Gas Flow Characteristics Research Articles

Numerical simulation of natural gas flow characteristics and hydrate formation risk in deepwater submarine pipelines

The development of flow assurance technology in submarine pipelines affects the safety, efficiency, and economy of deepwater natural gas development. In this study, in order to accurately predict the hydrate formation risk in deepwater submarine pipelines, a novel mathematical prediction model of hydrate formation risk has been established. The model has been applied and sensitivity analysis of typical factors has been carried out. The model prediction results show that: (1) Due to the low temperature of the seabed, hydrate formation region (HFR) often exists in submarine pipelines. (2) When other conditions are constant, hydrate formation region increases with the decrease in seawater temperature. (3) When other conditions are constant, the temperature drop, and the length of hydrate formation region decrease with the increase of gas transmission rate. (4) When other conditions are constant, the temperature drop, and the length of hydrate formation region decreases with the increase of gas transport temperature. (5) Reasonable setting of gas transmission temperature and gas transmission rate can help to reduce the hydrate risk and consumption of inhibitors during submarine natural gas transmission.

Theoretical analysis on macro-mesoscopic gas flow performances in gas dynamic bearing with three pads

The Reynolds equation based on the continuum medium assumption fails to meet the accuracy requirements of numerical simulation for mesoscale gas flow. In this research, the gas flow performances and bearing performances of gas dynamic bearing with three pads (GDBTPs) are theoretically analyzed from macroscopic to mesoscopic perspectives. A modified lattice Boltzmann equation is exploited considering the wall effect ψ(y/λ) with gas density ratio ρ/ρref, and the dimensionless gas flow velocity is analyzed for smooth, square cavity, half-sine asperity, triangular asperity, and a combination of surface morphologies. A modified Reynolds equation considering the gas compressibility and gas rarefaction effect is developed to study the static bearing performances of GDBTPs. Results show that the relative roughness Δh and asperities geometries are key factors to affect the mesoscale gas flow characteristics. The load-carrying capacity of GDBTPs increases with the growth of length-to-diameter ratio L/D, rotational speed ω, and eccentricity ratio ɛ and decreases with the increase of gas film thickness hg.

Gas-assisted electrospinning of high-performance ceramic fibers: Optimal design modelling and experimental results of the gas channel of the nozzle

Electrospinning (ES) of ceramic fibers has mostly remained in the research level, which can be because of the hard process and parameters controlling the low rate of production. The yield of fiber production by solution blow spinning (SBS) is exciting but the production process is unstable due to the reverse flow phenomenon. In this paper, we prepared high-performance ceramic fibers by gas-assisted electrospinning (GES), which combined the advantages of ES and SBS. Also, comprehensive numerical and experimental analysis for nanofibers produced using GES are provided. The gas flow characteristics through different parameters' nozzle were investigated numerically using computational fluid dynamics and experimentally in a custom-built gas-assisted electrospinning setup to produce SiO2 nanofibers.

Mechanical response and gas flow characteristics of pre-drilled coal subjected to true triaxial stresses

Many gas pre-drainage boreholes are generally constructed in coal seams to ensure safe underground operation. True triaxial experiments were conducted to study the mechanical response and gas flow characteristics of pre-drilled coal to reveal the in-situ behavior at pre-drilled regions in coal seams. The mechanical parameters, failure modes, and flow rate evolutions of pre-drilled coal samples were collected. The gas flow rate of pre-drilled coal samples showed an S-shaped trend with the increase of strain, and no obvious descending progress was found in the flow rate-strain curves. The typical failure mode for pre-drilled coal samples was shear-type during the true triaxial stress compression. V-shaped macro-fractures around the boreholes were observed when boreholes were perpendicular to bedding planes and parallel to face cleats. In contrast, single shear macro-fractures around the boreholes were observed when boreholes were parallel to butt cleats. The pre-drilled coal samples exhibited lower peak strength values when boreholes were parallel to butt cleats, induced by the relatively low cohesion parameter. Pre-drilled coal's initial flow rates perpendicular to bedding planes and parallel to butt cleats directions were only 33.33% and 41.67% of values measured along face cleats. More complex macro-fractures were formed, and up to a 39.30% decrease in strength was observed in pre-drilled coal samples under true triaxial unloading stress paths. The variations in volumetric strain level and the flow rate evolution were further discussed with an anisotropic conceptual failure model. These mechanical responses and flow characteristics of pre-drilled coal would guide the design of borehole layout and prevention of coal dynamic disasters.

Experimental and modeling study of gas flow characteristics in the compressible powder bed during gas pressurization

Gas pressurization of powder beds is important in some industrial chemical processes. This paper describes an experimental and modeling study of gas flow characteristics in the compressible powder bed during gas pressurization. Powder compression characteristics under gas pressurization and gas permeation characteristics in the powder are obtained. The average compression ratios of the coal powder bed are larger than that of the glass powder bed. The source of this gas-induced compression and the corresponding characteristics are analyzed. The pressure drop across the powder bed increases to a maximum and then decreases during pressurization. The mechanisms for the pressure drop evolution are discussed. Furthermore, a model considering both the porosity change and the effect of the particle shape is proposed to describe the gas flow in the compressible powder bed during pressurization. The model provides acceptable predictions for the pressure drop in the compressible powder bed.

Characteristics of Gas Seepage and Pore Structure Response in CO2-ECBM Process of Low Permeability Coal Seam

CO2-ECBM is a method of enhanced coalbed methane extraction followed by cutting greenhouse gas emissions and new energy development. In order to reveal the characteristics of gas flow in porous media and the pore structure response characteristics of coal rocks, the experiments were carried out to simulate the process of CO2 displacement of N2 at a buried depth of 900 m, including monitoring the changes in gas permeability and strain of coal samples along with a comparison of the pore structure of low-temperature liquid nitrogen adsorption on coal samples both before and after displacement were both done. The findings of the experiment are listed below. The N2 permeability of the LiuZhuang sample ranges from 0.0008mD to 0.0014mD, whereas the permeability of QiDong is around 0.0003mD. With an increase in gas injection duration and an expansion of the coal matrix for N2 adsorption, the permeability steadily decreases. The efficient stress compression of the coal pore fracture structure during sample preparation and testing avoids the visible fracture region, which results in poor permeability. The displacement stages of CO2 can be divided into three phases. Free nitrogen flows from the end of the position and the permeability diminishes during the phase of free nitrogen. When CO2 is introduced into the penetration stage, the permeability tends to rise, however when there is no penetration, the permeability test values are frequently low. During the CO2 steady displacement phase, gas permeability gradually declines. Axial and radial strains are progressively raised during the initial stage of the CO2 injection whereas they are gradually reduced during the initial stage of the N2 injection. While CO2 is continuously supplied through the coal body stage, there are modest axial and radial strain changes. The axial and radial stresses are stabilized by the CO2 displacement. The overall pore volume of the coal significantly rises following the displacement. The increase part of the pore volume is primarily focused on the pore of absorption and filling (aperture < 10nm), whereas the decreased part is mainly concentrated in the diffusion pore of the Fick type and the permeability part (aperture > 50nm). The increased in pore volume ratio surface area is centered mostly in the fill pore region (aperture 10 nm) and is four times greater than it was before the displacement. The CO2 injection exerts an expansion impact on the adsorptionfilled and diffusion pores during the CO2-ECBM process, whereas the compression effect on the percolation pores results in a reduction in permeability.

Improving the energy-efficiency of small-scale methanol production through the use of microturboexpander units

The issue of improving the energy-efficiency of container-based gas chemical plants for methanol production in field conditions is considered. The relevance of the direction is determined by the necessity for development of remote Arctic hydrocarbon fields. The object of research is energy-efficient conversion of waste gases energy and surplus thermal energy in small-scale system of methanol production using technology of synthesis gas generation by non-catalytic partial oxidation of natural gas. Approaches to the design and analysis of structural solutions for microturboexpander units are considered. A technique combining traditional approaches to the calculation of equipment and modeling by the finite element method in ANSYS is proposed. The developed methodology facilitates calculation of design parameters for microturboexpanders and allows taking into account peculiarities of working medium, thermobaric conditions and gas flow characteristics.

Heat transfer and pyrolysis gas flow characteristics of light-weight ablative thermal protection system in the blunt body

Thermal protection system (TPS) is the critical system to protect the structure and electronic components of hypersonic vehicles from aerodynamic heating. Since the blunt body suffers the most severe thermal environment in a flight vehicle, the design of TPS for the blunt body is crucial. To investigate the thermal performance of the light-weight ablative material in the blunt body, a multi-dimensional thermal response model is proposed considering heat transfer, pyrolysis gas flow, and gas blowing effect. The characteristics of heat diffusion, pyrolysis process, gas flow, and the effect of pyrolysis gas blowing are investigated. It shows that the developed model can accurately predict temperature and gas flow. The temperature and charred thickness at the stagnation point are the largest, decrease along the surface of the sphere nose, and keep almost the same at the cone. Due to the surface pressure distribution, a large part of the pyrolysis gas in the sphere nose flows through the ablative material and injects into the air at the sphere-cone junction. In contrast, the gas at the cone flows vertically to the cone surface. The gas flow rate and pressure decrease as time elapses. Moreover, gas blowing mainly influences the thermal response near the sphere-cone junction, leading to a minimum blowing factor of 0.965 and a max temperature reduction of 7.4% at 100s. The effect of gas blowing is enhanced with the increase of phenolic resin content. This study deepens the understanding of the thermal performance of light-weight ablative material in the blunt body and guides the ablative thermal protection design.

CFD Analysis of Exhaust System of a Formula Racing Vehicle

This study investigates about the designing and Computational Fluid Dynamics (CFD) analysis of the exhaust system of a formula student vehicle. Based on FSAE rules KTM Duke 390 engine is used and the noise level is to keep below 110 dB. The main aim of the design is to have a smooth flow exhaust gases without restriction to increase engine efficiency and to keep minimal backpressure. An absorptive type of muffler is finalized to attenuate the sound levels. Based on three different equations, exhaust runner dimensions are calculated and CFD analysis is performed to choose the optimum runner dimensions. Using ASHRAE guidelines muffler dimensions range is calculated. Using Ricardo software based on effective volumetric efficiency analysis, volume of muffler that fits in ASHRAE dimension range was finalized. Both runner and muffler are analyzed and CFD analysis was carried out which resulted in streamline velocity profile of the exhaust gas and acceptable values of pressure, velocity and velocity streamline was found. CFD analysis of the full exhaust system was carried out to understand the flow characteristics of exhaust gases.

Pore-Scale Simulation of Gas and Water Two-Phase Flow in Rough-Walled Fractures Using the Volume of Fluid Method

The gas and water flow behavior in rough-walled hydrophilic fractures at the pore scale is crucial for understanding the gas production characteristics of naturally fractured formations. This paper presents a systematic analysis of the gas and water flow characteristics in both the single-fracture and Y-shaped junction fracture models using the volume of fluid (VOF) method. Numerical simulations showed that the gas/water rate ratio is the most significant factor influencing gas bubble/slug geometry, phase distribution, and saturation. The effect of fracture roughness and tortuosity is less significant than the gas/water ratio, whereas the total fluid rate has a negligible effect. For Y-shaped junction models, the phase distribution and referential pathways are predominantly controlled only by the channel aperture ratio, whereas the effect of the intersecting angle and fluid flow rate can be neglected.

Computational study of gas flow characteristics when using intra-nozzle interceptors for thrust vector control

This article proposes the use of cylindrical nozzle interceptors (probes) as an alternative method of rocket engine thrust vector control, which can replace traditional thrust vector control systems. The objective of this paper was to perform a three-dimensional CFD simulation of the gas flow in a rocket engine nozzle with a rod interceptor taken out of the wall without secondary injection, analyzing the calculated flow data and estimating the lateral force. The simulations will be performed in steady-state mode. In the CFD simulations, velocity distribution contours were obtained on the symmetry plane for all positions and values of the interceptor height.

A new calculation method and model of hydrate slurry flow of the multiphase pipeline in deep water gas field

The transportation environment of multiphase pipelines in deepwater gas fields is likely to cause the problem of hydrate flow safety. Aiming at the gas-liquid-solid three-phase flow problem containing hydrate, a hydrate slurry flow model for a multiphase pipeline in a deep-water gas field was developed based on the two-fluid model coupled with the population balance equation, and a mesh was carried out for the axial distance of pipeline and size difference of hydrate particles to obtain a transient solution. The multiphase flow characteristics of the pipeline are simulated upon engineering scale, the transient flow characteristics of gas and liquid phases, the aggregation and fragmentation characteristics of hydrate particles, and the coupling interaction between them were studied, which lays the foundation for further research on the characteristics of hydrate particle deposition and blockage based on particle size distribution. This study provides support for the safety of hydrate flow in multiphase pipelines in deepwater gas fields.

Research on purge gas flow characteristics in different pebble bed structures for fusion blanket

Lithium ceramics are equipped as pebble beds in the solid-type breeding blanket, with the tritium purge gas flowing through it at a low velocity and pressure to achieve tritium transport. This paper investigated the effects of friction coefficient on the packing and purge gas flow characteristics of the pebble bed. Furthermore, this research assessed the purge gas flow characteristics in the pebble bed and verified the dependency of the flow characteristics on the configuration of pebble beds. The discrete element method (DEM) was selected to analyze the packing characteristics of pebble beds with different friction coefficients. The simulation component was benchmarked. The computational fluid dynamics method was used to construct and simulate various pebble bed models. A series of numerical analyses revealed that particles with a lower friction coefficient are more beneficial in the pebble beds which could benefit the tritium exaction. The pressure drop is related to both the purge gas flow velocity and the structure of the pebble beds. The pressure drop increases with the decrease in the friction coefficient, whereas the proportion of mass flow in the internal region increases with the increase in the friction coefficient. Although a denser structure of pebble beds is preferable for high tritium breeding rates, it could generate considerable flow resistance inside the pebble beds, causing tritium retention. This research can serve as a foundation for resolving the practical challenges such as purge gas flow, fragmentation and cracks, pebbles resettlement, among others, in the design of the blanket system.

MD-CFD simulation on the miscible displacement process of hydrocarbon gas flooding under deep reservoir conditions

In this study, the microscopic miscible mechanism and the macroscopic flow characteristics of hydrocarbon gas and crude oil are investigated by combining molecular dynamic (MD) simulation and computational fluid dynamics (CFD) simulation. Under the deep reservoir conditions, the MD results manifest that compared with water flooding, hydrocarbon gas flooding could be more miscible with oil molecules, due to their stronger interactions. Based on the calculated density, viscosity and diffusion coefficient by the MD method, the CFD model is constructed to study the miscible displacement process of hydrocarbon gas flooding at 413 K and 50 MPa. The CFD results illustrate that the ability of oil displacement of different injection mediums follows the order of methane > ethane > propane > water. Because of the oil-gas miscibility, hydrocarbon gas could weaken the negative effect of the porosity and the wettability, leading to the decrease of the residual oil (RO) content. Moreover, the multi-component injection method is proposed for multi-scale porous media including nano-pore and micron-pore with small pore size. Notably, the variable velocity injection method is firstly designed for enhanced oil recovery. Compared with the constant low-velocity method, the RO content and the injection time of this method are effectively reduced by 12.4% and 66.7%, respectively.

Comparative Analysis of Riser Base and Flowline Gas Injection on Vertical Gas-Liquid Two-Phase Flow

Gas injection is a frequently used method for artificial lift and flow regime rectification in offshore production and transportation flowlines. The flow behaviour in such flowlines is complex and a better understanding of flow characteristics, such as flow patterns, void fraction/hold up distributions and pressure gradient is always required for efficient and optimal design of downstream handling facilities. Injection method and location have been shown to strongly affect downstream fluid behaviour that can have important implications for pumping and downstream facility design, especially if the development length between pipeline and downstream facility is less than L/D = 50 as reported by many investigators. In this article, we provide the results of an experimental investigation into the effects of the gas injection position on the characteristics of the downstream upwards vertical gas flow using a vertical riser with an internal diameter of 52 mm and a length of 10.5 m. A horizontal 40-m-long section connected at the bottom provides options for riser base or horizontal flow line injection of gas. The flowline gas injection is performed 40 m upstream of the riser base. A 16 by 16 capacitance wire mesh sensor and a gamma densitometer were used to measure the gas-liquid phase cross-sectional distribution at the riser top. A detailed analysis of the flow characteristics is carried out based on the measurements. These include flow regimes, cross-sectional liquid holdup distributions and peaking patterns as well as analysis of the time series data. Our findings show that flow behaviours differences due to different gas injection locations were persisting after a development length of 180D in the riser. More specifically, core-peaking liquid holdup occurred at the lower gas injection rates through the flowline, while wall-peaking holdup profiles were established at the same flow conditions for riser base injection. Wall peaking was associated with dispersed bubbly flows and hence non-pulsating as against core-peaking was associated with Taylor bubbles and slug flows. Furthermore, it was found that the riser base injection generally produced lower holdups. It was noted that the circumferential injector used at the riser base promoted high void fraction and hence low liquid holdups. Due to the bubbly flow structure, the slip velocity is smaller than for larger cap bubbles and hence the void fraction is higher. The measurements and observations presented in the paper provides valuable knowledge on riser base/flowline gas introduction that can directly feed into the design of downstream facilities such as storage tanks, slug catchers and separators.

Study on flow characteristics of natural gas containing CO2 invading wellbore during drilling

The dissolution of invaded gas in the drilling fluid during drilling results in an increase in the gas invasion concealment. This is of great significance for the development of acid gas reservoirs to determine the solubility change and multiphase flow law in an annulus after invasion by natural gas with high CO 2 content. In this study, control equations of gas–liquid flow during drilling gas invasion are established considering the influence of gas solubility. For the prediction of gas solubility, the interaction parameters of CH 4 and water in the Peng–Robinson equation of state are optimised to establish a gas solubility prediction model. The solubility of natural gas with high CO 2 content in water and brine solution is measured through phase-equilibrium experiments. The results indicate that the newly optimised solubility model can accurately predict the solubility of CH 4 and CO 2 in water, and the prediction error is within 5%. Moreover, the prediction error for the solubility of CH 4 and CO 2 mixed gas is within 15%. The analysis of gas invasion in example engineering drilling applications reveals that an increase in the CO 2 content in the invaded gas leads to a slow change in the mud-pit increment, and the concealment strengthens as the distance between the gas-migration front and the wellhead increases. Gas solubility has a significant impact on the monitoring of gas invasion in low permeability reservoirs.

Design and multi-objective optimization of a new annular constructal bifurcation Stirling regenerator using response surface methodology

The irreversible losses such as the flow loss and axial heat conduction loss in traditional porous regenerators have limited the specific power and thermal efficiency of Stirling engines to a great degree. Thereby, the objective of this paper is to design and optimize a novel annular constructal bifurcation regenerator for diminishing the flow and axial heat conduction losses in the regenerator based on constructal concept and response surface methodology. First, the bifurcation type structure units with an inclined angle to the flow direction and the layered approach were applied to construct the regenerator matrix. Thereafter, the numerical simulations were employed to investigate the gas flow and heat transfer characteristics of the constructal bifurcation regenerator. Based on the numerical data, the quadratic polynomial regression models between the geometric parameters and the regenerator performance were established using response surface methodology, and the specific effects of the geometric dimensions were analyzed via 2-D and 3-D response surface plots. Subsequently, a multi-objective optimization was conducted to minimize the flow resistance and maximize the heat transfer rate by genetic algorithm. A most eclectic solution with the global friction factor f = 3.478 and the number of heat transfer units NTU = 1.135 was selected from the optimal Pareto front. Finally, the overall performance of the constructal bifurcation regenerator was compared with that of the porous regenerator and the parallel geometry regenerator. The results indicate that a low flow resistance, low axial heat conduction, and high thermal performance are obtained by the constructal bifurcation regenerator. Therefore, it is reasonable to conclude that the annular constructal bifurcation regenerator achieves a high comprehensive performance, with the potential to improve the performance of Stirling engines. The findings of this paper may provide some new ideas and guidelines for the design and optimization of the regenerator structures.

Research on the gas migration trend and mechanism of the transition flow regime in coal based on MRT-LBM simulation

In order to reveal the process and mechanism of gas flow in a low-permeability coal seam, a new multiple-relaxation-time lattice Boltzmann method (MRT-LBM) model of gas migration in coal micro/nanopores based on Langmuir monolayer adsorption theory, the slip boundary scheme and Bosanquet effective viscosity was established. The software MATLAB was used to carry out the simulation study of uniform pore gas flow based on the MRT-LBM model, and the results were compared and verified with the porous anodic alumina membrane gas flow experimental results. On this basis, the gas flow in coal pores with different micro/nanopore sizes considering adsorption was simulated. The results show that the dimensionless permeability coefficient increases with decreasing pore size under the same pressure, which reflects the subsequent enhancement of the microboundary constraint effect and reveals that the pore system becomes the main controlling factor of coal seam permeability within the coal matrix in the middle and late stages of coal seam gas extraction, while the role of the microboundary constraint effect needs to be considered. The gas adsorption layer weakens the pore gas flow capacity, but for pores with a radius greater than 16 nm, the apparent change in permeability caused by the adsorption layer is less than 5%, and the adsorption effect can be ignored. N2, CH4, and CO2 enter the transition flow regime under different pressure conditions; with gas extraction, the gas pressure decreases, and the difference in the gas flow characteristics of the three gases increases.

Effects of Flow Coefficient on Turbine Aerodynamic Performance and Loss Characteristics

The effects of flow coefficient on the gas flow and loss characteristics inside the high-pressure turbine is investigated using a numerical simulation. In this paper, the midspan of the first stator of the “Lisa” 1.5 stage high-pressure turbine is used as a prototype to obtain different flow coefficients by changing the stagger angle and the exit angle. The boundary conditions of all cases are consistent with the experimental data of “Lisa”. The results show that the flow coefficient is decreased from 0.478 to 0.374 as the stagger angle is varied from 44.2° to 56.2° and from 0.630 to 0.341 as the exit angle is varied from 63° to 75°. Large stagger angle or large exit angle both cause an increase in turbine aerodynamic losses. The similarity between the two is that both cause enhanced effect of transverse secondary flow in the passage. The difference is that with large stagger angle, the adverse pressure gradient affects a large area, resulting in large boundary layer losses; with large exit angle, the passage vortex is weakened but with a large influence area.

Investigation of shale gas flows under confinement using a self-consistent multiscale approach

This report summarises our recent findings on non-ideal gas flow characteristics in shale nanopores facilitated by our strongly-inhomogeneous kinetic model. As there are a significant portion of nano-scale pores in shale, gas molecule size is comparable to both the gas mean free path and the characteristic length of the flow domain, and various factors including fluid-solid and fluid-fluid interactions, pore confinement, surface roughness, and non-equilibrium effect need to be considered in a self-consistent manner. These factors are either considered in the governing equation according to the dense gas and mean-field theories, or through the boundary condition based on molecular dynamics simulations. Our kinetic model results are consistent with the molecular dynamics data at the molecular scale and converge to the continuum predictions when pores become large. This model serves as an accurate tool to investigate multiscale transport of shale gas and is helpful for upscaling from the microscopic to continuum levels with a firm theoretical basis. Cited as: Shan, B., Ju, L., Guo, Z., Zhang, Y. Investigation of shale gas flows under confinement using a self-consistent multiscale approach. Advances in Geo-Energy Research, 2022, 6(6): 537-538 . https://doi.org/10.46690/ager.2022.06.11