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Article
Publication date: 29 August 2019

Wei Long, Mimi Wu, Fasha Li, Jiyao Wang and Wei Deng

The purpose of this paper is to develop the micro-electro-mechanical systems (MEMS) technology has created the conditions for the study of microfluidic technology…

Abstract

Purpose

The purpose of this paper is to develop the micro-electro-mechanical systems (MEMS) technology has created the conditions for the study of microfluidic technology. Microfluidic technology has become a very large branch in the MEMS field over the past decade. For aerostatic thrust bearing, the micro-fluidic gas flow in a small-scale gas film between two parallel plates is the subject of many studies. Because of the thin gas in the film, velocity slip occurs at the interface, which causes the gas flow pattern to change in the lubricating film. So, it is important to clarify the mechanism and pressure characteristics in thin firm gas flow.

Design/methodology/approach

First, a new assumption and corresponding models for the flow regime were established by theoretical analysis. Second, computational simulations about pressure distribution and velocity were given by a large-scale atomic/molecular massively parallel simulator (LAMMPS). Third, comparison of the results of LAMMPS simulation and direct simulation Monte Carlo calculation were made to verify the reliability of above results.

Findings

The gas flow mechanism and corresponding regulations are significantly different from traditional pneumo dynamics, which can be described by Navier–Stokes equations accurately. Combining theatrical study and computational results, the stratification theory of the gas film was verified. The research shows that when the gas flow rate increased, the pressure of the gas film decreased, the thickness of the continuous flow layer increased, the thickness of the thin layer decreased and the layered pressure in the gas film disappeared. In this case, velocity slippage could be ignored.

Originality/value

First, this paper established an analytical model of the gas film support and proposed a film stratification theory. The gas film was divided into the near wall layer, the thin layer and the continuous layer, which was proved by the calculation of LAMMPS flow simulation. The velocity slip boundary conditions theory is feasible. Second, the gas film size of the flat plate is at the micron level, which cannot be observed in its flow regimen, only determined by calculation and simulation. This paper proposes a new model and a new tool to analyze gas flow in gas films.

Details

Industrial Lubrication and Tribology, vol. 73 no. 1
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 1 March 2005

Giorgio Cignolo, Franco Alasia, Andrea Capelli, Roberto Goria and Gaetano La Piana

A prototype gas prover was constructed to serve as the Italian primary standard for gas flow rates in the range 0.1 ml/min to 2 l/min. The new prover is used to calibrate…

Abstract

Purpose

A prototype gas prover was constructed to serve as the Italian primary standard for gas flow rates in the range 0.1 ml/min to 2 l/min. The new prover is used to calibrate high‐quality industrial standards, as well as the MFCs used in microelectronic fabrications and preparation of reference gas mixtures.Design/methodology/approach – The prover measures gas volume transfers caused by displacements of a 120 mm dia. motor‐operated piston, which is introduced into a temperature‐controlled chamber containing up to 3 l of the required working gas at near ambient conditions. Gas delivery is made at constant rate, whereas possibly variable incoming flows are measured at constant pressure. Displacements of the piston are measured by an optical interferometer.Findings – The analysis shows that standard uncertainty ranges between 0.013 and 0.03 percent. Owing to the very accurate control and measurement of both pressures and temperatures, these figures refer equally to volume and mass flowrate. Experimental comparisons with similar national standards at LNE‐France and NIST‐USA confirmed the consistency of measurement results in the three Nations.Research limitations/implications – The gas prover should be used with inert gases only.Practical implications – The national industrial gas standards and the best flow transducers can now be calibrated accurately down to unprecedented flowrate values.Originality/value – The need for measurement of extremely low gas flows is quite recent, therefore possibly less than ten primary national standards are available today worldwide. Several completely different principles and designs have been developed; description of design and performance of each instrument is important to assess their respective merits. The described apparatus is innovative as regards measurement range, accuracy and control techniques.

Details

Sensor Review, vol. 25 no. 1
Type: Research Article
ISSN: 0260-2288

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Article
Publication date: 13 February 2017

Adesina Fadairo, Olusegun Oyedele-Adeyi, Adebowale Oladepo and Ogunkunle Temitope

The production of natural gas from the reservoir is always associated with entrained solid particle of different sizes mainly sand particles and crystalline salts…

Abstract

Purpose

The production of natural gas from the reservoir is always associated with entrained solid particle of different sizes mainly sand particles and crystalline salts. Entrained solid transport along the gas phase has been a great concern for gas production engineer, as the detrimental consequences are often associated to a desirable high operational parameters such rate and pressure transverse in producing well.

Design/methodology/approach

A variety of models for predicting pressure transverse in flowing gas wells have been reported in the literatures. Most of the models were based on steady state fluid flow equation that did not consider time factor which results in inaccurate at early production time. Some of the early investigators overlooked the effect of the entrained solid on the pressure transverse phenomena in a gas well. Hence, there is a need for developing a more realistic model for estimating pressure transverse at all times in flowing solid-gas vertical well.

Findings

This study presents equation for pressure drop in flowing vertical well without neglecting any term in the momentum equation by the inclusion of accumulation and kinetic term. The solution of the resulting differential equation gives functional relationship between solid-gas flow rates and pressure at any point in flowing well at any given production time.

Originality/value

The results show improvement over previous studies, as the assumptions previously neglected were all considered.

Details

World Journal of Engineering, vol. 14 no. 1
Type: Research Article
ISSN: 1708-5284

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Article
Publication date: 2 October 2017

Adesina Fadairo, Olusegun Oyedele-Adeyi, Adebowale Oladepo and Temitope Ogunkunle

The purpose of this study showcase a realistic model for estimating pressure drop at any production time in any location along the vertical flowing solid-gas well. Also to…

Abstract

Purpose

The purpose of this study showcase a realistic model for estimating pressure drop at any production time in any location along the vertical flowing solid-gas well. Also to simulate the impact of solid particles on the pressure transient in gas well. The production of natural gas from the reservoir is always associated with entrained solid particle of different sizes, mainly sand particles and crystalline salts. Entrained solid transport along the gas phase has been a great concern for gas production engineer, as the detrimental consequences are often associated to desirable high operational parameters, such as rate and pressure transverse in producing well.

Design/methodology/approach

A variety of early models for predicting pressure transverse in gas wells were based on steady state flow equation that did not consider time factor, which results in inaccuracy at early production time. Some of the early investigators overlooked the effect of the solid on the pressure transverse phenomena in a gas well. Hence, there is a need for developing a model for estimating pressure transverse at all times in solid–gas well. This study presents an equation for pressure drop in flowing vertical well without neglecting any term in the momentum equation by the inclusion of accumulation and kinetic term.

Findings

The solution of the resulting differential equation gives functional relationship between solid–gas flow rates and pressure at any point in flowing well at any given production time. The results show improvement over previous studies, as the assumptions previously neglected were all considered.

Originality/value

A more realistic result that includes the initial unsteadiness phenomenon is obtained; hence, predicting pressure transient at any given production time has been established for both gas that flows along with solid particles and gas without particles. At the onset of production, the effect of all possible wellbore pressure losses is highly pronounced and decreased as the production time increases. The newly developed model, however, can be used at all depths. The effect of using the Sukkar and Cornell model is extremely adverse for the calculation of other parameters, such as flow rate, and carrying out economic analysis.

Details

World Journal of Engineering, vol. 14 no. 5
Type: Research Article
ISSN: 1708-5284

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Article
Publication date: 26 August 2014

Balázs Illés

This paper aims to compare and study two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics simulation results of gas flow velocity in a convection…

Abstract

Purpose

This paper aims to compare and study two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics simulation results of gas flow velocity in a convection reflow oven and show the differences of the different modeling aspects. With the spread of finer surface-mounted devices, it is important to understand convection reflow soldering technology more deeply.

Design/methodology/approach

Convection reflow ovens are divided into zones. Every zone contains an upper and a lower nozzle-matrix. The gas flow velocity field is one of the most important parameters of the local heat transfer in the oven. It is not possible to examine the gas flow field with classical experimental methods due to the extreme circumstances in the reflow oven. Therefore, numerical simulations are necessary.

Findings

The heat transfer changes highly along the moving direction of the assembly, and it is nearly homogeneous along the traverse direction of the zones. The gas flow velocity values of the 2D model are too high due to the geometrical distortions of the 2D model. On the other hand, the calculated flow field of the 2D model is more accurate than in the 3D model due to the finer mesh.

Research limitations/implications

Investigating the effects of tall components on a printed wiring board inside the gas flow field and further analysis of the mesh size effect on the models.

Practical implications

The presented results can be useful during the design of a simulation study in a reflow oven (or in similar processes).

Originality/value

The presented results provide a completely novel approach from the aspect of 2D and 3D simulations of a convection reflow oven. The results also reveal the heat transfer differences.

Details

Soldering & Surface Mount Technology, vol. 26 no. 4
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 September 1953

D.G. Ainley

A comprehensive series of tests have been made on an experimental single‐stage turbine to determine the cooling characteristics and the overall stage performance of a set…

Abstract

A comprehensive series of tests have been made on an experimental single‐stage turbine to determine the cooling characteristics and the overall stage performance of a set of air‐cooled turbine blades. These blades, which arc described fully in Part I of this paper had, internally, a multiplicity of passages of small diameter along which cool air was passed through the whole length of the blade. Analysis of the test data indicated that, when a quantity of cooling air amounting to 2 per cent, by weight, of the total gasflow through the turbine is fed to the row of rotor blades, an increase in gas temperature of about 270 dcg. C. (518 deg. F.) should be permissible above the maximum allowable value for a row of uncoolcd blades made from the same material. The degree of cooling achieved throughout each blade was far from uniform and large thermal stresses must result. It appears, however, that the consequences of this are not highly detrimental to the performance of the present type of blading, it being demonstrated that the main effect of the induced thermal stress isapparently to transfer the major tensile stresses to the cooler (and hence stronger) regions of the blade. The results obtained from the present investigations do not represent a limit to the potentialities of internal air‐cooling, but form merely a first exploratory step. At the same time the practical feasibility of air cooling is made apparent, and advances up to the present arc undoubtedly encouraging.

Details

Aircraft Engineering and Aerospace Technology, vol. 25 no. 9
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 6 July 2018

Sam Ban, William Pao and Mohammad Shakir Nasif

The purpose of this paper is to investigate oil-gas slug formation in horizontal straight pipe and its associated pressure gradient, slug liquid holdup and slug frequency.

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Abstract

Purpose

The purpose of this paper is to investigate oil-gas slug formation in horizontal straight pipe and its associated pressure gradient, slug liquid holdup and slug frequency.

Design/methodology/approach

The abrupt change in gas/liquid velocities, which causes transition of flow patterns, was analyzed using incompressible volume of fluid method to capture the dynamic gas-liquid interface. The validity of present model and its methodology was validated using Baker’s flow regime chart for 3.15 inches diameter horizontal pipe and with existing experimental data to ensure its correctness.

Findings

The present paper proposes simplified correlations for liquid holdup and slug frequency by comparison with numerous existing models. The paper also identified correlations that can be used in operational oil and gas industry and several outlier models that may not be applicable.

Research limitations/implications

The correlation may be limited to the range of material properties used in this paper.

Practical implications

Numerically derived liquid holdup and holdup frequency agreed reasonably with the experimentally derived correlations.

Social implications

The models could be used to design pipeline and piping systems for oil and gas production.

Originality/value

The paper simulated all the seven flow regimes with superior results compared to existing methodology. New correlations derived numerically are compared to published experimental correlations to understand the difference between models.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 6
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 27 September 2011

Mohammad Asaduzzaman Chowdhury, Dewan Muhammad Nuruzzaman, Khaled Khalil and Mohammad Lutfar Rahaman

Solid thin films have been deposited on stainless steel 314 (SS 314) substrates in a chemical vapor deposition (CVD) reactor at different flow rates of natural gas mostly…

Abstract

Purpose

Solid thin films have been deposited on stainless steel 314 (SS 314) substrates in a chemical vapor deposition (CVD) reactor at different flow rates of natural gas mostly methane (CH4). The purpose of this paper was to investigate experimentally the variation of thin film deposition rate with the variation of gas flow rate.

Design/methodology/approach

During experiment, the effect of gap between activation heater and substrate on the deposition rate has also been observed. To do so, a hot filament thermal CVD unit is used. The flow rate of natural gas varies from 0.5 to 2 l/min at normal temperature and pressure and the gap between activation heater and substrate varies from 4 to 6.5 mm.

Findings

Results show that deposition rate on SS 314 increases with the increase of gas flow rate. It is also seen that deposition rate increases with the decrease of gap between activation heater and substrate within the observed range. These results are analyzed by dimensional analysis to correlate the deposition rate with gas flow rate, surface roughness and film thickness. In addition, friction coefficient and wear rate of SS 314 sliding against SS 304 under different normal loads are also investigated before and after deposition. The obtained results reveal that the values of friction coefficient and wear rate are lower after deposition than that of before deposition.

Originality/value

In this study, thin film deposition rate on SS 314 was investigated using CVD. The obtained results were analyzed by dimensional analysis to correlate the deposition rate with gas flow rate, surface roughness and film thickness. The friction coefficient and wear rate of SS 314 were also examined before and after deposition.

Details

Industrial Lubrication and Tribology, vol. 63 no. 6
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 5 December 2016

Samarth D. Patwardhan, Fatemeh Famoori and Suresh Kumar Govindarajan

This paper aims to review the quad-porosity shale system from a production standpoint. Understanding the complex but coupled flow mechanisms in such reservoirs is…

Abstract

Purpose

This paper aims to review the quad-porosity shale system from a production standpoint. Understanding the complex but coupled flow mechanisms in such reservoirs is essential to design appropriate completions and further, optimally produce them. Dual-porosity and dual permeability models are most commonly used to describe a typical shale gas reservoir.

Design/methodology/approach

Characterization of such reservoirs with extremely low permeability does not aptly capture the physics and complexities of gas storage and flow through their existing nanopores. This paper reviews the methods and experimental studies used to describe the flow mechanisms of gas through such systems, and critically recommends the direction in which this work could be extended. A quad-porosity shale system is defined not just as porosity in the matrix and fracture, but as a combination of multiple porosity values.

Findings

It has been observed from studies conducted that shale gas production modeled with conventional simulator/model is seen to be much lower than actually observed in field data. This paper reviews the various flow mechanisms in shale nanopores by capturing the physics behind the actual process. The contribution of Knudson diffusion and gas slippage, gas desorption and gas diffusion from Kerogen to total production is studied in detail.

Originality/value

The results observed from experimental studies and simulation runs indicate that the above effects should be considered while modeling and making production forecast for such reservoirs.

Details

World Journal of Engineering, vol. 13 no. 6
Type: Research Article
ISSN: 1708-5284

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Article
Publication date: 5 March 2018

Jinya Zhang, Yongjiang Li, K. Vafai and Yongxue Zhang

Numerical simulations of a multistage multiphase pump at different operating conditions were performed to study the variational characteristics of flow parameters for each…

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170

Abstract

Purpose

Numerical simulations of a multistage multiphase pump at different operating conditions were performed to study the variational characteristics of flow parameters for each impeller. The simulation results were verified against the experimented results. Because of the compressibility of the gas, inlet volume flow rate qi and inlet flow angle ßi for each impeller decrease gradually from the first to the last stage. The volume flow rate at the entrance of the pump q, rotational speed n and inlet gas volume fraction (IGVF) affect the characteristics of qi and ßi.

Design/methodology/approach

The hydraulic design features of the impellers in the multistage multiphase pump are obtained based on the flow parameter characteristics of the pump. Using the hydraulic setup features, stage-by-stage design of the multistage multiphase pump for a nominal IGVF has been conducted.

Findings

The numerical simulation results show that hydraulic loss in impellers of the optimized pump is substantially reduced. Furthermore, the hydraulic efficiency of the optimized pump increases by 3.29 per cent, which verifies the validation of the method of stage-by-stage design.

Practical implications

Under various operating conditions, qi and ßi decrease gradually from the first to the fifth stage because of the compressibility of the gas. For this characteristic, the fluid behavior varies at each stage of the pump. As such, it is necessary to design impellers stage by stage in a multistage rotodynamic multiphase pump.

Social implications

These results will have substantial effect on various practical operations in the industry. For example, in the development of subsea oilfields, the conventional conveying equipment, which contains liquid-phase pumps, compressors and separators, is replaced by multiphase pumps. Multiphase pumps directly transport the mixture of oil, gas and water from subsea oilwells through a single pipeline, which can simplify equipment usage, decrease backpressure of the wellhead and save capital costs.

Originality/value

Characteristics of a multistage multiphase pump under different operating conditions were investigated along with features of the inlet flow parameters for every impeller at each compression stage. Our simulation results have established that the change in the inlet flow parameters of every impeller is mainly because of the compressibility of the gas. The operational parameters q, n and IGVF all affect the characteristics of qi and ßi. However, the IGVF has the most prominent effect. Lower values of IGVF have an insignificant effect on the gas compressibility. Higher values of IGVF have a significant effect on the gas compressibility. All these characteristics affect the hydraulic design of the impellers for a multistage multiphase pump. In addition, the machining precision should also be considered. Considering all these factors, when IGVF is lower than 10 per cent, all the impellers in the pump can be designed uniformly. When IGVF varies from 10 to 30 per cent, the first two stages should be designed separately, and the latter stages are uniform starting with the second stage. When IGVF varies from 30 to 50 per cent, the first three stages should be designed separately, and the latter stages are going to be similar to the third stage. An additional increase in IGVF results in degeneration of the differential pressure of the pump, which will reduce the compressibility of the gas. As such, it can be deduced that only the first three stages should be designed separately, and the latter stages will be similar to the third stage. In addition, for the pump working under a lower volume flow rate than 25 m3/h, the first three stages should be designed individually while keeping the geometrical structure of the subsequent stages the same as the third stage.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

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