Mechanism Of Two-phase Flow Research Articles

Study on mechanisms of two-phase flow in digital rocks: a case of irreducible storage efficiency of CO2

Study on mechanisms of two-phase flow in digital rocks: a case of irreducible storage efficiency of CO2

Lagrangian coherent structures and mass transport in T-junctions

The mechanisms of air water two-phase flow and phase distribution in T-junctions are studied using Lagrangian methods such as the Lagrangian Coherent Structure (LCS) and the particle tracking method. First, the air water two-phase flow field in the T-junctions is numerically simulated. In particular, characteristics such as phase distribution, pressure distribution, and streamline diagrams in mixing and separating regions are captured. Then, the ridges in finite-time Lyapunov exponent fields are extracted as LCSs. The mass transport process is discussed through contrasting the phase distribution and the LCSs. In the mixing region, the air water interfaces almost coincide with the attracting LCSs. At the same time, the attracting LCSs can demonstrate the evolution process of the vortices, which is crucial for the mixing of phases. In the separating region, employing the particle tracking method reveals that particles are entrained by the most attractive LCSs, while repelling LCSs demarcate regions with distinct flow directions, thereby playing a pivotal role in phase separation. In summary, we investigated mass transport in air water two-phase flow in T-junctions from the perspective of LCSs.

Analysis and identification of gas-liquid two-phase flow pattern based on multivariate multi-scale dispersion entropy and interconnected dispersion pattern complex network

Gas-liquid two-phase flow is polymorphic and unstable. The investigation of the flow behavior of two-phase flow is vital for the application of gas-liquid transport in ocean engineering areas. We propose an analytical framework that combines multivariate multi-scale dispersion entropy (mvMDE) and interconnected dispersion pattern complex networks (IDPCN) for flow patterns. The resistance sensor array is used to capture the two-phase flow fluctuation signals in the riser, and the dimensionally reduced time series are nonlinearly mapped into a multivariate symbolic sequence. The mvMDE of the multivariate symbolic sequence is computed to measure the complexity of the flow pattern signals at the level of amplitude variation. In addition, a new multis-cale complex network based on the symbolic sequence is proposed to study the pseudo spatial coupling behavior of flow patterns. The evolution of the flow pattern from bubble to churn flow is quantitatively characterized using the mean value of the complex network indices in the optimal scale range. Finally, we construct the joint plane of mvMDE and two network indices to complete flow pattern identification. The research results show that the framework can effectively fuse multi-channel flow pattern information at different time scales to reveal the evolution mechanism of gas-liquid two-phase flow.

Analysis of stability and internal flow mechanisms in spiral annular flow with different swirlers

Spiral annular flow within ducts is widely utilized in modern industry, with the swirler serving as a critical component in generating such flow patterns. The structure of the swirler significantly influences the generation and stability of the spiral annular flow. This study selected four different swirler structures with outstanding performance from previous research and analyzed their characteristics through visual image processing combined with numerical simulations. By analyzing the amplitude information of the wave fluctuations in the annular swirling flow liquid film under different operating conditions using probability density functions, it was found that the swirler A(Flat-vane swirler) and swirler B(Flat-vane swirler with hub) produced smaller fluctuations in the annular swirling flow liquid film, indicating better stability compared to the swirler C(Arc-vane swirler) and swirler D(Spiral-vane swirler), which exhibited poor performance. Combining the numerical simulation results with the analysis of the internal mechanism of the swirlers, it was discovered that within the swirler A and swirler B, the fluid between the swirler vanes experienced a larger pressure gradient, resulting in phenomena such as “jump” and “pull” under this pressure gradient. This, in turn, contributed to the generation of greater tangential velocity and radial pressure gradient after the fluid exited the swirler. Due to the influence of the swirler structure, the swirler A and swirler B did not completely separate the fluid region into four independent spaces. Instead, in the central connection area of the rear section of the swirler, the gas phase components aggregated earlier, greatly promoting the downstream generation of spiral annular flow. This study analyzed the two-phase flow process and mechanism inside the swirler, filling a gap in previous research and providing important references for the optimization and selection of swirlers.

Study on mechanism of unsteady gas-liquid two-phase flow in liquid-ring vacuum pump

To investigate the gas-liquid two-phase flow mechanism in liquid-ring vacuum pump, the large-eddy simulation coupled with volume-of-fluid method (LES-VOF) was used to numerically simulate the unsteady gas-liquid flow characteristics in pump. The structure of gas-liquid flow within pump and its dynamic evolution characteristics were studied, and the hydraulic excitation characteristics induced by gas-liquid flow were analyzed. The result shows that the channel vortex inside the impeller on the pump suction side gradually flows out of the flow passage with the rotation of the impeller, and continuously mixes with the wake vortex at the outlet of the impeller and the separation vortex at the inner wall of the casing. The evolution and development of vortex structures with different intensities and scales near the inner wall of the suction side casing have a relatively large contribution to pressure fluctuation. The wake vortex at the impeller outlet of the exhaust side gradually enters the flow passage and dissipates gradually with time. There is an obvious high-intensity backflow vortex in the exhaust section due to the pressure difference between the flow channels near the leading edge of the exhaust port, which leads to obvious rotor-stator interaction in the exhaust section.

A modified comprehensive prediction model for wellbore temperature-pressure field and liquid loading of gas wells

Wellbore liquid loading is a severe problem in the late stage of natural gas production, and precise prediction of liquid loading is helpful for taking dewatering measures timely to avoid the related hazards. Based on the flow and heat transfer mechanisms of gas-liquid two-phase annular flow in wellbore, a new model for calculating temperature and pressure field of the gas well considering the effects of the velocity difference between the gas core and liquid film and the migration of liquid droplets was established first, which laid a foundation for the prediction of liquid loading in the whole wellbore. Then, based on the flow mechanism of liquid film, a liquid loading prediction model for the whole wellbore of gas well was established, with the zero shear force between tubing wall and liquid film under low liquid holdup and the critical liquid holdup of liquid film bridging and plugging gas core taken as criteria for judging liquid loading, and the coupling solution method for the above model was worked out. Production data pairs of gas wells were used to verify the reliability of the model. The results show that our model can accurately calculate the wellbore temperature and pressure of liquid-producing gas wells. The temperatures predicted by the model have a maximum relative error of 11. 86% and an average relative error of 5. 96%, while the pressures predicted have a relative error range from 0. 09% to 8. 42%. In terms of prediction accuracy and prediction error of gas well liquid loading state, the modified model has much more precise prediction results of liquid loading than three classical liquid loading models. Finally, the sensitivity analysis of liquid loading was carried out with an example. The research results can provide theoretical support for the early prediction of liquid loading and dewatering process in liquid-producing gas wells.

Numerical Modeling of Shale Oil Considering the Influence of Micro- and Nanoscale Pore Structures

A shale reservoir is a complex system with lots of nanoscale pore throat structures and variable permeability. Even though shale reservoirs contain both organic and inorganic matter, the slip effect and phase behavior complicate the two-phase flow mechanism. As a result, understanding how microscale effects occur is critical to effectively developing shale reservoirs. In order to explain the experimental phenomena that are difficult to describe using classical two-phase flow theory, this paper proposes a new simulation method for two-phase shale oil reservoirs that takes into account the microscale effects, including the phase change properties of oil and gas in shale micro- and nanopores, as well as the processes of dissolved gas escape, nucleation, growth and aggregation. The presented numerical simulation framework, aimed at comprehending the dynamics of the two-phase flow within fractured horizontal wells situated in macroscale shale reservoirs, is subjected to validation against real-world field data. This endeavor serves the purpose of enhancing the theoretical foundation for predicting the production capacity of fractured horizontal wells within shale reservoirs. The impact of capillary forces on the fluid dynamics of shale oil within micro- and nanoscale pores is investigated in this study. The investigation reveals that capillary action within these micro- and nanoscale pores of shale formations results in a reduction in the actual bubble point pressure within the oil and gas system. Consequently, the reservoir fluid persists in a liquid monophasic state, implying a constrained mobility and diminished flow efficiency of shale oil within the reservoir. This constrained mobility is further characterized by a limited spatial extent of pressure perturbation and a decelerated pressure decline rate, which are concurrently associated with a relatively elevated oil saturation level.

Study on the mechanism of gas-water two-phase flow in carbonate reservoirs at pore scale

Study on the mechanism of gas-water two-phase flow in carbonate reservoirs at pore scale

Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway: The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents. An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system. We investigated the release characteristics of main energy sources in coal seam, and obtained the dynamic characteristics of outburst two-phase flow in a roadway. Additionally, we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure. The results indicate that the outburst process exhibits pulse characteristics, and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon. The outburst energy is released in stages, and the elastic potential energy is released in the vertical direction before the horizontal direction. In a straight roadway, the impact force oscillates along the roadway. With an increase in the solid–gas ratio, the two-phase flow impact force gradually increases, and the disaster range extends from the middle of the roadway to the coal seam. In the area near the coal seam, the disaster caused by the two-phase flow impact is characterized by intermittent recovery. In a bifurcated roadway, the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow, and the impact force tends to weaken with increasing solid-gas ratio. The impact force is asymmetrically distributed; it is higher on the left of the bifurcated roadway. With an increase in the solid-gas ratio, the static pressure rapidly decreases, and the bifurcated structure accelerates the attenuation of static pressure. Moreover, secondary acceleration is observed when the shock wave moves along the T-shaped roadway, indicating that the bifurcated structure increases the shock wave velocity.

Theoretical analysis of threshold pressure in tight porous media under stress

The threshold pressure is critical to characterizing multi-phase nonlinear flow through tight porous media under effective stress. Due to the complex and heterogeneous pore structures, the essential controls on the threshold pressure of tight porous media are not determined. In this study, based on the fractal theory, a theoretical model for the threshold pressure of gas–water two-phase flow through tight porous media is proposed. The derived model considers the effective stress, pore structures, gas–water capillary pressure, and boundary layer. The predicted threshold pressure from the developed model is in good agreement with the available experimental results, which validates the model. Moreover, based on the derived model, the effects of relevant parameters (e.g., gas–water surface tension, contact angle, initial porosity, and elastic modulus) on the threshold pressure are studied. Under a given effective stress, threshold pressure decreases as the initial porosity (or elastic modulus) increases. However, threshold pressure increases with the increase in gas–water surface tension (or contact angle). In addition, a positive relationship exists between threshold pressure and water saturation in tight porous media. From a practical standpoint, this model is of great significance in predicting threshold pressure and researching on the gas–water two-phase flow mechanism in tight sandstone gas reservoirs.

Impact of Crossflow and Two-Phase Flow on Gas Production from Stacked Deposits

The gas production from stacked gas deposits with coalbed, shale, and tight sandstone reservoirs in the coal measure is an effective new technology to enhance per well gas production. However, previously developed numerical models for stacked gas deposits usually target one or two reservoir types. The contribution and impact mechanism of crossflow and two-phase flow on gas production from stacked gas deposits are unclear for the stacked gas deposits with coalbed, shale, and tight sandstone reservoirs in the coal measure. This paper develops a numerical simulation model for the gas production from stacked deposits with shale, coalbed, and tight sandstone reservoirs. This numerical simulation model considers the two-phase flow, gas diffusion in different porosity, pore deformation, and interlayer crossflow. After verification with available data from the literature, this numerical simulation model is used to explore the effects of crossflow across interlayers and two-phase flow on gas transport and production efficiency. The simulation results show that the main sources of gas production from stacked deposits are shale and coalbed reservoirs. The gas in these two reservoirs can be rapidly transported to the wellbore through the tight sandstone reservoir. The gas production from stacked deposits will be underestimated without the interlayer crossflow and overestimated if the two-phase flow is ignored. The gas production efficiency can be effectively improved through the enhancement of the crossflow rate at the interlayer and the decrease of the water saturation in the reservoir.

Interfacial wave of the gas-liquid two-phase flow in unsaturated reservoir pores

Unsaturated reservoir pores exist widely in porous self-lubricating materials for the continuous consumption of lubricant. The complex gas-liquid two-phase flow behavior in the pores significantly affects the self-lubricating performance. In this paper, the two-phase flow model in unsaturated pores was established based on the Couple Level Set and Volume of Fluid method. Two kinds of porous materials with significantly different wettability, stainless steel and polytetrafluoroethylene (PTFE), were concerned. The two-phase flow behaviors were investigated to reveal the flow mechanism in the unsaturated pores. The different flow behaviors caused by the wettability of materials were quantitative characterization. Results show that, the gas rises with a convex interface in the stainless steel pore, and the bubble is generated after the contact line is pinned on the edge of the pore at 35 ms. While in the PTFE pore, the gas rises with a concave interface. And the gas profile changes from concave to convex after the contact line is pinned at 32 ms. In the two pores, the gas-liquid interface fluctuates periodically. In the hydrophilic stainless steel pore, the fluctuation amplitude decreases and finally tends to be stable with the increase of time. In the hydrophobic PTFE pore, the interface has constant fluctuation amplitude for the attraction between gas and the hole wall. The fluctuation of the gas-liquid interface has an important influence on the flow state of the lubricant film. The results help to clarify the two-phase flow mechanism within unsaturated pores, and provide guidance for the self-lubrication design of the porous materials.

Influence mechanism of brine-gas two-phase flow on sealing property of anisotropic caprock for hydrogen and carbon energy underground storage

As the simplest saturated hydrocarbon, methane is an important hydrogen and carbon energy. The stability and sealing of caprock are keys to ensure the safe storage of energy in the process of hydrogen and carbon energy underground storage. A fully coupled two-phase flow model is established to analyze the migration mechanism of methane in caprock. This model considers the characteristics of dual porosity medium composed of caprock fractures and matrix, including the seepage of methane and brine. In the model, the replacement process of methane and brine exists in the fracture network, and the dynamic adsorption desorption process of methane exists in the matrix. Under the action of tectonic stress, obvious differences are observed in the fracture and permeability in different directions. All these characteristics are considered in the fully coupled two-phase flow model. The restraining and strengthening effects of caprock in the process of methane leakage are analyzed. The results show that the gas induces the adsorption expansion of the caprock matrix and reduces the fracture opening and permeability of the caprock. With the gradual invasion of gas into the caprock, the sealing characteristics of caprock show the evolution of self-inhibition first and then self-enhancement. With the increase in dip angle, gas tends to invade vertically rather than horizontally. Realizing gas–brine replacement is easier with the existence of large fractures. This study provides an effective numerical analysis method, which can be used to evaluate the sealing efficiency in the caprock in underground methane storage.

Numerical simulation of two-phase evaporation and condensation

The evaporation and condensation mechanism of two-phase flow is studied. The Euler-Euler pattern is used to express the evaporation and condensation properties of two-phase flow. The research shows that the tracking program can accurately track the interface. The thermal resistance on the confluence of the condensation part and insulation part becomes larger. The working fluids have significant influence of two-phase.

Dissipative Particle Dynamic Simulation of Oil-Water Two-Phase Flow in Quartz Slits

Aiming to study the characteristics and mechanism of oil-water two-phase flow, based on the method of dissipative particle dynamics (DPD), meso-scale models of pressure-driven flow in quartz slits with width of 5-15 nm were simulated. Water is the driving phase. The results show that, as the liquid flew, it stratified gradually. The stratification came earlier as the width, and the driving force increased. The flow in slit of 5 nm was slug flow, while velocity profiles in other models showed parabolic characteristics. When the liquid stratified, the velocity gradient in the near-wall area decreased as a result of the low momentum exchange rate between from water to oil. The density peaks of fluid appeared at the fluid-solid interface and the oil-water interface, caused by the fluid-solid interaction force and the oil-water repulsion, respectively. The oil phase showed stronger aggregation due to the attractive force from the wall. When the water saturation was 25%, the water phase was a water droplet surrounded by oil. When the water saturation was 75%, oil and water stratified. As the repulsive force between the two phases decreased, the surface tension decreased, the mixing degree increased, and the parabolic characteristics of the velocity profile were more obvious.

Research on methane hydrate formation in porous media with gas–water two-phase flow

The study of hydrate formation in porous media is crucial for the efficient production of natural gas hydrate. Current research on gas hydrate formation in porous media has primarily focused on the static state. A prediction model of hydrate formation under the condition of gas–water two-phase flow was established by combining the heat transfer and gas–water two-phase flow mechanisms in porous media. Methane hydrate formation in quartz sand was experimentally investigated under a gas–water two-phase flow. The results revealed an obvious pressure difference with hydrate formation at different positions; the pressure difference increased with time, which can be used as an important basis to assess the distribution of flow obstacles in porous media. COMSOL Multiphysics was used to solve the proposed model, and the accuracy of the model prediction results was verified using the experimental data. Further, the hydrate formation process and evolution law in the experiment were simulated and inverted. Flow parameters, such as pressure, hydrate saturation, and water saturation, presumably exhibit non-uniform distributions with the formation of hydrates in porous media. The longer the time, the more distinct the non-uniform distribution of the aforementioned parameters and the higher the risk of flow obstacles in porous media. This study provides an important theoretical basis for the efficient development of natural gas hydrate in the future.

Research Progress on Numerical Simulation of Heterogeneous Flow Resistance in Sludge Conveying System

Sludge pipeline transportation is increasingly used in different fields. Flow resistance is an important influencing factor in the pipeline transportation of solid-liquid two-phase flow slurry, and studying its characteristics is of great significance for optimizing pipeline design, reducing pipeline erosion and wear, and reducing transportation energy consumption. In view of the complexity of sludge as the resistance characteristics of solid-liquid two-phase flow, it is often necessary to analyze the inline mechanism of solid-liquid two-phase flow in slurry with the help of high-precision turbulent flow model in computational fluid dynamics (CFD), which has become the research focus of heterogeneous solid-liquid two-phase flow pipeline transportation. This paper analyzes and summarizes the CFD simulation status of heterogeneous solid-liquid two-phase flow resistance in pipelines, points out the future research direction, and provides reference for the analysis of heterogeneous flow resistance of sludge pipeline transportation and the optimization design of conveying system.

Characterizing gas-liquid two-phase flow behavior using complex network and deep learning.

Gas-liquid two-phase flow is polymorphic and unstable, and characterizing its flow behavior is a major challenge in the study of multiphase flow. We first conduct dynamic experiments on gas-liquid two-phase flow in a vertical tube and obtain multi-channel signals using a self-designed four-sector distributed conductivity sensor. In order to characterize the evolution of gas-liquid two-phase flow, we transform the obtained signals using the adaptive optimal kernel time-frequency representation and build a complex network based on the time-frequency energy distribution. As quantitative indicators, global clustering coefficients of the complex network at various sparsity levels are computed to analyze the dynamic behavior of various flow structures. The results demonstrate that the proposed approach enables effective analysis of multi-channel measurement information for revealing the evolutionary mechanisms of gas-liquid two-phase flow. Furthermore, for the purpose of flow structure recognition, we propose a temporal-spatio convolutional neural network and achieve a classification accuracy of 95.83%.

Investigation of the condensation mass transfer time relaxation parameter for numerical simulation of the thermosyphon

The condensation mass transfer time relaxation (rc) is a critical empirical factor that reflects the change in the process from a non-equilibrium state and indicates the rate of the condensation. The determination of rc in the Lee model is crucial for the Computational Fluids Dynamics (CFD) simulation of thermosyphons. In this paper, the relationship between rc and internal parameters influencing the heat transfer performance of the thermosyphon are investigated in detail. The effects of working fluid properties, saturation temperature, filling ratio, and heat input on the temperature distribution of the wall surface of the thermosyphon were studied. Moreover, the corresponding CFD model of the thermosyphon was established. The result indicated that the simulated average condenser temperature rises with increasing rc and gets closer to the experimental average temperature in the form of a log function. By comparing the experimental data with the simulation results, the appropriate rc values for various conditions were determined to be around 104 s−1, within a margin of error of 1.5%. The empirical relationship equations of rc were fitted with experimental results to the key parameters. It was found that the effect on rc of vapor density was relatively minor, while the effect of the filling ratio was the most significant. By applying the obtained relational expression, the simulation results are in good agreement with other references, proving the accuracy and applicability of the calculations. This paper aims to refine the thermosyphon model and, facilitate the exploration of the phase-change heat and mass transfer mechanism of two-phase flow.

Liquid–Gas Jet Pump: A Review

To promote the development and application of the liquid–gas jet pump (LGJP), the research status of its design theory, internal flow mechanism, structural optimization and practical application are reviewed. The development history of the LGJP is briefly reviewed, the latest research and application progress of the LGJP is introduced, and the pulse-type of LGJP, especially the centrifugal jet vacuum pump (CJVP), is emphatically discussed. The research and development direction of the LGJP is analyzed and proposed: CFD will be more deeply applied to the mechanism research and performance improvement of the LGJP; the diversity and heterogeneity of the fluid medium and its influence on the internal flow mechanism are the research highlights of the LGJP; it is urgent to study the gas–liquid two-phase flow and pumping mechanism inside the pulsed liquid–gas jet pump (PLGJP), especially the CJVP.