Resonance analyses of a pipeline-riser system conveying gas-liquid two-phase flow with flow-pattern evolution

Investigation of pressure wave propagation and attenuation characteristics in wellbore gas-liquid two-phase flow

Summary Complex gas-liquid two-phase flow occurs in the wellbore after overflow during drilling operations. Accurate prediction of the wellbore flow pattern distribution and void fraction is crucial for real-time formation pressure inversion and efficient well killing. A large-scale vertical annular gas-liquid two-phase flow experimental system was used to measure the gas-liquid two-phase flow patterns distribution and void fraction at liquid viscosities ranging from 16 to 39 mPa·s. A research database was established using literature data on the flow patterns and void fraction of gas-liquid two-phase flow. A deep learning model based on long short-term memory (LSTM) networks, integrated with convolutional neural networks (CNN) and attention mechanisms, was developed to predict the flow patterns and void fraction of gas-liquid two-phase flow. The results show that increasing liquid viscosity shifts the transition boundary from bubbly flow to slug flow to lower superficial gas velocities, while the transition boundary from slug flow to churn flow shifts to higher superficial gas velocities. At a constant gas-liquid superficial velocity, the void fraction in the annulus increases as liquid viscosity rises. As the gas superficial velocity increases, the contribution of small bubbles to the section void fraction decreases in annular flow, reducing the influence of viscosity on void fraction. The deep learning prediction model demonstrates an excellent performance, achieving over 90% accuracy in predicting slug flow, churn flow, and annular flow void fractions, which surpasses the performance of the drift-flux model.

Accurate identification of the flow pattern of gas-liquid two-phase flow is of great significance to ensure the transportation safety of industrial pipelines. We propose a flow pattern identification method based on dual-domain and multi-scale feature fusion. Firstly, the gas-liquid two-phase flow pattern information in the vertical pipeline is collected by array resistance sensors, and the measured data is processed by dimensionality reduction. Firstly, the gas-liquid two-phase flow pattern information in the vertical pipeline is acquired using array resistance sensors, and the measured data undergoes dimensionality reduction for preprocessing. Subsequently, the reduced-dimensional data is segmented through a sliding window approach. The segmented data is analyzed using Choi-Williams Distribution (CWD) and Discrete Fourier Transform (DFT) to extract the energy signal and power spectrum signal, respectively. These signals are then encoded into two-dimensional grayscale images by pseudo-image encoding, providing a basis for investigating the flow pattern transition mechanisms in two-phase flow. Finally, the two grayscale images are fed into the dual-domain multi-scale feature fusion network for flow pattern recognition. The results show that this method can reveal the evolution behavior of gas-liquid two-phase flow from both the frequency domain and the time-frequency domain. The average recognition accuracy reaches 97.78%, achieving accurate identification of flow patterns.

An earthquake is one of the most serious phenomena to consider for the safety of a nuclear reactor in Japan. Therefore, structural safety of nuclear reactors has been studied and nuclear reactors were contracting with structural safety for a big earthquake. However, it is not enough for safety operation of nuclear reactors because thermal-fluid safety is not confirmed under the earthquake. For instance, behavior of gas-liquid two-phase flow is unknown in seismic conditions. Especially, fluctuation of void fraction is an important factor for the safety operation of the nuclear reactor. In previous work, fluctuation of void faction in bubbly flow was studied experimentally and theoretically to investigate the stability of the bubbly flow. In such studies, flow rate or void fraction fluctuations were given to the steady bubbly flow. In case of the earthquake, the fluctuation is not only the flow rate, but also a body force on the two-phase flow and shear force through the pipe wall. Interactions of gas and liquid through their interface also act on the behavior of the two-phase flow. The fluctuation of the void fraction is not clear for such complicated situation during the earthquake. Therefore, the behavior of gas-liquid two-phase flow is investigated experimentally and numerically in a series of studies. In this study, to develop the predictive technology of two-phase flow dynamics under earthquake acceleration, a detailed two-phase flow simulation code with an advanced interface tracking method TPFIT (Two-Phase Flow simulation code with Interface Tracking) was expanded to two-phase flow simulation in seismic conditions. In a previous study, we performed a numerical simulation of a two-phase bubbly flow in a horizontal pipe and a vertical bubble motion in a water tank in seismic conditions. And it was confirmed that the modified TPFIT can be applicable to the bubbly flow in seismic conditions. In this paper, the two-phase bubbly flow in a simulated single-subchannel excited by oscillation acceleration was simulated by using the expanded TPFIT. A calculation domain used in this simulation was a simplified subchannel in a BWR core. And time-series of void fraction distributions were evaluated based on predicted bubble distributions. When no oscillation acceleration was added, void fraction concentrated in a region near the wall. When oscillation acceleration was added, void fraction distribution was changed by time. And coalesces of bubbles occurred in the numerical simulation, and bubbles with relatively large diameter were observed. In the results, complicated void fraction distribution was observed, because the response of void fraction distribution on the oscillation acceleration was dependent on not only imposed acceleration, but also the bubble diameter.

Modeling the simultaneous flow of gas and liquid or two-phase gas-liquid flow in pipes is a key aspect in petroleum production. These models can enhance our ability to estimate fluid properties, predict pressure loss, liquid holdup, and flow pattern, and to see the effects of introducing concepts such as heat transfer to the system. Modeling two-phase flow phenomenon also allows visualization of the interaction of one property or parameter to another. The understanding of heat transfer in two-phase gas-liquid flow is important for economic and optimized operations.;This work focuses on the design of a PC-Based Software for modeling the effect of convective heat transfer on flow patterns in two-phase gas-liquid flow in pipes at all inclinations from -90° to +90° from horizontal, with the utilization of a temperature and pressure traverse along the length of the pipe. The implementation of this model in a computer program involves substantial calculations and correlations, some of which require iterative procedures.

Two-phase gas-liquid systems have wide applications both on Earth and in space. On Earth, they occur in a variety of process equipment, such as petroleum production facilities, condensers and re-boilers, power systems and core cooling of nuclear power plants during emergency operation. The potential space applications include active thermal control system, power cycle, storage and transfer of cryogenic fluids, and so on. Reliable design of such systems requires a thorough understanding of the mechanism of two-phase flow, such as the phase distributions (flow patterns), pressure drops and heat transfer coefficients at different gas and liquid flow rates. Among them, flow patterns will play an important role because of strong influence of the phase distributions on pressure drops and heat transfer coefficients and thus attract more attentions of the academic and technical communities all over the world. With the aid of numerous meticulous experiments, our present knowledge on two-phase gas-liquid systems has been built. It is, however, far from complete due to the complicate influence of gravity which is a dominant factor in normal gravity. Gravity strongly affects many phenomena of two-phase gas-liquid systems by creating forces in the systems that drive motions, shape boundaries, and compress fluids. Furthermore, the presence of gravity can mask effects that ever present but comparatively small. Depending on the flow orientation and the phase velocities, gravity can significantly alter the flow patterns, and hence the pressure drops and heat transfer rates associated the flow. Advances in the understanding of two-phase flow have been greatly hindered by masking effect of gravity on the flow. Therefore, the microgravity researches will be conductive to revealing of the mechanism underlying the phenomena, and then developing of more mechanistic models for the two-phase flow and heat transfer both on Earth and in space. Research on two-phase gas-liquid flow in microgravity has a history of more than 50 years with a short pause in the 1970s and has been advanced with the development of various microgravity facilities and with increased experimental opportunities, especially in the last two decades. Due to much strict restriction on flight chance, weight and size of the test facility, power supply, and so on, studies on two-phase gas-liquid flow in microgravity are

As a highly efficient and compact heat exchanger, printed circuit heat exchangers have been successfully used in various industrial applications, including electric energy, petrochemicals, and aerospace. They also have broad development potential. This paper builds a visual experimental platform for a single-layer PCHE microchannels heat exchanger with a structure of rectangular and semi-circular flow channels. It uses a high-speed camera to observe the two-phase flow pattern, interface, and bubble behavior in the single-layer PCHE microchannels. By combining MATLAB image processing technology to analyze the evolution of the gas-liquid flow pattern, bubble shape, and void fraction distribution characteristics in the flow channels, we can also analyze the impact of different PCHE flow channel structures and experimental working conditions parameters on the gas-liquid two-phase flow pattern and pressure drop in the PCHE microchannels. Experimental results show that the flow patterns in rectangular and semicircular cross-section flow channels are mainly bubble flow and slug flow with different lengths. Wave flow will appear when the gas-liquid phase flow rate is relatively large, and bubble merging behavior occurs in the flow channel that causes wave flow. The void fraction distribution in the flow channels of the rectangular and semicircular structures is high in the middle and low on both sides. With an increase in the gas phase flow rate, large-sized bubbles are generated and small-sized bubbles accumulate at the inlet head, leading to partial blockage of the flow channels. This results in a more pronounced difference in the distribution of void fraction. Within the range of experimental flow parameters, different gas phase flow rates are fixed, as the liquid phase flow rate increases, the pressure drop of the flow channels also increases. The pressure drop of the semicircular structure flow channels are smaller under the condition of small gas phase flow, while under big gas phase flow conditions, the pressure drop of the rectangular structure flow channels are small.

Influence of gravity on gas–liquid two-phase flow in horizontal pipes

The identification of flow pattern is a basic and important issue in multiphase systems. Because of the complexity of phase interaction in gas-liquid two-phase flow, it is difficult to discern its flow pattern objectively. In this paper, we make a systematic study on the vertical upward gas-liquid two-phase flow using complex network. Three unique network construction methods are proposed to build three types of networks, i.e., flow pattern complex network (FPCN), fluid dynamic complex network (FDCN), and fluid structure complex network (FSCN). Through detecting the community structure of FPCN by the community-detection algorithm based on K -mean clustering, useful and interesting results are found which can be used for identifying five vertical upward gas-liquid two-phase flow patterns. To investigate the dynamic characteristics of gas-liquid two-phase flow, we construct 50 FDCNs under different flow conditions, and find that the power-law exponent and the network information entropy, which are sensitive to the flow pattern transition, can both characterize the nonlinear dynamics of gas-liquid two-phase flow. Furthermore, we construct FSCN and demonstrate how network statistic can be used to reveal the fluid structure of gas-liquid two-phase flow. In this paper, from a different perspective, we not only introduce complex network theory to the study of gas-liquid two-phase flow but also indicate that complex network may be a powerful tool for exploring nonlinear time series in practice.

Stratified flow is one of the most basic flow pattern in the analysis of gas-liquid two-phase flow in pipes. In the present paper, different interfacial friction factor correlations were used to predict the liquid holdup and pressure gradients. The comparison of predictions with experimental observations shows that most existing correlations for the interfacial friction factor can lead to large deviations from measurements and that the standard method underestimates the liquid phase wall friction factors. New correlations for both the liquid phase wall friction factor and the interfacial friction factor were developed based on large amounts of available experimental data. The resulting correlations were used to predict liquid holdup and pressure gradient for different experiments. Considerable improvement in predictions was observed. Introduction Gas-liquid flow in pipes is of practical importance in petroleum, chemical, nuclear and geothermal industries, and has been the subject of intensive research for dozens of years. Theoretical analyses and experiments have been conducted to predict key factors, such as pressure drop, liquid holdup, gas-liquid interfacial area, heat and mass transfer and temperature distribution. In general, gas-liquid two-phase flow is much more complicated than single phase flow, due primarily to the existence of a phase interface and the spatial distribution of the phases. Some consequences of the complex nature of gas-liquid pipe flow are:–Pressure drop in transmission lines increases significantly even with the presence of very small quantities of condensate. Significant energy loss occurs as a result of acceleration and transportation of the liquid which wets the pipe wall and creates waves at the gas-liquid interface. The liquid film reduces the area of the pipe and increases the effective roughness.–Whereas in hilly terrain the pressure loss because of gravity head on the uphill side of a pipe would be recovered on the downhill side for single phase flow, this is often not the case for gas-liquid two-phase flow.–In hilly terrains and in submerged river crossings, energy is lost in lifting the liquid over natural obstacles. If the pressure is insufficient to overcome the obstacle, there may be flooding of the pipe, thus further reducing the area accessible for gas flow and therefore creating an even larger pressure drop.–In single phase flow, pressure drop decreases as pipe diameter increases, but this is not necessarily so in gas-liquid flow. Under certain conditions, pressure drop exhibits a minimum with pipe diameter. Due to the complex nature of gas-liquid two-phase flow, the problem was first approached through empirical or engineering methods. This approach is based on empirical or semi-empirical relations and has dominated practical design procedures. It leads to correlations that should be extrapolated with caution outside the range of parameters investigated in the experimental work. Most of the available correlations deal with air-water or steam-water systems, their reliability for other systems of industrial importance is questionable. Recently the trend has shifted towards the modeling approach, or mechanistic models. This approach is based on the fundamentals of multiphase flow and fluid dynamics. The fundamental postulate in this kind of approach is the existence of flow patterns or flow regimes and it has greatly contributed to the basic understanding of the nature of gas-liquid two-phase flow. P. 285

A two-phase flow is the simplest form of multi-phase flow. Two-phase flow has basic parameters, including flow behavior, flow pattern, void fraction, pressure gradient, or pressure drop. The development and application of fluid flow in small channels (mini and micro) are in the Micro Electromechanical System (MEMS). In general, the application of two-phase flow can be found in various applications in the industrial world, such as boilers, cores, and steam generators in nuclear reactors, petroleum transportation, electronic cooling, and different other types of chemical reactors. One of the most common challenges is void fractions and flow patterns in horizontal and vertical pipelines. The purpose of this study was to find out the significant difference in the characteristic value of fundamental parameters, primarily void fractions and flow patterns that occur in capillary pipes with a slope of 15o to horizontal. The fraction value and shape of this flow pattern are essential because it determines the pressure drop value, which means determining the level of danger that can occur if the pressure drop value reaches the extreme value. The fluid used a mixture of air-water and glycerin with 0, 10, 20, and 30% concentrations. To determine the void fraction is used digital image processing method with MATLAB R2014a application. A 1200 fps high-speed camera and 640 x 480-pixel resolution are used for video shooting. The experiment was conducted at superficial gas (JG) velocities of 0.025 - 66.3 m/s and superficial fluid velocities (JG) intervals of 0.033 – 4.935 m/s. The experiment results showed a significant difference between the void fraction value for the bubbly flow pattern and the churn flow pattern, which has not been widely discussed in previous studies. The analysis concluded that the higher the velocity of superficial gases, the void fraction value increases. This increase in the void fraction is why there is a significant change in flow patterns from bubble flow patterns to churn. In addition, it was also found that the increased viscosity of the fluid significantly affected changes in flow patterns, incredibly bubbly and plug, but its velocity decreased. It is also the result that the higher homogeneous void fraction (β) value affects the increase in the length of bubbly flow patterns and plugs.

Fluidelastic instability of flexible tubes subjected to two-phase internal flow

This paper points out the influence of the internal flow of two-phase oil and gas mixtures on the motion of slender risers hanging from floating production units in curved configurations (for instance, catenary risers) used for offshore petroleum production in deep waters. The internal flow mass and momentum may impose a natural whipping displacement adding to the concerns of stress and fatigue. Usually, the internal flow may display different two-phase patterns (bubble, slug, churn, annular or stratified mixtures) possessing completely different characteristics; in the case of slugs, their intemittency may induce an oscillatory movement on the suspended pipeline. The fluid dynamic forces depend on the flow rates of both oil and gas phases, requiring the simulation of the pipeline movement under production conditions. In this paper, a modeling of induced forces caused by the internal two-phase slug flow is described, and results from numerical simulations are presented for a steel catenary riser configuration, showing the importance of the internal flow forces on the movements of a production riser.

Identification of gas-liquid two-phase flow patterns in dust scrubber based on wavelet energy entropy and recurrence analysis characteristics

In this paper the frictional pressure drop, void fraction and flow pattern of an air-water two-phase flow in helically coiled tubes are presented. The coils are constructed of 9.92 mm I.D. copper tube and the ratios of inside diameter to coil diameter are 1/11 and 1/22.7, and the lengths are 4 m and 4.5 m respectively. The experiments were conducted in the range of superficial water velocity wlo: 0.35∼1.16 m/sec and superficial air velocity wgo: 0∼5 m/sec. The frictional pressure drop of the two-phase flow in these coils is 1.1 to 1.5 times as much as that in a straight tube in the range of the experiment. Three types of empirical equations for the frictional pressure drop are proposed, and also the experimental data are correlated by a modified Lockhart-Martinelli method. The values of void fraction in the coils are approximately equal to those in a straight tube for the same water and air flow rates.