Large Gas Flow Rates Research Articles

Investigation of Changes in Natural Gas Parameters along a Damaged Gas Pipeline

The paper presents a mathematical model of the stationary flow of natural gas in an inclined gas pipeline, which makes it possible to calculate the gas parameters (pressure, temperature, compressibility factor) in every cross-section of gas pipeline. An improved mathematical model is also proposed by the authors, which considers the change in the gas flowrate along the gas pipeline. Complex 1 characterizing the effect of frictional forces and pressure losses and Complex 2 determining the effect of flow velocity were proposed to confirm the need to use an improved mathematical model. Based on the ratio of these complexes, a quantitative criterion was formed for the application of the improved mathematical model. An example of a comparison of complexes for a long pipeline and a short pipeline with a large gas flowrate is presented. Provided that the complexes are of the same order, the relative deviation of the pressures at the end of the gas pipeline obtained by the known and improved model can differ by 8 – 10%. Therefore, in such a case, it is necessary to apply the mathematical model improved by the authors. An example of the application of mathematical models is presented for the analysis of gas pressure and temperature distribution along a gas pipeline with significant damage. The pressure profile along this gas pipeline was obtained for its operating mode with gas flowrate limitation at the inlet and without limitation. It is shown that when the area of damage increases, the change in the pressure profile for these operating modes has features that can be used during the development of a system for determining the volume of gas lost because of sudden damage to gas pipelines.

Ppb-level NH3 photoacoustic sensor combining a hammer-shaped tuning fork and a 9.55 µm quantum cascade laser

We present a quartz enhanced photoacoustic spectroscopy (QEPAS) gas sensor designed for precise monitoring of ammonia (NH3) at ppb-level concentrations. The sensor is based on a novel custom quartz tuning fork (QTF) with a mid-infrared quantum cascade laser emitting at 9.55 µm. The custom QTF with a hammer-shaped prong geometry which is also modified by surface grooves is designed as the acoustic transducer, providing a low resonance frequency of 9.5 kHz and a high-quality factor of 10263 at atmospheric pressure. In addition, a temperature of 50 °C and a large gas flow rate of 260 standard cubic centimeters per minute (sccm) are applied to mitigate the adsorption and desorption effect arising from the polarized molecular of NH3. With 80-mW optical power and 300-ms lock-in integration time, the detection limit is achieved to be 2.2 ppb which is the best value reported in the literature so far for NH3 QEPAS sensors, corresponding to a normalized noise equivalent absorption coefficient of 1.4 × 10−8 W cm−1 Hz−1/2. A five-day continuous monitoring for atmospheric NH3 is performed, verifying the stability and robustness of the presented QEPAS-based NH3 sensor.

Strong ectopic adsorption on single cobalt site accelerates the direct catalytic oxidation of low concentration acetonitrile on CuO nanoparticles embedded in SAPO-34

It is usually inevitable for the usage of zeolite rotor concentrator to increase the level of volatile organic compounds (VOCs) concentration, which in turn enables the regenerative catalytic oxidation of VOCs with large gas flow rate to achieve autothermal operation. Herein, we present a new strategy for the preparation of autothermal oxidation catalyst (AOC) with strong ectopic adsorption ability for VOCs molecules by the on-site doping of single cobalt sites on CuO nanoclusters confined in zeolitic materials SAPO-34, which exhibits a strong enrichment ability for low concentration acetonitrile even at 300 °C. Meanwhile, a distinguished enhancement on the catalytic oxidation activities has also been achieved according to the formation of CoⅡ-oxo and/or Co-Ovac sites on CuO nanoparticles.

Recent Development of Anion Exchange Membrane Fuel Cells and Performance Optimization Strategies: A Review.

Anion exchange membrane fuel cells (AEMFCs) are the most promising low-temperature fuel cells and have received extensive attention. Compared to PEMFCs, the cost per unit of power can be significantly reduced for AEMFCs because, in theory, they allow the usage of non-precious metal catalysts and low-cost cell components. Owing to the development of advanced materials and performance improvement strategies, AEMFCs have achieved new records in both initial performance and durability. However, the high performance currently achieved is contingent on certain conditions, e. g., high Pt loading, large gas flowrates, and operation in pure O2 , which are far from practical applications. Therefore, the transition to commercially relevant performance and durability is the next goal of AEMFCs. This paper reviews the performance data of H2 -fueled AEMFCs since 2010 and summarizes possible performance optimization schemes, which can provide useful insights for developing next-generation AEMFCs.

Stratified-to-annular gas-liquid flow patterns transition in a horizontal pipe

Air-water flow in a 20 mm horizontal pipe is studied using side-view visualization with a background image and Brightness-Based Laser-Induced Fluorescence technique. The investigation is focused on the transition from stratified to annular flow patterns. Stratified flow is organized at the pipe inlet, and the dynamics of liquid lifting up the pipe walls is investigated. During the transition to annular flow, the liquid film is spread over the pipe walls in a stable and gradual manner; the spreading begins before the disturbance waves are formed. Two transition regimes are identified. At large gas and low liquid flow rates, the film is spread up the pipe walls reaching a stable height unaffected by the passing waves. At low gas and large liquid flow rates, the liquid can be lifted by the large-scale waves, but it promptly drains downwards between the waves. Secondary flow in the gas phase is considered the main mechanism of liquid lifting and the only mechanism able to create a stable annular film. The processes of formation and development of disturbance waves are qualitatively the same as previously observed in vertical pipes. Namely, the disturbance waves are formed due to the coalescence of high-frequency initial waves appearing near the inlet; the disturbance waves undergo coalescence and grow in amplitude and speed. Quantitatively, the disturbance wave formation occurs at larger distances from the inlet compared to the vertical flow, and the acceleration rate is much lower. An estimation of circumferential shear stress due to secondary flow is made based on the roughness of the liquid film surface at the bottom of the pipe. An increase in this shear stress increases the height of the liquid film on the pipe walls.

The effect of H2O on the sulfation of Havelock limestone under oxy-fuel conditions in a thermogravimetric analyser.

A gas mixture representing oxy-fuel combustion conditions was employed in a thermogravimetric analyser to determine the effect of water vapor and SO2 concentration on limestone sulfation kinetics over the temperature range of 800 to 920 °C. Here, experiments used small samples of particles (4 mg), with small particle sizes (dp < 38 µm) and large gas flow rates (120 mL/min@NTP) in order to minimize mass transfer interferences. The gas mixture contained 5000 ppmv SO2, 2% O2, and the H2O content was changed from 0% to 25% with the balance CO2. When water vapor was added to the gas mixture at lower temperatures (800–870 °C), the limestone SO2 capture efficiency increased. However, as the temperature became higher, the enhancement in total conversion values decreased. As expected, Havelock limestone at higher temperatures (890 °C, 920 °C, and 950 °C) experienced indirect sulfation and reacted at a faster rate than for lower temperatures (800–870 °C) for direct sulfation over the first five minutes of reaction time. However, the total conversion of Havelock limestone for direct sulfation was generally greater than for indirect sulfation.

Experimental study of the characteristics of gas-injection barrier in two-dimensional porous media

The inflow of groundwater into the oil shale in-situ pyrolysis zone reduces the heating efficiency and has negative impacts on soil ecology and drinking water safety. Thus, we propose a sealing system for oil shale in-situ pyrolysis exploitation with a gas-injection barrier. In this study, the characteristics of gas-injection barrier were investigated comprehensively in the two-dimensional porous media. First, the evolution and distribution of hydraulic conductivity were studied. Results showed that gas injection promoted water flow in the central subregion when the gas flow rate was less than 50 mL/min. With a further increase in the gas flow rate, a significant inhibition effect on the water flow within all subregions was achieved. Then, the gas-injection barrier mechanism was quantitatively analyzed, showing that a pressure-balanced state in the extended front of the upstream gas flow served as one mechanism when a larger gas flow rate was reached, which was verified by experiments for the first time. Finally, the distribution of the gas flow fitted by a Gaussian curve was explored. In addition, the sensitivity of hydraulic conductivity was discussed; with increasing water flow rate and the coarsening of glass beads, the relative hydraulic conductivity improved comprehensively. All results obtained are conducive to a comprehensive understanding and application of the gas-injection barrier.

Technical note: Mobile open dynamic chamber measurement of methane macroseeps in lakes

Abstract. Methane (CH4) seepage (i.e., steady or episodic flow of gaseous hydrocarbons from subsurface reservoirs) has been identified as a significant source of atmospheric CH4. However, radiocarbon data from polar ice cores have recently brought into question the magnitude of fossil CH4 seepage naturally occurring. In northern high latitudes, seepage of subsurface CH4 is impeded by permafrost and glaciers, which are under an increasing risk of thawing and melting in a globally warming world, implying the potential release of large stores of CH4 in the future. Resolution of these important questions requires a better constraint and monitoring of actual emissions from seepage areas. The measurement of these seeps is challenging, particularly in aquatic environments, because they involve large and irregular gas flow rates, unevenly distributed both spatially and temporally. Large macroseeps are particularly difficult to measure due to a lack of lightweight, inexpensive methods that can be deployed in remote Arctic environments. Here, we report the use of a mobile chamber for measuring emissions at the surface of ice-free lakes subject to intense CH4 macroseepage. Tested in a remote Alaskan lake, the method was validated for the measurement of fossil CH4 emissions of up to 1.08 × 104 g CH4 m−2 d−1 (13.0 L m−2 min−1 of 83.4 % CH4 bubbles), which is within the range of global fossil methane seepage and several orders of magnitude above standard ecological emissions from lakes. In addition, this method allows for low diffusive flux measurements. Thus, the mobile chamber approach presented here covers the entire magnitude range of CH4 emissions currently identified, from those standardly observed in lakes to intense macroseeps, with a single apparatus of moderate cost.

Numerical Analysis of Effect of Initial Bubble Size on Captured Bubble Distribution in Steel Continuous Casting Using Euler-Lagrange Approach Considering Bubble Coalescence and Breakup

A mathematic model considering the bubble coalescence and breakup using the Euler-Lagrange approach has been developed to study the effect of the initial bubble size on the distribution of bubbles captured by the solidification shell. A hard sphere model was applied for dealing with the bubble collision. Advanced bubble coalescence and breakup models suitable for the continuous casting system and an advanced bubble captured criteria have been identified established with the help of user-defined functions of FLUENT. The predictions of bubble behavior and captured bubble distribution agree with the water model and plant measurements well respectively. The results show that the number of small bubbles captured by solidification shell is much higher than that of large bubbles. What is more, the number of captured bubbles at the sidewalls decreases with the distance from the meniscus. For the case of large gas flow rate (gas flow fraction of 8.2%), the initial size of bubbles has little effect on bubble captured distribution under various casting speeds. When the gas flow rate is small (gas flow fraction of 4.1%), the number density of captured bubbles increases as the initial bubble size increases, and the effect of initial bubbles size on captured bubble number density is amplified when the casting speed decreases. The average captured bubble diameter is about 0.12–0.14 mm. Additionally, for all cases, the initial bubble size hardly affects the average size of captured bubbles.

Design and characteristics of a triple-cathode cascade plasma torch for spheroidization of metallic powders

Arc plasma torch is an effective tool for spheroidization of metallic powders. However, as most conventional plasma torches were not specifically designed for plasma spheroidization, they may exhibit the disadvantages of the radial injection of powders, large fluctuations in the arc voltage, large gas flow rate, and disequilibrium between multiple plasma jets during the spheroidization process. Therefore, this paper presents a triple-cathode cascade plasma torch (TCCPT) for plasma spheroidization. Its structural design, including three cathodes, a common anode, and three sets of inter-electrodes, are detailed to ensure that powders can be inserted into the plasma jet by axial injection, the arc voltage fluctuations are easily maintained at a low level, and the plasma torches can work at a relatively small gas flow rate. Experimental results showed that the proposed TCCPT exhibits the following characteristics: (1) a relatively small arc voltage fluctuation within 5.3%; (2) a relatively high arc voltage of 75 V and low gas flow rate range of 10–30 SLM; (3) easy to be maintained at the equilibrium state with the equilibrium index of the three plasma jets within 3.5 V. Furthermore, plasma spheroidization experiments of SUS304 stainless steel powers were carried out using the proposed TCCPT. Results verified that the proposed TCCPT is applicable and effective for the spheroidization of metallic powders with wide size distribution.

Investigation of the inner structure of gas–liquid flow in airlift pumps by laser‐high speed visualization technology

AbstractExperiments were conducted to investigate the inner structure of gas–liquid flow in airlift pumps by a laser Doppler velocimetry (LDV) system and a laser‐high speed photography. The measured central plane of the riser pipe was illustrated by a laser device, and the corresponding gas–liquid flow in this plane was recorded by a high speed camera. The results showed it was the wispy annular flow, rather than the annular flow, dominated the pump performance under a high gas flow rate. This wispy annular had a thick film with a maximal value 0.2 times of pipe diameter, and it kept pump working with a high output liquid flow rate at large gas flow rates. Moreover, new flow regime maps were presented with a function of accurately estimating the flow regime transition and presenting the airlift pump performance.

Energy storage efficiency optimization of methane reforming with CO2 reactors for solar thermochemical energy storage☆

In CO2 reforming of methane solar thermochemical energy storage, much research has been conducted to enhance the thermochemical performance of the reactor. However, there has been little research conducted to investigate the effects of dimensions on the reactor thermochemical performance. Moreover, little innovation has occurred on optimizing reactor dimensions and operating conditions simultaneously. In this paper, a model has been developed to simulate CO2 reforming of methane reaction in a tubular packed reactor. By comparing with experimental and simulation data from another publication, the model is validated to be more accurate. A parametric study has been performed to investigate the effects of dimensions and operating conditions on the reactor thermochemical conversion and energy storage efficiency. The result shows that there is a trade-off between achieving a higher energy storage efficiency and decreasing the conversion by having smaller reactor with larger gas flow rate. An optimization study of all the design parameters, based on the reaction model coupled with a multistart optimization algorithm, is performed to find the maximum energy storage efficiency for a fixed required conversion. Without sacrificing the conversion, an energy storage efficiency of 0.77, which is 10% higher than the highest established experimental data, is obtained through optimization. The study provides a baseline for further thermodynamic analysis of the entire system.

Measurement of radial temperature distributions of the blown CO2 arcs under different conditions

In this paper, the radial temperature distributions of the blown CO2 arcs in a model gas circuit breaker were investigated by optical emission spectroscopy methods. The CO2 flows with different flow rates (50, 100 and 150 l min−1) were created to axially blow the arcs burning in a polymethyl methacrylate (PMMA) nozzle. Discharges with different arc currents (200 and 400 A) were conducted in the experiment. The absolute intensity method was applied for a carbon ionic line of 657.8 nm to obtain the radial temperature profiles of the arc columns at a cross-section 1 mm above the nozzle. The calibration for the intensity of the C II 657.8 nm line was achieved by the Fowler–Milne method with the help of an oxygen atomic line of 777.2 nm. The highest temperature obtained in the arc center was up to 19 900 K when the arc current was 400 A and the CO2 flow rate was 50 l min−1, while the lowest temperature in the arc center was about 15 900 K when the arc current was 200 A and the CO2 flow rate was 150 l min−1. The results indicate that as the arc current increases, the temperature in the arc center would also increase apparently, and a larger gas flow rate would lead to a lower central temperature in general. It can also be found that the influence of the CO2 flow rate on the arc temperature was much less than that of the arc current under the present experimental conditions. In addition, higher temperature in the arc center would cause a sharper temperature decrease from the central region towards the edge.

Numerical simulation on gas–liquid multiphase flow in hot metal ladle with top submerged lance

ABSTRACT The gas–liquid multiphase flow behaviours in hot metal ladle are simulated by using Eulerian–Eulerian approach. The effects of wall lubrication force and virtual mass force on bubble behaviours are investigated, and the influences of bubble diameter and gas flow rate on bubble behaviours and liquid flow characteristics are also analysed. The results show that the established model eliminates the gas-adhering wall phenomenon in the water model of hot metal ladle. When the wall lubrication force is considered, some bubbles are pushed away from the submerged lance wall. The penetration depth of the bubble trajectory increases under the action of virtual mass force, increasing the bubble dispersion in the liquid phase. As the bubble diameter increases, the gas velocity increases, while the maximum values of liquid velocity and liquid turbulent energy decrease. At larger gas flow rate, the liquid region impacted by gas flow is larger.

Electrochemical Impedance Analysis of Ni/CGO10-Based Electrolyte-Supported Cells

To obtain a better understanding of the behavior of Ni/CGO fuel electrodes, this work presents a comprehensive investigation of Ni/CGO10-based electrolyte-supported cells. Commercial Ni/CGO10|CGO10|3YSZ|CGO10|Ni/CGO10-based symmetrical cells were characterized between 550–975 °C at pH2=0.8 bar and pH2O=0.2 bar and for different H2/H2O gas mixtures at 550 °C. Small electrode area, thin anodes and large gas flow rates were used to minimize mass transport contributions. The distribution of relaxation times (DRT) is calculated and based on the results, an equivalent circuit model is derived. Electrode process contributions on Ni/CGO were calculated by means of a complex non-linear square fit of the equivalent circuit model to experimental data. One low frequency and one middle frequency electrode process were identified and correlated to a surface and a bulk process, respectively. Apparent activation energy barriers for both processes were derived.

The conditions for the implementation of the convective mode of combustion for granular mixtures of Ti + xC

An experimental-theoretical method is proposed for calculating the burning velocity of Ti + xC granulated mixtures in a convective mode. The quadratic dependence of the burning velocity on the gas flow rate is shown. The behavior of the burning velocity in the convective mode was studied on the governing parameters and the gas flow rates are calculated, at which the convective mode of combustion replaces the conductive one. The transition between the combustion modes of a granulated mixture of Ti + 0.5C was experimentally realized, and a good agreement between the gas flow rate at the boundary of modes and the calculated value in the transition point was shown. The results can be used to explain and predict fast forest fires, since the fast convective combustion mode is realized with large gas flow rates (high wind speed) and low ignition temperatures typical of forests during the drought period.

Nonmonotonous Phenomenon of Corona Discharge Characteristics Under Different Airflow Rates

Corona discharge is extensively researched due to the wide applications in the fields of electrostatic precipitator, flow control, thermal management, and so on. Previous researches observe that the characteristics of the corona discharge, such as the average current in the Trichel pulse regime, could be influenced by the airflow velocity. In this paper, the effect of the airflow rate on the corona discharge is further investigated by using a needle-mesh discharge structure. The experimental results show that the discharge is transferred from a large amplitude, long pulse interval time condition to a small amplitude, short interval time condition when increasing the airflow rate and, at the same time, the discharge region is shrunk toward the centerline of tube channel (i.e., shrinking regime). However, after a stable regime around a certain airflow rate, the above-mentioned parameters are changed toward the opposite direction and the discharge region is expanded, when further increasing the airflow rate (i.e., expanding regime). This nonmonotonous phenomenon has not been observed in literature before, and we further investigate it under different tube channel diameters. It is found that, under a larger tube channel diameter, the transition point (corresponding to the minimum pulse amplitude and interval time) moves toward a larger gas flow rate. The physical mechanisms for this phenomenon are analyzed by considering the transport effect by airflow under different Reynolds numbers. It can be caused by a comprehensive effect of the mass transfer, heat transfer, movement process of particles, and frictional loss in the discharge space. The phenomenon revealed in this paper is possibly utilized to improve the application of corona discharge under airflow.

Experimental Investigation of the Influence of a Centered Line Sparger on the Jet from the Shroud in a 1:3 Water Model of a Tundish

In a continuous casting plant a tundish serves two main purposes. Firstly, it is a buffer vessel between the ladles and the mold and secondly, it is designed to remove non‐metallic particles from the melt. As the demands on the quality of the cast product have increased strongly, floatation (removal of particles using bubbles) of the particles becomes necessary. These bubbles alter the global flow field in the tundish. At large gas flow rates this influence needs to be considered in the positioning of mechanical flow control devices such as wears or impact pads. In this paper the influence of a line sparger on the global flow field is investigated using a 1:3 water model. A series of PIV (Particle Image Velocimetry) measurements have been performed at a wide range of air and water flow rates showing the influence of the bubbles on the shape of the liquid jet from the shroud. In addition, a dimensionless number is derived, which can be used to scale the gas flow rate from different experiments. This number is shown to be valid within the range of the experiments presented in this paper.

Electrochemical Impedance Analysis of Symmetrical Ni/Gadolinium-Doped Ceria (CGO10) Electrodes in Electrolyte-Supported Solid Oxide Cells

One of the most powerful tools in solid oxide cell (SOC) characterization is electrochemical impedance spectroscopy, which can unfold important insights into SOC performance characteristics and degradation behavior. To obtain a better understanding of the electrochemical behavior of Ni/CGO fuel electrodes, this work presents a comprehensive investigation of state-of-the-art Ni/CGO10-based electrolyte-supported cells. Commercial Ni/CGO10|CGO10|3YSZ|CGO10|Ni/CGO10 symmetrical cells were characterized between 550–975°C at pH2 = 0.8 bar and pH2O = 0.2 bar, and for different H2/H2O gas mixtures at 550°C. (i) Small electrode area, (ii) thin electrodes and (iii) large gas flow rates were used to minimize mass transport contributions. Based on distribution of relaxation times (DRT) analysis an equivalent circuit model was derived. Electrode process contributions on Ni/CGO were determined by means of a complex non-linear least square fit of the equivalent circuit model to the experimental data. One low frequency process at 0.1–1 Hz and one middle frequency process at 10–100 Hz were identified and correlated to a surface and a bulk process, respectively. Values for the apparent activation energy barriers and reaction orders with respect to steam and hydrogen content were determined.

Observation of arc modes in a magnetically rotating arc plasma generator

An arc plasma can present various forms under the influence of an external magnetic field. In this study, a magnetically rotating arc plasma generator has been developed to produce three arc modes, namely rigid arc, distorted arc, and diffuse arc, which are obtained by controlling the gas flow rate. The evolution of these arc modes are experimentally studied and discussed. Results show that, as the gas flow rate increases, the arc mode is first transformed from the rigid to the distorted mode, and then to the diffuse mode. Comparisons show that the location of the arc attachment is a key factor in determining the rigid and distorted modes. The diffuse arc is observed under larger gas flow rates, but the completely diffuse arc can exist only within a narrow range of gas flow rates. Compared to the distorted arc, the diffuse arc has not only better stability but also a wider high‐temperature plasma zone, which indicates that the diffuse mode may be more useful in industry.