Direct Numerical Simulations (DNS) of Particles in Spatially Varying Electric Fields

2014 ◽  
Author(s):  
Edison C. Amah ◽  
Pushpendra Singh ◽  
Mohammad Janjua
Keyword(s):  
Electric Fields ◽  
Numerical Scheme ◽  
Particle System ◽  
Particle Diameter ◽  
Solid Particles ◽  
Body Motion ◽  
Point Dipole ◽  
Electric Force ◽  
Combined System ◽  
Splitting Technique

A numerical scheme is developed to simulate the motion of dielectric particles in uniform and nonuniform electric fields of a micro fluidic device. The particles are moved using a direct simulation scheme in which the fundamental equations of motion of fluid and solid particles are solved without the use of models. The motion of particles is tracked using a distributed Lagrange multiplier method (DLM) and the electric force acting on the particles is calculated by integrating the Maxwell stress tensor (MST) over the particle surfaces. One of the key features of the DLM method is that the fluid-particle system is treated implicitly by using a combined weak formulation where the forces and moments between the particles and fluid cancel, as they are internal to the combined system. The MST is obtained from the electric potential, which, in turn, is obtained by solving the electrostatic problem. In our numerical scheme the Marchuk-Yanenko operator-splitting technique is used to decouple the difficulties associated with the incompressibility constraint, the nonlinear convection term, the rigid-body motion constraint and the electric force term. A comparison of the DNS results with those from the point-dipole approximation shows that the accuracy of the latter diminishes when the distance between the particles becomes comparable to the particle diameter; the domain size is comparable to the diameter; and also when the dielectric mismatch between the fluid and particles is relatively large.

scholarly journals Direct Numerical Simulation of Particles in Spatially Varying Electric Fields †

Fluids ◽  
2018 ◽  
Vol 3 (3) ◽  
pp. 52 ◽  
Author(s):  
Edison Amah ◽  
Muhammad Janjua ◽  
Pushpendra Singh
Keyword(s):  
Particle Size ◽  
Electric Fields ◽  
Numerical Scheme ◽  
Particle System ◽  
Particle Interaction ◽  
Body Motion ◽  
Numerical Code ◽  
Electric Force ◽  
Combined System ◽  
Splitting Technique

A numerical scheme is developed to simulate the motion of dielectric particles in the uniform and nonuniform electric fields of microfluidic devices. The motion of particles is simulated using a distributed Lagrange multiplier method (DLM) and the electric force acting on the particles is calculated by integrating the Maxwell stress tensor (MST) over the particle surfaces. One of the key features of the DLM method used is that the fluid-particle system is treated implicitly by using a combined weak formulation, where the forces and moments between the particles and fluid cancel, as they are internal to the combined system. The MST is obtained from the electric potential, which, in turn, is obtained by solving the electrostatic problem. In our numerical scheme, the domain is discretized using a finite element scheme and the Marchuk-Yanenko operator-splitting technique is used to decouple the difficulties associated with the incompressibility constraint, the nonlinear convection term, the rigid-body motion constraint and the electric force term. The numerical code is used to study the motion of particles in a dielectrophoretic cage which can be used to trap and hold particles at its center. If the particles moves away from the center of the cage, a resorting force acts on them towards the center. The MST results show that the ratio of the particle-particle interaction and dielectrophoretic forces decreases with increasing particle size. Therefore, larger particles move primarily under the action of the dielectrophoretic (DEP) force, especially in the high electric field gradient regions. Consequently, when the spacing between the electrodes is comparable to the particle size, instead of collecting on the same electrode by forming chains, they collect at different electrodes.

Direct Numerical Simulation (DNS) of Suspensions in Spatially Varying Electric Fields

2007 ◽  
Author(s):  
M. Janjua ◽  
S. Nudurupati ◽  
P. Singh ◽  
I. Fischer ◽  
Nadine Aubry
Keyword(s):  
Rigid Body ◽  
Electric Fields ◽  
Lagrange Multiplier ◽  
Numerical Scheme ◽  
Rigid Body Motion ◽  
Solid Particles ◽  
Lagrange Multiplier Method ◽  
Body Motion ◽  
Multiplier Method ◽  
Point Dipole

We have developed a numerical scheme to simulate the motion of dielectric particles in uniform and nonuniform electric fields. The particles are moved using a direct simulation scheme in which the fundamental equations of motion of fluid and solid particles are solved without the use of models. The motion of particles is tracked using a distributed Lagrange multiplier method (DLM) and the electric force acting on the particles is calculated by integrating the Maxwell stress tensor (MST) over the particle surfaces. One of the key features of the DLM method is that the fluid-particle system is treated implicitly by using a combined weak formulation where the forces and moments between the particles and fluid cancel, as they are internal to the combined system. The flow inside the particles is forced to be a rigid-body motion using the distributed Lagrange multiplier method. The MST is obtained from the electric potential, which, in turn, is obtained by solving the electrostatic problem. In our numerical scheme the Marchuk-Yanenko operator-splitting technique is used to decouple the difficulties associated with the incompressibility constraint, the nonlinear convection term, and the rigid-body motion constraint. A comparison of the DNS results with those from the point-dipole approximation shows that the accuracy of the latter diminishes when the distance between the particles becomes comparable to the particle diameter, the domain size is comparable to the diameter, and also when the dielectric mismatch between the fluid and particles is relatively large.

Direct Simulation of Electrorheological Suspensions

2001 ◽  
Author(s):  
Aijun Wang ◽  
Pushpendra Singh ◽  
Nadine Aubry
Keyword(s):  
Electric Field ◽  
Stokes Equations ◽  
Hydrodynamic Force ◽  
Particle System ◽  
Electrostatic Force ◽  
Body Motion ◽  
Three Dimensions ◽  
Spherical Particles ◽  
Point Dipole ◽  
Direct Simulation

Abstract A new distributed multiplier/fictitious (DLM) domain method is developed for direct simulation of electrorheological (ER) suspensions subjected to spatially uniform electrical fields. The method is implemented both in two and three dimensions. The fluid-particle system is treated implicitly using the combined weak formulation described in [1,2]. The governing Navier-Stokes equations for the fluid are solved everywhere, including the interior of the particles. The flow inside the particles is forced to be a rigid body motion by a distribution of Lagrange multipliers. The electrostatic force acting on the polarized spherical particles is modeled based on the point-dipole approximation. Using our code we have studied the time evolution of particle-scale structures of ER suspensions in channels subjected to the pressure driven flow. In our study, the flow direction is perpendicular to that of the electric field. Simulations show that when the hydrodynamic force is zero, or very small compared to the electrostatic force, the particles form chains that are aligned approximately parallel to the direction of electric field. But, when the magnitude of hydrodynamic force is comparable to that of the electrostatic force the particle chains orient at an angle with the direction of the electric field. The angle between the particle chain and the direction of the electric field depends on the relative strengths of the hydrodynamic and electrostatic forces.

Direct Simulation of Electrorheological Suspensions Subjected to Spatially Nonuniform Electric Field

2002 ◽  
Author(s):  
J. Kadaksham ◽  
P. Singh ◽  
N. Aubry
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Lagrange Multiplier ◽  
Dipole Approximation ◽  
Nonuniform Electric Field ◽  
Lagrange Multiplier Method ◽  
Body Motion ◽  
Multiplier Method ◽  
Point Dipole ◽  
Time Step

A numerical method based on the distributed Lagrange Multiplier method (DLM) [2,8] is developed for direct simulations of electrorheological (ER) liquids subjected to spatially varying electric fields. The flow inside particle boundaries is constrained to be rigid body motion by the distributed Lagrange multiplier method. The point-dipole approximation [6] is used to model the electrostatic forces acting on the polarized particles. The code is verified by performing a convergence study that shows that the results are independent of mesh and time step sizes. In a spatially nonuniform electric field the particles move to the regions where the magnitude of electric field is locally maximum when the particle permittivity is greater than that of the liquid. On the other hand, when the particle permittivity is smaller than that of the liquid the particles move to the regions of local minimum of electric field.

On a dusty-gas shock tube

1982 ◽  
Vol 382 (1783) ◽  
pp. 373-388 ◽  
Keyword(s):  
Shock Wave ◽  
Shock Tube ◽  
Pressure Ratio ◽  
Finite Thickness ◽  
Operator Splitting ◽  
Particle Diameter ◽  
Particle Number Density ◽  
Solid Particles ◽  
Splitting Technique ◽  
Effective Contact

Analytical and numerical methods were used to investigate the flow in­duced by a shock wave in a shock-tube channel containing air laden with suspended small solid particles. Exact results are given for the frozen and equilibrium shock-wave properties as a function of diaphragm-pressure ratio and shock-wave Mach numbers. The driver contained air at high pressure. A modified random-choice method together with an operator-splitting technique show clearly both the decay of a discontinuous frozen shock wave and a contact discontinuity, and the formation of a stationary shock structure and an effective contact front of finite thickness. The effects of particle diameter, particle-number density and diaphragm- pressure ratio on the transitional behaviour of the flow are investigated in detail. The alteration of the flow properties owing to the presence of particles is discussed thoroughly and compared with classical shock-tube flows.

Experimental Investigation of Convective Melting of Granular Packed Bed Under Microgravity

2000 ◽  
Author(s):  
J. Jiang ◽  
Y. Hao ◽  
Y.-X. Tao
Keyword(s):  
Experimental Investigation ◽  
Average Particle Size ◽  
Particle Diameter ◽  
Vertical Direction ◽  
Packed Bed ◽  
Melting Rate ◽  
Control Flow ◽  
Solid Particles ◽  
Average Particle ◽  
Ice Particles

Abstract To improve the understanding of convective melting of packed solid particles in a fluid, an experimental investigation is conducted to study the melting characteristics of a packed bed by unmasking the buoyancy forces due to the density difference between the melt and solid particles. A close-loop apparatus, named the particle-melting-in-flow (PMF) module, is designed to allow a steady state liquid flow under a specified temperature. The module is on board NASA’s KC-135 reduced gravity aircraft for the experiments. In the test module, water is used as the fluid, and ice particles are fed to the test section at the beginning of the test. As the liquid flows though the bed, the solid grains melt. A perforate plate, through which liquid can flow while the ice particles are retained, bounds the downstream of the packed bed. From the digital video images the local packed bed thickness is measured under control flow rate, and the melting rate is determined. The temperature distribution along the horizontal direction and vertical direction is measured using 19 thermocouples. An infrared camera is mounted to record the local temperature variation between liquid and solid. The melting rates are presented as a function of upstream flow velocity, temperature and initial average particle size of the packed bed. It is found that the melting rate is influenced mainly by the ratio of the Reynolds number (Re, based on the initial particle diameter) to the square of the Froud number (Fr), and me Stefan number (Ste). In general, the dimensionless melting rate decreases as Re/Fr2 increases and increases as Ste increases. With the absence of gravity, i.e., Froud number approaches infinity, a maximum melting rate can be achieved for otherwise the same test conditions. The increase in the melting rate with the increase in Stephan number also becomes more pronounced under the zero gravity condition.

Modeling evaluation on solid-liquid mixing characteristics in a dislocated guide impeller stirred tank

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Deyin Gu ◽  
Fenghui Zhao ◽  
Xingmin Wang ◽  
Zuohua Liu
Keyword(s):  
Power Consumption ◽  
Solid Particle ◽  
Particle Diameter ◽  
Solid Particles ◽  
Stirred Tank ◽  
Mixing Process ◽  
Solid Holdup ◽  
Aperture Ratio ◽  
Liquid Mixing ◽  
Solid Liquid

Abstract The solid-liquid mixing characteristics in a stirred tank with pitched blade impellers, dislocated impellers, and dislocated guide impellers were investigated through using CFD simulation. The effects of impeller speed, impeller type, aperture ratio, aperture length, solid particle diameter and initial solid holdup on the homogeneity degree in the solid-liquid mixing process were investigated. As expected, the solid particle suspension quality was increased with an increase in impeller speed. The dislocated impeller could reduce the accumulation of solid particles and improve the cloud height compared with pitched blade impeller under the same power consumption. The dislocated guide impeller could enhance the solid particles suspension quality on the basis of dislocated impeller, and the optimum aperture ratio and aperture length of dislocated guide impeller were 12.25% and 7 mm, respectively, in the solid-liquid mixing process. Smaller solid particle diameter and lower initial solid holdup led to higher homogeneity degree of solid-liquid mixing system. The dislocated guide impeller could increase solid particle integrated velocity and enhance turbulent intensity of solid-liquid two-phase compared with pitched blade impeller and dislocated impeller under the same power consumption.

scholarly journals Numerical Simulations and Experiments of Ignition of Solid Particles in a Laminar Burner: Effects of Slip Velocity and Particle Swelling

2020 ◽  
Author(s):  
Antonio Attili ◽  
Pooria Farmand ◽  
Christoph Schumann ◽  
Sima Farazi ◽  
Benjamin Böhm ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ignition Delay ◽  
Delay Time ◽  
Slip Velocity ◽  
Ignition Delay Time ◽  
Flame Structure ◽  
Particle Diameter ◽  
Point Particle ◽  
Solid Particles ◽  
Experimental Measurements

Abstract Ignition and combustion of pulverized solid fuel is investigated in a laminar burner. The two-dimensional OH radical field is measured in the experiments, providing information on the first onset of ignition and a detailed characterization of the flame structure for the single particle. In addition, particle velocity and diameter are tracked in time in the experiments. Simulations are carried out with a Lagrangian point-particle approach fully coupled with an Eulerian solver for the gas-phase, which includes detailed chemistry and transport. The numerical simulation results are compared with the experimental measurements in order to investigate the ignition characteristics. The effect of the slip velocity, i.e. the initial velocity difference between the gas-phase and the particle, is investigated numerically. For increasing slip velocity, the ignition delay time decreases. For large slip velocities, the decrease in ignition delay time is found to saturate to a value which is about 40% smaller than the ignition delay time at zero slip velocity. Performing a simulation neglecting the dependency of the Nusselt number on the slip velocity, it is found that this dependency does not play a role. On the contrary, it is found that the decrease of ignition delay time induced by the slip velocity is due to modifications of the temperature field around the particle. In particular, the low-temperature fluid related to the energy sink due to particle heating is transported away from the particle position when the slip velocity is non-zero; therefore, the particle is exposed to larger temperatures. Finally, the effect of particle swell is investigated using a model for the particle swelling based on the CPD framework. With this model, we observed negligible differences in ignition delay time compared to the case in which swelling is not included. This is related to the negligible swelling predicted by this model before ignition. However, this is inconsistent with the experimental measurements of particle diameter, showing a significant increase of diameter even before ignition. In further simulations, the measured swelling was directly prescribed, using an analytical fit at the given conditions. With this approach, it is found that the inclusion of swelling reduces the ignition delay time by about 20% for small particles while it is negligible for large particles.

scholarly journals Influence of DC Electric Fields on Pollution of HVDC Composite Insulator Short Samples with Different Environmental Parameters

Energies ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 2304 ◽  
Author(s):  
Xinhan Qiao ◽  
Zhijin Zhang ◽  
Xingliang Jiang ◽  
Tian Liang
Keyword(s):  
Power Systems ◽  
Electric Fields ◽  
Particle Motion ◽  
Particle Diameter ◽  
Environmental Parameters ◽  
Composite Insulator ◽  
High Voltage Direct Current ◽  
Electrical Stress ◽  
Motion Characteristics ◽  
Dc Electric Fields

Pollution-induced flashover is a serious threat to the safe operation of power systems. With the development of High Voltage Direct Current (HVDC), it is necessary to study insulator contamination in DC electric fields. In this paper, the energized wind tunnel contamination test was conducted in order to systematically study the pollution ratio, k (ratio of non-soluble deposit density (NSDD) of a DC-energized condition to a non-energized condition), under different environmental parameters. Later, a two-dimensional contamination model of short samples of an HVDC composite insulator was established. The particle motion characteristics under different environmental parameters were then analyzed by the finite element method (FEM). The research results showed that—the DC electric field had an influence on particle motion but in different environments, the degree of influence was different. In addition, k was found to largely vary, with a variation in the environmental parameters. When the electrical stress (Es) increased from 0 to 70 kV/m, k increased gradually. However, when the wind speed (ws) increased, k experienced a decreasing trend. Finally, as the particle diameter (dp) decreased, k increased at first, followed by a decrease, and then again showed an increase. The results of the pollution ratio, k, for different environmental parameters are of great importance for guiding anti-pollution work in power systems.

Sign in / Sign up

Export Citation Format

Share Document