Numerical Analysis of the Characteristics of an Arc in Laminar and Turbulent Gas Flows

The equations of magnetic gas dynamics are used to calculate the characteristics of an electric arc in a plasmotron channel versus the gas flow rate. The results obtained with the aid of the laminar and the two-parameter k– model of turbulence with allowance for deviations from equilibrium in the plasma and for the swirling of the gas are compared with experimental data. The stability of a laminar flow to the effect of weak hydrodynamic perturbations is investigated.     

Measurements of Particle Velocity and Concentration for Dilute Swirling Gas-Solid Flow in a Vertical Pipe

Experimental studies concerning the characterization of a dilute swirling gas-solid flow were carried out in a vertical pipe with a height of 12 m and an inner diameter of 80 mm. Polyethylene pellets, with mean diameter of 3.2 mm, were used as test particles. The initial swirl number varied from 0.0 to 0.94, the mean gas velocity varied from 9 to 25 m/s, and the solid-gas ratio varied from 0.2 to 0.7. In this study, the particle velocity and concentration profiles were measured by the photographic image technique for both nonswirling (axial) and swirling gas-solid flows. It was found that the particle velocity of the swirling flow is lower than that of the axial flow in the range of high gas velocity; however, high particle velocity in the former flow can be obtained in the range of low gas velocity. The particle velocity profiles, on the other hand, were found to be nearly uniform in both the swirling and axial flows. The particle concentration profiles in the swirling flow exhibited symmetric distributions with respect to the pipe axis, and a higher particle concentration appeared in the vicinity of the wall located in the acceleration region.

gas-solid two-phase flow particle concentration particle velocity pipeline swirling flow     

A Numerical Simulation of Swirling Flow Pneumatic Conveying in a Vertical Pipeline

A numerical prediction for the axial and swirling pneumatic conveying in a vertical pipe was performed based on an Eulerian approach for the gas and a stochastic Lagrangian approach for the particles, where κ – ? turbulence model, the model of particle-particle and particle-wall collisions, was adopted. The numerical results are presented for polyethylene pellets of 3.2mm diameter conveyed through a pipeline of 12m in height with an inner diameter of 80mm. The initial swirl number was 0.0 and 0.68, the mean gas velocity varied from 11 to 17m/s, and the solid mass flow rate was 0.03 and 0.084 kg/s. From the numerical analysis, the swirl decay of the swirling gas-solid flow was found to be rapid in the acceleration region and approached the clean swirling flow in a fully developed region. The turbulent kinetic energy and energy dissipation rates of the swirling gas-solid flow increased near the wall and reduced in other regions. The comparison of predicted values with measured data showed a good agreement.     

The structure of gasdynamic flow in a supersonic separator of natural gas

Results are given of calculations of flow within the two-dimensional Euler model of supersonic swirling flow of gas in a supersonic separator of natural gas. The formulation of the problem is given, numerical experiment is performed, and the basic parameters of gas flow (velocity components, pressure, and so on) are obtained as functions of radius. The process of relaxation of flow to steady state with the formation of shock wave is considered, and the shock wave structure is determined. The behavior of gasdynamic parameters is analyzed under conditions of separation in the region of shock wave and behind it.     

Numerical investigation of the interaction of isothermal,oppositely swirling flows in an annular channel

The influence of swirling of the flow in the recirculation zone behind the end surface separating oppositely swirling flows, in an annular channel in conditions of isothermal flow, is subjected to theoretical analysis.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 4, pp. 674–677, October, 1981.     

Calculation of the Characteristics of the Initial Section of the Plasma Generator Channel

An equilibrium magnetogasdynamic model of plasma is used to calculate the flow and heating of gas in the initial section of the plasma generator channel. The gas is heated by an electric arc. The distribution of the electric field intensity, temperature, velocity, and pressure drop is obtained depending on changes in the current strength, gas flow rate, and the wall thickness of the electrode nozzle. It is found that axial zones of return flow are formed in the vicinity of the initial section of the channel. The calculation results are compared to the experimental data.     

Mathematical simulation of the vertical part of an upward swirling flow

The motion of air in the vertical part of an upward swirling flow is simulated by constructing solutions of the system of equations of gas dynamics. The properties of the solutions have been compared to the laboratory experiments on creation and control of behavior of free vortices. In particular, the ring structure of a flow in the vertical part of the upward swirling flow has been simulated. The numerical values of the gasdynamic characteristics of the flow are close to the respective parameters of free vortices reproduced in the experiments.     

Features of the transverse discharge glow depending on the gas flow rate in a vortex chamber

Experimentally observed features in the formation of glowing zones in gas discharge at various mass flow rates are qualitatively explained based on the numerical simulation of a turbulent swirling flow with a local source of heat release.     

Effect of gas stream swirls on the instability of viscous annular liquid jets

Summary. A linear temporal instability analysis has been carried out for a viscous annular liquid jet moving in two swirling gas streams of unequal velocities with the gas stream swirling motion represented by free-vortex rotation. It is found that two modes of unstable surface waves exist, the para-sinuous and para-varicose mode. The results of the two limiting flow situations, which are a cylindrical liquid jet in a swirling gas stream and a swirling gas jet in a liquid stream, indicate that their instabilities are associated with the para-varicose mode on the outer interface and para-sinuous mode on the inner interface of the annular liquid jet, respectively. It is shown that the centripetal force induced by the inner gas stream rotation is destabilizing and enhances the jet instability, while the centripetal force produced by the outer gas stream rotation is stabilizing and reduces the instability of annular liquid jets. It is interesting to find that for a para-varicose mode an increase in the outer gas rotation not only reduces the upper cut-off wave number, but also increases the lower cut-off wave number, leading to the significant reduction in the unstable wave number range. The stabilizing effect of the outer gas rotation is much more significant for para-varicose mode, and the destabilizing effect of the inner gas rotation is much more influential for para-sinuous mode. In general, the para-sinuous mode has a much larger growth rate and is predominant in the annular liquid jet breakup process. Therefore, increasing the inner gas stream rotation can significantly enhance the breakup of annular liquid jets for practical spray applications.     

The effect of plasma-forming gas flow swirling on the energy characteristics of swirl plasmatrons

We investigate the effect of swirling of a plasma-forming gas on the energy characteristics of two-sided outflow swirl plasmatrons with a “blind≓ tubular and end-wall electrodes. The results obtained indicate the effect of flow swirling on the energy characteristics of the plasmatrons investigated.     

Investigation of the defocusing properties of a vortical gas flow

Results are presented of measurements of the focal length of a gas lens formed in a swirling gas flow as well as during combustion of a glow discharge therein. An analytic dependence is obtained to estimate the focal length.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 5, pp. 742–747, November, 1990.     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

ABSTRACT

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-? turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-ε turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.     

An Investigation of Spatial Distribution of Characteristics of a Plasma Stream Formed by a Hall Discharge in a Channel with Metal Walls

The effect of the system of delivery of the working medium on the characteristics of a plasma stream in a Hall accelerator with closed azimuthal current is experimentally investigated. The gas delivery system utilizes a porous diaphragm from a carbon–carbon composite material whose pore size is comparable with the Debye radius of the electrons of plasma formed in a discharge channel. The calorimetric method is used to determine the degree of azimuthal and radial nonuniformity of distribution of the energy of plasma stream developed by the accelerator, namely, the distribution of temperature of a titanium target mounted perpendicularly to the incident stream is taken with the aid of an infrared imager. The probe method is used to measure the spatial distribution of temperature and the concentration of charge-exchange plasma at the accelerator channel exit. It is shown that the ratio of the kinetic energy of the flow of heavy particles to the expended electric energy (energy efficiency) exceeds 0.5.     

Velocity measurements in a strongly swirling natural gas flame

The present study was focused on the turbulent velocity field of a central annular natural gas jet which penetrated a strongly swirling air flow. Due to the high swirl number S=0.95 and the high momentum ratio, the fuel jet was almost immediately integrated into the air stream. High rates of shear resulted in an intensive turbulent mixing process between natural gas and air. The central hub of the fuel exit annulus stabilized the reverse flow zone at a fixed location. The present nozzle configuration resulted in a very stable and symmetric flame.     

Spectral measurements of the gas and electron temperatures in the flame of a single-phase ac plasma generator

High-power electric-arc ac plasma generators find extensive application which is primarily associated with the problem of processing of organic waste and production of synthesis gas. The structure of a high-power single-chamber multiphase ac plasma generator with rail-type electrodes includes an injector of primary charge carriers which is a single-phase high-voltage plasma generator with a power of 10 kW or lower. This latter plasma generator may be further employed for solving other problems. Results are given of spectroscopic measurements of gas temperature fields at the nozzle exit section of a high-voltage plasma generator with rod electrodes located in a cylindrical channel. The pattern of variation of the temperature fields as a function of working gas flow rate is investigated.     

Evaluation of natural gas dehydration in supersonic swirling separators applying the Discrete Particle Method

The natural gas flow fields and particles separation characteristics were numerically calculated with the RNG k ? ε turbulence model and Discrete Particle Method (DPM) in the supersonic swirling separator. An experimental system was set up for testing the separation efficiency of three new designed separators with wet air. The numerical results showed that the new annular nozzle not only expanded the natural gas to supersonic velocity with resulting in low temperature (?72 °C), but also strengthened the swirling flow with the centrifugal field of 640 000g (g is the acceleration of gravity), both of which created good conditions for natural gas dehydration. Under the strong swirling flow field, most particles collided with the walls or entered into the liquid-collection space directly, while only few particles escaped together with the gas flow. The separation efficiency reached over 95%, when the length of the cyclone separation section was about 10 times of the diameter of the wall at throat. The experimental results indicated that the water can be efficiently removed from the wet air. The numerical results were in good agreements with the experimental findings, which demonstrated that the Discrete Particle Method (DPM) was accurate and stable enough to evaluate the dehydration characteristics of the supersonic swirling separator.     

Numerical Investigation of the Heat Exchange and Firing of Reactive Channel Walls by a High-Temperature Swirling-Gas Flow

A study is made of the process of firing of reactive channel walls by a swirling flow of hot gases. It is shown that the swirl of the flow leads to a reduction in the time of establishment of thermal equilibrium and that of firing; these times are reduced in a stepwise manner with the appearance of a recirculation zone in the strong-swirling flow. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 3, pp. 123–128, May–June, 2005.     

CFD simulation and performance optimization of a new horizontal turbo air classifier

A new horizontal turbo air classifier equipped with two inclined air inlets has been introduced. The flow field and classification performance of the classifier have been investigated using CFD method and response surface methodology (RSM). Simulation results show that the flow field is composed of the primary swirling flow and the secondary upward washing air, and the uniformly distributed swirling flow occupies the classifying chamber. The tangential gas velocity reaches the maximum value on the outer surface of the rotor cage, generating strong centrifugal force for the particle classification. The discrete phase model (DPM) can predict the cut sizes, but cannot present the fish-hook phenomenon. The desirable experimental condition by targeting the cut size of 20 μm and minimizing the classifying accuracy index is, rotor speed of 1373.6 rpm, primary air volume flow rate of 261.8 m³/h and secondary air volume flow rate of 42.4 m³/h. The corresponding fine and coarse fraction loss are less than 1.42% and 7.24%, respectively. This study provides a new strategy to design the horizontal turbo air classifier.     

Wavelet Multi-Resolution Cross-Correlation Analysis of Swirling Gas-Solid Flow in a Horizontal Pipe

A wavelet multi-resolution cross-correlation analysis was developed and applied to experimental pressure-time signals in order to analyze the characteristics of swirling gas-solid flow in both Fourier and physical spaces. The experiment was carried out in a horizontal pipe with a length of 7.5 m and an inner diameter of 76 mm. The initial swirl number based on the total inflow was varied from 0.0 to 0.61, the mean gas velocity was varied from 6 to 28 m/s, and the solid mass flow rate was varied from 0.08 to 0.5. From the wavelet multi-resolution correlation analysis of the fluctuating pressure in the range of low air velocity, the characteristics of swirling gas-solid two-phase flows were extracted at various frequencies. Much stronger correlations were found in the range of low frequency, which implied periodic motion of dunes and sliding clusters. Additionally, it was revealed that the motion of a large cluster sliding flow contains two smaller clusters and the moving velocities of dunes were 1 m/s and 2 m/s, respectively. However, no correlation existed at smaller scales of correlation features, which indicated heterogeneous suspension flow.