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The flow of gas-liquid two-phase flow in reservoir fractures may exhibit various flow regimes, such as bubble flow, slug flow, and annular mist flow. Identifying the conditions for the transition between these flow regime is essential for understanding the formation mechanism of gas-liquid flow and has significant implications for the production pipeline management of natural gas Wells. Based on the flow characteristics of different flow regimes of gas-liquid two-phase flow, combined with the theory of continuous medium control and the principle of momentum conservation, transformation mathematical models between flow regimes such as bubble flow, slug flow, and annular mist flow were established. The decisive conditions and key controlling variable that govern the transitions between various flow regimes have been precisely identified. Furthermore, the precision of the mathematical model was rigorously validated through microscopic physical simulation experiments focused on gas-liquid transportation. The results indicated that, the flow state transition of gas-liquid two-phase flow in fractures was the result of the coupling effect of factors such as the physical properties of the gas/liquid phase, the pore size of the gas injection channel, the pore size of the fracture flow channel, the gas phase fluid velocity, and the liquid phase fluid velocity. The transition between bubble flow and slug flow mainly depended on the size of the initial bubble, the flow channel space, and the height of the liquid phase interface wave. The transition between slug flow and annular mist flow depended on whether the gas phase fluid can break down the liquid phase fluid and suspend it. The main control factors for the transition between different flow states were different. The pore size of the fracture system was one of the most important factors in the mutual transformation of bubble flow and slug flow, when the injection channel aperture was larger and the flow channel aperture was smaller, it was more likely to form slug flow. The mutual transformation between slug flow and annular mist flow was primarily influenced by fluid velocity and the physical properties of gas/liquid phase fluids. A higher relative velocity between the gas-liquid phases, a smaller density difference between the phases, and a lower liquid surface tension all increase the likelihood of forming annular mist flow. These research findings established a theoretical foundation for understanding the mechanism of gas-liquid two-phase flow formation in reservoir fractures and natural gas transport production.

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Liquid-film flow appears in widely industrial fields, and its characteristics can impact product reliability and efficiency. Steam turbines, for example, notorious erosion and moisture loss are significant problems due to water droplets generated on the blade surface under humid lowpressure environments. A method for directly measuring the liquid-film flow in the machine is required. However, measuring the liquid-film flow is difficult by conventional methods under high temperature and pressure. Moreover, the thin liquid-film flow is frequently accompanied by disturbance waves in such an extreme environment. This study demonstrated the thickness measurement of the thin and wavy liquid-film flow using an Optical-fiber-based Reflective Probe (ORP). This technique can measure local film thickness utilizing the relationship between the distance and the light intensity reflected at the interface. At first, we investigated the ORP signal of a pseudo liquid-film flow using a wavy-stainless steel surface. According to the results, the ORP signal tends to peak at the locally flat positions of the wave. The ORP signal processing was newly established based on this fact. After that, we performed the ORP measurement in the thin-liquidfilm flow condition with its average thickness of less than 500 μm. The experiment was conducted in a blowdown wind tunnel. We flowed air (jG=41~75 m/s) into the rectangle test section and injected tap water (Γ=1~3x10-5 m2 /s) from holes on the channel base. The ORP was fixed at this section to obtain time-series data of the liquid-film thickness. Furthermore, we visualized the liquidfilm flow from the side via a high-speed camera, then estimated the film thicknesses. The results showed a good agreement, and consequently, we confirmed the ORP successfully evaluates the thickness even in the liquid-film flow with disturbance waves. [ABSTRACT FROM AUTHOR]

The unsteady gas-liquid two-phase flow has often posed a great threat to the pump performance, particularly with the increase of inlet gas void fraction during transportation. The traditional two-fluid model cannot consider the variation of bubble diameter and the interaction between bubbles. In this study, a group equilibrium model (Musig model) was proposed to simulate the internal flow in the centrifugal pump with the semi-open impeller under different inlet gas void fractions. The simulation works were then verified by the experimental pump performance and visualization test. Some parameters were obtained, including the pump performance, the bubble distribution in the middle section, and the turbulent kinetic energy distribution under different inlet void fractions at the design flow rate. A proper cause was analyzed for the deterioration of pump performance under a large void fraction, together with the velocity distribution and bubble variation at the tip clearance between blade and pump casing. The results show that the maximum handing ability was 4.6% about the inlet gas void fraction of the model pump at 1000 r/min. When the void fraction was greater than 3%, the Musig model was more accurate to predicate the pump performance, particularly suitable for the evolution of gas-liquid two-phase flow, such as bubble morphology, fragmentation, and polymerization, compared with the Euler-Euler two fluid model. Specifically, the maximum errors of head coefficient and efficiency were 1.6% and 5%, respectively, when the inlet gas void fraction was 4% at a pump design flow rate. Moreover, the predicted bubble distribution and flow pattern were consistent with the visualization experiment. The flow patterns (such as the uniform/polymeric bubble, cavitation, and separated flow) gradually appeared in the impeller and volute channels, with the increase of inlet gas void fraction. There was a mainly uniform distribution of bubble flow inside the channel at a design flow rate when the inlet gas void fraction was less than 1%. The polymeric bubble flow appeared, when the inlet gas void fraction reached 3%. The cavitation flow then dominated, when the inlet gas void fraction reached 4%. Further, the separate flow appeared, when the inlet gas void fraction reached 4.2%, where the flow channel was gradually blocked. The tip clearance was an important parameter to determine the distribution of gas-liquid two-phase flow pattern in the pump, which promoted the bubbles’ transposition from the blade pressure side to the suction side. The maximum velocity was distributed at the gap between the impeller outlet and the volute, where was the place with the most bubble aggregation and distribution patterns of gas-liquid two-phase flow. There were the increasing large-scale vortex and outlet reflux in the impeller channel, with the increase of inlet gas void fraction, leading to the large distribution of turbulent kinetic energy in the high void fraction area, where the unstable flow was intensified inside the pump, and finally leading to the pump idling after the inlet gas void fraction reached 4.6%. This finding can also provide a sound reference for the comprehensive analysis of unsteady flow characteristics in a centrifugal pump. [ABSTRACT FROM AUTHOR]

Effective drainage gas recovery technology is the key to solving the problem of the liquid loading of gas well and of enhanced gas recovery. An internal vortex tool is designed for solving the problem of liquid loading in horizontal wells. This study conducted a computational fluid dynamics analysis the efficiency of the drainage gas recovery of the tool in the horizontal well, to optimize the structure of the tool. The results show that most of the liquid film flows along the pipe wall in the internal vortex tool, and the gas flows through the central area of the pipe at a high speed with fog. The internal vortex tool can increase the gas phase velocity and separate the gas and liquid. The structural parameters of the internal vortex tool for minimum pressure loss and the maximum drainage efficiency is the same diameter as the tubing and casing for the runner diameter, 42.8° for the swirl angle, 8 mm for the helix height, 6 mm for helix width and 4 for the number of lead. The study on the flowing of a gas liquid swirling flow in the internal vortex tool proves the feasibility of its application in horizontal wells. It can provide theoretical guidance and a practical basis for efficient liquid loading using the internal vortex tool in the future. • An internal vortex tool is proposed firstly which is designed for solving the problem of liquid loading in horizontal wells. • The internal vortex tool can increase gas phase velocity and separate the gas-liquid two-phases. • Most of the liquid film flows along the pipe wall and the gas flows through the central area of the pipe with fog. • The structure of the internal vortex tool had been optimized. [ABSTRACT FROM AUTHOR]

Ultrasonic measurement techniques for velocity estimation are currently widely used in fluid flow studies and applications. An accurate determination of interfacial position in gas-liquid two-phase flows is still an open problem. The quality of this information directly reflects on the accuracy of void fraction measurement, and it provides a means of discriminating velocity information of both phases. The algorithm known as Velocity Matched Spectrum (VM Spectrum) is a velocity estimator that stands out from other methods by returning a spectrum of velocities for each interrogated volume sample. Interface detection of free-rising bubbles in quiescent liquid presents some difficulties for interface detection due to abrupt changes in interface inclination. In this work a method based on velocity spectrum curve shape is used to generate a spatial-temporal mapping, which, after spatial filtering, yields an accurate contour of the air-water interface. It is shown that the proposed technique yields a RMS error between 1.71 and 3.39 and a probability of detection failure and false detection between 0.89% and 11.9% in determining the spatial-temporal gas-liquid interface position in the flow of free rising bubbles in stagnant liquid. This result is valid for both free path and with transducer emitting through a metallic plate or a Plexiglas pipe.

In this study, the gas liquid two-phase flow of low-temperature fuel cells is simulated to study the water removal process in the anode channel utilizing VOF (volume of fluid) method. It is found that the water removal process in the cathode channel is easier compared to that in the anode under the same operating condition and inlet velocity. Increasing the humidification rate and contact angle is helpful for water removal. Moreover, further simulations show that in the semicircle-U channel, the water can be removed successfully, but it will be stuck in the corner in the rectangular-U channel, which can be prevented by changing the contact angle of specific walls into extremely hydrophilic or hydrophobic. Extremely hydrophilic wall would make the entire water pave on the wall and smash into little droplets which is not only helpful in water removal and evaporation but also prevents the water from blocking the holes on the Gas Diffusion Layer (GDL). And different hydrophilic/hydrophobic levels also influence the water removal. [ABSTRACT FROM AUTHOR]

Ultrasonic measurement techniques for velocity estimation are currently widely used in fluid flow studies and applications. An accurate determination of interfacial position in gas-liquid two-phase flows is still an open problem. The quality of this information directly reflects on the accuracy of void fraction measurement, and it provides a means of discriminating velocity information of both phases. The algorithm known as Velocity Matched Spectrum (VM Spectrum) is a velocity estimator that stands out from other methods by returning a spectrum of velocities for each interrogated volume sample. Interface detection of free-rising bubbles in quiescent liquid presents some difficulties for interface detection due to abrupt changes in interface inclination. In this work a method based on velocity spectrum curve shape is used to generate a spatial-temporal mapping, which, after spatial filtering, yields an accurate contour of the air-water interface. It is shown that the proposed technique yields a RMS error between 1.71 and 3.39 and a probability of detection failure and false detection between 0.89% and 11.9% in determining the spatial-temporal gas-liquid interface position in the flow of free rising bubbles in stagnant liquid. This result is valid for both free path and with transducer emitting through a metallic plate or a Plexiglas pipe. [ABSTRACT FROM AUTHOR]

The authors present a predicting model concerning pressure, temperature, density, and velocity of gas liquid two-phase transient flow in high-temperature–high-pressure wells, according to mass, momentum, and energy balances. The finite difference method is used to solve the model. A high-temperature–high-pressure gas well (6,115 m deep) in Sichuan Province of China is used to check the efficiency of the proposed model and the algorithms. [ABSTRACT FROM AUTHOR]