Electrohydrodynamic Flow Patterns Research Articles

Electrohydrodynamic flows in electrostatic precipitator of five shaped collecting electrodes

The electrohydrodynamic (EHD) flows in wire-plate electrostatic precipitators (ESP) of five shaped collecting electrodes are simulated by employing the CFD code FLUENT with the aid of a user defined function (UDF). The results show that the EHD flow patterns are different in the five configurations. Bending of the collecting plate can easily lead to the peak of the electric field intensity near the collecting surface. The space charge density near the W-type collecting surface is more uniform than those of the other four types. The flow induced by ionic wind in the C-type plate is strongest among the five channels.

Characterization of electrohydrodynamic (EHD) flow in electrostatic precitators (ESP) by numerical simulation and quantitative vortex analysis

Electrohydrodynamic (EHD) flow is a very common physical phenomenon in industry application, such as corona induced electrical pump and electrostatic precipitator (ESP). There are many available researches reporting investigations of the EHD flow patterns by numerical method and qualitatively analyzing the flow characteristics. In present study, the quantitative method was adopted to analyze EHD flow in different ESP types. This study utilized a hybrid method using the Finite Element Method (FEM) to simulate the ionized electric field and the Finite Volume Method (FVM) to predict the EHD flow in ESP simulation. Based on the validated model, the EHD flow patterns in several widely used types of ESP were investigated numerically. In previous studies, the EHD flow types were qualitatively classified by observing the vortex size and number. In present paper, the corona induced EHD flow was also analyzed quantitatively using the Qkubo-Weiss index. The results show that the flow vorticity was dominant in the area of the vortex center. In the interspace between vortexes, the flow deformation was dominant. The relationship between the EHD flow types and quantitative parameters (such as pressure drop, turbulence intensity and flow vortex index) was studied, too. In future, the concept of quantitative vortex indexes could be utilized in experimental, numerical or theoretical work and it would improve the existing research related to EHD flow.

Numerical study on the effect of EHD flow on mass transfer of gas mixtures

PurposeThe paper aims to discuss the mass transfer of gas mixtures under the influence of electrohydrodynamic (EHD) flow induced by direct current (DC) corona discharge of wire-to-plane electrode, using a coupled numerical model.Design/methodology/approachA coupled numerical method is developed in this paper. Lattice Boltzmann model of binary gas mixtures coupled with the Coulomb force as an external force is introduced to predict the gas flow and species transport affected by EHD flow. Meanwhile, the distributions of electric field and space charge density during DC corona discharge are obtained using the finite difference method and the method of characteristics.FindingsThe numerical results of mass transfer effected by EHD flow reveal that the high electric field intensity is observed near the surface of corona wire, which causes the higher Coulomb force to form the EHD flow pattern of anticlockwise vortex. The EHD vortex flow plays a considerable role in the mass transport enhancement of gas species emit from the plane electrode, and the significant difference of the local Sherwood number is presented along the direction parallel to plane electrode. In addition, the enhance effectiveness with the different applied voltage is assessed, and the influencing mechanism of enhancement is investigated in this work.Originality/valueThe proposed numerical model will be useful in the study of mass transfer and fluid flow effected by EHD.

Correlation of design parameters with performance for electrostatic Precipitator. Part I. 3D model development and validation

• Development and validation of 3D modeling for electrostatic precipitators. • Shielding effects between wires are captured for the multi-wire precipitators. • Validation considers both global and local performances of the precipitator. • Good agreement with six experimental and four numerical works from literature. As the first part of a two-paper series, this paper develops a three-dimensional model that describes corona discharge, turbulent flow, particle charging and tracking in electrostatic precipitators (ESP). To capture the shielding effects between discharge wires in a multi-wire ESP, the corona-discharge-induced space charge density at an arbitrary point between the discharge wire and grounded plates is specified as the sum of two components: (i) a uniform value on the wire surface which is resolved individually for each wire; and (ii) a space-dependent variation relative to the uniform part. The present model is solved with the finite element method and validated with experimental and numerical results from literature. Good agreement is obtained and illustrated in terms of distributions of electric potential, current density, electrohydrodynamic flow pattern, and particle trajectories, as well as corona current and particle collection efficiency. This validated model will be applied in Part II and integrated with the design-of-experiment approach to analyze both individual and interactive effects of design parameters on ESP performance.

Experimental Study on EHD Flow Transition in a Small Scale Wire-plate ESP

Abstract The electrohydrodynamic (EHD) flow induced by the corona discharge was experimentally investigated in an electrostatic precipitator (ESP). The ESP was a narrow horizontal Plexiglas box (1300 mm×60 mm×60 mm). The electrode set consisted of a single wire discharge electrode and two collecting aluminum plate electrodes. Particle Image Velocimetry (PIV) method was used to visualize the EHD flow characteristics inside the ESP seeded with fine oil droplets. The influence of applied voltage (from 8 kV to 10 kV) and primary gas flow (0.15 m/s, 0.2 m/s, 0.4 m/s) on the EHD flow transition was elucidated through experimental analysis. The formation and transition of typical EHD flows from onset to the fully developed were described and explained. Experimental results showed that the EHD flow patterns change depends on the gas velocity and applied voltage. EHD flow starts with flow streamlines near collecting plates bending towards the wire electrode, forming two void regions. An oscillating jet forming the downstream appeared and moved towards the wire electrode as voltage increased. For higher velocities (≥0.2 m/s), the EHD transition became near wire phenomenon with a jet-like flow structure near the wire, forming a void region behind the wire and expanding as voltage increased. Fully developed EHD secondary flow in the form of counter-rotating vortices appeared upstream with high applied voltage.

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.

Transient Two-Phase Flow Patterns by Application of a High Voltage Pulse Width Modulated Signal and the Effect on Condensation Heat Transfer

The objectives of this study are (i) to determine the transient phase redistributions of a two-phase flow in a smooth horizontal annular channel by applying high voltage pulses to induce electric fields and (ii) to quantify the resultant changes in the condensation heat transfer. The experiments were performed using refrigerant R-134a flowing in the annular channel that was cooled on the outside by a counter-current flow of water. The electric fields are established by applying high voltage to a concentric rod electrode inside a grounded tube. The effect of the electrohydrodynamic (EHD) forces on the changes to the initial stratified/stratified wavy flow pattern was visualized using a high speed camera. The EHD effect results in the redistribution of the liquid–vapor phase within the channel and unique flow structures, such as twisted liquid cones and entrained droplets, are observed. These structures only appear during the initial application of EHD and are absent in the steady state. Experiments were performed using a 8 kV pulse width modulated (PWM) signal with duty cycles ranging from 0% to 100% to evaluate the heat transfer and pressure drop characteristics of the transient EHD flow patterns. The resultant heat transfer increased with the duty cycle to approximately 2.7-fold at a mass flux of 45–55 kg/m2s and 1.2-fold at a mass flux of 110 kg/m2s. The enhancement was higher as the pulse width was increased.

3D PIV measurements of the EHD flow patterns in a narrow lectrostatic precipitator with wire-plate or wire-flocking electrodes

The results of 3{dimensional (3D) Particle Image Velocimetry (PIV) measurements of the electrohydrodynamic (EHD) ∞ow patterns in a narrow electrostatic precipitator (ESP) are presented in this paper. The ESP was an acrylic parallelepiped with a wire discharge electrode and two plane collecting electrodes. In contrary to typical ESPs the wire electrode was placed along the gas ∞ow, in the ESP centre, in the halfway between collecting electrodes. Either two smooth stainless steel plates or two stainless steel meshes with nylon ∞ocks were used as the collecting electrodes. They were placed on the top and bottom of the ESP. The PIV measurements were carried out in two parallel planes, placed perpendicularly to the collecting electrodes and parallel to the wire electrode. The obtained results showed some similarities and difierences of a 3D particle ∞ow in the ESP with plate or ∞ocking electrodes.

Simulation of the Electrohydrodynamic Flow Pattern in an Asymmetric System of Electrodes

Computer-aided simulation of the electrohydrodynamic flow pattern in an asymmetric system of electrodes (configured as “narrow depression under plane” or “blade above plane”) is carried out. The objective of the simulation is to reveal a correspondence between the kinematic flow pattern and the distribution of driving (Coulomb) forces. The kinematic pattern of the flow simulated is compared with the results of experimental data processing. Good agreement between the simulation results and experimental data is found.

An Experimental Visualization and Image Analysis of Electrohydrodynamically Induced Vapor-Phase Silicon Oil Flow under DC Corona Discharge

A DC corona discharge induced electrohydrodynamic (EHD) flow phenomenon for a multi-phase fluid containing a vapor-phase dielectric liquid in the fresh air was investigated. The experimental electrode system was a simple arrangement of needle-plate electrodes for the corona discharges and high-resistivity silicon oil was used as the vapor-phase liquid enclosure. The qualitative observation of EHD flow patterns was conducted by an optical processing on computer tomography and the time-series of discharge current pulse generations at corona discharge electrode were measured simultaneously. These experimental results were analyzed in relationship between the EHD flow motions and the current pulse generations in synchronization. The current pulses and the EHD flow motions from the corona discharge electrode presented a continuous mode similar to the ionic wind in the fresh air and an intermittent mode. In the intermittent mode, the observed EHD flow motion was synchronized with the separated discharge pulse generations. From these experimental results, it was expected that the existence of silicon oil vapor trapped charges gave an occasion to the intermittent generations of the discharge pulses and the secondary EHD flow.

Observation of Squint-A Nonlinear Feature of Flow Patterns in Nematics

Abstract Evidence is presented for the existence of squint as previously predicted by Ben-Abraham. A quantitative measure of this nonlinear feature of electrohydrodynamic flow patterns as observed in MBBA is presented.