Binary Gas Flow Research Articles

Investigating the Simulation Rate of an Axially Symmetric Rarefied Gas Flow Using v-DSMC

This article reports a comparative study of the convergence rate of an axially symmetric binary gas flow inside a rotating cylinder using an improved direct simulation Monte Carlo algorithm for rarefied gases (v-DSMC) and the conventional DSMC. Subsequently, a comparison between the convergence behavior of the v-DSMC and analytical data is carried out to scrutinize the validity of the v-DSMC algorithm. This method makes use of a modified collision model of variable hard sphere (VHS) termed Maxwell-VHS, which considers an equal contingency of collision but an arbitrary viscosity variation with temperature, for all adjacent gas particles. The results of the numerical simulation declare the convergence rate of the v-DSMC is noticeably faster than those performed by the conventional DSMC; however, a slight computational error occurs at the same simulation time due to higher accuracy of collision sampling in the conventional DSMC. Moreover, the results show a good agreement between the convergence behaviors of the v-DSMC in comparison with the analytical data.

Asymptotic modelling of thermal binary gas flows in circular micro-channels

Many industrial and medical tools include micro-metric channels. These are found, for example, in micro-filters. The DSMC methods are commonly used to compute gas flows in these sub-millimeter-sized channels. Nevertheless, these statistical methods are expensive in computation time (Bird in Gas dynamics and the direct simulation of gas flows. Clarendon Press, Oxford, 1994; Aktas et al. in J Microelectromech Syst 10:538–549, 2001). Consequently, the development of alternative methods, with lower computation cost, is an approach of main interest. This paper focuses on binary gas mixture flows with low Mach numbers and low to moderate Knudsen numbers. In a phenomenological point of view, this case corresponds to the slip regime. An asymptotic model for two compressible gases is presented in the case of axisymmetric flows in circular micro-pipes. This model is derived from a BGK-type model for the mixture. Its results are compared to DSMC simulations, and the impact on the flow of the mass flow rates, the wall temperature and the molecular weights are discussed.

Dryout of counter-current two-phase flow in a vertical tube

Dryout of counter-current two-phase flow is one of key issues in chemical and/or industrial systems. The aim of the present study is to provide insights into the dryout phenomena of such counter-current two-phase flow of binary gas and liquid in a vertical tube. Experimental results suggest a significant influence of the subcooling of water and the binary gas flow rate on the dryout characteristics. The observed dryout was classified into three modes, i.e., film breakdown, dryout due to flooding and dryout due to critical flooding. At the low inlet air flow rate, dryout characteristics were affected by subcooling of water. The test section was partially overheated owing to the liquid film breakdown due to the Marangoni effect. At the moderate inlet air flow rate, the dryout is induced by the reduction on the falling liquid film due to flooding. At the high gas flow rate, most of the water was carried over due to the critical flooding. In the latter two cases, there was no influence of subcooling of water on dryout. These dryout phenomena were successfully realized in the numerical simulation based on the one-dimensional heat and mass transfer model, i.e., energy balance of a heat input, a heat release rate from the heating surface and a mass transfer rate due to phase change.

Effect of CO2 injection on heterogeneously permeable coalbed reservoirs

Enhanced coalbed methane (ECBM) can be recovered by injecting a gas such as carbon dioxide into the reservoir to displace methane. The contrast between density, viscosity, and permeability of the resident and displacing fluids affects the efficiency of ECBM recovery. The prediction of earlier breakthrough becomes complex as the permeability may vary by orders of magnitude during gas injection and methane recovery. Predominantly, the reservoir permeability is modulated by the pore pressure of the sorptive gas (CH4 and CO2) and effective stresses. Here we explore the possibility of early breakthrough and its implications for managing coalbed reservoirs during CO2 assisted ECBM. A coupled finite element (FE) model of binary gas flow, diffusion, competitive sorption and permeability change is used to explore the effect of CO2 injection on net recovery, permeability evolution and injectivity in uniform and homogeneously permeable reservoirs. This effect is evaluated in terms of dimensionless pressure (pD), permeability (kD) and fracture spacing (xD) on the recovery of methane and permeability evolution for ECBM and non-ECBM scenarios. We have considered two scenarios (4MPa and 8MPa) of constant pressure injection of CO2 for ECBM. The increase in production rate of CH4 is proportional to kD but inversely proportional to xD.Further, a reservoir with initial permeability heterogeneity was considered to explore the effect of CO2 injection on the evolution of permeability heterogeneity – whether heterogeneity increases or decreases. The evolution of permeability heterogeneity is investigated for the same two CO2 injection scenarios. For the specific parameters selected, the model results demonstrate that: (1) The injection of CO2 in coalbed reservoirs increases the production nearly 10-fold. (2) At higher injection pressures the recovery is rapid and the production increases dramatically – the production increases 2-fold on increasing the CO2 injection pressure from 4MPa to 8MPa. (3) However, CO2 breakthrough occurs earlier at higher injection pressures. (4) The permeability heterogeneity in the reservoir is reduced after a threshold time (∼500days) although the overall heterogeneity is increased relative to the initial condition and is overall increased for both non-CO2 and CO2 injection scenarios. This indicates that the homogenizing influence of CO2-sorption-swelling is outpaced by CH4-desorption-shrinkage and effective stress influences. This leaves the reservoir open to short-circuiting and earlier breakthrough of CO2 rather than having this effect damped-out by the homogenizing influence of swelling. (5) The cumulative volume of CO2 produced and stored in the reservoir is proportional to the injection pressure.

A combined ultrasonic flow meter and binary vapour mixture analyzer for the ATLAS silicon tracker

We describe a combined ultrasonic instrument for gas flow metering andcontinuous real-time binary gas composition measurements. The combinedflow measurement and mixture analysis algorithm employs sound velocitymeasurements in two directions in combination with measurements of thepressure and temperature of the process gas mixture.The instrument has been developed in two geometries following extensivecomputational fluid dynamics studies of various mechanical layouts. Aversion with an axial sound path has been used with binary gas flows upto 230 l.min−1, while a version with a sound path angled at45° to the gas flow direction has been developed foruse in gas flows up to 20000 l.min−1.The instrument with the axial geometry has demonstrated a flowresolution of ⩽ 1 % of full scale for flows up to 230 l.min−1and a mixture resolution of 3.10−3 for C3F8/C2F6 molar mixtures with ∼ 20 %C2F6. Higher mixture precision is possible in mixtures ofgases with widely-differing molecular weight (mw): a sensitivity of < 5.10−5 to traces of C3F8 in nitrogen (mw difference 160)has been seen in a long duration ( > 1yr) continuous study.A prototype instrument with 45° crossing angle hasdemonstrated a flow resolution of 1.9 % of full scale for linear flowvelocities up to 15 ms−1.Although this development was motivated by a requirement of the ATLASsilicon tracker evaporative fluorocarbon cooling system, the developedinstrument can be used in many applications where continuous knowledgeof binary gas composition is required. Applications include theanalysis of hydrocarbons, vapour mixtures for semi-conductormanufacture and anaesthetic gas mixtures.

Variance-reduced DSMC for binary gas flows as defined by the McCormack kinetic model

A variance-reduced direct simulation Monte Carlo method is presented for binary gas flows as defined by the McCormack kinetic model. Two types of flow configuration, namely pressure driven flow between two parallel plates and through rectangular channels, are considered. The kinetic model is transformed into one- and two-dimensional projected formalisms. Both cases are modeled by the variance-reduced DSMC. Simulations are performed to compare the method to the analytical discrete ordinate and discrete velocity methods. For both flow configurations, very good agreement is obtained between the results of different approaches. The results of the approach are also compared to the prediction of the moment method and the results of hard-sphere gases. The model can be beneficial for computing slow rarefied gaseous mixture flows, especially in nano- and microscale devices.

A dual poroelastic model for CO2-enhanced coalbed methane recovery

Although CO2-enhanced coalbed methane (ECBM) recovery has been comprehensively investigated, the impact of coal matrix-fracture interactions on the evolution of coal permeability under in-situ conditions is still unclear. In prior studies on this issue, the influences of coal matrix-fracture interactions have not rigorously coupled with the binary gas transport system. In this work, general porosity and permeability models are developed to explicitly quantify the interactions between binary mixtures (CO2 and CH4) and dual solid media (coal matrix and fracture) under the full spectrum of mechanical conditions spanning prescribed in-situ stresses through constrained displacement. These models are implemented into a fully coupled finite element (FE) model of coal deformation, binary gas flow and transport in the matrix system, and binary gas flow and transport in the fracture system. The FE model represents important non-linear responses due to the effective stress effects that cannot be recovered where mechanical influences are not rigorously coupled with the binary gas transport system. The FE model is applied to simulate the results of a single well injection micro-pilot test performed in the anthracitic coals of the South Qinshui basin, Shanxi Province, China. The modeled CH4 production rates are in good agreement with the observed production history. In addition to this agreement, model results also demonstrate (1) CO2 injection increases the total pressure gradients; (2) as the CO2 injection progresses the partial CO2 pressure increases while the partial CH4 pressure decreases; (3) without CO2 injection the CH4 content at a specific point decreases almost linearly while with the CO2 injection the CH4 content at a specific point decreases exponentially; (4) without CO2 injection the CH4 production rate decreases linearly while with CO2 injection the CH4 production rate increases dramatically; (5) without CO2 injection coal permeability increases almost linearly while with CO2 injection coal permeability decreases near exponentially; (6) CO2 injection enhances cumulative CH4 production and the enhancement is proportional to the injection pressure; and (7) cumulative CO2 injection volume is also proportional to the injection pressure.

Comparative study between computational and experimental results for binary rarefied gas flows through long microchannels

A comparative study between computational and experimental results for pressure-driven binary gas flows through long microchannels is performed. The theoretical formulation is based on the McCormack kinetic model and the computational results are valid in the whole range of the Knudsen number. Diffusion effects are taken into consideration. The experimental work is based on the Constant Volume Method, and the results are in the slip and transition regime. Using both approaches, the molar flow rates of the He–Ar gas mixture flowing through a rectangular microchannel are estimated for a wide range of pressure drops between the upstream and downstream reservoirs and several mixture concentrations varying from pure He to pure Ar. In all cases, a very good agreement is found, within the margins of the introduced modeling and measurement uncertainties. In addition, computational results for the pressure and concentration distributions along the channel are provided. As far as the authors are aware of, this is the first detailed and complete comparative study between theory and experiment for gaseous flows through long microchannels in the case of binary mixtures.

Sorption-induced swelling/shrinkage and permeability of coal under stressed adsorption/desorption conditions

Abstract This paper presents experimental investigations on CO 2 /CH 4 binary gas flow in bulk coal under controllable stress conditions, focusing on sorption-induced swelling/shrinkage and gas permeability associated with CO 2 -sequestration enhanced coalbed methane (CO 2 -ECBM) recovery. The gas flush tests with carbon dioxide were conducted on a specially designed true tri-axial stress coal permeameter (TTSCP) using a large coal sample pre-adsorbed methane. These tests simulate the in-situ conditions of CO 2 -ECBM recovery from coal and provided experimental information for better understanding of the gas transport in coals. The swelling/shrinkage coefficients of coal associated with CO 2 -ECBM process have been evaluated using the experimental data. The results show that adsorption and desorption of gases CH 4 and CO 2 can significantly affect the volumetric change of micro- and macropores in coal, leading to coal swelling/shrinkage and fluctuation of permeability, and hence controlling the transport and flow of gases through coal.

Numerical simulation of a binary gas flow inside a rotating cylinder

A new approach to calculate the axially symmetric binary gas flow is proposed. Dalton’s law for partial pressures contributed by each species of a binary gas mixture (argon and helium) is incorporated into numerical simulation of rarefied axially symmetric flow inside a rotating cylinder by using the time relaxed Monte-Carlo (TRMC) scheme and the direct simulation Monte-Carlo (DSMC) method. The results of flow simulations are compared with the analytical solution and results obtained by Bird [1]. The results of the flow simulations show better agreement than the results obtained by Bird [1] in comparison with the analytical solutions. However, the results of the flow simulations using the TRMC scheme show better agreement than those obtained using the DSMC method in comparison with the analytical solutions.

Concentration Probe Measurements in a Mach 4 Nonreacting Hydrogen Jet

A new probe technique is introduced for the measurement of concentration in binary gas flows. The new technique is demonstrated through application of the probe in a Mach 4 nonreacting jet of hydrogen injected into a nominally quiescent air environment. Previous concentration probe devices have mostly used hot wires or hot films within an aspirating probe tip. However, the new technique relies on Pitot pressure and stagnation point transient thin film heat flux probe measurements. The transient thin film heat flux probes are operated at a number of different temperatures and thereby provide stagnation temperature and heat transfer coefficient measurements with an uncertainty of around ±5 K and ±4% respectively. When the heat transfer coefficient measurements are combined with the Pitot pressure measurements, it is demonstrated that the concentration of hydrogen within the mixing jet can be deduced. The estimated uncertainty of the reported concentration measurements is approximately ±5% on a mass fraction basis.

Low power laser Rayleigh probe for flow mixing studies

A laser Rayleigh correlation probe was constructed, which allows the application of low cost, low power (milliwatt) laser sources. It was tested for basic mixing studies in isothermal binary gas flows. Here, it can be used for the time and space resolved measurement of the concentration mean value and of all important statistical quantities, which give information on the distribution around the concentration mean value (rms, skewness, kurtosis) and on the relation of adjecent fluctuations in time or space (autocorrelation function, power spectral density).

Skin friction and heat transfer for incompressible laminar flow over porous wedges with suction and variable wall temperature

The boundary-layer differential equations for laminar flow over permeable wedges with suction, including isothermal and variable wall temperature distributions, have been solved. By use of the present solutions, the heat transfer and skin friction for laminar flow over any arbitrary geometry can be calculated. The application of the solutions to the binary gas flow and condensation is demonstrated, and the relation between the mass condensed, the heat removed, and the surface temperature is derived.