Analysis Of Gas Flow Research Articles

Micro molecular tagging velocimetry for analysis of gas flows in mini and micro systems

A new micro molecular tagging velocimetry (μMTV) setup has been developed to analyze velocity fields in confined internal gas flows. MTV is a little-intrusive velocimetry technique. It relies on the properties of molecular tracers which can experience relatively long lifetime luminescence once excited by a laser beam with an appropriate wavelength. The technique has been validated for acetone seeded flows of argon inside a 1 mm depth rectangular minichannel, with a multilayer design offering two optical accesses. Velocity profiles have been obtained using a specific data reduction process, with a resolution in the order of 15 μm. The experimental data are compared to theoretical velocity profiles of compressible pressure-driven flows. A good agreement is observed, except close to the walls, where the accuracy would still need to be improved. Following these first results obtained at atmospheric pressure, the influence of pressure on the luminescence intensity of acetone molecules is analyzed. The obtained data lead to a discussion of MTV applicability to rarefied flows and its possible use for a direct measurement of velocity slip at the channel walls.

Experimental analysis of the non isothermal rarefied gas flow through a packed bed of spheres

We present the results of an experimental study concerning the gas flow through a packed bed of spheres located between two concentric cylinders, in non isothermal conditions. This problem is prototypal for more complex geometries which can be found in Micro Electro-Mechanical Systems (MEMS) where the heat transfer is a crucial issue. In these applications the characteristic lengths are such that the gas flow regime could fall in almost rarefied regime where the features of heat and mass flows can be markedly different with respect to the continuum regime. We investigated a wide range of regimes, spanning from the compressible continuum flow to rarefied conditions with a variation of the peculiar Knudsen number of about three orders of magnitude, i.e. from Kn=10−3, which corresponds to almost continuum regime, to Kn≈1 which falls in the transitional region. The heat transfer through the porous medium have been studied by the analysis of the temperature field and the heat flux as a function of the flow rate, the boundary conditions and the porous materials.

Network flows modeling applied to the natural gas pipeline in Brazil

The use of natural gas during the last decades has been growing, and this trend will continue until 2030, according to the Brazilian energy plan issued by Ministry of Mines and Energy (2007a). However, the capacity of transportation is one of the important elements of the supply chain in response to the distribution market. In this context, the present study aims at identifying, in a regional and integrated way, the transportation capacity of the natural gas pipeline network. Therefore, a database and a mathematical model were developed to calculate the network maximum flow in order to enable analysis of the natural gas flow in the national network. The complex natural gas flow and the forecast of increasing demand justify the study of this issue, and the development of tools to help analyze the feasibility of implanting the decennial energy plan. The mathematical model used considers a linear programming to calculate the flows in the network. Data were collected about the operating companies, existing pipelines, handling capacity, historical flow and demand forecast. The delivery capacity in the consumer markets is also analyzed by means of economic and population index compared to the 2020 target. The results show a maximum nominal capacity of 213 MM m3 per day at reception points, and 227 MM m3 per day at delivery points. Idleness was found in the networks of the Northeast and Espírito Santo area (14% and 6.1%), and lack of capacity was found in the Southeast and South networks (11.6% and 9%), compared with the economic index of consumer centers near the networks. In comparison to the current flow, 75% of idleness was found. Idleness was identified in the networks of the Northeast and Espírito Santo areas (55% and 68%), and lack of capacity was identified in the Southeast and South networks (7% and 74%), in comparison to the 2020 target. In the analysis of the 2020 target, compared to the capacity in the metropolitan areas, lack of capacity was found in the metropolitan areas of Sao Paulo, Belo Horizonte, Fortaleza and South area (68%, 5%, 59% and 74%) and idleness was found in the areas of Vitória, Recife, Rio de Janeiro, Maceió, Aracaju, Salvador and Natal (85%, 72%, 40%, 93%, 8%, 58% and 17%).

A new method for production data analysis of tight and shale gas reservoirs during transient linear flow period

Pseudo-pressure has historically been used in analytical solutions of the diffusivity equation for analysis of real gas flow in conventional gas reservoirs. The accuracy of analytical solutions during the transient flow period is contingent on the validity of the assumption of constant hydraulic diffusivity which is implicit in the background formulations. However, the assumption of pseudo-pressure-independent hydraulic diffusivity during transient flow is not valid for the cases of high pressure drawdown at the wellbore. For tight and shale gas reservoirs, this dependency is more pronounced due to the complexities associated with non-Darcy flow, adsorption/desorption phenomena, stress-sensitivity of permeability and porosity, and condensation in porous media.The current study focuses on rate transient analysis of tight and shale gas reservoirs during transient linear flow period for a single fractured well producing under constant well bottom-hole pressure. The results of the analytical solution of real gas flow in porous media are corrected for the effects of high pressure drawdown, non-static permeability, and condensate formation. The method proposed in this study includes three key elements: introducing a measure of nonlinearity (departure of dimensionless hydraulic diffusivity from linearity); differential and integral formulation of the correction factor (used to correct the slope of the square-root-of-time plot); implementing the iterative integral method for solution of flow equation; and evaluating the correction factor for constant-pressure production during transient linear flow period. The results show that the correction factor becomes more important for higher values of drawdown, permeability modulus, and condensate saturation.

Computational Fluid Dynamic Analysis of Gas Flow Characteristics in a New Type of Scrubber Based on Mechanical Materials

In this paper, a new type of vertical scrubber is designed and a computational fluid dynamic analysis of gas flow through the device is presented. The simulation results are obtained by FLUENT 6.3. Through the two-dimension simplification of mist-mat, the resistance characteristic of the wire-mesh is gained. To simulate the gas flow of the scrubber, mist-mat is replaced by porous media. Through the analysis of simulate results, flow characteristic and pressure drop of the scrubber is obtained. Additionally, CFD analysis results show the entrance direction of the gas in vane inlet symmetry plane is benefit to avert severely velocity impulse and scrubber’s pressure drop rises with the growth of the eliminator’s velocity.

Modelling of Gas Flow in the Underground Coal Gasification Process and its Interactions with the Rock Environment

The main goal of this study was the analysis of gas flow in the underground coal gasification process and interactions with the surrounding rock mass. The article is a discussion of the assumptions for the geometric model and for the numerical method for its solution as well as assumptions for modelling the geochemical model of the interaction between gas-rock-water, in terms of equilibrium calculations, chemical and gas flow modelling in porous mediums. Ansys-Fluent software was used to describe the underground coal gasification process (UCG). The numerical solution was compared with experimental data. The PHREEQC program was used to describe the chemical reaction between the gaseous products of the UCG process and the rock strata in the presence of reservoir waters.

Ventilation patterns of the songbird lung/air sac system during different behaviors

Unidirectional, continuous airflow through the avian lung is achieved through an elaborate air sac system with a sequential, posterior to anterior ventilation pattern. This classical model was established through various approaches spanning passively ventilated systems to mass spectrometry analysis of tracer gas flow into various air sacs during spontaneous breathing in restrained ducks. Information on flow patterns in other bird taxa is missing, and these techniques do not permit direct tests of whether the basic flow pattern can change during different behaviors. Here we use thermistors implanted into various locations of the respiratory system to detect small pulses of tracer gas (helium) to reconstruct airflow patterns in quietly breathing and behaving (calling, wing flapping) songbirds (zebra finch and yellow-headed blackbird). The results illustrate that the basic pattern of airflow in these two species is largely consistent with the model. However, two notable differences emerged. First, some tracer gas arrived in the anterior set of air sacs during the inspiration during which it was inhaled, suggesting a more rapid throughput through the lung than previously assumed. Second, differences in ventilation between the two anterior air sacs emerged during calling and wing flapping, indicating that adjustments in the flow pattern occur during dynamic behaviors. It is unclear whether this modulation in ventilation pattern is passive or active. This technique for studying ventilation patterns during dynamic behaviors proves useful for establishing detailed timing of airflow and modulation of ventilation in the avian respiratory system.

A Unified View of Topological Invariants of Barotropic and Baroclinic Fluids and their Application to Formal Stability Analysis of Three-Dimensional Ideal Gas Flows

Noether's theorem associated with the particle relabeling symmetry group leads us to a unified view that all the topological invari- ants of a barotropic fluid are variants of the cross helicity. The same is shown to be true for a baroclinic fluid. A cross-helicity representation is given to the Casimir invariant, a class of integrals including an arbitrary function of the specific entropy and the potential vorticity. We then develop a new energy-Casimir convexity method for three-dimensional stability of equilibria of gen- eral rotating flows of an ideal baroclinic fluid, without appealing to the Boussinesq approximation. By fully exploiting the Casimir invariant, we have succeeded in ruling out a term including the gradient of a dependent variable from the energy-Casimir function and have established a sharp linear stability criterion, being an extension of the Richardson-number criterion.

Experimental Analysis of Welding Parameters on Variable Polarity Plasma Arc Pressure

Variable polarity plasma arc welding has been widely used to manufacture industries. The effects of welding current and plasma gas flow as the most important parameters on variable polarity plasma arc pressure were discussed experimentally. To welding current, two experimental were designed to discuss the effects of straight polarity current and reversed polarity current on arc pressure respectively. It could be concluded that arc pressure is quadratic with welding current. To plasma gas flow, both experimental and numerical analysis are used to discuss the mechanisms of plasma gas flow to arc pressure, and it could be conclude that arc pressure is quadratic with plasma gas flow rather than linear.

CFD Based Parametric Analysis of Gas Flow in A Counter-Flow Wet Scrubber System

Environmental protection measures regarding industrial emissions and tightened regulations for air pollution led to the selection of a counter-flow wet scrubber system based on applicability and economic considerations. The flow dynamics of gas transporting particulate matter and gaseous contaminants is a key factor which should be considered in the scrubber design. In this study, gas flow field were simulated using ANSYS Fluent computational fluids dynamic (CFD) software based on the continuity, momentum and k-ε turbulence model so as to obtain optimum design of the system, improve efficiency, shorten experimental, period and avoid dead zone. The result shows that the residuals have done a very good job of converging at minimum number of iterations and error of 1E-6. The velocity flow contours and vectors at the inlet, across the scrubbing chamber and the outlet shows a distributed flow and the velocity profiles have fully conformed to the recommended profile for turbulent flows in pipes. The total pressure within the scrubber cross-section is constant while the minimum and maximum pressure drops was obtained to be 0.30pa and 3.03pa which has conformed to the recommended pressure drop for wet scrubbers. From the results obtained, it can be deduced that the numerical simulation using CFD is an effective method to study the flow characteristics of a counter-flow wet scrubber system.

The Gas Flow Simulation of Tokamak’s Inflatable Pipeline

Inflatable pipe is an important part of the tokamak's experimental device. This paper first introduces the composition, functions and working mode of the inflatable pipe. Then it's based on the fluid dynamics to establish model of the inflatable pipeline and the nodes. Finally, using the finite volume method to complete a numerical analysis of gas flow in the tokamak's pipeline. The results show that, if it needs to get the gas flow of the H2 that is 400 Pa•m3/s at the valve in the Pipeline, it needs to set the value of the inlet pressure that is 1.5 bar. The larger diameter of the pipeline, the more increase rate of gas flow in the pipeline.

Thermal Stress Analysis in Structural Elements of HRSG Casing

Heat recovery steam generators (HRSGs) are arranged at the tail end of gas turbines in combined cycle power plants (CCPPs), and are designed to withstand the hot gas environment approaching 600℃. In addition to higher thermal to power efficiency, CCPPs show superior response characteristics compared to those of other conventional steam power plants. For that reason, frequent load changes on the system, which sometimes include daily start and stop (DSS) operation, would impose additional burden on the structural elements. The main objective of this work is to analyze the thermal stress conditions as related to the observed failure on the structural elements of HRSG casing, and to find root causes of failure of mechanical integrity. To achieve this goal, field measurements were performed to record temperatures of wall and stiffener of the casing from a real plant in operation. To consider the effect of hot gas on the casing, computational fluid dynamic (CFD) analysis of gas flow inside the HRSG with appropriate wall conditions using FLUENT V12. Thermal stress analysis on the thin wall of the casing and stiffeners of HRSG was conducted with the temperature data from the CFD results, using ANSYS Workbench V12. Summarizing the computational results, some limited ideas were presented which would be useful to prevent damages.

A Unified Gas and Power Flow Analysis in Natural Gas and Electricity Coupled Networks

The restructuring of energy markets has increased the concern about the existing interdependency between the primary energy supply and electricity networks, which are analyzed traditionally as independent systems. The aim of this paper is focused on an integrated formulation for the steady-state analysis of electricity and natural gas coupled systems considering the effect of temperature in the natural gas system operation and a distributed slack node technique in the electricity network. A general approach is described to execute a single gas and power flow analysis in a unified framework based on the Newton-Raphson formulation. The applicability of the proposed approach is demonstrated by analyzing the Belgian gas network combined with the IEEE-14 test system and a 15-node natural gas network integrated with the IEEE-118 test system.

Characterization of nanochannel delivery membrane systems for the sustained release of resveratrol and atorvastatin: new perspectives on promoting heart health

Novel drug delivery systems capable of continuous sustained release of therapeutics have been studied extensively for use in the prevention and management of chronic diseases. The use of these systems holds promise as a means to achieve higher patient compliance while improving therapeutic index and reducing systemic toxicity. In this work, an implantable nanochannel drug delivery system (nDS) is characterized and evaluated for the long-term sustained release of atorvastatin (ATS) and trans-resveratrol (t-RES), compounds with a proven role in managing atherogenic dyslipidemia and promoting cardioprotection. The primary mediators of drug release in the nDS are nanofluidic membranes with hundreds of thousands of nanochannels (up to 100,000/mm(2)) that attain zero-order release kinetics by exploiting nanoconfinement and molecule-to-surface interactions that dominate diffusive transport at the nanoscale. These membranes were characterized using gas flow analysis, acetone diffusion, and scanning and transmission electron microscopy (SEM, TEM). The surface properties of the dielectric materials lining the nanochannels, SiO(2) and low-stress silicon nitride, were further investigated using surface charge analysis. Continuous, sustained in vitro release for both ATS and t-RES was established for durations exceeding 1 month. Finally, the influence of the membranes on cell viability was assessed using human microvascular endothelial cells. Morphology changes and adhesion to the surface were analyzed using SEM, while an MTT proliferation assay was used to determine the cell viability. The nanochannel delivery approach, here demonstrated in vitro, not only possesses all requirements for large-scale high-yield industrial fabrication, but also presents the key components for a rapid clinical translation as an implantable delivery system for the sustained administration of cardioprotectants.

Rarefied gas flow in a planar channel caused by arbitrary pressure and temperature drops

The paper presents a numerical analysis of the nonlinear rarefied gas flow through a long planar channel of finite length. The solution is constructed for the arbitrary pressure and temperature drops, including flow into vacuum. The obtained results for the flow rates are compared with the linearized solutions in the large range of degree of gas rarefaction. The boundaries of the validity of the linearized approximation are established.

Velocity field measurements in gas phase internal flows by molecular tagging velocimetry

The goal of the present work is to implement Molecular Tagging Velocimetry (MTV) for the analysis of internal gas flows in mini-channels. A MTV experimental setup has been designed. Tagging and detecting steps are respectively insured by a UV laser and a CCD camera coupled to intensified relay optics. A specific channel with 1 × 5 mm2 rectangular cross section has been designed and equipped with integrated temperature sensors along its 20 cm length. It has been manufactured in PEEK (PolyEtherEther-Ketone) and Suprasil® optical windows have been integrated for the tagging access. Image processing allows extraction of velocity profiles for a pressure driven steady flow of argon through this channel. These profiles are compared to the theoretical profiles of laminar flows and the accuracy of the method is discussed. The MTV potential for the analysis of internal gaseous flows is commented on, with a discussion on perspectives for velocity measurement in rarefied flows and direct access to slip velocity at the walls.

The analysis of fresh gas flow in a circle anaesthetic breathing system, and its influence on CO2 absorbent desiccation

Background: If at the end of anaesthesia, the gases on the anaesthetic machine are not turned off, they continue to flow through the breathing circuit and may dry out the carbon dioxide absorbent in the absorber. At the beginning of the next anaesthetic procedure, the desiccated absorbent decomposes the volatile anaesthetic, resulting in the formation of toxic gas mixtures, which are dangerous for the patient. In such circumstances, the measured level of the volatile anaesthesic in the breathing circuit differs from the selected value. In the paper, we analyse potentially dangerous possible directions of continuous flow of fresh gas mixture in different anaesthetic breathing circuits. Methods: In the first part of the study, we simulated the continuous flow of gases in a Sulla anaesthesia machine using an experimental method in a simulation setting. In the second part, we analysed whether a retrograde flow through the absorber was possible in a convential anaesthetic breathing circuit and in the Fabius GS, Cato, Julian and Primus circuits with the Y-piece connector open or closed. Information on users’ requests for maintenance services due to discrepancies between the desired and measured levels of the volatile anaesthetic in the breathing circuit were obtained from the manufacturer’s local servicing agent. Results: In a Drager ISO 8 circle system (Sulla anaesthetic machine) with a standard gas supply connector, a retrograde flow is not possible. If the Y-piece connector is left open, the gases are vented to the outside via the absorber and the inspiratory tube. If the Y-piece connector is closed or open, the absorbent in the canister dries because of the continuous flow of gas. A retrograde flow is possible only in those Sulla anaesthetic machines where the fresh gas inlet is located below the inspiratory valve. A retrograde flow of gases causing absorbent desiccation can occur in a Cato, Julian, Fabius GS, or Primus anaesthetic machines with the Y-piece connector closed. Maintenance engineers point out that problems are reported mostly on Monday mornings before the first operation. Conclusions: After completed anaesthesia, the fresh gas inlets on the anaesthetic machine must always be closed. Especially in older machines, the carbon dioxide absorber must be checked before the first operation on a Monday morning. In new-generation machines, we must make sure that the emergency ventilation valve is closed after the end of anaesthesia.

Computational study of a rarefied gas flow through a long circular pipe into vacuum

The paper presents an analysis of the non-linear rarefied gas flow through a circular pipe into vacuum. The main attention is given to the case of the large length to radius ratio. The problem is studied on the basis of the numerical solution of the S-model kinetic equation. Results are compared with the available DSMC data for short tubes as well as with the asymptotic solution corresponding to the infinitely long pipe.

Development of applied software for analysis of gas flows in vacuum devices

The paper presents some results of computing gas mixture flows in Knudsen and Holweck pumps. Transient flow development processes and attainment of the steady state are considered. The calculations were performed using a problem solving environment developed by the authors. A conservative projection method of solving the Boltzmann kinetic equation upon which the problem solving environment is based is described. The paper is aimed to demonstrate the capabilities of the software at the actual stage of its development.

Quantitative Analysis of Gas Flow in a Planar SOFC

Computational Fluid Dynamics (CFD) method was adopted to establish the three dimensional model for cathode gas channel of planar SOFC and simulate the gas flow in the channel of a single cell. A quantitative analysis method was presented to research the status of gas flow. The characteristics and diagram of velocity change were obtained by using the quantitative analysis method. Furthermore, it was found that gas leak has a negative effect on the uniformity of gas flow, which is more obvious in the region near the leak side.