Gas Concentration Distribution Research Articles

Stratified micro-environments using a sidewall air supply: An experimental and simulation study

The idea of providing stratified micro-environments in a shared environment by utilizing a sidewall air supply is proposed, to provide different thermal comfort and air quality levels to satisfy individual needs at different occupied positions. Experimental cases with various supply air parameters and room layouts are conducted in a mock consultation room consisting of two face-to-face occupants. Further, parametric studies using computational fluid dynamics (CFD) are performed. Overall thermal sensation and local thermal comfort are both evaluated. Tracer gas (i.e., CO2) concentration distributions are investigated experimentally, while the air age is used as an indicator in CFD simulations. The results show that the proposed strategy simultaneously provides displacement ventilation (DV) and stratum ventilation (SV) in a shared environment, satisfying individual preferences and needs. The demarcation thermal length of the supply air jet between DV and SV is around 0.8 m. The normalized contaminant concentration at the breathing level is 0.00–0.30 with both table and floor contaminant sources. Better air quality is achieved in the area served by a higher thermal length. The local discomfort and “lock-up” effect under DV is reduced, by the interaction between the supply air jets, which is validated, as the partition impeding the interaction brings a significant influence. Short jet spacing of 0.75 m implies that multiple stratified micro-environments can be provided in a medium room, while a medium distance between the occupant and the supply air terminal (i.e., 1.7 m) is the most efficient in cooling and renewing the air age.

Modeling of Gas Sorption Process by Dispersed Liquid Flow

A mathematical model of the process of gas propagation in the atmosphere and its sorption by fine flow has been developed. The use of the finite difference method in modeling allows to obtain numerical solutions of the spatial distribution of gas concentration during its deposition by a jet of arbitrary intensity and shape. The proposed method of mathematical description of the process of sorption of hazardous gases allows you to choose an arbitrary number and spatial location of nodal points that satisfy the Courant-Friedrichs-Levy condition. The developed model allows to predict the intensity of gas sorption in technological processes and in the elimination of the consequences of emergencies. The use of the developed model will increase the efficiency of emergency management and choose effective methods of sorption of hazardous gases in the atmosphere. The results of numerical calculations confirmed the efficiency of the developed model and theoretically demonstrated the effectiveness of using water curtains for the sorption of ammonia from the atmosphere. According to the simulation results, it is established that the use of fine spray jets can significantly reduce the distance of distribution of hazardous gas.

Performance improvement of solid oxide fuel cells by combining three-dimensional CFD modeling, artificial neural network and genetic algorithm

Solid oxide fuel cell (SOFC) is the electrochemical device that directly convert the chemical energy of fuels into electrical energy, which are considered one of the promising methods for achieving high power generation efficiency. However, the commercialization of SOFC encounters the challenge due to its high manufacturing and operating cost. This study aims to present a framework and methodology for improving SOFC’ performance assisted by computational fluid dynamic (CFD) modeling, artificial neural network (ANN), and genetic algorithm (GA). Firstly, a three-dimensional computational fluid dynamic (CFD) model, referring to three types of parameters, e.g. geometry parameters, microscopic parameters and operating conditions, was developed and then the databases were obtained. Then 19 widely used intelligence algorithms, e.g. Artificial Neural Network (ANN), Boltzmann Machines (BMs), Support Vector Machines (SVMs), etc., were employed to train the databases. Next, the developed ANN surrogate model was used to replace the complicated and time-consuming CFD model and to predict SOFC’s performance and optimize the power density output of SOFC. Finally, the system optimization was performed by using genetic algorithm (GA) to maximize the power density. The results showed that artificial neural network (ANN) achieved the best accuracy (R2 = 0.99889) in terms of predictions of SOFC performance. Besides, it was found that the optimal SOFC had a better gas concentration distribution which can enhance the mass transfer in the electrode, and thus the SOFC performance was improved. The combination of CFD modeling, ANN and GA can provide a promising solution for the performance prediction, improvement and optimization of SOFC accurately and rapidly.

Effect of suction process on the growth of a convective gas bubble in diver’s tissues

The motivation of this research is to study the effect of suction process on a growing gas bubble and concentration distribution around this bubble in tissues of divers who surface too quickly. The effect of bubble motion is also considered. The method of combined variables is used to solve the problem by combining the radial and time variables into one variable by using a suitable similarity transformation that enables to divide the diffusion equation into two ODEs, the first concerns to concentration distribution and the other concerns to the bubble radius evolution. The resultant formulae are valid for both growth stages whenever the ambient pressure is variable at ascending of the diver, or constant as the diving stops or at sea-level. The effects of physical parameters are discussed when applying suction process and show that the dominant parameter is the initial void fraction. The research findings reveal the role of suction process to activate the systemic blood circulation and delay the growth of gas bubbles in the tissues and reduce the incidence of decompression illness (DCI). This research also provides evidence and agrees with the previous experimental studies to support the use of suction therapy to reduce the DCI harmful effects.

Gas exchange model using heterogeneous diffusivity to study internal browning in ‘Conference’ pear

Internal gas gradients in pear fruit during controlled atmosphere storage depend on the effective gas diffusivity of the tissue. The diffusivity varies over the fruit organ due to the heterogeneous tissue microstructure across the fruit. This study implemented effective diffusivity maps reflecting the heterogeneous structure to predict internal gas gradients and relate the result to the occurrence of internal browning. Diffusivity maps of different pears were calculated from X-ray CT based porosity maps. Internal oxygen (O2), carbon dioxide (CO2) and respiratory quotient (RQ) levels were computed using a reaction-diffusion model incorporating the heterogeneous effective diffusivity map. Critical O2 and RQ levels for the shift from respiration to fermentation were defined based on the respiratory-fermentative energy balance of the cells. The model was indirectly validated by comparing RQ level contours with non-destructive 3D images of the internal browning of the pears after storage at 1.0 kPa and 0.5 kPa O2, combined with 0.7 kPa CO2 at 1 °C. The distribution of the internal gas concentrations and RQ was affected by the heterogeneity of the diffusivity. The results also confirmed the incidence of internal browning when the O2 and RQ were under or above critical O2 and RQ limits, respectively. The fermentation process was indicated to be dominant when the tissue’s RQ limit (RQ*) went above 2.12 (or at 0.044 kPa O2). The tissue volumes where O2 and RQ levels were critical corresponded reasonably well to browning-affected tissues of pears with different shapes. The pear with more shallow gas gradients showed less symptoms of browning.

Prediction of gas leakage and dispersion in utility tunnels based on CFD-EnKF coupling model: A 3D full-scale application

Natural gas compartment accommodated in utility tunnels is beneficial in meeting the pressing demand of energy supply and sustainable urban environment. However, the leaking gas characterized by flammable and explosive can pose a huge threat to the safe operation of the utility tunnel. When an unexpected gas leakage accident happens in the actual situation, the prior information associated with the leakage source is commonly unclear or unknown. Therefore, the absence of an available tool for reasonable leakage and dispersion prediction in the above scenario precludes the timely and appropriate emergency response treatment. In this study, a three-dimensional source term estimation (3D-STE) model with the combination of the computational fluid dynamics (CFD) and ensemble Kalman filter (EnKF) algorithm is proposed to achieve spatiotemporal gas concentration prediction and gas emission source estimation. In the proposed approach, the observation data can be incorporated into the gas dispersion simulations continuously, thus the simulation results can be revised by the observation data and the source term estimation of gas leakage can be achieved by employing the EnKF algorithm. A twin experiment is employed to validate the effectiveness and practicability of the proposed model. The results show that the proposed model can revise the prior errors in the gas leakage rate significantly and obtain an accurate prediction of gas concentration distribution as well as gas leakage rate. A feasible framework is also proposed serving as a good paradigm for the 3D-STE model application. This study helps for consequence assessment and emergency response of gas leakage accidents in utility tunnels.

Spread of SARS-CoV-2 aerosols via two connected drainage stacks in a high-rise housing outbreak of COVID-19

Vertical transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) along a vertical column of flats has been documented in several outbreaks of coronavirus disease 2019 (COVID-19) in Guangdong and Hong Kong. We describe an outbreak in Luk Chuen House, involving two vertical columns of flats associated with an unusually connected two-stack drainage system, in which nine individuals from seven households were infected. The index case resided in Flat 812 (8th floor, Unit 12), two flats (813, 817) on its opposite side reported one case each (i.e., a horizontal sub-cluster). All other flats with infected residents were vertically associated, forming a vertical sub-cluster. We injected tracer gas (SF6) into drainage stacks via toilet or balcony of Flat 812, monitored gas concentrations in roof vent, toilet, façade, and living room in four of the seven flats with infected residents and four flats with no infected residents. The measured gas concentration distributions agreed with the observed distribution of affected flats. Aerosols leaking into drainage stacks may generate the vertical sub-cluster, whereas airflow across the corridor probably caused the horizontal sub-cluster. Sequencing and phylogenetic analyses also revealed a common point-source. The findings provided additional evidence of probable roles of drainage systems in SARS-CoV-2 transmission.

Performance study on a large-scale proton exchange membrane fuel cell with cooling

The output performance of PEMFC (proton exchange membrane fuel cell) is limited by the operating conditions of the fuel cell, including the control temperature, gas concentration distribution and working pressure. In order to simplify the calculation process, the existing literatures mostly use single channel to study the output indexes of batteries. Initially, based on 3D (three-dimensional) CFD (computational fluid dynamics) simulation, a method to optimize the gas distribution in the flow field by using the distribution area is proposed for a commercial large-scale PEMFC with an activation area of 107.44 cm2. The uniformity of gas concentration distribution in anode and cathode flow field is taken into consideration to test the influence of flow field. The relationship between liquid saturation and gas velocity in the flow field is also analyzed. Furthermore, the effects of anode and cathode gas flow direction on gas concentration in CL (catalytic layer) and water content in PEM (proton exchange membrane) is studied, and both methods have little effect on PEMFC. Additionally, the performance of PEMFC is obviously improved by increasing operating pressure, and the reactant gas molar concentration and membrane water content are increased significantly. Finally, study proves that it is more beneficial to the performance of PEMFC when cooling flow direction is consistent with oxygen.

Impact of Lateral SnO2 Nanofilm Channel Geometry on a 1024 Crossbar Chemical Sensor Array.

We propose a rational strategy to fabricate thermally robust, highly integrated molecular and gas sensors utilizing a lateral SnO2 nanofilm channel geometry on a 1024 crossbar sensor array. The proposed lateral channel geometry substantially suppresses the detrimental effects of parasitic interconnect wire resistances compared with those of a conventional vertical sandwich-type crossbar array because of its excellent resistance controllability. A conductive oxide top-contact electrode on the lateral SnO2 nanofilm channel enhances the thermal stability at temperatures of up to 500 °C in ambient air. Integrating this lateral SnO2 nanofilm geometry with analog circuits enables the operation of a 1024 crossbar sensor array without selector devices to avoid sneak currents. The developed 1024 crossbar sensor array system detects the local spatial distribution of the molecular gas concentration. The spatial data of molecular concentrations include molecule-specific data to distinguish various volatile molecules based on their vapor pressures. Thus, this integrated crossbar sensor array system using lateral nanofilm geometry offers a platform for robust, reliable, highly integrated molecular and gas sensors.

Multicomponent Alkane IR Measurement System Based on Dynamic Adaptive Moving Window PLS

Infrared (IR) spectroscopy for multicomponent alkane measurement has shown excellent potentials in unconventional oil and gas exploration. However, the cross-sensitivity of alkane IR absorption and the complexity of unconventional oil and gas components place extreme demands on quantitative IR spectroscopy models. To cope with these problems, an adaptive moving partial least square (AMW-PLS) modeling method for the quantitative analysis of IR spectra is proposed in this paper. Based on the designed moving control function and dual endpoint independent moving strategy, AMW-PLS can quickly determine the optimal local modeling interval location and width by tracking the accuracy of the calibration model dynamically. By transposing the proposed AMW-PLS into the designed infrared gas logging system in this paper, 88 samples of 2 different mixture types were tested and compared with the other three typical analytical methods. The experimental results show that AMW-PLS can dynamically track the IR characteristic shifts caused by the changes in the gas mixture component complexity and concentration distribution, and thus achieves the best performance. The instrument achieved an average relative error of 3.3651% for five alkane substances in three standard industrial gas mixtures under strong interference, which provides new technical support for early discovery of oil and gas reservoirs.

Leakage source estimation by retrospective search for high concentration points in infrared gas concentrarion images

In recent years, there has been a concern about the occurrence of gas leakage and fire accidents in plant facilities due to damage caused by aging deterioration of gas piping. However, conventional gas leakage source estimation methods require prior teacher data or calculated data of gas clouds to be compared, which requires large computation time and may not be applicable under unexpected circumstances. Therefore, this study proposes a method to estimate the source of gas leakage by visualizing the leaking gas cloud using an infrared camera and performing an inverse problem analysis based on the concentration information without the need for prior teacher data or calculation data. It is found that the leakage source can be estimated by retrospective search from the gas concentration distribution to the location where the infrared absorption is large. In addition, the leak source estimation is achieved with high accuracy by removing the initial search position data and using only the position data near the leak source in the retrospective search.

Study on CO diffusion law and concentration distribution function under ventilation after blasting in high-altitude tunnel

Multiple toxic gases, such as carbon monoxide (CO), are generated after blasting of plateau tunnel. To study the influence of high-altitude environment on the diffusion and concentration distribution of hazardous gases after tunnel blasting, a ventilation model for construction tunnel was established based on a tunnel of the Sichuan-Tibet Railway, and the dynamic diffusion of CO at different altitudes was numerically simulated. The obtained results demonstrate that: In the area near the working face with forced ventilation, a vortex area was formed under the combined action of jet and backflow, the distribution of CO in the tunnel was closely related to the flow field. The CO migrated to the outside of the tunnel due to ventilation, and was gradually diluted and diffused in the process. The equivalent mass concentration of CO in the tunnel increased exponentially with the increase of altitude, the altitude correction coefficient of CO mass concentration was e0.1H at an altitude of H (km), the concentration value increased by 88% when the altitude rose from 0m to 6000m. To directly obtain the CO concentration value in the construction tunnel under different conditions by calculation, the functional relationship between the CO concentration after blasting and the time (t), distance (x) and other parameters was determined according to the simulation results, and the calculation function was verified by considering field data. The fitting function has wide applicability and can be used to judge whether the environment in the tunnel has reached a safe state, thus providing guidance for the safety of plateau tunnel construction.

Study on the gas migration laws of non-pillar mining with gob-side entry retaining in high gas outburst coal seam

Mining fractures are the channel of gas migration, and it is important to figure out the gas migration laws for gas control. Combined with the actual geological conditions of Shaqu No. 2 coal mine, a numerical model of no-pillar mining with automatically retained entry was built to simulate the deformation and fracture of overburden rock and the evolution laws of cracks above the goaf during mining. Subsequently, CFD software is used to theoretically stimulate the gas concentration distribution laws of non-pillar mining with the automatically retained entry in the stope under non-drainage and high-level borehole drainage conditions. The laws of gas concentration in the stope were compared and analyzed under the condition of the Y-type ventilation of non-pillar mining and U-type ventilation of coal pillar mining. The results show that Y-type ventilation of non-pillar mining reduces the gas concentration in the upper corner of the working face and the goaf, and effectively solves the gas accumulation problem in the upper corner of the working face in the mode of U-type ventilation of coal pillar mining. On this basis, the high-level borehole drainage technology is adopted to effectively reduce the gas concentration in the goaf. The research has certain guiding significance for the gas management of non-pillar mining with gob-side entry automatically retained.

Software-Supported Visualization of Mathematical Spatial-Time Distribution Models of Air-Pollutant Emissions

Atmospheric pollution due to emissions of harmful gases from different sources is one of modern society's critical problems. Resolving the consequences of air-pollutants is part of the risk management process aimed at monitoring the crisis, restoration and remediation of the environment, returning to its original state, and removing the risk of a re-emergence of accidents. The need for environmental risk assessment emerged due to increased awareness of the necessity for environmental protection. Modeling air polluter dispersion processes is an essential mathematical tool for exploring pollution's impact on the natural environment. This work describes an analytical and numerical solution to the two-dimensional transport equation of turbulent diffusion in a stationary state. We present a software-based visualization of a numerical model of the harmful gas concentration distribution, depending on weather conditions, terrain configuration, and urbanization.

Quantitative risk assessment of gas leakage and explosion accidents and its security measures in open kitchens

In this study, a quantitative risk assessment methodology is developed for gas leakage and explosion accidents in open kitchens. Meanwhile, the corresponding security measures are investigated. The physical and computational model of a typical open kitchen and the corresponding traditional kitchen is firstly developed, using CFD code FLACS, respectively. Based on the similarity principle, a small scale low-pressure natural gas leakage and explosion experiment platform like a kitchen was constructed to validate the accuracy of CFD model. Subsequently, gas leakage and dispersion behavior is performed to analyze the gas concentration distribution. Meanwhile, a time-of-exposure model is introduced to calculate the overall ignition probability during the whole gas leakage and dispersion process. And then, the explosion simulation with a real inhomogeneous flammable gas cloud is carried out to analyze the overpressure distribution. In addition, the maximum weighted average overpressure is estimated accurately. According to the overall ignition probability and the maximum weighted average overpressure, the integrated risk caused by gas leakage and explosion accidents is assessed. Furthermore, the active and passive security measures are investigated to reduce the integrated risk in open kitchens. This methodology and its security measures are applied to a typical open kitchen, located in Harbin, China. The results show that the simulation results reproduced by the CFD model are in good agreement with the experimental results. The explosion accident probability in open kitchens is much higher than that in traditional kitchens, whereas the explosion accident consequences in open kitchens are less than that in traditional kitchens. The integrated risk in open kitchens is greater than that in traditional kitchens. These achievements provide an effective theoretical guidance and technical support for safety gas supply design of open kitchens.

Investigation of reactive multiphase characteristics in a chemical looping combustion process of biomass with hematite as oxygen carrier

Chemical looping combustion is a new combustion technology to reduce the costs and energy penalty for the capture of carbon dioxide. In this work, a three-dimensional fuel reactor model with hematite as oxygen carrier is established by computational fluid dynamics coupled with the multiphase particle-in-cell method. After model validation, the thermochemical properties of gas and solid phases in the fuel reactor are explored, including the components, slip velocity, Reynolds number and temperature. The results show that the asymmetric distribution of combustible gas concentrations is attributed to biomass injection. The oxygen carrier particles have a larger heat transfer coefficient than the biomass particles. The heat transfer coefficient of both particle species negatively correlates to the solid concentration, but positively correlates to the slip velocity and Reynolds number. The biomass particles behave with a wide range and higher value of the Reynolds number. Different axial variations of the temperature can be observed for the oxygen carrier and biomass. Moreover, a nearly 50 K temperature difference exists between the biomass and oxygen carrier. Reducing the oxygen carrier size and enlarging the superficial velocity increase the heat transfer coefficient and temperature of both particle species.

Early Warning of Gas Concentration in Coal Mines Production Based on Probability Density Machine.

Gas explosion has always been an important factor restricting coal mine production safety. The application of machine learning techniques in coal mine gas concentration prediction and early warning can effectively prevent gas explosion accidents. Nearly all traditional prediction models use a regression technique to predict gas concentration. Considering there exist very few instances of high gas concentration, the instance distribution of gas concentration would be extremely imbalanced. Therefore, such regression models generally perform poorly in predicting high gas concentration instances. In this study, we consider early warning of gas concentration as a binary-class problem, and divide gas concentration data into warning class and non-warning class according to the concentration threshold. We proposed the probability density machine (PDM) algorithm with excellent adaptability to imbalanced data distribution. In this study, we use the original gas concentration data collected from several monitoring points in a coal mine in Datong city, Shanxi Province, China, to train the PDM model and to compare the model with several class imbalance learning algorithms. The results show that the PDM algorithm is superior to the traditional and state-of-the-art class imbalance learning algorithms, and can produce more accurate early warning results for gas explosion.

Numerical Analysis of the Local Current Efficiency Distribution in a Protonic Ceramic Fuel Cell Considering Gas Concentration Distributions

Protonic ceramic fuel cells (PCFCs) are expected as highly efficient energy conversion devices due to the high proton conductivity at relatively lower operating temperature (400 ºC~600 ºC) compared to solid oxide fuel cells (SOFCs). The water steam is generated at air side so that there is less fuel dilution at fuel side. Therefore, PCFCs could operate with higher fuel utilization. However, besides the main proton conductivity, some other chargers including electron holes, oxygen ions, and electrons can also be conductive in PCFCs leading a performance decrement. Especially, the electron hole conductivity cannot be neglected inducing a decrease of current efficiency under some operating conditions. The conductivities in PCFCs are not only affected by the operating temperature, but the gas concentrations also strongly influence their values [1]. The conductivities of proton and hole are respectively show positive relationship to steam and oxygen concentrations [2-3]. These properties of PCFCs cause complex for investigating the performances.In this study, the defect transports in a PCFC electrolyte with BaZr0.8Yb0.2O3-δ (BZYb20) material were numerical solved with a quasi-two-dimensional Nernst-Planck-Poisson (NPP) model and the effect of gas concentration on the cell performance was discussed. For the NPP model calculation algorithm, the Nernst-Planck equation (or flux continuity equation) and the Poisson equation are successively solved by finite difference method (FDM) until convergence criteria are obtained with the defect concentration boundary conditions. The defect concentrations at electrolyte membrane surfaces (boundary conditions of NPP model) are derived by equilibrium assumptions of the reactions such as hydration and oxidation reactions. The charge neutrality condition is also added to the boundary conditions for the exact solutions [4]. Subsequently, the local defects (i.e., proton and electron hole) concentrations are revealed, so that the local current efficiency distribution in the PCFC can be revealed.The utilizations of fuel and oxygen are set at 80% and 30%, respectively. The vapor concentration at anode and cathode side are assumed as 3%. The electrolyte thickness is 8 μm in the present study. A constant temperature distribution is assumed in the numerical model. An example result under co-flow gas supply including proton current density and current efficiency distributions is shown in the following figure. The proton current density along fuel flow direction is found to increase from inlet to outlet. The reason can be considered as the influences of water steam distributions. The water steam concentration (or partial pressure) at both fuel and air side increase from inlet to outlet. The current efficiency at downstream are higher than that of upstream. This is contributed by the increase of oxygen in gas flow direction. Moreover, the influences of gas flow direction on cell performances have also been investigated. Acknowledgements This research is primarily based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) Grand Number JPNP20003, Japan. We also extend out special thanks to members of AIST Solid State Ionics Materials Group for useful information and discussions. References Li, et al ., Int. J. Hydrogen Energy, 45 (2020), 34139-149.Okuyama, et al ., Int. J. Hydrogen Energy, 39 (2014), 20829-36.Somekawa T, et al ., Int. J. Hydrogen Energy, 41 (2016), 17539-47.Vøllestad E, et al ., Int. J. Electrochem Soc, 161 (2014), F114-24. Figure 1

Numerical Analysis of the Local Current Efficiency Distribution in a Protonic Ceramic Fuel Cell Considering Gas Concentration Distributions

Intermediate-temperature protonic ceramic fuel cells (PCFCs) are expected to be highly efficient energy conversion devices because of their high proton conductivity in the electrolyte. However, besides the main proton conductivity, some other charge carriers, such as electron holes, are also conductive in PCFCs, leading to a decrease in current efficiency. The conductivities are not only affected by the operating temperature but are also strongly influenced by the gas concentrations, which causes complexities in PCFC performance. To reveal the performance and provide feedback to the operating condition selections considering the reaction overpotential, a quasi-two-dimensional Nernst-Planck-Poisson (NPP) numerical model was successfully used to investigate the current efficiency distribution in a planar-type PCFC electrolyte with BaZr0.8Yb0.2O3-δ (BZYb20). The influence of the gas flow direction was also revealed in the present study. The results showed almost the same average current efficiency with co- and counter-flows but flat proton distributions with counter-flows.

Modeling the mass transfer process in membranes for carbon capture and separation with concentration polarization effect

Membrane separation is regarded as the most promising carbon capture technology due to its low operating cost and requirements for installation. The main parameters in membrane separation are selectivity and permeability. This study presents a mathematical model to analyze factors influencing membrane separation. The separation process was investigated based on mass transfer theory by analyzing the influence of pressure, initial composition, permeability and doped gas on the separation result. An increase in pressure ratio, mole fraction of CO2 and permeability will improve the separation efficiency. The influence of doped gas on the separation efficiency is depended on the permeability and the content of the doped gas. Moreover, the study also presents the effect of concentration polarization on the separation. Results of studied cases provide a reference for the membrane separation for carbon capture. It is found that the concentration polarization significantly affects the membrane gas separation process. The two-dimensional distribution of concentration was obtained with concentration polarization. The concentration of CO2 on the retentate side becomes lower near the membrane due to permeation. Influences of pressure and permeability on the two-dimensional distribution of gas concentrations were also analyzed.