Calculation Of Gas Flow Research Articles

Calculation of gas flow through the flow of axial turbocompressors

When designing centrifugal compressors, much attention is paid to increasing the efficiency of the compression process with a wide range of changes in the operating modes of the stages. In this regard, the role of methods that make it possible to calculate the characteristics taking into account the compressibility of the gas flow through the elements of the flow path increases. In this work, the development of the method for solving the second two-dimensional problem is given, which makes it possible to calculate the subsonic gas flow. In this case, impellers with both single-row and multi-row blade elements are considered.

Transformation of a mathematical model of gas flow distribution to solve the problems of gas supply system development

This paper proposes taking into account new properties of gas supply systems in a mathematical model of flow distribution in comparison with the traditional formulation. The approach suggests introducing an arc coefficient, which allows for changes in the magnitude of gas flow passing along the arc, a vector of an increase in the arc throughput, and lower constraints on the gas flow along the arc. We also propose considering a new economic environment, namely, new criteria for optimizing the flow distribution and setting fictitious gas prices for consumers. These criteria enable us to take account of the priority gas supply to a definite group of consumers. As an example, the calculation of gas flows for the aggregated Unified Gas Supply System (UGSS) for 2030 is considered. This calculation takes into account the arc coefficients and the increase in the throughput of arcs.

Results of Supersonic Gas Flow Calculations near AGARD-B Model

Results of Supersonic Gas Flow Calculations near AGARD-B Model

An application of the Chebyshev polynomials for the calculation of a rarefied gas flow in the cylindrical geometry of the channels

An application of the Chebyshev polynomials for the calculation of a rarefied gas flow in the cylindrical geometry of the channels

A Multi-State Model for Reliability Assessment of Integrated Gas and Power Systems Utilizing Universal Generating Function Techniques

Large-scale adoption of gas-fired power plants (GPPs) significantly accelerates the integration of power systems and natural gas systems (NGSs). Because the operation of NGS has a significant impact on the reliability of power system, it is important to simultaneously evaluate the reliabilities of power system and NGS. Moreover, due to the stochastic failures and various operating characteristics of components, the integrated gas and power systems (IGPS) considering multiple states can be viewed as a multi-state system. Therefore, a multi-state model is proposed for reliability evaluation of IGPS based on universal generating function (UGF) techniques. First, a framework is proposed to evaluate the reliability of NGS: multi-state models for different components in the NGS are developed as the corresponding UGFs. These UGFs are aggregated utilizing the gas flow calculation operator to obtain the multi-state model of NGS. Moreover, a gas-to-power calculation operator is developed to convert the multi-state model of gas injection at each node to the power output models of GPPs in power system. In this manner, the impacts of NGS could be incorporated into the reliability evaluation of power system. Furthermore, nodal reliability indices for both the NGS and the power system are proposed to evaluate the reliability performances of IGPS. The proposed methods are validated using the integrated gas and power test system.

Quartz crystal microbalance for real-time monitoring chlorosilane gas transport in slim vertical cold wall chemical vapor deposition reactor

Chlorosilane gas transport in ambient hydrogen in a slim vertical cold wall chemical vapor deposition reactor was real-time monitored using a quartz crystal microbalance (QCM) using its behaviour responding to the properties of the gas mixture. The QCM frequency quickly decreased by introducing the trichlorosilane gas, while it slowly decreased by the dichlorosilane gas. The QCM frequency behavior was explained by the gas flow condition, such as the plug flow and recirculating flow, in the reactor. The relationship was consistent with the gas flow calculations, because the heavy and light gases could directly flow downward and recirculate, respectively, in the chamber due to natural convection. The information obtained from the QCM frequency behavior is expected to be utilized for the real-time gas monitoring and for the process design.

Анализ основных тенденций инновационного преобразования математической модели потокораспределения в газоснабжающих системах и приобретаемых ими новых свойств

The purpose of the paper is to consider the proposals for the possible account of new properties of gas supply system in a mathematical model of the generalized problem of flow distribution as compared to the traditional formulation; to introduce an arc coefficient considering gas flow value alteration when passing through the arc, increment vector of arc flow rate and lower limits on gas flows in the arcs; to analyze new management conditions (optimization criteria of load flows and establishment of fictitious gas consumption prices allowing to take into account a high priority supply of a certain group of consumers). Network analysis methods are widely used in solving the problems of long-term planning and development of gas supply systems for mathematical modeling of optimal gas flows. The account of new trends of innovative transformation in mathematical models is caused by the modern development of gas supply systems, their renovation and modernization. To solve the problems of gas load flow in gas supply systems the network analysis methods based on the graph theory are used when dealing with the problems of gas supply system operation in various conditions. Based on the traditional problem of flow modeling a generalized solution of load flow is formulated taking into account the new properties of gas supply system. A mathematical formulation is given, its implementation is successively executed in the computational program. The gas flow calculation for the aggregate Unified gas supply system in 2030 is given as an example of the proposed approaches. This calculation takes into account the capacity increments of gas transmission system arcs and the coefficients showing a decrease in the volumes of gas supply for own needs and leakages. To solve the problems of load flows in the optimization of gas supply system development the following innovative improvements have been proposed: arc coefficients taking into account gas flow value alteration when passing through the arc are introduced; increment vectors of arc capacities and gas flow lower limits in the arcs are given, new economic conditions (flow load optimization criteria and fictitious prices on gas consumption) allowing to consider a high priority supply of a certain group of consumers are taken into account.

Determination of Discharge Coefficients for Valves of High Voltage Circuit Breakers

Nowadays, high voltage circuit breaker (CB) simulations are mostly based on Computational Fluid Dynamics (CFD) models. Such simulations require significant computer resources. An alternative approach is to use enthalpy flow models, which do not use space discretization of the interrupter unit chambers and valves. Gas flow is calculated based on state of gas in adjacent chambers and valve settings. However, the valve shape has significant influence on the effective flow cross section between chambers. Therefore, in order to ensure correct simulation results, it is necessary to determine the correct values of discharge coefficients for all valves in the interrupter unit of a circuit breaker. In this paper, the discharge coefficients were determined by combining a series of CFD and enthalpy flow simulations for each valve in the interrupter unit. After that, discharge coefficients are used as input for further simulations based on the enthalpy flow model. This way, benefits from both models are combined: more precise gas flow calculation and faster simulations. The proposed novel approach is validated in a high-power laboratory by pressure measurements on a 420 kV 63 kA self-blast circuit breaker.

A Numerical Investigation on Gaseous Stratification Break-Up Phenomenon of Air Fountain Experiment by Code_Saturne

Since the Fukushima nuclear power plant accident, the nuclear safety experts devote a number of efforts to explore the potential risk of hydrogen detonation and measures for the mitigation of hydrogen safety during a severe accident in the nuclear power plant. A series of experiments have been performed to investigate the behavior of hydrogen distribution during a severe accident in the nuclear power plant. This study aims to investigate the gaseous stratification break-up phenomenon in the presence of a vertical gas fountain on the top of containment using Code_Saturne. The computed results not only analyze the flow field of the gas and the density distribution in the containment, but also measure the adequacy of Code_Saturne concerning the multi-component gas flow calculation.

Day-Ahead Dispatch of Integrated Electricity and Natural Gas System Considering Reserve Scheduling and Renewable Uncertainties

For secure operation of integrated electricity and natural gas system (IEGS), reserve is a useful support to manage renewable uncertainties and N − 1 contingencies. Thus, a day-ahead economic dispatch model of IEGS with reserve scheduling is presented in this paper. Considering the uncertainty of gas flow direction, a novel second-order cone (SOC) relaxation of Weymouth equation is designed to address the nonconvexity. Then, the proposed robust nonconvex model is mathematically transformed into a solvable mixed integer second-order cone programming (MISOCP) problem. To guarantee the tightness of SOC relaxation and achieve accurate dispatch solutions, MISOCP results are corrected accordingly by the multi-slack-node gas flow calculation with the Newton–Raphson method. Numerical cases are performed on IEEE 39-bus-15-node and IEEE 118-bus-40-node test IEGSs, demonstrating the proposed approach is feasible and effective for exact IEGS day-ahead dispatch and the proposed MISOCP model can provide a more economic dispatch solution with a shorter computational time than conventional MISOCP and mixed integer linear programming (MILP) models.

Permeability calculation of rarefied gas flows through 2D porous structures using the lattice Boltzmann method

In the perspective of understanding the flow behavior of atmosphere gases through porous thermal protection systems (TPS) for spacecrafts, permeability calculation has been performed by implementing a modified lattice Boltzmann model. This realization allows the simulation of rarefied gas flows through the TPS micro-porous media. Rarefaction, characterized by the Knudsen number (Kn) is taken into account in the Multi-Relaxation Time (MRT) collision operator. In order to capture slippage effects encountered at solid interfaces in rarefied regimes, a diffuse bounce-back approach has been followed. Numerical simulations have been performed on structured 2D arrays of circular and square cylinders and permeability has been calculated according to Darcy's law. The effects of rarefaction, porous media geometry and porosity on permeability have been investigated.Computed results show that permeability increases as the gas becomes more rarefied. In the frame of the current study, it was also found that the rate of increase in permeability caused by rarefied effects appears to be independent of any geometric parameter. Finally, numerical results have shown to be well suited within the range of permeability values given by the correlations used for comparison.

A Comparison of Data Reduction Methods for Average Friction Factor Calculation of Adiabatic Gas Flows in Microchannels.

In this paper, a combined numerical and experimental approach for the estimation of the average friction factor along adiabatic microchannels with compressible gas flows is presented. Pressure-drop experiments are performed for a rectangular microchannel with a hydraulic diameter of 295 μm by varying Reynolds number up to 17,000. In parallel, the calculation of friction factor has been repeated numerically and results are compared with the experimental work. The validated numerical model was also used to gain an insight of flow physics by varying the aspect ratio and hydraulic diameter of rectangular microchannels with respect to the channel tested experimentally. This was done with an aim of verifying the role of minor loss coefficients for the estimation of the average friction factor. To have laminar, transitional, and turbulent regimes captured, numerical analysis has been performed by varying Reynolds number from 200 to 20,000. Comparison of numerically and experimentally calculated gas flow characteristics has shown that adiabatic wall treatment (Fanno flow) results in better agreement of average friction factor values with conventional theory than the isothermal treatment of gas along the microchannel. The use of a constant value for minor loss coefficients available in the literature is not recommended for microflows as they change from one assembly to the other and their accurate estimation for compressible flows requires a coupling of numerical analysis with experimental data reduction. Results presented in this work demonstrate how an adiabatic wall treatment along the length of the channel coupled with the assumption of an isentropic flow from manifold to microchannel inlet results in a self-sustained experimental data reduction method for the accurate estimation of friction factor values even in presence of significant compressibility effects. Results also demonstrate that both the assumption of perfect expansion and consequently wrong estimation of average temperature between inlet and outlet of a microchannel can be responsible for an apparent increase in experimental average friction factor in choked flow regime.

Results of calculation of transonic gas flow in a flat channel separated by perforated walls

Results of calculation of transonic gas flow in a flat channel separated by perforated walls

Mathematical Modeling of Hydrothermal Treatment of MSW to form a Solid Fuel in a Commercial Scale Plant

A numerical model is developed to describe the hydrothermal decomposition of MSW in pilot scale facilities. The modeling process involves the use of high-pressure steam to directly heat MSW to temperature and pressure at which decomposition reactions decompose organic matter into solid coal with properties suitable for commercial gasifiers. The model used in the present work namely, the COMMENT code. In order to deal fully with the transient behavior of the inherent batch process, the transient model is developed. The model allows the calculation of important process temperature, pressure, gas flow and composition based on time. The model has been used to determine the possible operational scenarios of the proposed pilot scale test, and these results are given. Based on the calculated results, the numerical predictions of the model are compared to experimental profiles obtained in the base case of hydrothermal treatment of pilot scale. These comparisons show very good agreement.

Calculation of Gas Flow Between Two Coaxial Cylinders in a Free-Molecular Regime Under Specular-Diffuse Boundary Conditions

Using the method of characteristics, within the framework of the kinetic approach, an analytical solution of the problem on gas heat and mass transfer in a long channel formed by two coaxial cylinders in a free-molecular regime has been constructed. As the basic equation describing the kinetics of the process, use is made of the Boltzmann kinetic equation for a collisionless gas and as a boundary condition of the channel walls — a model of specular-diffuse reflection. The profile of the heat flux vector in the channel has been constructed, and the gas heat and mass flows through the channel cross section have been calculated as functions of the accommodation coefficients of the gas molecule pulses tangent to the surfaces of the cylinders.

Computation of non-isothermal and compressible low Mach number gas flows by fully explicit scheme using control method for speed of sound

Computation of non-isothermal and compressible low Mach number gas flows by fully explicit scheme using control method for speed of sound

Innovative transformations of a model for flow distribution in gas systems and their new properties

The methods of network analysis are widely used in mathematical modelling of optimal gas flows to solve the problems of long-term planning and development of gas systems. However, the modern development of gas systems, their renovation and modernization require that the new trends in innovative transformation should be taken into account in the mathematical models for their research as well. This paper is focused on the proposals for considering the new properties of gas system in the mathematical flow distribution model as compared to the traditional formulation. Case study involves the calculation of gas flows for an aggregated unified gas supply system for the period up to 2030. This calculation allows for the edge coefficients and a gain in the transmission capacities of the edges.

Modelling of gas dynamical properties of the Katrin tritium source and implications for the neutrino mass measurement

The Katrin experiment aims to measure the effective mass of the electron antineutrino from the analysis of electron spectra stemming from the β-decay of molecular tritium with a sensitivity of 200 meV/c2. Therefore, a cumulative amount of about 40 g of gaseous tritium is circulated daily in a windowless source section. An accurate description of the gas flow through this section is of fundamental importance for the neutrino mass measurement as it significantly influences the generation and transport of β-decay electrons through the experimental setup. In this paper we present a comprehensive model consisting of calculations of rarefied gas flow through the different components of the source section ranging from viscous to free molecular flow. By connecting these simulations with a number of experimentally determined operational parameters the gas model can be refreshed regularly according to the measured operating conditions. In this work, measurement and modelling uncertainties are quantified with regard to their implications for the neutrino mass measurement. We find that the magnitude of systematic uncertainties related to the source model is represented by |Δmν2|=(3.06±0.24)⋅10−3eV2/c4, and that the gas model is ready to be used in the analysis of upcoming Katrin data.

Calculation of Gas Flow in High-Altitude Engine Nozzle and Experience of Using Water-Cooled Nozzle Head during Tests

Calculation of Gas Flow in High-Altitude Engine Nozzle and Experience of Using Water-Cooled Nozzle Head during Tests

Modified Extended Finite Element Methods for Gas Flow in Fractured Reservoirs: A Pseudo-Pressure Approach

Fluid flow in fractured porous media has always been important in different engineering applications especially in hydrology and reservoir engineering. However, by the onset of the hydraulic fracturing revolution, massive fracturing jobs have been implemented in unconventional hydrocarbon resources such as tight gas and shale gas reservoirs that make understanding fluid flow in fractured media more significant. Considering ultralow permeability of these reservoirs, induced complex fracture networks play a significant role in economic production of these resources. Hence, having a robust and fast numerical technique to evaluate flow through complex fracture networks can play a crucial role in the progress of inversion methods to determine fracture geometries in the subsurface. Current methods for tight gas flow in fractured reservoirs, despite their advantages, still have several shortcomings that make their application for real field problems limited. For instance, the dual permeability theory assumes an ideal uniform orthogonal distribution of fractures, which is quite different from field observation; on the other hand, numerical methods like discrete fracture network (DFN) models can portray the irregular distribution of fractures, but requires massive mesh refinements to have the fractures aligned with the grid/element edges, which can greatly increase the computational cost and simulation time. This paper combines the extended finite element methods (XFEM) and the gas pseudo-pressure to simulate gas flow in fractured tight gas reservoirs by incorporating the strong-discontinuity enrichment scheme to capture the weak-discontinuity feature induced by highly permeable fractures. Utilizing pseudo-pressure formulations simplifies the governing equations and reduces the nonlinearity of the problem significantly. This technique can consider multiple fracture sets and their intersection to mimic real fracture networks on a plain structured mesh. Here, we utilize the unified Hagen–Poiseuille-type equation to compute the permeability of tight gas, and finally adopt Newton–Raphson iteration method to solve the highly nonlinear equations. Numerical results illustrate that XFEM is considerably effective in fast calculation of gas flow in fractured porous media.