Analysis Of Gas Flow Research Articles

MRT-LBM modelling of the oscillatory gas slide film damping in the transition regime

In this paper, the slide film damping (SFD) of micro-scale oscillatory Couette flow has been researched by an effective multiple relaxation time lattice Boltzmann method (MRT-LBM). The validity and effectiveness of MRT-LBM for solving SFD have been verified through contrasting the velocity distribution between the upper plate and the substrate of MRT-LBM and the direct simulation Monte Carlo (DSMC) model. The impacts of the vibration frequency and gap of plates on the damping are discussed, and the result shows that the nonlinear character of velocity profiles is manifest and SFD increases substantially for a larger vibration frequency in the oscillatory gas flow; SFD reduces obviously with the gap increases. Consequently, the results further confirm the implementation of LBM in analysis of the non-equilibrium micro-scale gas flow.

Numerical analysis and optimization of gas flow and impurity control in directional solidification multi-crystalline Si

In order to study the mechanisms of gas flow and impurity transport in an industrial directional solidification furnace for producing multi-crystalline silicon (mc-Si), a 3D global modeling, including argon flow, thermal conduction, thermal radiation, chemical reaction, and mass transfer was established. Simulation results show that the backflow at crucible outlet near the midcourt plane is mainly attributed to buoyancy, which will induce SiO and CO impurities accumulation and affect the chemical reaction intensity on the graphite components. With the increasing of argon flow rate, the backflow is restrained, and the CO concentration at the melt free surface decreases exponentially. When the flow rate is exceed 30 L/min, the benefit is limited. An argon gas guidance system was designed and numerically analyzed, it is found that when the ratio a/b = 0.5, the backflow at crucible outlet almost disappears and the impurity concentration further decreases. According to the newly discovered mechanisms of the flow, chemical reaction and impurity transport, the new designed argon gas guidance system will beneficial for improving the quality of mc-Si.

1D-3D coupling algorithm for unsteady gas flow analysis in pipe systems

Numerical analysis of intake and exhaust systems in diesel engines has been used to reduce harmful emissions from them. An unsteady gas flow analysis in 3D format of the intake and exhaust systems was inefficient due to the need for a high-resolution workstation and enormous time for analysis. Therefore, a 1D-3D coupling algorithm was developed to resolve this issue. The algorithm was based on the method of characteristics coded in the C language for ID, and utilized ANSYS FLUENT R15.0, a commercial computation fluid dynamics program for 3D. The 1D-3D coupling method employed a User-Defined Function to share the computation between ID and 3D. Numerical analyses of unsteady gas flow in a pipe system were performed under four conditions including ID, 3D, 1D-3D and 3D-1D coupling. As a result, the characteristics of gas flow including pressure and velocity distributions were similar and the calculation time of 1D-3D coupling model was 11.46 times faster than in 3D. Therefore, the proposed algorithm was strongly expected to enhance the results and shorten the calculation time.

Unsteady CHT analysis of a solid state, sensible heat storage for PHES system

Purpose The aim of this study is to identify key factors limiting efficiency of pumped heat energy storage systems and determine some general features of transient behavior of solid state, sensible heat storages. Moreover, it aimed at establishing a feasible approach to transient conjugate heat transfer (CHT) analyses for such applications. Design/methodology/approach A zero-dimensional analytical model is used to determine the system efficiency sensitivity to efficiency of its components. Analysis of argon gas flow in an exemplary configuration of layered bed thermal energy storage is presented. The analysis incorporates a unsteady reynolds averaged navier stokes model with conjugate heat transfer between gas and solid storage core. Findings It is established that exergetic efficiency of the heat storage is one of the key factors for the system’s overall performance. Three full cycles of storage charging and discharging having 17 h physical time in total are simulated, with calculation of exergetic efficiency for each of the cycles. From standpoint of the system efficiency, it is concluded that the presented heat storage kind has limited exergetic efficiency because of severe temperature drop at the solid–fluid interface in comparison to granular kind of heat storage devices. From the methodological standpoint, it is concluded that calculating the exergetic efficiency of the heat storage by direct computational fluid dynamics (CFD) analysis requires significant amount of walltime and computational resources. Originality/value The paper presents unconventional approach to using standard CFD tools by exploiting numerical diffusion to numerically suppress high-frequency solution oscillations. This strategy grants that the analysis, otherwise requiring impractically long computation walltime, is completed within a practical time.

Analysis of gas flows in ships turbines

In this paper comparison was made of an experimental study of gas flows and CFD simulation of turbine blades steam turbines for ships. For CFD simulation develop solid models, samples were taken from three blades similarly studied in the experiment. An analysis of experimental data and CFD simulation results of the gas flow near lattice the considered type shows the inappropriateness of their application at supersonic speeds. The calculations performed on the CFD model show that the use of CFD modelling methods allows, at the early stages of designing turbine blades, to select the most optimal (in terms of energy losses) forms of profiles for specific modes of operation of the ship's turbine. Further improvement of the profiles that have passed the preliminary calculation check is advisable to conduct on the basis of more detailed experimental tests to obtain dependences of losses in the lattice, the exit angle of the flow from the parameters of the lattice and the angle of gas flow.

Computational Analysis of Gas Flow in Gas Distributor Breadboard for Creating Efficient Devices to Remove Volatile Organic Compounds

The paper presents the results of CFD modeling of air flows in a gas distributor breadboard at the inlet of structured catalytic cartridges. The calculation results were used for modifying the gas distributor. Comparison of the experimental and calculated data yielded the most adequate model of turbulence; relationship between the boundary conditions and the accuracy of the modeling results was revealed. Recommendations for improving the distribution of gas flow rates in the selected gas distributor breadboard are formulated.

Modeling gas-granular flow in molecular using the DSMC method and continuum regions by Onsager’s pancake equation with mass sources and sinks in a rotating cylinder

Increasing the speed of rotation in a gas rotating cylinder leads the gas to be transferred to a small section of the rotating cylinder. The Navier–Stokes equations are conventionally used to analyze gas flow in this area. By moving away from the wall and approaching the cylinder axis, the gas is diluted, and the Knudsen number increases, and as a result, it decreases the precision of Navier–Stokes equations for gas flow analysis. Solving the Boltzmann equation in the molecular region is an accurate method. One of the methods for solving the Boltzmann equation is using the DSMC method. This paper aims to model the whole gas rotating cylinder (molecular and continuum regions). Initially, the molecular region was completely modeled using the DSMC method and its results (the exact function of the mass sources or ( $${\mathcal{M}}_{0}$$ )) were used to solve the continuum region equations. For the continuum region, the Onsager’s pancake equation with a mass source/sink along with finite difference method is used. The results indicated that with the correction of the mass sources function proposed by earlier researchers, a more precise solution is obtained for analyzing gas flow inside a rotating cylinder.

Problems of coordinating the solutions of quasigasdynamic equations with results of molecular-dynamic calculations in analysis of real gas flows

This paper is devoted to the numerical study of complex gas-dynamic processes in microchannels of technical systems. The analysis is carried out on the basis of the equations of quasigasdynamics, taking into account the real dependences of the equation of state and kinetic coefficients on temperature and pressure, as well as the realistic description of the channel walls. As an example, the flow of nitrogen in the nickel channel of the actual structure is selected. The task is considered in the context of a multiscale approach. The main idea of this approach is to combine models of continuum with models of particles. Combining models is implemented in the framework of the method of splitting by physical processes. The correctness of this approach is ensured by the selection of suitable time intervals and the conjugation of scale levels. The goal is to develop a numerical algorithm that integrates grid methods for solving quasigasdynamic equations and molecular dynamics method, allowing to take into account the properties of real substances in the general model. In work the method of coordination of numerical solutions at different scale levels in time and space is investigated. Based on the proposed methodology, direct molecular modeling of the flow in the channel was carried out and data were prepared for calculating such a flow using the equations of quasigasdynamics. The study confirmed the possibility of synthesizing these two numerical methods.

Analysis of non-equilibrium gas flows near a liquid surface using the variance-reduced Monte Carlo method

Analysis of non-equilibrium gas flows near a liquid surface using the variance-reduced Monte Carlo method

Evaluation of mechanical ventilators' accuracy in clinical settings: A quality control study

Background: A mechanical ventilator (MV) is one of the most important devices in critical care units. Improper ventilator settings may adversely affect patients' health. The objective of this study is to evaluate the accuracy of volume, pressure, and flow delivered by the ventilators in clinical settings. Materials and Methods: Thirty randomly chosen MVs from four randomly selected main hospitals in the eastern province of Saudi Arabia were included in this study. All types of modern intensive care unit ventilators brands along with all versions were targeted. Pressure, volume, and flow were evaluated at two levels by using Fluke Biomedical VT PLUS HF Gas Flow Analyzer. Results: High-pressure mean was 28.7 ± 4.9 cm H2O and low-pressure mean was 14.6 ± 1.3 cm H2O. 95% limits of agreement (LA95%) between the measured and setting in high pressure was −0.74–2.86 cm H2O and −0.114–0.84 cm H2O in low pressure. The mean of volume measurements was 676.9 ± 45.5 ml in high setting and 342.9 ± 24 ml in low setting. In high volume setting, LA95%of 104.76–138.05 ml, wherein low volume LA95%of 47.7–65.3 ml. High flow mean was 53.4 ± 4.6 lpm with LA95%of 3.3–6.8 lpm and low flow mean was 36 ± 3.7 lpm with LA95%of 1.87–4.6 lpm. Conclusion: The present data reveal that MVs in clinical settings have some variations in their performance. The delivered flow and volume might not be accurate as it might be anticipated. These differences should be considered while their use in critically ill patients.

Linear-analog transformation approach for coupled gas and power flow analysis

In this paper, we present a methodology to analyze the integrated operation of coupled natural gas and electricity networks in steady-state. The interaction of the gas network with the electrical grid is modeled through mathematical equations that represent the energy exchange between the two infrastructures. The joint natural gas and power flow is solved using the linear-analog transformation (LAT) and the Newton-Raphson (NR) algorithm, respectively. Here, a unified solution framework of the two systems is presented using the previous proposed methods. The applicability of the methodology is illustrated using two case studies: IEEE-14 bus test system combined with a 16-node natural gas network and the IEEE-30 bus test system integrated with a 15-node natural gas network with 4 compressors. The proposed methodology proves to be useful for the assessment of coupled natural gas and electricity critical infrastructures.

Analysis of the ideal gas flow over body of basic geometrical shape

An approximate mathematical model of the heat transfer processes in the laminar and turbulent boundary layers, which occur near the surface of an aircraft moving at the hypersonic speed in the Earth’s atmosphere, is derived. This mathematical model makes it possible to calculate the convective heat transfer on the surface of typical structural elements of modern perspective aircrafts. 2D versions of the calculations of convective heat fluxes for bodies of simple geometric shapes are performed.

A Numerical simulation of delamination caused by internal gas pressure for mid-density CFRP

Interlaminar debonding (delamination) is a major problem for carbon fiber-reinforced plastic (CFRP) when it is used in thermal protection systems subjected to rapid heating, such as in a re-entry situation. In this study, the possibility of avoiding delamination by controlling material porosity was investigated experimentally and numerically. CFRP specimens having various initial porosities (mid-density CFRP) were prepared and rapid heating tests (∼6 MW/m2) were performed, and the specimens were examined to determine whether delamination had occurred. To predict the delamination, heat transfer and pyrolysis gas-induced internal gas pressure growth were simulated numerically as a function of heating time. The parameters regarding temperature-dependent chemical reaction rate, orthotropic coefficients for gas permeability, and flatwise tensile strength were determined by individual experiments using the CFRP specimens. The coupled analysis of thermal transfer and pyrolysis gas flow following Darcy’s law was conducted by finite-difference form, employing the experimentally obtained parameters. When the gas pressure exceeds the flatwise tensile strength of CFRP, delamination is assumed to occur. The numerical results show good agreement with the experimental results, and it is concluded that delamination can be eliminated by using mid-density CFRP.

Numerical analysis of gas flow through the labyrinth seal of piston rings of an automotive IC engine

In the paper a model of transient gas flows through the labyrinth seal: piston-rings-cylinder (PRC) has been presented. The results of calculations for a ring pack of three piston rings operating on a cylinder liner of a spark ignition internal combustion engine have been shown. The analysis of the gas dynamics and a parametric study considering this phenomenon has been carried out. It allowed evaluating the influence of the most important parameters of this sealing on the gas pressure acting on the rings and blow-by to the crankcase. The simulation results show the necessity of taking into account the following parameters: uneven wear of cylinder liner and its thermal and mechanical deformation, thermal deformation of piston rings, heat transfer between the flowing gas and the labyrinth walls, dynamics of axial ring displacements in piston grooves.

Analysis of Protective Gas Flow in a Snout and Modification of Inflow Configuration of Humid Nitrogen

Analysis of Protective Gas Flow in a Snout and Modification of Inflow Configuration of Humid Nitrogen

Analysis of Temperature and Gas Flow Distribution in Chamber with Wafer Batch

ABSTRACTWafer temperature distribution and gas flow inside a tube of a chemical vapor deposition chamber, which is a semiconductor fabrication equipment, were analyzed. The control volume was assumed to be a two-dimensional space, and calculation program was developed based on a MATLAB code. The program is divided into two parts – heat transfer and gas flow analyses. The results of the calculation and the temperature test agreed well with each other. Heat loss was observed at both ends of the wafer batch, and gas convection momentum was not enough for the flow to invade into the wafer spacing. Thus, the flow rate and the temperature of the wafer needed to be increased to make the film thickness uniform. To increase the wafer temperature, the radiation adiabatic pedestal was considered. Low emissivity made the pedestal almost adiabatic, which increased the temperature of the wafer batch. To increase the flow rate in the wafer spacing, the eccentric wafer batch was proposed.

Analysis of the high speed gas flow over a sphere in the range of Mach numbers 2–12

In this paper, the results of analysis of the high speed gas flow over a sphere are presented. Numerical investigations were carried out using the UST3D code developed at the Ishlinsky Institute for Problems in Mechanics of RAS (IPMech RAS). The code implements numerical simulation of aerothermodynamics of aircrafts in the context of integration of the full system of Navier – Stokes equations on unstructured mesh using the perfect gas model.

Steady state and transient simulation for electricity‐gas integrated energy systems by using convex optimisation

The increasing interdependence between electric power and natural-gas systems requires integrated simulation tools applicable to the coupled system. Therefore, this study proposes steady-state and transient simulation tools for electricity-gas integrated energy systems (IESs) by using convex optimisation. Steady-state IES simulation is designed for long-term planning studies while transient IES simulation, which includes line-pack storage, is designed for real-time operational research. The proposed convex steady-state gas flow model introduces binary variables to represent gas flow directions, and employs the second-order cone (SOC) to relax non-convex pipeline gas flow equations. As a result, steady-state gas flow analysis is formulated as a mixed integer SOC programming problem. The proposed transient gas flow model employs the implicit finite difference method to transform partial differential equations into algebraic difference equations. Moreover, the short-term gas flow directions are specified and SOC relaxations are used. Simulation results on an integrated IEEE 24-node system and Belgian 20-node gas system verify the effectiveness of the proposed SOC models. The impacts of wind power forecast errors on multi-period gas network operations are also investigated.

Modeling of the process of the extinguishing gas concentration changes in the protected compartment

The article discusses the aspect of the fire safety of rooms protected by Fixed Gaseous Extinguishing System (FGE-system). On the basis of a literature study, including the analysis of design standards, it was claimed that analytical models of gas outflow from the compartment ignore some parameters that can affect the process of extinguishing gas concentration changes in time. Correct prediction of the gas flow process may affect the retention time value, which is an important determinant of the fire safety of rooms protected by FGE-system. The density of extinguishing gas was indicated as a parameter with a large potential for extending the retention time. It was noted that the density of gas depends on atmospheric conditions like temperature, pressure and humidity, which are omitted in the standard models. In the research part, the concentration distribution of nitrogen and nitrogen-argon mixtures were analyzed using three methods. Obtained experimental data were compared with analytical calculations using a standard model (model N) and a new proposed model extended by an impact of the atmospheric conditions (model PK). Model PK showed greater accuracy of determining the process of extinguishing gas concentration changes. The new proposed model might be a valuable tool for further analysis of gas flow through the room.

Entropy generation and irreversibility analysis of a compressible gas flow inside a two-dimensional uniform microchannel

The entropy generation for steady, compressible gas flow inside two-dimensional rectangular microchannel at slip flow regime with constant walls temperature has been investigated. The obtained solutions of the flow field are used to evaluate the entropy generation, Bejan number and irreversibility ratio inside the microchannel. Finally, the influence of Knudsen number, Brinkman number, aspect ratio, and pressure ratio on entropy generation rate and irreversibility were presented.