Swirling Gas Flow Research Articles

Effects of inlet/outlet configurations on the electrostatic capture of airborne nanoparticles and viruses

Motivated by capture and detection of airborne biological agents in real time with a cantilever biosensor without introducing the agents into liquids, we present the effects of inlet/outlet configurations of a homemade particle collector on the electrostatic capture of airborne 100 nm diameter nanoparticles under swirling gas flows. This particle collector has three different inlet/outlet configurations: forward inlet/outlet (FO), backward inlet/outlet (BO) and straight inlet/outlet (SO) configurations. We also present the electrostatic capture of Vaccinia viruses using the same particle collector and compare these virus measurements with the nanoparticle cases. The most particles were collected in the FO configuration. The numbers of particles captured in the BO and SO configurations were close within their standard deviations. For all the three configurations tested, the number of particles captured in the center electrode C was much smaller than those captured in the other electrodes at a flow rate of 1.1 l min−1 and an applied potential of 2 kV. Using a commercial CFD code FLUENT, we also simulated the effects of the three inlet/outlet configurations on the particle capture in terms of particle trajectories, velocities and travel times. This simulation was in a good agreement with measurements that the FO configuration is the most favorable to particle capture among the tested configurations at a flow rate of 1.1 l min−1. The effects of particle diameters on the capture will also be discussed. This collector can be used for real-time monitoring of bioaerosols along with cantilever biosensors.

Cyclostrophic adjustment in swirling gas flows and the Ranque-Hilsch vortex tube effect

A theoretical analysis of cyclostrophic adjustment is presented; i.e., adjustment to balance between pressure gradient and centrifugal force in axisymmetric flow of an inviscid gas is examined. The solution to the problem is represented as the sum of a time-independent (balanced) and time-dependent (wave) components. It is shown that the wave component of the flow in an unbounded domain decays with time, and the corresponding solution reduces to the balanced component. In a bounded domain, the balanced flow component exists against the background of undamped acoustic waves. It is found that the balanced flow is thermally stratified at Mach numbers close to unity, with a substantial decrease in gas temperature (to between −50 and −100°C) in the axial region. This finding, combined with the results of special experiments, is used to explain the Ranque-Hilsch vortex tube effect.

Enhancement of Mass Transfer in a Spray Tower Using Swirling Gas Flow

Spray towers are commonly used in the chemical and process industries for a number of applications including absorption, desorption and humidification. However, the main disadvantage of a spray tower compared with that of a packed tower is its lower contact efficiency. The present study is concerned with the enhancement of mass transfer between a continuous gas phase and liquid droplets in a spray tower by imparting swirl to the axial gas flow through the tower. It is well known that swirling flow has the ability to augment the rates of heat and mass transfer. Experimental investigations into the hydrodynamics and mass transfer in a laboratory-scale spray tower for air-NH3/H2O system using axial and swirling gas flows have been carried out. The hydrodynamic studies included measurements of the gas velocity distributions and overall pressure drop in the tower, and characterization of water sprays generated by a pressure-swirl nozzle where radial liquid distributions, droplet size and its distribution and mean droplet size in terms of SMD were measured. As for the mass transfer performance of the spray tower, the effect of the gas and liquid flow rates on the overall gas phase mass transfer coefficient, Kga, was investigated for both swirling and non-swirling axial gas flows in order to quantify the effect of swirl. It has been found that Kga increases with increasing gas/liquid flow rates and imparting swirl in the gas flow enhances Kga up to 20% compared with that in axial flows. Correlations of Kga as a function of the gas/liquid flow rates, and also as a function of the gas flow rate and initial droplets SMD are developed. A design methodology to determine the height of a spray tower required to achieve a specified amount of removal of a solute from a gas mixture is proposed.

Experimental Study of Heat and Mass Transfer in a Swirling Gas Flow

Experimental Study of Heat and Mass Transfer in a Swirling Gas Flow

The unstable spectrum of swirling gas flows

The asymptotic structure of the discrete spectrum of a compressible inviscid swirling flow with arbitrary radial distributions of density, pressure and velocity is described for disturbances with large wavenumbers. It is shown that discrete eigenmodes are unstable when a criterion derived by Eckhoff & Storesletten (1978) is satisfied. In general, these modes are characterized by a length scale of order .

Development of gas–solid direct contact heat exchanger by use of axial flow cyclone

A heat exchanger between particulate or granular materials and gas is developed. It makes use of a swirling gas flow similar to the usual cyclone separators but the difference from them is that the swirl making gas is issued into the cyclone chamber with downward axial velocity component. After it turns the flow direction near the bottom of the chamber, the low temperature gas receives heat from high temperature particles supplied from above at the chamber's center. Through this configuration, a direct contact and quasi counter-flow heat exchange pattern is realized so that the effective recovery of heat carried by particles is achieved. A model heat exchanger was manufactured via several numerical experiments and its performances of heat exchange as well as particle recovery were examined. Attaching a small particle diffuser below the particle-feeding nozzle brought about a drastic improvement of the heat exchange performance without deteriorating the particle recovery efficiency. The outlet gas temperature much higher than the particle outlet temperature was finally obtained, which is never realized in the parallel flow heat exchanger.

Current density at the refractory cathode of a high-current high-pressure arc (two modes of cathode spot attachment)

The attachment of a high-pressure arc at a refractory cathode was investigated theoretically and experimentally. Simple model considerations showed that an isolated cathode spot (CS) could function in two different modes. At relatively low currents and pressures, the CS mode (first mode) corresponds to the existing model (Bade W L and Yos Y M 1963 Technical Documentary Report No ASD-TDR-62-729 vol 1 (part II); Neumann W 1969 Beitr Plasmaphysik 9 499–526; Benilov M S 1993 Phys. Rev. 48 506–15, 1994 IEEE Trans. Plasma Sci. 22 73–7, 1999 J. Phys. D: Appl. Phys. 32 257–62; Benilov M S and Marotta A 1995 J. Phys. D: Appl. Phys. 28 1869–82; Benilov M S and Cunha M D 2002 J. Phys. D: Appl. Phys. 35 1736–50, 2003 J. Phys. D: Appl. Phys. 36 603–14). In this mode current density does not depend on the arc current and is directly proportional to the gas pressure. At higher currents and/or higher pressures the CS exists in a different mode (second mode). In this mode current density does not depend on pressure and decreases as the current increases.If the product of the arc current, I, and the gas pressure, p, is lower than some critical value, then the first mode is realized; at a higher Ip product, the second one is realized. For discharges in nitrogen, the critical value was estimated as ∼7 × 107 A Pa.In the experimental part of this work, we investigated the footprints that the arc left at the cathode after it was terminated. Cathodes were made of pure and thoriated tungsten and the gases were nitrogen and argon. We have observed both modes. At 3 × 105 Pa, the second mode was observed at currents higher than ∼300 A; at 200 A, it was observed at pressures higher than ∼3 × 105 Pa.The CS footprint appearances are quite different. In the first mode the footprint has a smooth central part and a heavily eroded periphery. We believe that the cathode temperature is maximal not at the CS centre but at its periphery in this mode. With a thoriated tungsten cathode and swirling gas flow, the CS footprint exhibits a very specific crown-like pattern.

Cathode erosion rate in high-pressure arcs: influence of swirling gas flow

Cathode erosion in a 400-A arc burning in oxygen at 4-atm pressure was measured at different gas dynamic conditions near the cathode. The flow pattern near the cathode was changed by varying the swirl of the gas entering the discharge chamber. Experiments showed that the erosion rate depends on the swirl in a very strong way. Model calculations of velocity distribution showed that the gas velocity near the cathode increases as the swirl intensifies. According to our model, it leads to an increase of the net evaporation rate (evaporation rate minus rate of previously evaporated particles returning back to the cathode).

Analysis of a Swirling Flow of Gas in the Diaphragmed Channel of a Plasma Generator

A two-temperature magnetogasdynamic model of plasma is used to calculate a swirling flow of gas (argon) in the diaphragmed channel of a plasma generator and the heating of this flow and to investigate the dependence of the flow on the strength of the current, geometry of the channel, and the flow rate and swirling moment of gas. The effect of the velocity field of swirling flow on the disequilibrium of plasma and on the arc characteristics in varying-area channels is treated. The calculation results are in qualitative agreement with the experimental data.

One-dimensional Steady-state Radial Swirling Gas Flow

One-dimensional Steady-state Radial Swirling Gas Flow

Rotating spiral edge flames in von karman swirling flows

Experimental observations of rotating spiral flame edges formed during near-limit combustion of a downward-facing, polymethylmethacrylate disk spinning in quiescent air are reported. These flames exhibit similarities to patterns commonly found in quiescent excitable media. The tail rotates rigidly while the tip executes a compound, meandering motion sometimes observed in Belousov-Zhabotinskii reactions. A model assuming a rigid-body rotation with a constant speed of propagation relative to the swirling gas flow generated by the spinning disk predicts the observed spiral shapes well.

On the scaling‐up of a two‐stage air blown entrained flow coal gasifier

AbstractA two‐stage air blown entrained flow gasifier is being developed in Japan for the IGCC process. However, its scale‐up up faces significant difficulties because of ash/slag deposition problems. The ash/slag deposition in the gasifier depends on both the ash properties and entrainment produced by the swirling gas flow. Therefore, the flow hydrodynamics are critical issues for the control of the ash behavior. In this paper, a comprehensive simulation model is used to examine the effects of the gasifier geometry and jet configuration on the flow hydrodynamics in order to control the ash deposition on the gasifier walls. A swirl number for the multi‐stage injection swirling gas flow is defined and proved to be the most important hydrodynamic scaling law for the entrained flow gasifier.

Combustion characteristics of a direct-injection stratified charge S.I. engine

A direct-injection stratified charge gasoline engine has been developed that can run on an air–fuel ratio of 40–50 : 1. Major characteristics of the engine system include swirl gas flow and fuel injection in a swirl spray at a maximum fuel pressure of 10 MPa. Another notable feature is that the intake port configuration is virtually identical to that of a conventional engine, allowing flexibility for shared use of components among different engines. This new engine achieves better fuel economy, lower cold-start HC emissions and higher power output than conventional multipoint injection engines.

The Ranque Vortex Effect in a Rotating Plasma

The Ranque-Hilsch vortex tube effect is observed in a rotating magnetoplasma. INTRODUCTION In 1934 George Ranque patented a simple cylindrical tube (Fig. 1) into which compressed air is injected tangentially in order to induce gas swirling (Ranque, 1934; Hilsch, 1947). A radial temperature gradient was observed in the rotating gas vortex and the introduction of baffles (Fig. 1) permits one to extract selectively cold air from the vortex core or hot air from the periphery. During the course of experiments on rotating plasmas I have observed what I believe to be the Ranque-Hilsch effect occurring in the plasma state. METHODS The present experiments were conducted in the device illustrated in Figure 2. A discharge is struck between the rod cathode, C, and a grid anode disc, A. Plasma, P, streams down the magnetic field, B, until it strikes the aperture disc, a. The central core plasma can pass through the aperture into the downstream region, 2. An electrostatic energy analyzer (Jones, 1978, 1979), E, H C_ _ 8 Figure 1. Longitudinal cross section of Ranque vortex tube. Tangentially injected gas jet, a, drives swirling gas flows which direct hot gas out pipe H and cold gas out pipe C. This content downloaded from 157.55.39.231 on Thu, 06 Oct 2016 04:18:34 UTC All use subject to http://about.jstor.org/terms 110 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE B .A a P

Numerical Simulation of the Effects of Center Tube and Multiple Air Injection on the Gas Flow Field in a Vortex Combustor

This paper presents systematic numerical simulations of the strongly swirling gas flows in a novel coal-fired vortex combustor (VC) recently developed for commercial heating applications. The nonisotropic turbulence of strongly swirling flows was closed by a new version algebraic Reynolds stress model. The calculated results, compared with the measurements of a 25em J.D. bench-scale VC test chamber,delineate the detailed effects of the center tube height and the flow rates of multiple air injection on gas tangential and axial velocities, flow pattern, pressure drop, and turbulent intensity.

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.

Stability of swirling gas flows

The stability of inviscid swirling gas flows to small nonaxisymmetric perturbations is considered. For small Brunt–Väisälä frequencies, the problem reduces to the classical Sturm–Liouville form and the oscillation theorem can be applied. The resulting necessary and sufficient stability condition is compared to various criteria in the literature and a limited numerical study of isothermal rigidly rotating Poiseuille flow. For given azimuthal and axial wavenumbers, it is found numerically that the higher inertial modes become unstable for successively lower Rossby numbers and that this sequence of critical values approaches the theoretical value from above.

Investigation of the influence of the conditions of swirling on the structure of a two-phase flow in an expanding channel

Both experimental and theoretical investigations show that the main feature in the structure of sufficiently strongly swirling gas flows is the presence in then of reverse circulation regions whose configuration depends very strongly both on the law of swirling of the flow and the conditions at the entrance as well as on the channel geometry [1–6]. In expanding channels, the occurrence of such regions is most probable in the axial region [7, 8]. In short annular channels for which the characteristic transverse and longitudinal dimensions are of the same order, reverse flow arises in the exit part of the channel along its inner wall [6, 9]. Hitherto, the investigations have been made for single-phase gas flows. The present paper reports a numerical investigation of the influence of particles of a condensed phase on the intensity of the reverse flow and the structure of the gas flow in an annular expanding channel under conditions of thermal, mass, and mechanical interaction of the phases. The method of stabilization was used to solve the boundary-value problem. The system of equations describing the axisymmetric unsteady flow of the two-phase medium was integrated by means of Godunov's difference scheme [10, 11]. The calculations were made for different conditions of injection of the particles of the condensed phase into the channel.

On two types of swirling gas flows

Two classes of exact solutions of the three-dimensional stationary equations of gas dynamics are constructed. The solutions are used to describe isentropic gas flows with two types of swirling in axisymmetric divergent channels. The effect of swirling on the thrust of special-type nozzles is studied.

Transonic swirling gas flow through a nozzle

Transonic swirling gas flow through a nozzle