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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.

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.

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.

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.

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.

Powder bed fusion processes are common due to their ability to build complex components without the need for complex tooling. While additive manufacturing has gained increased interest in industry, academia and government, flaws are often still generated during the deposition process. Many flaws can be avoided through careful processing parameter selections including laser power, hatch spacing, spot size and shielding gas flow rate. The purpose of this paper is to study the effect of shielding gas flow on vapor plume behavior and on final deposition quality. The goal is to understand more fully how each parameter affects the plume and deposition process.

A filtered-photodiode based sensor was mounted onto a commercial EOS M280 machine to observed plume emissions. Three sets of single tracks were printed, each with one of three gas flow rates (nominal, 75% nominal and 50% nominal). Each set contained single-track beads deposited atop printed pedestals to ensure a steady-state, representative build environment. Each track had a set power and speed combination which covered the typical range of processing parameters. After deposition, coupons were cross-sectioned and bead width and depth were measured. Finally, bead geometry was compared to optical emissions originating in the plume.

The results show that decreasing gas flow rate, increasing laser power or increasing scan speed led to increased optical emissions. Furthermore, decreasing the gas cross-flow speed led to wider and shallower melt pools.

To the best of the authors’ knowledge, this paper is among the first to present a relationship among laser parameters (laser power, scan speed), gas flow speed, plume emissions and bead geometry using high-speed in situ data in a commercial machine. This study proposes that scattering and attenuation from the plume are responsible for deviations in physical geometry.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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 gas‐flow 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.

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.

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.

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.

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

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

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

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.

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.

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.

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.

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.

The purpose of this paper is to propose a prediction method of gas-liquid two-phase flow patterns and reveal the flow characteristics in the suction chamber of a centrifugal pump.

A transparent model pump was experimentally studied, and the gas-liquid two-phase flow in the pump was numerically simulated based on the Eulerian–Eulerian heterogeneous flow model. The numerical simulation method was verified from three aspects: the flow pattern in the suction chamber, the gas spiral length and the external characteristics of the pump. The two-phase flow in the suction chamber was studied in detail by using the numerical simulation method.

There are up to eight flow patterns in the suction chamber. However, at a certain rotational speed, only six flow patterns are observed at the most. At some rotational speeds, only four flow patterns appear. The gas spiral length has little relationship with the gas flow rate. It decreases with the increase of the liquid flow rate and increases with the increase of the rotational speed. The spiral flow greatly increases the turbulence intensity in the suction chamber.

A method for predicting the flow pattern was proposed. Eight flow patterns in the suction chamber were identified. The mechanism of gas-liquid two-phase flow in the suction chamber was revealed. The research results have reference values for the stable operation of two-phase flow pumps and the optimization of suction chambers.