties is of utmost importance for the design of improved dual phase steel grades. While multiple corresponding simulation studies have been dedicated to the investigation of dual phase steel micromechanics, numerical tools and experiment techniques for characterizing and simulating real 3D microstructures of such complex materials have been emerged only recently. Here we present a crystal plasticity simulation study based on a 3D dual phase microstructure which is obtained by EBSD tomography, also referred to as 3D EBSD (EBSD—electron backscatter diffraction). In the present case we utilized a 3D EBSD serial sectioning approach based on mechanical polishing. Moreover, sections of the 3D microstructure are used as 2D models to study the effect of this simplification on the stress and strain distribution. The simulations are conducted using a phenomenological crystal plasticity model and a spectral method approach implemented in the Düsseldorf Advanced Material Simulation Kit (DAMASK).     

3D numerical analysis on mechanisms of flow and heat transfer in a square channel with right triangular wavy surfaces

Numerical investigations on thermo-hydraulic performance and mechanisms of flow and heat transfer in a square channel heat exchanger inserted with right triangular wavy surfaces are examined. The influence of the flow attack angles (30°, 45° and 60°) is investigated for laminar flow (Re = 100–2000). The configurations of the right triangular wavy surfaces are varied as inclined and V-shaped wavy surfaces (the pointing of V-tip with downstream and upstream called “V-downstream” and “V-upstream”, respectively). The insertions of the wavy surfaces in the channel heat exchanger are divided into two types: middle and diagonal insertions. The computational results reveal that the maximum thermal enhancement factor, TEF, is around 2.31 for the 30° V-downstream wavy surface with diagonal insertion at Re = 2000.     

Modification of the ultrasound induced activity by the presence of an electrode in a sono-reactor working at two low frequencies (20 and 40 kHz). Part II: Mapping flow velocities by particle image velocimetry (PIV)

Sonoelectrochemical experiments differ from sonochemical ones by the introduction of electrodes in the sonicated reaction vessel. The aim of the study is to characterize the changes in the ultrasonic activity induced by the presence of an electrode located in front of the transducer. The scope of our investigations concerns two low frequency vibration modes: 20 and 40 kHz. For this purpose, two laser visualization techniques have been used. The first part of the study, described in a previous paper (Part I), deals with the laser tomography technique which provides an accurate picture of the reactor active zones, related to numerous cavitation events. The second part of the paper (Part II) will describe the particle image velocimetry (PIV) technique used to measure the velocity vector field in the fluid portion between the horn and the electrode. As for the previous study, two parameters were studied: the electrical power supplied to the transducer and the electrode/transducer distance. The velocity vector fields show a main flow in the reactor axis. This flow seems to correspond to the conical cavitation bubbles structure which is observed on the laser tomography pictures. When an electrode is introduced into the reactor, two additional symmetric transversal flows can be quantified on both sides of the electrode.     

Parametric and high-frequency instability of Alfvén and magnetoacoustic waves in a plane waveguide run through by an ionized gas flow with a transverse magnetic field

We study the parametric and high-frequency instability of Alfvén waves and magnetic sound in a plane waveguide run through by a plasma flow. The mode energies and synchronism conditions are described and the possibility of efficient spectral up-conversion of Alfvén modes and magnetic sound is shown. State Technical University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 4, pp. 469–474, April, 1998.     

Impurity-related optical response in a 2D and 3D quantum dot with Gaussian confinement under intense laser field

ABSTRACT

Using the two-dimensional (2D) diagonalisation method, the impurity-related electronic states and optical response in a 2D quantum dot with Gaussian confinement potential under nonresonant intense laser field are investigated. The effects of a hydrogenic impurity on the energy spectrum and binding energy of the electron and also intersubband optical absorption are calculated. The obtained numerical results show that the degeneracies of the excited electron states are broken and the absorption spectrum exhibits a redshift with the values of the laser field. The findings indicate a new degree of freedom to tune the performance of novel optoelectronic devices, based on the quantum dots and to control their specific properties by means of intense laser field and hydrogenic donor impurity. Using the same Gaussian confinement model, the electronic properties of a confined electron in the region of a spherical quantum dot are studied under the combined effects of on-centre donor impurity and a linearly polarised intense laser radiation. The three-dimensional problem is used to theoretically model, with very good agreement, some experimental findings reported in the literature related to the photoluminescence peak energy transition.     

Weak localization with a specific role of t symmetry (2D and 3D holes in tellurium)

The anomalous magnetoresistance in crystalline tellurium is analyzed for different p-type carrier dimensions: a bulk sample, size-quantized accumulation layers on different tellurium crystallographic surfaces, and tellurium clusters (tellurium embedded in a dielectric opal matrix). It is shown that the effect can be interpreted in all cases in terms of the theory of weak localization of noninteracting particles with inclusion of the specific features of the tellurium band spectrum, namely, fully lifted spin degeneracy, trigonal spectrum distortion, and a specific role played by the t symmetry in inter-valley scattering. The differences observed among the various manifestations of the weak localization effect are determined by the hole wave function phase-relaxation channel which is dominant in a particular case. A case is discussed where the time characterizing the inter-valley transition probability becomes comparable to the momentum relaxation time. Fiz. Tverd. Tela (St. Petersburg) 41, 879–881 (May 1999)     

Steady and decaying flow of He II in a channel with ends blocked by superleaks

We report a new thermally generated steady-state flow of He II and its decay. An upward superflow through vertical channels of a square cross section with ends blocked by sintered silver superleaks is induced by a fountain pump. On increasing the heat power Q[over ] a vortex-free superflow and, above an intrinsic critical velocity of about 1.5 cm/s, two distinctly different turbulent steady-state flows characterized by the vortex line density L proportional, variantQ[over ];{2} and L proportional, variantQ[over ] are observed using the second sound attenuation technique. When Q[over ] is switched off, after a fast initial decay an exponential decay law is observed. A simple phenomenological model is introduced, capturing the observed features.     

Aging effects and dynamic scaling in the 3D Edwards-Anderson spin glasses: a comparison with experiments

We present a detailed study of the scaling behavior of correlations functions and AC susceptibility relaxations in the aging regime in three-dimensional spin glasses. The agreement between simulations and experiments is excellent confirming the validity of the full aging scenario with weak sub-aging effects. Received 21 December 2000 and Received in final form 22 February 2001     

Bright and dark solitons in a quasi-1D Bose-Einstein condensates modelled by 1D Gross-Pitaevskii equation with time-dependent parameters

We investigate the exact bright and dark solitary wave solutions of an effective 1D Bose-Einstein condensate (BEC) by assuming that the interaction energy is much less than the kinetic energy in the transverse direction. In particular, following the earlier works in the literature Pérez-García et al. (2004) [50], Serkin et al. (2007) [51], Gurses (2007) [52] and Kundu (2009) [53], we point out that the effective 1D equation resulting from the Gross-Pitaevskii (GP) equation can be transformed into the standard soliton (bright/dark) possessing, completely integrable 1D nonlinear Schrödinger (NLS) equation by effecting a change of variables of the coordinates and the wave function. We consider both confining and expulsive harmonic trap potentials separately and treat the atomic scattering length, gain/loss term and trap frequency as the experimental control parameters by modulating them as a function of time. In the case when the trap frequency is kept constant, we show the existence of different kinds of soliton solutions, such as the periodic oscillating solitons, collapse and revival of condensate, snake-like solitons, stable solitons, soliton growth and decay and formation of two-soliton bound state, as the atomic scattering length and gain/loss term are varied. However, when the trap frequency is also modulated, we show the phenomena of collapse and revival of two-soliton like bound state formation of the condensate for double modulated periodic potential and bright and dark solitons for step-wise modulated potentials.     

Generation of electromagnetic waves by relativistic electrons in a cavity with crossed radial electrostatic and axial magnetic fields under plasma resonance conditions

A theoretical analysis is made of the conditions for generation of electromagnetic waves by a thin cylindrical layer of relativistic electrons rotating in crossed axial magnetic and radial electrostatic fields in a cylindrical cavity. A dispersion equation is obtained to describe the interaction between waves and electrons under plasma resonance conditions. The dependence of the growth rates on the relativistic factor and the magnetic field are studied. Zh. Tekh. Fiz. 69, 112–114 (June 1999)     

Masking of short stimuli by noises with spiked spectra: II. Time summation and frequency selectivity of hearing in a narrow frequency range

The thresholds of masking of short high-frequency pulses with either different durations (1.25–25 ms) and similar central frequency or different central frequencies (3.6–4.4 kHz) but similar durations were measured to reveal manifestations of the properties of peripheral encoding in auditory perception. Noises with a spiked amplitude spectrum structure were used as maskers. The central frequency and the frequency band of a masker were 4 and 1 kHz, respectively. The central frequencies of a stimulus and a masker being equal, the noise the central frequency of which coincided with the frequency corresponding to a dip of an indented spectrum was called an off_(rip)-frequency masker. Owing to the off_(rip)-masker, stimuli-induced masking thresholds were formed taking into account excitation in a narrow region of a basila membrane and auditory nerve fibers with characteristic frequencies from a narrow range. High-frequency pulses with an envelope in the form of the Gaussian function and sinusoidal filling were used as stimuli. At masker levels of 30 dB above the auditory threshold, frequencies of off_(rip)-masker spectra spikes of 500–2000 Hz, and a central stimulus frequency of 4 kHz, the thresholds of tonal stimuli (25 ms in duration) masking in two out of three probationers were higher than the thresholds of masking of compact stimuli (1.25 ms in duration). In the third probationer, on the contrary, the thresholds of tonal stimuli masking were lower than the thresholds of compact stimuli masking. At masker levels of 50 dB, individual threshold differences disappeared. The obtained results were interpreted in the context of implementation of different methods of auditory encoding of the intensity. The methods were based on either the average frequency of auditory nerve pulsations or the number of fibers participating in the response. The interpretation was also carried out in the context of revealing manifestations of nonlinear properties of basila membrane displacements in auditory thresholds. The fact that the dependence of detection thresholds of compact stimuli on their central frequency in one of the two probationers did not reveal the minimum in case of coincidence of off_(rip)-masker and stimulus frequencies pointed to the presence of an auditory “problem zone” that was likely to be localized at the periphery of the auditory system.     

Bifurcation phenomena and processes in the flow formed in a three-dimensional phase space by a dynamic system with square-law nonlinearity

The basic laws of operation of a dynamic system with square-law nonlinearity and three-dimensional phase space are studied analytically, numerically, and experimentally. Results of analytical investigations of the stability of special points in the system and of numerical and full-scale experiments that indicate the existence of a sequence of bifurcation phenomena described by the Feigenbaum scenario are presented. The existence of two critical values of the control parameter, the first of which characterizes the first Hopf bifurcation and the second describes the destruction of motion at the expense of confluence of the chaotic attractor with the vicinity of the special repeller-type point, is proved. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 78–86, September, 2006.