Gas Volume Flow Research Articles

MATHEMATICAL MODEL OF PNEUMATIC CHANNEL OF GAS PRESSURE MEASURING TRANSDUCER

The paper is devoted to the study of the impact of operational factors, particularly gas leakage through the damages of pneumatic channels of measuring transducers of gas pressure and pressure drop, on the measuring result of these parameters and, therefore, on the measured value of gas flow rate and volume using pressure differential flowmeters. During the operation of gas metering units, connecting tubes, valve blocks, and averaging chambers of the standard primary device must be hermetic. However, they may become non-tight because of operational factors, and gas leakage may occur. Such leaks distort the measured pressure drop or pressure value, which can lead to a distortion of the measurement result of the gas flow rate by the metering unit.
 The authors developed a mathematical model of a pneumatic channel of gas pressure measuring transducer with existing damage. For this purpose, a mathematical model of the connecting tube, which connects the pressure averaging chamber with the pressure transducer chamber, has been developed for the stationary gas mode. A mathematical model of gas leakage through damage like "through-hole" was also developed. Based on the mathematical model of the connecting tube and the model of the process of gas leakage through the hole, a mathematical model of the pneumatic channel with a gas leakage hole was obtained.
 Modeling and investigating the impact of gas pressure, geometric characteristics of damage, and connecting line on the measuring result of pressure or pressure drop was performed. Particularly, the value of the negative systematic error of the gas pressure measurement, which occurs as a result of gas leakage through the hole in the connecting tube, is calculated for a set of fixed values of the geometric characteristics of the pneumatic channel.
 The paper shows that an increase in the pressure in the measuring tube leads to an increase in the modulus of pressure absolute error caused by the gas leakage through the hole in the connecting tube. The gas flow rate through the hole in the connecting tube and, accordingly, the pressure measurement error depends on the diameter of the through-hole and the location of the leakage. An increase in the hole diameter leads to an increase in the modulus of the absolute error of the pressure measurement.
 As the length of the connecting tube from the connection point with the measuring pipeline to the point of gas outflow increases, the pressure measurement error increases by the modulus.

Economical Silicon Nanowire Growth via Cooling Controlled Solid–Liquid–Solid Mechanism

AbstractConventional vapor–liquid–solid mechanism of nanowire growth opens up new opportunities of fabricating nanowires with controllable morphologies and aspect ratios. However, gaseous precursors have disadvantages of high material and processing cost, high toxicity, and limited scalability. By contrast, synthesizing nanowires via solid–liquid–solid mechanism could be a facile alternative since the low cost and nontoxic solid precursor is adopted in the process. In this study, the cooling control is found to be very critical for the solid–liquid–solid nanowire growth. Without a sufficient negative vertical temperature gradient, the nucleation and continuous growth of silicon nanowires could not occur. High volume gas flow cooling, fluctuating the heating temperature, decreasing the cooling rate, and applying a heat sink are all efficacious to promote silicon nanowire formation. In addition to the nanowires formed under high gas flow cooling on the silicon wafer sputtered with a nickel thin film, the solid–liquid–solid mechanism‐derived silicon nanowire growth can also be economically achieved by adopting a solution‐based coating of a nickel precursor onto the silicon substrate paired with a programmed slow cooling condition without using any gas, which could be transferred to other eutectic systems for cost‐effective nanomaterial fabrication.

Effect of N2 and CO2 bubbles on gas volume fraction and flow pattern in a quasi-2D bubble column by shadow imaging

This study reports the effect of N2 and CO2 bubbles on dilute to dense gas-liquid two-phase bubbly flow. A shadowgraph imaging technique captured bubble images at a high spatiotemporal resolution. The recordings of bubble images allow us to compute gas fraction distribution. It requires challenging segmentation and gas-liquid interface detection approaches in image processing. Hence a novel gas contour characterization technique has been introduced in this study that analyses light intensity per pixel for quantifying the effect of local gas volume fraction. The dominant gas structure and repetitive gas pattern have also been determined here using Fourier transform-based power spectral density and 2D cross-correlation functions, respectively. Gas-liquid flow regimes of dissolved CO2 bubbles are found quite different than that of N2 bubbles. The plausible reasons are that gas fraction distribution at the sparger region may inhibit bubble coalescence and the positive surface charge of CO2 bubbles acts as a barrier to the interface deformation.

The Investigation of Gas Distribution Asymmetry Effect on Coriolis Flowmeter Accuracy at Multiphase Metering.

Multiphase flows are encountered in various industries, and the Coriolis flowmeter (CFM) is considered a high potential flowmeter for the metering of these flows. However, the decoupling effect and asymmetrical gas distribution in a CFM might decrease the accuracy of its multiphase flow metering The asymmetry of gas distribution in a CFM and its influence on the metering accuracy have only been qualitatively investigated in a few studies. The present paper quantitatively describes the gas distribution asymmetry in several CFMs under different flow conditions by numerical simulation. The simulation methodology is developed and validated by a results comparison with a conducted experiment and published data for bubbly, stratified and transitional flow regimes. U-shaped and triangle-shaped CFMs of different diameters are investigated at different gas volume fractions and flow rates. It is shown that the increase in the gas volume fraction and the reduction in the mixture flow rate lead to the increase in the gas distribution asymmetry. The strong correlation between the gas distribution asymmetry and the experimentally observed CFM error is demonstrated. The correction of the CFM error is proposed based on this correlation allowing the metering error to be decreased from 34% to 10% for the investigated conditions.

Modification of the weld penetration characteristics in laser deep welding by the use of instationary gas flows

The present report focuses on the integration of a technology for generating temporally alternating (pulsed) gas flows in the field of laser welding. The technical realization required the specific adaptation of the three core elements of the gas pulse system (valve, section of measurements, control system) to realize new parameters for laser welding. These parameters allow for a positive influence on the joining process and on the results of welding, respectively. By means of temporal control of the gas volume flow in combination with the laser welding process, it was possible to produce a force effect on the molten pool and subsequently to improve the characteristics of laser-welded seams. The effects occurring through the use of an instationary gas flow were evaluated by using the "classically" metallography and through the use of digital image processing. In parallel, the effect of a pulsating gas flow on the melting zone was simulated by using specific software in order to be able to make further statements about the effects.

Implementation and verification of a Quasi-Eulerian-Eulerian-IATE model for the high-efficient prediction of polydispersed bubbly flows in a continuous casting mold

We implement a new gas–liquid two phase model for the high-efficient prediction of polydispersed bubbly flows in a continuous casting mold. This model shares similarity with the Euler–Lagrange (E-L) method, in which the gas velocity is updated by bubble Lagrangian tracking, and with coupling the phase transport equation in Euler-Euler (E-E) method, thus, it is called the Quasi-Eulerian-Eulerian-IATE (Q-E-E-IATE) model. The local mean bubble size is obtained from solving the interfacial area transport equation (IATE). Various interfacial forces including drag force, lift force, virtual mass force, and turbulent dispersion force are incorporated in this model. This model is verified against published experimental data. Good agreement of gas volume fraction, flow field and bubble size distribution are obtained by adding the virtual mass force and adopting optimized IATE constants. The computational cost of the Q-E-E-IATE model is much lower compared to that of the traditional E-L and E-E models.

Aerodynamic Window Sealing of a Large-Aperture Channel for High-Power Laser Transmission

In this study, the sealing of a large-aperture channel for high-power laser transmission is achieved using an aerodynamic window. Further, a numerical model of the gas and dust particle motion in the channel is established under three different blowing schemes, and the sealing performance of the large-aperture channel is analyzed and compared under different blowing schemes. The results indicate that the larger the proportion of purge gas volume flows in the axial direction, the better the sealing effect of the channel. More importantly, the axial blowing scheme can ensure that the large-aperture channel maintains the relative positive pressure to the external environment, effectively blocking the ambient gas and dust particles blowing in. The axial blowing scheme can achieve the sealing requirements of the large-aperture channel in an environment where the ambient wind speed is less than 20 m/s, and the dust particle mass concentration is less than 8×10−3 kg/m3. In this case, the minimum non-zero z-directional wind speed is stable and positive at a position 100 mm away from the port in the channel, and the particle mass concentration is zero.

Water Model Experiments on the Influence of Phase Distribution in the Submerged Entry Nozzle Considering Varying Operating Conditions

Continuous casting of steel argon injection into the submerged entry nozzle (SEN) via the stopper is common practice. Nonetheless, the resulting phase distribution in the SEN is still under discussion. The main available casting parameters at the steel plant to determine the flow situation in the SEN are usually the stopper rod position, the argon feeding pressure, the argon flow rate, and the casting speed. To show the potential influence of the phase distribution on the stopper characteristic and on the argon feeding pressure, experiments using a 1:3 scale water model are presented. For the experiment, the water flow rate is scaled using Froude similarity, while the air flow rate is chosen to keep the ratio between the liquid and gas volume flow rate constant. The casting parameters and the pressure at three distinct levels of the SEN are measured. To relate this measurement data to the corresponding phase distribution, two cameras are used to document the phase distribution in the SEN. The images show four major phase distribution patterns. These patterns can be linked to significant changes in the measured pressure levels and the behavior of the stopper.

Metrological research of a reference installation based on a high-pressure vessel

The urgency of development and metrological research of reference installations based on high-pressure vessels, which meet the requirements of the implementation of traceability of instruments for measuring gas volume and gas volume flow rate, is considered. The operation algorithm of the specified reference installations when transferring the unit of gas volume to the gas meters under consideration is studied. Based on the algorithm and features of the operation of PVTt-type standards, a list of the analysed uncertainties of type A is formulated when estimating the volume of the calibrated high-pressure vessel; when measuring the absolute pressure and absolute temperature of gas due to the influence of instability of pressure and temperature on the gas meter under consideration due to the presence of a temperature gradient in the vessel. Uncertainties of type B, which are determined by metrological characteristics of measuring instruments, as well as the uncertainty of parameters evaluated by means of calculation, in particular the compressibility factor of the working environment, the influence of water vapour on the working environment and the influence of the discreteness of the device for collecting information about measurements from the gas meter are considered.
 Formulas to quantify the combined uncertainty of measuring the volume of the calibrated vessel, the absolute pressure and absolute temperature as well as to calculate the air compressibility factor for the operating conditions of the installation are given. These parameters are the absolute pressure and absolute temperature of the gas and the compressibility factor of the working environment in the vessel at the beginning and at the end of the reproduction of the reference volume as well at the inlet of the gas meter. The expressions for calculating the combined and expanded uncertainties of PVTt-type standards are given.

Bilateral comparisons on COOMET Project 684/MD/16 “Pilot comparisons of national standards in the field of gas flow”

Abstract The article describes the procedure for performing international bilateral comparisons of the national measurement standards of the units of gas volume and volume flow in Ukraine and Moldova. The comparisons were carried out within COOMET Project 684/MD/16 “Pilot comparisons of national standards in the field of gas flow”. The list of reference standards that took part in comparisons is indicated. The range of gas volume flow, in which the comparisons were carried out, is from 0.5 m3/h to 50 m3/h. For the flow range from 0.5 m3/h to 1 m3/h, a drum-type meter was used, and for the range from 2 m3/h to 50 m3/h, comparisons were performed using a rotary gas meter. It is indicated that the national state primary and secondary standards of the gas volume and volume flow units took part in the comparisons from Ukraine, while from Moldova it was the national standard of the gas volume flow unit. A brief description of the national measurement standards and the principle of reproduction of the gas volume and volume flow units is presented. In particular, it was noted that the primary and secondary standards of Ukraine are built on the basis of bell-type prover, and the standard of Moldova combines a piston and bell-type prover. The method of calculating, calculation of expanded uncertainty and determining the degree of equivalence of the national standards of Ukraine and Moldova are demonstrated. The results of bilateral comparisons in the form of Table 1 are presented and shown in Fig. 4. The degree of equivalence of the national standards does not exceed 0.41, which indicates that the primary and secondary standards reproduce the gas volume and volume flow units with declared uncertainties, and transfer standards retain their metrological characteristics throughout the cycle of comparisons. General conclusions are drawn about the success of bilateral comparisons.

Numerical Investigations for the Two-Phase Flow Structures and Chemical Reactions within a Tray Flue Gas Desulfurization Tower by Porous Media Model

The computational cost of the full-scale flue gas desulfurization (FGD) tower with perforated sieve trays is too high, considering the enormous scale ratio between the perforated hole at the sieve tray and the relevant size of the full-scale tower. As a result, the porous media model is used to replace the complex perforated structure at the sieve tray in this study, which has been validated for the measured data for both the small- and full-scale FGD tower. Under a lower inlet gas volume flow rate, the simulation result of the four-tray tower indicates that the uprising gas flow of high SO2 mass fraction can move along the wall of the tower. This region lacks two-phase mixing and, hence, its desulfurization efficiency is similar to that of empty and one-tray towers under the same flow conditions. However, when the gas volume flow rate increases, the liquid column becomes larger because of the stronger inertial of the uprising gas flow. In this situation, the implementation of the sieve tray suppresses the deflection of liquid flow and provides a better mixing within sieve trays, leading to a noticeable increase in desulfurization efficiency. This study provides insightful information for the design guideline for the relevant industries.

Spatial and temporal evolution of tar during ex-situ underground coal gasification

Underground coal gasification is a promising technology for exploiting deep coal seams, while the evolution behaviors of pollutants such as tar in the reaction zone are still not clear. In this work, an ex-situ experimental system of UCG was built, and a series of experiments were carried out with different gasification agents and flow rates to study the concentration and composition of tar samples from different positions and time. Shenmu bituminous coal is cut into specific blocks with drilled holes as initial gasification channel and sampling channels. Tar concentration is calculated according to the weight of tar samples and the corresponding gas flow volume during sampling, while tar composition is analyzed by GC–MS. For the involved conditions, the maximum relative gap of tar concentrations between L = 36 cm and 102 cm is around 296% under 10 L/min oxygen case. The maximum relative gap of PAH percentage in tar between L = 36 cm and 102 cm is around 84% under 10 L/min air case. For oxygen gasification, increasing flow rate from 10 L/min to 15 L/min causes a lower tar concentration at reaction zone and a higher tar concentration at outlet, as well as a lower PAH percentage for all positions. For air gasification, increasing flow rate from 10 L/min to 50 L/min leads to a more uniform distribution of tar concentration and composition. Tar concentration for air gasification is far smaller than that for oxygen gasification. Changing from 10 L/min to 15 L/min for oxygen gasification decreases the carbon emission in gases and increases the percentage of product tar. Changing from 10 L/min to 50 L/min for air gasification decreases the carbon emission in gases but increases the percentage of pollutant tar.

Research on the Influence of Combustion Methods on NO x Emissions from Co-combustion of Various Tannery Wastes.

To further increase combustion efficiency and reduce nitrogen oxide pollution caused by tannery wastes, three raw materials, including tannery sludge, chrome-tanned buffing dust, and chrome shavings, were burned together in a dual-bed model reactor under various conditions. In addition, a thermogravimetric analysis of co-combustion of three tannery wastes was studied in this study, which was conducive to understanding the combustion characteristics and positive effects. The comprehensive combustibility index S, the flammability index Kr, and the stable combustion characteristic index Gb all increased when the tannery sludge was blended with chrome-tanned buffing dust and chrome shavings, indicating that the combustion behavior was improved by co-combustion. For normal combustion, decreasing the gas volume flow and temperature resulted in a decrease in the oxidation of nitrogen compounds, consequently lowering the NOx emission. During air staged combustion, at an appropriate secondary gas ratio of about 10–40%, the NOx reduction would be increased from 10.9 to 19.3%. By increasing the tertiary gas volume flow from 0.2 to 1.1 L/min in decoupling combustion, an average relative NOx reduction efficiency of 47% was attained compared with normal combustion. The results offered a viable technology that resulted in a lower NOx emission and realized the application of decoupling combustion.

Model of an iron ore sinter plant with selective waste gas recirculation

The use of sinter influences hot metal production substantially and significantly affects an integrated steel mill’s total emissions. Sintering of iron ores is an enormous energy-intensive and resources consuming process. Introducing a selective waste gas recirculation (SWGR) to the sintering process reduces the energy consumption, stack gas volume flow, and sulfur dioxide emissions of an iron sinter production. Simulating this complex process in flowsheet simulations of integrated iron and steelworks is a fast and cost-effective opportunity to validate new operation settings. The implementation of a sinter plant in gPROMS ModelBuilder®characterizes the sintering processes by three main sub-models. A burner model describes the gas combustion, a black-box model consider the main sintering processes, and a wind box model divides the total off-gas into a recycle gas and a stack gas. A specific temperature polynomial represents the temperature distribution across the wind boxes to allow detailed investigations on SWGR in complex flowsheet simulations. Implementing SWGR to the sintering process, the model shows a reduction of coke consumption, stack gas flow rate, and sulfur dioxide emissions by 11%, 27%, and 27%, respectively. In the SWGR scenario, the utilization rate of carbon monoxide increases and less coke is consumed. The chlorine emissions of the sintering process differ with and without SWGR insignificantly.

Falling film co-current flow cyclone demister for separating high-boiling droplets: Gas-liquid flow pattern and performance

In many processes, the product gas stream contains liquid droplets that easily condense or solidify, which can deteriorate demister performance and even block equipment during gas–liquid separation. We proposed a falling film co-current flow cyclone demister (F2CFCD) to solve the above problems. The novel idea is that an additional stream of solvent fluid is added to the gas stream containing the droplets. After injecting the demister, the solvent fluid forms a film on the wall of F2CFCD. When the droplets are separated to the wall surface by centrifugal force, they are dissolved by the liquid film, thereby avoiding crust formation. In this work, the gas–liquid flow characteristics and the performance of F2CFCD are investigated numerically and experimentally. A hot-wire anemometer (HWA) is used to measure the gas velocity, and a conductivity method is used to measure the liquid film thickness. A coupled numerical model of the RSM-DPM and Eulerian wall film (EWF) model is applied to discuss the effect of the gas–liquid flow rate on the flow field in the demister. The liquid volume flow rates ranges from 0.5–10.5 m3/h, and the gas volume flow rates range from 640–894 m3/h. The gas flow pattern and the liquid film flow regimes are explored in the F2CFCD. A film thickness model is established to evaluate the average film thickness in the waterfall regime. Experimental observations illustrate that F2CFCD has a high separation efficiency for droplets under all conditions.

Signal Analysis of Characteristics Using Passive Acoustic Emission Technique in Gas‐Solid Pipeline Flows

This paper investigates a case study of the use of a passive acoustic sensor for online measurement of the dilute phase gas‐solid pipeline flows. The acoustic emission sensor is mounted externally on a stainless steel line conveying silica powders. For different experimental conditions, including the solid to air mass ratios from 0.6 to 1.4 and the gas volume flows from 160 to 240 m3/h, the sound signals in the pipeline are discussed using the wavelet transform technique. The measured values of transmission mechanism of two different lengths, 25 mm and 35 mm, are analyzed. The results show that the variation tendency of standard deviations is consistent and that the noninvasive, online acoustic detect technique can be regarded as a satisfactory tool in gas‐solid flows.

Synthesis of stabilizer-free, homogeneous gold nanoparticles by cold atmospheric-pressure plasma jet and their optical sensing property

Recently, cold atmospheric-pressure plasma has been studied extensively as an efficient and green method to synthesize gold nanoparticles (AuNPs). Although the characteristics of the AuNPs, especially their homogeneousness, depend very much on the plasma synthesis parameters, there is a lack of a study involving these parameters systematically. Moreover, most of AuNPs-cold-plasma synthesis reports so far either required organic capping agents or resulted in highly non-uniform AuNPs. In this work, we systematically study the effect of most important synthesis parameters— including distance from the plasma jet to the solution, gas flow rate, plasma frequency, volume and concentration of the precursor, plasma interaction time as well as the effect of the synthesis environment (humidity and temperature)—on the uniformity of the AuNPs. Through various characterization measurements, we show that homogeneous and highly stable intrinsic AuNPs with an average size of 45 nm can be obtained with optimized synthesis parameters and in the absence of a stabilizer. The synthesized AuNPs yield advanced optical sensing properties in comparison with commercial AuNPs and can be further applied in developing versatile and high-sensitivity biosensors.

Experimental investigation in the permeability of methane hydrate-bearing fine quartz sands

The permeability is one of the intrinsic parameters that determines the fluid flow in the porous media. The permeability in hydrate-bearing sediments affects the gas recovery and production of hydrate reservoirs significantly. The irregular permeability characteristics are challenging for fine-grained hydrate-bearing sediments. In this study, a series of experiments was conducted using an one-dimensional pressure vessel to investigate the hydrate formation characteristics and the permeability in hydrate-bearing fine quartz sands (volume weighted mean diameter was 36.695 μm). Hydrate saturations (0–26% in volume) were controlled and calculated precisely based on the amount of injected water and gas, the system pressure and temperature. The results indicated that the hydrate nucleation induction period was completed during gas injection, and the average time of hydrate formation was within 500 min. The permeability of methane hydrate-bearing fine quartz sands was investigated by steady gas volume flow. For hydrate saturation lower than 13.94%, the hydrate mostly formed in grain-coating, the permeability reduction exponent calculated by Parallel Capillary, Kozeny Grain Coats and Simple Cubic Filling models were 2.00, 2.10 and 1.74 respectively, and Simple Cubic Filling model was in accordance with the experimental data best. However, for hydrate saturation ranged from 13.94% to 25.91%, the permeability increased due to the flocculation structure formation of fine quartz sands and hydrate, which caused the increase of effective porosity. A new relationship among hydrate saturations, effective porosity, the ratio of permeability in the presence and the absence of hydrate was developed. This study developed the mathematical models for predicting the permeability with hydrate saturation in fine quartz sands, which could be valuable for understanding the characteristics of hydrate-bearing fine-grained sediments.

Change of existing circulating fluidized bed boilers to oxy-firing conditions for CO2 capture

This work investigates a circulating fluidized bed boiler, originally designed for air-firing, retrofitted to oxy-firing with the purpose of removing the CO2 emission from coal combustion. Previous studies have shown that the heat balance on the gas-particle side can be satisfied without changes in the boiler, but then the volume flow of gas is reduced. To retain the operation like that during air-firing, the volume flow, that is the fluidization velocity, in oxy-firing should be equal to that in air-firing. It is the main purpose of this work to determine the conditions for the transition from air to oxy-firing, while the heat transfer conditions are maintained at a constant fluidization velocity. Measures to achieve this, such as adjusting the supply of additional gas and the heat transfer surface, are analysed. The fulfilment of the furnace's heat balance requires extra fuel or reduction of the heat-transfer surface in the furnace. These changes affect the performance of the back pass, which must be modified to accommodate the change in gas composition and the higher sensible heat content of the flue gas. Strategies to deal with these circumstances in CFB boilers are discussed.

Nanoporous polypropylene membrane contactors for CO2 and H2S capture using alkali absorbents

The paper reports a comprehensive review of the performance of nanoporous gas-liquid polypropylene membrane contactor with NaOH absorbents for removal of H2S and CO2 components from the gas streams. The experiments at different operation conditions, including variation of acid gas content in a feed stream, alkali concentration in absorbent, gas and liquid absorbent volume flow rates, absolute and gas-liquid differential pressures are discussed as a function of the absorbent saturation levels. In-liquid diffusion of components and gas/membrane contact times were determined as main governing factors limiting contactor efficiency. Mass transfer rates of acid gas removal on the membrane contactor over 3 × 10−3 mol/(m2 × s) for CO2 and 7.5 × 10−3 mol/(m2 × s) for H2S were attained. Ultimate processed gas quality with H2S content below 5 ppm and CO2 content below 0.01% was achieved at the contactor performance over 7 m3/(m2 × h) and initial acidic gas content of 2%, while achieving a membrane packing density in the contactor over 3000 m2/m3. The paper also provides an experimentally-proven theoretical model for calculating removal efficiency and residual acid gas partial pressures depending on the membrane parameters and operation conditions. It is shown, the mass transfer coefficient and removal efficiency differ significantly for H2S and CO2 due to the difference in dissolution mechanism involving kinetically limited deprotonation reaction of solvated water in case of CO2(aq) while engaging direct deprotonation of H2S. This allows to attain residual partial pressure of H2S in retentate stream equal to the equilibrium pressure above the absorbent solution, while CO2 residual pressure exceeds an equilibrium value few orders of magnitude. The effect has been successfully utilized for the selective removal of H2S from both CO2 and H2S-containing mixtures with H2S/CO2 selectivity exceeding 1500.