Gas Flow Pattern Research Articles

Experimental evaluation of an indirectly-irradiated packed-bed solar thermochemical reactor for calcination–carbonation chemical looping

The two-step calcium oxide based calcination–carbonation cycle is studied for carbon dioxide capture and solar thermochemical energy storage applications. An indirectly-irradiated packed-bed solar thermochemical reactor is experimentally evaluated using simulated high-flux solar irradiation provided by a multi-source solar simulator. Experimental runs include a single calcination reaction step as well as single and multiple (up to four) consecutive calcination–carbonation cycles. The samples are characterised using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The reactor temperature peaked at 1,035°C. The average solar-to-chemical conversion efficiency, defined as the ratio of heat consumed by the reaction to radiant heat supplied to the reactor, was found to be between approximately 1.3% and 8.6% for the five performed experimental runs. The necessary advancements to the presented reactor design identified during the experimental campaign include improvements in thermomechanical characteristics of ceramic and metallic parts of the reactor to prevent fast mechanical and chemical degradation, application of more robust high-temperature reaction chamber seals, and optimisation of reactor geometry and gas flow patterns towards spatially more uniform thermal conditions and chemical reaction rates.

Improved ventilation efficiency due to continuous gas flow compared to decelerating gas flow in mechanical ventilation: results of a porcine trial.

In pressure-controlled ventilation (PCV), a decelerating gas flow pattern occurs during inspiration and expiration. In contrast, flow-controlled ventilation (FCV) guarantees a continuous gas flow throughout the entire ventilation cycle where the inspiration and expiration phases are simply performed by a change of gas flow direction. The aim of this trial was to highlight the effects of different flow patterns on respiratory variables and gas exchange. Anesthetized pigs were ventilated with either FCV or PCV for 1 h and thereafter for 30 min each in a crossover comparison. Both ventilation modes were set with a peak pressure of 15 cmH2O, positive end-expiratory pressure of 5 cmH2O, a respiratory rate of 20/min, and a fraction of inspired oxygen at 0.3. All respiratory variables were collected every 15 min. Tidal volume and respiratory minute volume were significantly lower in FCV (n = 5) compared with PCV (n = 5) animals [4.6 vs. 6.6, MD -2.0 (95% CI -2.6 to -1.4) mL/kg; P < 0.001 and 7.3 vs. 9.5, MD -2.2 (95% CI -3.3 to -1.0) L/min; P = 0.006]. Notwithstanding these differences, CO2-removal as well as oxygenation was not inferior in FCV compared with PCV. Mechanical ventilation with identical ventilator settings resulted in lower tidal volumes and consecutive minute volume in FCV compared with PCV. This finding can be explained physically by the continuous gas flow pattern in FCV that necessitates a lower alveolar pressure amplitude. Interestingly, gas exchange was comparable in both groups, which is suggestive of improved ventilation efficiency at a continuous gas flow pattern.NEW & NOTEWORTHY This study examined the effects of a continuous (flow-controlled ventilation, FCV) vs. decelerating (pressure-controlled ventilation, PCV) gas flow pattern during mechanical ventilation. It was shown that FCV necessitates a lower alveolar pressure amplitude leading to reduced applied tidal volumes and consequently minute volume. Notwithstanding these differences, CO2-removal as well as oxygenation was not inferior in FCV compared with PCV, which is suggestive of improved gas exchange efficiency at a continuous gas flow pattern.

A Numerical Study of Scenarios for the Substitution of Pulverized Coal Injection by Blast Furnace Gas Enriched by Hydrogen and Oxygen Aiming at a Reduction in CO2 Emissions in the Blast Furnace Process

A numerical simulation procedure is proposed for analyzing the partial replacement of pulverized coal injection by hydrogen, oxygen, and blast furnace gas (BFG) injections mixed with pulverized coal (PCI) within the tuyeres of large blast furnaces. The massive use of hydrogen-rich gas is extremely interesting for ironmaking blast furnaces in the context of net-zero carbon hot metal production. Likewise, this new approach allows for increasing productivity and for reducing the specific emissions of carbon dioxide toward a net-zero carbon ironmaking technology. Nevertheless, the mixture of pulverized coal injection and gas injection is a complex technology. In addition to the impact on chemical reactions and energy exchange, the internal temperature and gas flow patterns can also change drastically. With a view to assessing the state of the furnace in this complex operation, a comprehensive mathematical model utilizing multiphase theory was developed. The model simultaneously handles bulk solids (sinter, pellets, small coke, granular coke, and also iron ore), gas, liquid metal and slag, and coal powder phases. The associated conservation equations take into account momentum, mass, chemical species, and energy while being discretized and solved using finite volume techniques. The numerical model was validated against the reference operating conditions using 220 kg per ton of pig iron (kg/tHM) of pulverized coal. Therefore, the combined injection of different concentrations of fuel hydrogen, blast furnace gas, and oxygen was simulated for replacing 40, 60, and 80 kg/tHM of coal injection. Theoretical analysis showed that the best scenario with stable operation conditions could be achieved with a productivity increase of 20% corresponding to a CO2 reduction of 15% and 60 kg/tHM of PCI replacement.

ДОСЛІДЖЕННЯ ТЕЧІЇ ГАЗОВОГО ПОТОКУ МЕТОДОМ ВІЗУАЛІЗАЦІЇ

The article describes the test conducted to study the patterns of gas flow for a channel with triangular protrusions using the visualization method to clarify the physical flow pattern. The proposed method makes it possible to obtain fixed patternsof the flow in different regimes and flow parameters. The obtained flow patterns are justified by theoretical dependencies

Directly irradiated fluidized bed autothermal reactor (DIFBAR): Hydrodynamics, thermal behaviour and preliminary reactive tests

The advancements of the Concentrating Solar Thermal (CST) technologies in the heat and power sector are pushing researchers to find new ways to exploit solar energy. Solar-driven thermochemical processes can open new scenarios and set a milestone towards a greener industry. This paper presents the development of a Directly Irradiated Fluidized Bed Autothermal Reactor (DIFBAR), that exploits fluidization technology and the principle of an autothermal reactor to carry out solar chemical processes with high efficiency. The viability of recovering the sensible energy of the solid products to preheat the reactants is studied in an experimental prototype that couples a cavity receiver/reactor and a countercurrent double-pipe heat exchanger. The prototype is operated as a circulating fluidized bed: the inner tube of the heat exchanger is a fluidized bed riser, the receiver works as a gas–solid separator, the outer tube (annulus) of the heat exchanger is an overflow standpipe and a buffer tank (reservoir) connects the annulus to the riser, closing the loop. The reservoir can also be operated as a fluidized bed reactor like in a dual-fluidized bed system. The first experimental results are reported using a Geldart B sand as bed inventory. A hydrodynamic study has been carried out to verify proper control of the system. Solid circulation rates have been determined and match the design target of 1.4 g/s. Pressure measurements have been used to control bed levels and the flow of the sand through the standpipe. The effects of gas velocities and outlet pressure drops are reported. Internal gas flow patterns have been determined by a gas tracing technique. Undesired gas by-passing streams are very small and can be zeroed by regulating the operating conditions. High temperature experiments have been conducted with a high-flux solar simulator under inert and reactive conditions, to prove the operating principle of the reactor. Steady state temperature profiles have been analyzed to assess the performance of the heat exchanger: the heat transfer coefficient ranges between 340 and 490 W/(m2 K). The operability of a solar-driven chemical process has been proved by calcining a batch of magnesium carbonate (MgCO3) particles, added to the inventory.

Revisit flame modulation towards low-NOx and uniform thermal field in heating flue of a coke oven

To alleviate the environmental issues from the coal coking process, many efforts have been conducted on air staging and flue gas recirculation to dilute oxygen content with only a modest success of a NO discharge between 500 and 1000 ppm. In this work, we have attempted to modulate the structure of the fuel inlet to dilute the fuel content for a further mitigation of NOx emission. By using the CFD technique, three key structural parameters were used to demonstrate the effect on NOx formation and thermal uniformity in the heating flue. A three-dimensional CFD model was established based on an industrial scale coke oven battery of 7.63 m in height, and its reliability was verified by validating the calculation against practical data collected on-site. Comparative simulations were carried out in terms of flue gas flow pattern, temperature profile, fuel species and NO concentration distribution. The results show that the benchmark battery has probably selected appropriate parameters for the internal recirculation, but falls short with respects to the size of fuel inlet and the space between the fuel and air inlets. Compared to the basic design, the modified one presents a 57.3% reduction in NO formation, and an improved vertical temperature uniformity.

Performance model evaluation of turbine flow meter in vertical gas-liquid two-phase flows

Aiming at the need for flow measurement of gas-liquid flows in domestic gas well production, this paper proposes a measurement method based on the combination of the turbine flow meter (TFM) and a rotating electric field conductance sensor (REFCS). In experiments, the REFCS is used for the measurement of the gas holdup. To verify the applicability of the TFM models investigated in the previous study, for the modeling part, the mass, momentum and torque models are evaluated in vertical upward gas-liquid two-phase flows. In our model test, the meter factor model of TFM considers the effects of the slip ratio between the gas and liquid phases and flow patterns. In particular, the gas holdup involved in calculating the slip ratio in the model evaluation is obtained from the REFCS measurements. Model test results show the torque model has better volumetric flow rate prediction accuracy than the mass and momentum models. In the present study, the ranges of the liquid and gas phases are Qw = 2–30 m3/d and Qg = 1–16 m3/d, it was found that the average absolute deviation (AAD) in the predicted volume flow rate is equal to 1.23 m3/d and the average absolute percentage deviation (AAPD) is equal to 7.69%. The evaluated results presented in this paper will allow better estimates of the volumetric flow rates of gas-liquid flows based on the combined TMF and REFCS measurements during the monitoring of gas well production.

A two-state Markov chain model for slug flow in horizontal ducts

Intermittent flows are common flow patterns in gas–liquid horizontal flow and attract attention and great research effort due to its importance for industrial and engineering applications. The slug flow is typically modelled based on a unit cell varying from an elongated air bubble with a liquid film in segregated flow pattern and an aerated liquid plug, the slug region, with remarkable stochastic characteristics of its alternating regions. In this paper, a two-state Markov chain model is proposed to represent the stochastic dynamics of developed slug flow in horizontal pipes. Each state represents either the liquid slug or the elongated bubble regions and the transition probabilities dictate the change of the given discrete time measurement to stay at a given state or change. This simple but insightful description of the phenomenon allows an analytical treatment of the statistics of Markov chain stochastic process. Measurement stations with two double wire resistive sensors are used to obtain the void fraction time series and a corresponding two-state representation. Each state is classified by a threshold defined by an unsupervised and non-parametric pattern recognition approach. The state transition matrix is then estimated for each corresponding experimental point. Thus random samples can be synthetically regenerated with the same statistical features of the corresponding measurements. It is shown that the Markov chain model can successfully represent second-order statistics of the measurement, such as the autocorrelation and power spectral density, given an appropriate choice of the chain order. Moreover, a cross correlation-based time delay estimation is proposed for the two-sensor measurement station and additional information is obtained from the slug flow. Subsequently, statistics of some slug flow features are estimated using the proposed approach and their interpretation as random variables derived from the void fraction stochastic process is discussed.

Hydrogen production by decomposition of ethanol in the afterglow of atmospheric-pressure nitrogen microwave plasma torch

The atmospheric-pressure microwave plasma torch (MPT) is employed to produce hydrogen via the decomposition of ethanol (C2H5OH). The ethanol aerosol is injected directly into the early afterglow of a nitrogen plasma and the products are analyzed with Fourier transformation infrared spectrometery and gas chromatography. Meanwhile, optical emission spectroscopy is used to diagnose the plasma. The influencing factors for the hydrogen production are investigated with respect to the location of the ethanol injection, the ethanol feed rate, the ethanol microdroplet size, the absorbed microwave power, the total flow rate of carrier gas, and the Ar–N2 mixture ratio, respectively. It is found that the excited species and high temperature play important roles in ethanol decomposition. In addition, the effect of the gas flow pattern in the reaction chamber on hydrogen production is analyzed with the aid of computational fluid dynamics and the mechanism of ethanol decomposition by MPT is discussed. Hydrogen production in our experiment was successful, with a production rate of up to 1309 l h−1, an energy yield of up to 468 l kWh−1, and a hydrogen yield of up to 95%, respectively.

Mathematical Model for Flow of High-pressure Gas in Microscale

Fused silica micro-tubes, whose size is similar to the pore throat in a low permeability reservoir, simplify the complex and tortuous of channels and throats and are used in this study to stimulate the flow pattern with micro-scale methods. A high-pressure micro-tube holder (designed and developed independently with a patent for invention) has been used to study gas flow patterns within the pressure range of 0.1MPa-30MPa. Moreover, we establish a gas flow equation and analysis the applicability of different inlet pressure based on the experiment result. The result shows: First, the pressure drop in the micro-tube is predominantly induced by friction resistance at low inlet pressure. While under relatively high inlet pressure, the impact of kinetic energy conversion and throttling effect on pressure drop shall be considered. Second, we build up a gas-flow equation in a micro-tube considering friction resistance, kinetic energy loss, and throttling effect. We also analyze the applicability for different diameters and inlet pressure. These research achievements were enriched in microtubule flow; different conditions have been identified for a different equation which has significant meaning to gas flow regulation in tight sandstorm reservoirs.

Evaporation characteristics of ethanol droplet in different gases under force convection condition

Ethanol is recognized as one of the finest alternative bio-fuels due to its natural characteristics. Fundamental studies on ethanol droplet evaporation process are mainly either in stagnant environment or using some semi-empirical co-relations. Here, a fully numerical model based on the first principle is solved to investigate the effects of various atmospheric gases (Ar, N2, O2 and CO2) on droplet evaporation phenomenon under force convective situation. Two-dimensional governing equations of species, momentum and energy transfer of spherical coordinate system are solved, and the simulation is validated quantitatively with the literature. Uniform convective strength (Re = 100) is maintained for all cases examined at T∞ = 500 K and P∞ = 0.1 MPa. From the simulation results, it is observed that the viscosity ratio (liquid to gas) has effect on droplet life time. The ethanol droplet life time increases in less viscous atmospheric gases. The ethanol droplet life time is shorter in Ar gas, but heat-up period, wet-bulb temperature, and the surface blowing effect are higher in Ar compared to other atmospheric gases. The heat-up periods of the ethanol droplet in Ar, CO2, N2 and O2 atmosphere occupy around 30%, 20%, 17% and 16.5% of the total life time of the droplet, respectively. It is also noticed that, the heat-up period increases with increase in the thermal conductivity ratio (liquid to gas) and vice versa. Furthermore, the flow pattern of both gas- and liquid-phase in terms of streamline and the internal temperature distributions of the droplet are visualized at various time instants.

A New Elastoplastic 3D Sand Production Model for Fractured Gas Fields

Reservoirs characterized by high temperature, high-pressure, medium high cementation strength, low porosity, and low permeability, in general, are not affected by sand production issues. Since 2009, however, it is known that cases exists where sand is present and may represent a significant technical problem (e.g., the the Dina II condensate gas field). In the present study, the main factors affecting sand production in this type of reservoir are considered (mechanical properties, stress fields, production system, completion method and gas flow pattern changes during the production process). On this basis, a new liquid-solid coupled porous elasto-plastic 3D sand production model is introduced and validated through comparison with effective sand production data. The related prediction errors are found to be within 15%, which represents the necessary prerequisite for the utilization of such a model for the elaboration of sand prevention measures.

Duality of the stream pattern of supersonic viscous gas flow past a blunt-fin junction: effect of a low sweep angle

Results of numerical solution of the problem of supersonic flow past a symmetric blunt fin mounted on a plate with a developing boundary layer are presented. Generally, the case considered corresponds to the flow configuration used in the experimental and computational study by Tutty et al. (2013), in which the laminar air flow with the freestream Mach number of 6.7 is considered. Previously, the authors have shown (2020) that for these conditions two stable solutions corresponding to metastable flow states with different configurations of the vortex structure and the pattern of local heat transfer are predicted. In present paper, the influence of a low sweep angle of a blunt leading edge on the vortex structure in the separation region, local heat transfer, and the possibility of obtaining a dual solution are investigated. The bifurcation diagrams showing for two solutions the main horseshoe vortex center location and the length of separation region versus the skew angle are presented.

Swirling supersonic gas flow in an EIGA atomizer for metal powder production: Numerical investigation and experimental validation

This paper is concerned with the modeling of the Electrode Induction Melting Gas Atomization (EIGA) process. This process employs a swirling supersonic inert gas jet to atomize a free-fall molten metal stream, with the aim to produce powders of highly reactive metals. As a first step towards the development of a complete model, this study aims to describe the behavior of the swirling gas flow through and downstream the EIGA gas nozzle and to highlight the influence of the main operating parameters on the jet characteristics. The developed model is based on the Reynolds-Averaged Navier-Stokes (RANS) approach using the Favre decomposition for compressible flow together with a k-ω SST turbulence model. The numerical results are partially validated against images of the gas flow patterns obtained using the Schlieren imaging technique. The simulation results show that the gas flow transits to a supersonic regime immediately before exiting the nozzle. In the atomization tower, it forms a swirling supersonic jet with an asymmetric geometry composed of several Mach diamonds. The inlet gas pressure has a significant effect on the jet structure and Mach number distribution. However, within the investigated range of pressure values (30–45 bar), the swirling motion of the jet, hence the jet geometry, remain little affected. In contrast, a small increase of the nozzle exit slit size significantly increases the swirling motion, which in turn strengthens the jet asymmetry. A reduction of the overpressure in the melting chamber has a similar effect, but to a lesser extent.

SCR형 탈질 시스템의 암모니아 분사 노즐의 유량 제어에 대한 CFD기법 적용에 관한 연구

In the present study, computational analysis tools have been applied to improving the performance of the denitrification process by flow control of the ammonia injection nozzles adjusting to the flow distribution of the nitrogen oxides in the inlet flue gas of the selective catalytic reduction system. The uniformity of NH3/NO molar ratio is selected as the performance parameter. Design Xplorer was used to minimize the root mean square of NH₃/NO. Four types of inlet flow pattern were chosen as the simulated parameters, i. e. uniform, parabolic, upper-skewed and random. The flow rate of the sixteen nozzles installed in the ammonia injection grid was adjusted to the inlet conditions. In order to solve the three-dimensional steady, incompressible and viscous flow fields, the commercial software named as ANSYS-Fluent were used with the turbulence model. From the present computational analysis, the denitrification performance was improved between 1.47% and 88.6% according to flow pattern of the inlet flue gas.

Modeling and Simulation of Carbon Dioxide Gas Reactive Desorption Process with Piperazine Promoted Diethanolamine Solvent in Sieve Tray Column

Carbon dioxide (CO2) is an acidic and corrosive gas, and the presence of this gas in the piping system can cause various problems in the industrial sector. Therefore, the CO2 must be separated from the gas stream. One of the CO2 gas separation processes from the gas stream is carried out in a CO2 removal unit, where a desorption unit serves as a solvent regeneration step. Therefore, this study aims to develop a rate-based model and simulation of the reactive desorption process of CO2 gas in a sieve tray column. The rate-based model in the reactive desorption process of CO2 gas is based on film theory, the liquid in the tray is assumed completely agitated due to gas bubbling, the flow pattern of gas is plug flow, and the effect of the reaction on the mass transfer follows the enhancement factor concept. The number of trays used in this study was 20. In addition, the effect of several variables, such as: desorber pressure, rich amine temperature, rich amine flow rate, and reboiler load, was also assessed on the CO2 stripping efficiency. The accuracy of our prediction model is 1.34% compared with industrial plant data. Compared with the chemical engineering simulator simulation results, the average deviation is 4%. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Using Particle Residence Time Distributions as an Experimental Approach for Evaluating the Performance of Different Designs for a Pilot-Scale Spray Dryer

The performances of four different designs for a pilot-scale spray dryer have been evaluated and compared based on experimentally measured particle residence time distributions (RTD), recovery rates and physical properties of spray-dried fresh skim milk. The RTDs have been measured using a dye pulse injection method, and the measurements have been fitted to models using continuous stirred-tank reactors in series (CSTR-TIS) for quantitative performance evaluation and comparison. Conical drying chambers and a box connection design have been used in the latest dryer design to reduce the amount of wall deposition and provide a smoother gas flow pattern. The particle-to-gas mean residence time ratio for the latest design is significantly closer to unity (1.6 s/s to 1.0 s/s) compared with earlier designs (2.6 s/s to 1.5 s/s). The latest design has a wider spread of RTD (n = 5–8) compared with earlier designs (n = 13–18), which may be linked to the recirculation zone in the box connection. Although the latest design has a wider spread of RTD, the conical design has shown promising results compared with a cylindrical drying chamber in terms of overall wall deposition behaviours.

3D Time-Lapse Electrical Resistivity Imaging of Rock Damage Patterns and Gas Flow Paths Resulting from Two Underground Chemical Explosions

Rock damage from underground nuclear explosions (UNEs) has a strong influence on sub-surface gas movement and on seismic waveform characteristics, both of which are used to detect UNEs. Although advanced numerical simulation capabilities exist to predict rock damage patterns and corresponding detection signals, those predictions are dependent on (generally) unknown properties of the host rock. For example, the effects of in-situ mechanical heterogeneities on the explosively generated damage/fractures that provide gas flow pathways to the surface are not well understood, due largely to the difficulty in accessing and characterizing the near-source region. In this paper we demonstrate the emerging use of electrical resistivity tomography (ERT) for imaging rock damage and gas flow patterns resulting from two relatively small-scale underground chemical explosions. Pre-explosion ERT and crosshole seismic imaging revealed a natural fracture zone within the test bed. Post-explosion imaging revealed that the damage zone was non-symmetric and was focused primarily within the pre-existing fracture zone, located 10 m above the first explosion and 5 m above the second explosion. Time-lapse ERT imaging of heated air injected into the detonation borehole revealed the primary gas flow paths to be within the upper margin of the same primary damage zone. These results point to the utility of ERT imaging for understanding rock damage and gas flow patterns under experimental conditions, and to the importance of understanding the effects of geologic heterogeneity on UNE detection signals, particularly gas surface breakthrough times.

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.

Numerical Investigation of Gas-Liquid Flow in a Multiphase Pump with Special Emphasis on the Effect of Tip Leakage Vortex on the Gas Flow Pattern

In this paper, the gas-liquid flow is comprehensively analyzed under different inlet gas void fractions, and the effect of tip leakage vortex (TLV) on the gas flow pattern in multiphase pumps is revealed. The results show that the gas flow pattern in an impeller is closely related to the centrifugal force, low-pressure region, and vortex motion. Most gas is present near the hub and suction surface of the blade as well as in the TLV. The two- and three-dimensional spatiotemporal evolution of the gas is presented, and the gas motion during the inception, development, and dissipation of TLV is revealed. It is reflected that the gas volume fraction is the highest at the TLV core and gradually weakens along the radial direction with the vortex core at the center. Additionally, the TLV energy dissipation is closely related to the gas and pressure difference, and strong energy dissipation occurs in the jet-wake flow.