Presence Of Gas Flow Research Articles

Commissioning of the St. Benedict RF carpet

The Superallowed Transition BEta NEutrino Decay Ion Coincidence Trap (St. Benedict) aims to measure the beta-neutrino angular correlation parameter for superallowed mixed beta decay transitions between mirror nuclei in order to conduct precision tests of the Standard Model. St. Benedict will include a gas catcher, a differentially pumped extraction system, a radio-frequency quadrupole (RFQ) cooler and buncher, and a Paul trap to utilize radioactive ion beams produced at the Nuclear Science Laboratory of the University of Notre Dame. The two-part differentially pumped extraction system contains a RF carpet at a helium gas pressure of around 3 mbar, and a radio-frequency quadrupole (RFQ) ion guide at a pressure of around 2×10−3 mbar. Transport efficiency of potassium ions in the first part of the extraction system using the RF carpet in the presence of gas flow was determined to be near 100% in the 0.75 to 5 mbar pressure range using the ion surfing transport method.

Experimental validation of a two equation RANS transitional turbulence model for compressible microflows

Laminar-to-turbulent flow transition in microchannels can be useful to enhance mixing and heat transfer in microsystems. Typically, the small characteristic dimensions of these devices hinder in attaining higher Reynolds numbers to limit the total pressure drop. This is true especially in the presence of a liquid as a working medium. On the contrary, due to lower density, Reynolds number larger than 2000 can be easily reached for gas microflows with an acceptable pressure drop. Since microchannels are used as elementary building blocks of micro heat exchangers and micro heat-sinks, it is essential to predict under which conditions, the laminar-to-turbulent flow transition inside such geometries can be expected. In this paper, experimental validation of a two equations transitional turbulence model, capable of predicting the laminar-to-turbulent flow transition for internal flows as proposed by Abraham etal. (2008), is presented for the first time for microchannels. This is done by employing microchannels in which Nitrogen gas is used as a working fluid. Two different cross-sections namely circular and rectangular are utilized for numerical and experimental investigations. The inlet mass flow rate of the gas is varied to cover all the flow regimes from laminar to fully turbulent flow. Pressure loss experiments are performed for both cross-sectional geometries and friction factor results from experiments and numerical simulations are compared. From the analysis of the friction factor as a function of the Reynolds number, the critical value of the Reynolds number linked to the laminar-to-turbulent transition has been determined. The experimental and numerical critical Reynolds number for all the tested microchannels showed a maximum deviation of less than 12%. These results demonstrate that the transitional turbulence model proposed by Abraham etal. (2008) for internal flows can be extended to microchannels and proficiently employed for the design of micro heat exchangers in presence of gas flows.

Revealing the effects of galaxy interaction in the main galaxies of the southern group Arp 314

ABSTRACT We present new Gemini imaging and spectroscopic data of the system Arp 314, which consists of a triplet of interacting galaxies. This new imagery exhibits tidal tails and stellar bridges between the galaxies' members and confirms the past interactions. Using this data set, we have analysed the physical properties of 22 star-forming regions located in the main disc of these galaxies, as well as in the intergalactic medium. All these regions have emission lines typical of young ages and a couple of them display very high Hα luminosities (LHα ∼ 1040 erg s−1). Using the star-forming regions located in Arp 314-1, we derive its gas-phase oxygen-abundance distribution, which suggests a flatter behaviour than the distribution shown by non-interacting systems. This is in agreement with results obtained for other interacting systems and simulations. The presence of gas flows, as indicated by its complex kinematics, could explain this finding. Most of the star formation in Arp 314-2 is located in a central starburst, where double Hα profiles can be identified, as shown by archival Fabry–Perot data. Additionally, we found that the irregular galaxy Arp 314-3 has a low oxygen abundance. Considering its luminosity, this object has a primordial origin, and it was not formed during the interaction event that this system has experienced.

Effect of solid dust particles on the propagation of shock wave in planar and non-planar gasdynamics

The aim of the present study is to analyze the propagation of shock wave along the characteristic path in planar and non-planar unsteady compressible ideal gas flow in presence of small solid dust particles. The analytical solution of the governing quasilinear hyperbolic system is computed in the characteristic plane and it is found that this analytical linear solution in this plane can exhibit non-linear phenomenon in the physical plane. The effect of the dust particles on the evolutionary behavior of the propagating shock wave in ideal gas flow is discussed. The transport equations leading to the evolution of shock wave is determined which introduces the conditions of shock formation. The growth and decay of compressive waves and expansive waves, respectively, in planar and non-planar ideal gas dynamics influenced by the presence of small solid dust particles, is discussed.

Hydrodynamic instability of premixed flame propagating in narrow planar channel in the presence of gas flow

The paper analyses the hydrodynamic instability of a flame propagating in the space between two parallel plates in the presence of gas flow. The linear analysis was performed in the framework of a two-dimensional model that describes the averaged gas flow in the space between the plates and the perturbations development of two-dimensional combustion wave. The model includes the parametric dependences of the flame front propagation velocity on its local curvature and on the combustible gas velocity averaged along the height of the channel. It is assumed that the viscous gas flow changes the surface area of the flame front and thereby affects the propagation velocity of the two-dimensional combustion wave. In the absence of the influence of the channel walls on the gas flow, the model transforms into the Darrieus–Landau model of flame hydrodynamic instability. The dependences of the instability growth rate on the wave vector of disturbances, the velocity of the unperturbed gas flow, the viscous friction coefficients and other parameters of the problem are obtained. It is shown that the viscous gas flow in the channel can lead, in some cases, to a significant increase in instability compared with a flame propagating in free space. In particular, the instability increment depends on the direction of the gas flow with respect direction of the flame propagation. In the case when the gas flow moves in the opposite direction to the direction of the flame propagation, the pulsating instability can appear.

Modelling of shaft based processes

ABSTRACTShaft based processes are used in many disciplines such as in metallurgical and chemical engineering. However, their performance suffers due to the lack in understanding of solid and gas flow thus the heat and mass transfer inside the shaft. Therefore, in this article the study of solid flow has been carried out in presence of gas flow under counter-current condition. A slow moving packed bed, inside the reactor, has been considered. Particles are discharged from the bottom and gas is injected laterally. Particles have been modelled using Discrete Element Method (DEM) and gas flow has been modelled using continuum based fluid flow equations. The effect of various parameters (like particle size, gas flow rate, solid discharge rate etc.,) on the residence time of solid particles has been studied in detail. It is found that gas flow is not symmetric inside the reactor due to asymmetric distribution of voids.

Control and Stabilization of Centimeter Scale Glow Discharge in Ambient Air Using Pulse-Width Modulation

Re-pulsing glow discharges in atmospheric-pressure air were experimentally investigated using a push-pull generator with pulse-width modulation. Discharges were ignited as a spark-glow discharge sequence and sustained in a glow regime after ignition in a gap of 2 cm and characterized by current and voltage measurements, as well as by optical emission spectroscopy. It was found that at a certain range of parameters, the discharge could be stabilized even in the presence of external airflow. It was demonstrated that the type of discharge and total power dissipated in the plasma volume could be precisely controlled by pulse-width modulation. Additionally, it was confirmed that the rotational temperature varied across a wide range (1640-2440 K) by using pulse-width modulation with gas-flow control, when vibrational temperature was around 4610 ± 770 K. The generation of stable glow discharge in the presence of gas flow with a wide range of parameters that could be precisely controlled by pulse-width modulation looks promising for use in energy-efficient gas conversion.

Ppb-level photoacoustic sensor system for saturation-free CO detection of SF6 decomposition by use of a 10 W fiber-amplified near-infrared diode laser

A photoacoustic sensor system for the ppb-level CO detection of sulphur hexafluoride (SF6) decomposition was developed by use of a 10 W fiber-amplified near-infrared (NIR) diode laser. A photoacoustic detection module with symmetrical construction was designed to allow a high power laser beam and a large gas flow. A theoretical model was developed to describe the dynamic equilibrium processes of CO molecular activation and deactivation in the presence of gas flow. The 10 W optical excitation power effectively compensates the CO weak absorption line strength in the NIR spectral region and realizes a saturation-free CO detection with the assistance of the gas flow, resulting in a ppb-level CO detection sensitivity, which is comparable with the detection sensitivity obtained using a mid-infrared CO sensor.

Measurements of water molecule density by tunable diode laser absorption spectroscopy in dielectric barrier discharges with gas–water interface

We measured water molecule (H2O) density by tunable diode-laser absorption spectroscopy (TDLAS) for applications in dielectric barrier discharges (DBDs) with a gas–water interface. First, the effects of water temperature and presence of gas flow were tested using a Petri dish filled with water and a gas injection nozzle. Second, the TDLAS system was applied to the measurements of H2O density in two types of DBDs; one was a normal (non-inverted) type with a dielectric-covered electrode above a water-filled counter electrode and the other was an inverted type with a water-suspending mesh electrode above a dielectric-covered counter electrode. The H2O density in the normal DBD was close to the density estimated from the saturated vapor pressure, whereas the density in the inverted DBD was about half of that in the former type. The difference is attributed to the upward gas flow in the latter type, that pushes the water molecules up towards the gas–water interface.

Coupled gas-particulate discharge from a bucket elevator

The vertical conveying of bulk materials is often performed using bucket elevators. Such devices use conveyor belts to drag a series of buckets in a circuit, up, around and then down within an enclosure. They are typically used for upward transport of fine granular materials. The speed at which these buckets travel can displace a large volume of air. Interaction between this air and the bucket contents can modify the discharge dynamics of the granular load. A coupled gas-particulate numerical model is presented using Finite Differences to solve for the gas flow with an Immersed Boundary Method (IBM) to represent the complex bucket and enclosure geometry in the model. The Discrete Element Method (DEM) is used for particulate flow. The combined method is used to investigate the effect of gas flow on particulate behavior, particularly at the time of discharge from the buckets. The bucket elevator design used is based on an existing installation with known operational issues. The presence of gas flow is shown to alter the preferential ejection of particles from the bucket, influence the shape of the trajectory of the ejected particle stream, and reduce the efficiency of particles exiting the elevator by 10–14%. These effects are also shown to be strongly size dependent with finer particles being much more susceptible to drag forces from the air flow. The retention of material inside the machine was found to consist of roughly 50% of material centrifugally ejected from near the bucket tip and roughly 70% of material located closer to the conveyor belt side of the bucket that spills off the splitter during the final stage of emptying and falls back down to the boot.

Investigation of Water Droplet Interaction with the Sidewalls of the Gas Channel in a PEM Fuel Cell in the Presence of Gas Flow

Water appears as a byproduct during normal operation of Proton Exchange Membrane Fuel Cell (PEMFC), and stagnates on the gas diffusion layer (GDL) affecting its performance under certain operating conditions. The primary goal of this study was to develop an ex-situ experimental setup to analyze the sidewall interactions and droplet dynamics under controlled gas flow rates. The channel open angle was varied from 30° and 90° and the superficial air flow velocities between 0.2-2 m/s. The growth of the droplet and its interaction with the side wall were captured using a high-speed camera with a microscopic lens. The experimentation revealed that the droplet-side wall interaction was dependent on the gas channel angles and also on the gas flow rate. The study provides an insight into the droplet removal process in a PEMFC and provides guidance in the gas channel design.

Investigation of Water Droplet Interaction with the Side Wall of the Gas Channel in the PEM Fuel Cell in the Presence of Gas Flow

not Available.

HCN and CN in Comet 2P/Encke: Models of the non-isotropic, rotation-modulated coma and CN parent life time

Axisymmetric models of the outgassing of a cometary nucleus have been constructed. Such models can be used to describe a nucleus with a single active region. The models may include a solar zenith angle dependence of the outgassing. They retrieve the outgassing flux at distances from the nucleus where collisions between molecules are unimportant, as function of the angle with respect to the outgassing axis. The observed emissions must be optically thin. Furthermore the models assume that the outflow speed at large distance from the nucleus does not depend on direction. The value of the outflow speed is retrieved. The models are applied to CN images and HCN spectra of Comet 2P/Encke, obtained nearly simultaneously in November 2003 with the 2 m optical telescope on Mount Rozhen, Bulgaria, and with the 10 m Heinrich Hertz Submillimeter Telescope on Mount Graham, Arizona, USA. According to Sekanina (1988), Astron. J. 95, 911–924, at that time a single outgassing source was active. Input parameters to the models like the rotation period of the nucleus and a small correction to Sekanina’s rotation axis are determined from a simpler jet position angle model. The rotation is prograde with a sideric period of 11.056 ± 0.024 h, in agreement with literature values. The best fit model has an outflow speed of 0.95 ± 0.04 km s −1. The same value has been derived from the corkscrew appearing in the CN images. The location of the outgassing axis is at colatitude δ a = 7.4° ± 2.9° and longitude λ a = 235° ± 17° (a definition of zero longitude is provided). Comet Encke’s outgassing corresponds approximately to the longitudinally averaged solar input on a spherical nucleus (i.e. very likely comes from deeper layers) but with some deficiency of outgassing at mid-latitudes and non-zero outgassing from the dark polar cap. The presence of gas flow from the dark polar cap is explained as evidence of gas flow across the terminator. The models rely mostly on the CN images. The HCN spectra are more noisy. They provide information how to determine the best fit outflow velocity and the sense of rotation. The model HCN spectra are distinctly non-Gaussian. Within error limits they are consistent with the observations. Models based solely on the HCN spectra are also presented but, because of the lower quality of the data and the unfavorable observing geometry, yield inferior results. As a by-product we determine the CN parent life time from our CN observations. The solar EUV and Ly α radiation field at the time of our observations is taken into account.

Behavior of Granular Material in Packed Bed Under Influence of Gas Injected Through a Nozzle

Cavity size hysteresis is an important phenomenon that affects the aerodynamics of any packed bed reactor significantly. Using the discrete element method approach, the mechanism of cavity size hysteresis in the presence of gas flow has been studied. The modeling results on cavity size have been compared with experiments and show a reasonable agreement. It is found that bed history, interparticle interaction forces, and gas drag all play an important role in the formation of cavities. The bed porosity in the decreasing gas velocity case was always found higher than the increasing gas velocity. The net gas drag at any location above the gas injection point in the bed decreases as the gas velocity is increased. It is also found that the change in interparticle interaction forces with gas flow rate is a major cause of the hysteresis phenomenon.

Modeling of Liquid Flow in a Packed Bed in the Presence of Gas Flow

Liquid metal and slag descend through a porous coke matrix in the lower part of an iron making blast furnace. The size of the raceway is an important factor in determining the gas penetration into the bed, which pushes the liquid toward the deadman region. This, in turn, affects the gas flow in the bed. The current study tries to explain theoretically the effect of cavity size hysteresis on gas-liquid distribution in a packed bed. The liquid flow has been modeled considering it to be discrete in nature. The turbulent nature of gas flow has been modeled using the k-e model for turbulent flow. The model results have been verified on a structured package. It is observed that the liquid is pushed away further from the nozzle-side wall in the case of decreasing gas velocity than increasing gas velocity at the same inlet gas velocity. The implications of the current study to the dropping zone of a blast furnace have been discussed.

Two-dimensional-simulation of thermal blooming effects in ring pattern laser beams

Thermal blooming is a major effect in high power laser beams transmitting through gaseous medium as well as the atmosphere. Due to this effect, the beam pattern is deformed through the propagation path. In this work, a ring pattern beam from a high-power CO2 laser with an unstable resonator is evaluated when propagating through a high-pressure CO2 gas, and the results are compared with those of the Gaussian beam. The results show that unlike the initial Gaussian beam from which a ring pattern formed when propagating through an absorbing medium, for the initial ring pattern beam, in the absence of the gas flow, a symmetrical two-fold pattern is formed due to the blooming effect. The results also show that such symmetry can be deformed in the presence of gas flow.

Packed Column Supercritical Fluid Chromatography with Splitless Flame Ionization Detection

The design and characterization of flame ionization detector (FID) that is compatible with the high flow rates of packed column supercritical fluid chromatography (pSFC) is presented. The modified FID uses a large quartz burner (4.0 mm i.d.) in place of the conventional burner (0.4 mm i.d.) and operates with a stable flame in the presence of gas flows tested up to nearly 3000 mL/min. This modification allows the full flow of effluent from a pSFC column (i.e. splitless mode) to be directed into the FID. Results demonstrate that the modified FID yields a response that is within a factor of 3 to that of a commercial FID. The attributes of the modified detector indicate that this approach could be a reliable and relatively simple means of achieving a splitless pSFC-FID system.

Packed-column supercritical fluid chromatography with splitless flame ionization detection

The design and characterization of a flame ionization detector (FID) that is compatible with the high flow rates of packed-column supercritical fluid chromatography (pSFC) is presented. The modified FID uses a large quartz burner (4.0 mm i.d.) in place of the conventional burner (0.4 mm i.d.) and operates a stable flame in the presence of gas flows tested up to nearly 3000 mL/min. This modification allows the full flow of effluent from a pSFC column (i.e., splitless mode) to be directed into the FID. Results demonstrate that the modified FID yields response that is within a factor of 3 to that of a commercial FID. The attributes of the modified detector indicate that this approach could be a reliable and relatively simple means of achieving a splitless pSFC-FID system.Key words: supercritical fluid chromatography, packed column, splitless, flame ionization detector.

Approach to Decaying Process of Arc Conductance after Current Zero on the basis of Thermodynamic and Transport Properties of High Temperature Gases

The decaying aspect of the conductance of an arc after a current zero for SF6, N2, O2, air, c-C4F8, CO2, H2, He and Ar was studied on the basis of thermodynamic and transport properties of high temperature gases: a mass density ρ, an enthalpy h, an enthalpy h300 at 300 K, a specific heat CP, and a thermal conductivity κ and an electrical conductivity σ. Theoretical calculation revealed two principal phenomena as follows:(1) for the case in presence of gas flow, the conductances for SF6, c-C4 F8, O2, CO2, H2, He and Ar decay rapidly just around a current zero and (2) the conductances for H2 and He in no axial gas-flow decrease in an almost similar aspect to that for the case in presence of the gas flow. To explain the phenomenon (2), a thermal diffusivity α expressed as α = κ /(ρ CP) was calculated. The H2 and He proved to have very much higher α than the others. This higher α of the H2 and He was found to result in the more rapid reduction in the conductance through a thermal conduction mechanism. To interpret the phenomenon (1), β expressed as β =(h-h300)/(ρCP) was calculated. The SF6, c-C4 F8, O2, CO2 and Ar were found to have higher β than N2 and air. This higher β of SF6, c-C4F8, O2, CO2 and Ar proved to cause the more rapid diminution in the conductance through convection mechanism.

In situ measurement of noise of induced-draft fans in a power plant stack

Induced-draft fans are commonly the most annoying sources of community noise associated with fossil-fuel power plants. The low frequency tones generated by the fans are usually radiated to the community from the top of a tall stack. Measurements of the tone levels in the community are hampered by environmental effects such as strong wind and thermal gradients. Measurements within the flue gas ducting are therefore desirable. However, the flue gas environment is hostile to microphones due to elevated temperatures, particulates, and the presence of gas flow. The interpretation of in-duct data is complicated by the possible effects of standing waves and cross modes in the duct and turbulence generated noise. The recent installation of a dissipative-reactive muffler in a coal-fired plant offered the opportunity to (1) investigate techniques for measuring noise in stacks, (2) evaluate the performance of the muffler under operating conditions, and (3) check the in-stack results against limited farfield data. Good agreement was obtained between reductions in tone levels measured in the stack and in the community.