Churn Flow Research Articles

CO2 capture using gas-lift pumps operating under two-phase flow conditions

CO2 capture through dissolution in water offers environmental benefits and industry applications. However, current studies mostly focus on CO2 extraction into solvents, overlooking its direct solubility in water. Alternatively, gas-lift pumps may hold significant potential for capturing and storing CO2 in water; but this ability remains unexplored. Therefore, this study experimentally delves into the CO2 capture capacity and hydraulic performance of a dual injection gas-lift pump with a 25.4 mm riser diameter. Operating at a constant submergence ratio of 70 %, the pump is fed with simulated flue gas with flow rates within 5–30 LPM at volumetric CO2 concentrations of 10 %, 15 %, and 25 %, and temperatures of 22 °C (isothermal operation) and 110 °C (non-isothermal operation). Two-phase flow hydrodynamics is also evaluated using high-speed imaging in conjunction with time-series void fraction measurements. Within the riser pipe, three distinct two-phase flow patterns — slug, intermittent, and churn flows — are identified. The results reveal that under both isothermal and non-isothermal operations and across all volumetric CO2 concentration levels, churn flow demonstrates superior mass transfer coefficient and lifted liquid flow rate, while slug flow achieves minimum energy consumption per ton of captured CO2, highest CO2 capture degree, and maximum lifting efficiency. Also, the highest degrees of sensitivity to inlet gas flow rate for volumetric mass transfer coefficient, delivered liquid flow rate, and void fraction were observed in slug flow regime. Both gas temperature and volumetric CO2 concentration positively impacted the mass transfer performance. However, the pump showed remarkably higher lifting efficiencies under isothermal operation conditions. Moreover, compared to four established CO2 capture methods (absorption, adsorption, cryogenic distillation, and membrane diffusion), the gas-lift pump exhibits moderately lower energy consumption, at 38-266 kWh/tonCO2, but with lower CO2 capture degree of 2.3 % to 6.7 %.

Experimental investigation on steam-water flow patterns in a vertical narrow rectangular channel utilizing conductance scanning measurement

In order to tackle the challenges in two-phase flow measurement in narrow rectangular channels, especially under pressurized conditions, a novel conductance scanning sensor, consisting of two ceramic-substrate printed circuit (CSPC) boards, has been developed based on the concept of wire mesh sensor. A leak-tight structure was also fabricated to avoid leakage at the penetrations of lead wires through the sensor housing. Measurements have been carried out in a narrow rectangular channel, with inner the cross-sectional dimension 70 mm × 2 mm, under pressure between 0.20 and 0.90 MPa. In the experiment, bubbly, churn and annular flows have been observed, except for slug flow. Flow pattern maps have been proposed for the steam-water two-phase flow. Comparing with those in the literature, it can be found that as the channel width/gap increases, the flow pattern transition boundaries shift towards the higher vapor superficial velocity direction. Additionally, the transition criteria for narrow rectangular channels were investigated by separately evaluating the critical void fraction and the superficial velocity calculation correlations. Results show that the critical void fraction of bubbly to churn flow and churn to annular flow can be approximately estimated as 0.2 and 0.75, respectively. However, the existing correlations for superficial velocity calculation are not suitable for the steam-water flows with a void fraction less than 0.5.

Examining the interfacial behavior of non-Newtonian gas-liquid two-phase flow in horizontal square microchannels

This study investigates the flow dynamics of a non-Newtonian two-phase flow within a horizontal square microchannel. The experimental apparatus employed an acrylic channel with a side length of 8 × 10−4 m. Nitrogen served as the test gas, and the test liquids consisted of water and CMC (Carboxymethylcellulose) aqueous solutions at concentrations of 0.2 and 0.4 %wt. The superficial velocity of working gas and liquids spanned ranges of 0.26–20 m/s and 0.05–1.0 m/s, respectively. A differential pressure transducer was used to measure pressure gradients, while a high-speed video camera captured the flow behavior for analysis with a custom image processing technique. Nonlinear regression statistical analysis was applied to establish the criteria for flow pattern transition. Furthermore, signal processing techniques such as PSD (Power Spectral Density), DWT (Discrete Wavelet Transform), ANN (Artificial Neural Network), and Kolmogorov entropy were employed to analyze the flow behavior based on the pressure gradient signals from the differential pressure transducers. Our findings reveal the occurrence of bubbly, slug, slug-annular, and churn flow patterns. The nonlinear regression statistical analysis offered ambiguous results for determining flow pattern transitions. However, an empirical coefficient was obtained for the nondimensional liquid height. Moreover, the empirical nondimensional liquid height aligned well with the experimental values. The PSD and DWT analysis corroborated each other in clearly characterizing the flow pattern based on pressure gradient fluctuation and wavelet energy. The Kolmogorov entropy effectively captured the chaotic flow pattern. Furthermore, the ANN analysis demonstrated a solid agreement between the predicted and actual flow patterns.

A simple and accurate model to predict pressure drop in vertical gas wells

ABSTRACT Predicting pressure drop in gas wells is one of the most important issues for designing deliquification technologies and optimizing gas production. Current pressure-drop prediction methods can be divided into analytical and empirical models. Although various models have been proposed to predict pressure drop in wellbores, no model has offered stable performance over wide liquid and gas flowrate ranges. Especially for gas wells with low liquid – gas ratios, very few models have been developed specifically. In this study, a simple and accurate three-point model is developed for predicting liquid holdup in wellbores. The model is based on the liquid holdups and gas velocities at the annular – churn, churn – slug and slug – bubble boundaries and is comprehensive for calculating the liquid holdup in vertical wellbores at different liquid/gas flowrates and pressures. The proposed method was verified with 39 collected laboratory and 182 field measured data points from the literature, which have wide parameter ranges. For comparison, some widely used models in the petroleum industry were also evaluated. In validation with the laboratory data with pipe diameters of 50.8 and 101.6 mm, although the new model has an average percentage error (E3) of 220.1% in the churn flow, ranking fourth of all the evaluated models, the other five indicators in the churn flow and six indicators in the annular flow are lowest of all these evaluated models, resulting in relative performance factors (RPFs) of 0.2 and 0, respectively. In the field measured data, gas and liquid productions range between 0.34 × 104—77.6 × 104 m3/d and 1—347.8 m3/d, tubinghead pressure ranges from 0.7 to 84.7 MPa, which can cover most gas wells. The validation demonstrates that the new model still has good performance with five indicators being lowest. The RPF of the new pressure-drop model in the field measured data ranges is 0.29, still lowest of all these evaluated models, showing better performance than these widely used models in petroleum industry for vertical gas wells. This indicates that the new model can accurately predict pressure drop under different conditions in vertical gas wells.

Visualization of the Two-Phase Flow Behavior Involved in Enhanced Dense Phase Carbon Dioxide Pasteurization by Means of High-Speed Imaging

This research explores the two-phase flow behavior involved in enhanced dense phase carbon dioxide inactivation of E. coli DH5α, which has been shown to possess a high microbial reduction efficiency of up to 3.7 ± 0.4 log. We present an experiment in which the liquid sample was pressurized with liquid carbon dioxide to 8.2 MPa and, after saturation, was forced to flow through a mini tube. An experimental setup was developed to visualize the flow patterns (plug, slug and churn flows) occurring in the mini tube by means of high-speed imaging. The values of the wall shear stress were estimated within the mini tube with the help of the gas slug velocities (8–9 m/s) and were compared with threshold shear stress values reported for the disruption of fresh E. coli cells. The results suggest that the preliminary pressurization phase may cause a substantial destabilization of the cell wall of E. coli DH5α.

Vertically downward gas-liquid flow: Void fraction and pressure drop

Using an air-water mixture and 34 mm ID pipe, a series of pressure drop and void fraction measurements were collected. The observed flow regimes were falling film, annular, bubbly, cap bubble, slug, and churn flows. The temporal fluctuations of void fraction and pressure drop measurements were firstly studied using signals visualization and PDF. It was revealed that both signals can be used to identify the flow regimes. A new flow pattern map is proposed based on the Froude number, calculated using the mixture velocity of the two phases, and the ratio of gas-to-liquid superficial velocities. The behaviors of the total and frictional pressure drops were studied and the influence of the superficial velocities as well as the flow regimes were identified. The experimental results were compared to four existing vertically downward frictional pressure drop models, none of which provided accurate predictions.

Visualization Experiments of Radial-Rotating Oscillating Heat Pipe Filled with Methanol

Oscillating heat pipes (OHP) have highly efficient heat transfer capability. Some researchers have applied OHPs to cutting tools and rotating machines by embedding tubular OHPs in machines or by making flow channels on metal plates. Most studies are on heat transfer performance, and there are few studies on the heat transfer behavior of radial-rotating oscillating heat pipes (RR-OHP) under operating conditions. This paper conducted the visualization test of an RR-OHP filled with methanol by studying the flow patterns and motion modes at rotation speed (0-860 rpm) and heat flux (20000-40000 W/m2). When the heat flux is increased from 20000 W/m2 to 40000 W/m2, the flow patterns include flowless, slug flow, annular flow, and churn flow, and the motion modes contain oscillatory motion, cyclic motion, unilateral boiling, and bilateral boiling. The distribution map of the flow patterns and motion modes with the centrifugal acceleration and the heat flux was plotted, which shows the evolution of the flow patterns and the transformation of the motion modes of the RR-OHP, and elucidates the effect of the centrifugal acceleration and the heat flux on the flow patterns and motion modes.

Uncovering flow dynamic behaviors underlying oil–gas–water three phase flow using multivariate synchrosqueezing transform

Abstract Oil-gas-water three-phase flow is distinguished by its intricate flow pattern. The analysis of experimental observations to reveal the oil-gas-water three phase flow’s dynamic behavior remains a challenging task. In this paper, firstly, a simulation investigation to compare the multivariate pseudo-winger distribution (MPWD) and multivariate synchrosqueezing transform (MSST) is presented. The cross term may be suppressed while maintaining high time-frequency concentration, according to our research on multivariate synchrosqueezing transform. The time-frequency analysis of various vertical oil–gas–water three phase flow patterns is then conducted utilizing MSST. The results from this study reveal that in various frequency bands, slug flow, bubble flow, and churn flow exhibit considerable temporal frequency variances. The MSST can effectively uncover the intrinsic connection between signal fluctuations and flow structure, and promote the understanding of various patterns of flow.

Investigation on the formation mechanism and flow characteristics of liquid carry-over in gas–liquid cyclone separator

The liquid carry-over (LCO) phenomenon brings about the performance deterioration of gas–liquid cyclone separator and an increase in pressure drop. However, the formation mechanism of the LCO and its manifestation in the separator cylinder and the overflow pipe have not been fully understood. This work investigated the flow process of the LCO by visual observation and quantitative measurement of the overflow liquid flow rate and liquid holdup. The transient gas–liquid flow feature in the overflow pipe and spatiotemporal relationship between the separator inlet and outlet were characterized by time-frequency analysis and wavelet coherence of liquid holdup, respectively. The results showed that the size of air core determines two kinds of sources of the LCO, including the surrounding liquid direct entry into the overflow pipe and the film short-circuit flow beneath the top wall of the separator. When the air core can continuously wrap up the overflow inlet, the film short-circuit flow became the primary source of the LCO, which was embodied in the significant reduction of the overflow liquid flow rate. Three flow patterns, namely, slug flow, churn flow, and annular flow, were classified in the overflow pipe. The inlet intermittent flow of the separator led to the distribution of churn flow expanding toward higher gas velocity, which was interpreted by flow pattern transition theory. The time-averaged overflow liquid holdup was well predicted by drift-flux model. The results are beneficial to the proposal of inhibition methods of the LCO and structure design of the separator.

Study of flow pattern transition criterion and heat transfer characteristics in vertical rectangular narrow channel for steam heating

This study clarifies the heat transfer characteristics of flow boiling in a narrow vertical rectangular channel at each stage and optimizes the performance of a heat exchanger. The flow pattern and local heat transfer characteristics in a narrow vertical rectangular channel of steam heating with dimensions of 1400 × 250 × 2.75 mm (l × w × s) were experimentally investigated using deionized water as the working medium. Based on the visualization data, the mechanical model and empirical formulas in previous literature, a preliminary derivation of the flow pattern transition criterion for steam heating in a vertical rectangular narrow channel was obtained. The effects of the inlet temperature, mass flux, and heating power on the local heat transfer characteristics were analyzed in conjunction with the flow patterns. Based on the parametric analysis of the experimental data, a new flow boiling heat transfer correlation formula was obtained and applied to the experimental conditions. The results showed that an increase in the inlet temperature had a positive effect on the nucleate boiling section, whereas the effect on the local heat transfer coefficient was minimal after entering the churn flow phases. The increase in mass flux decreased the local heat transfer coefficient in the nuclear state boiling stage and enhanced the local heat transfer coefficient in the evaporation zone of the liquid film flow. The peak of the local heat transfer coefficient tended to shift to the left as the heating power increased. The proposed heat transfer correlation equation could well predict the local heat transfer coefficient of flow boiling in a vertical rectangular narrow channel heated by steam under these experimental conditions.

Phase split of gas–non‐Newtonian fluid two‐phase flow in a ψ‐shaped branching microchannel

AbstractAn experiment of phase split was conducted in a horizontal ψ‐shaped branching microchannel to study the phase distribution and pressure drop at the bifurcation. The pressure drop at the test section and the flow rates of the gas and liquid phases through the three branches were measured. The pressure drop gradients at the inlet and branches were predicted by the correlation based on the separated flow model. The critical condition for the split of the two‐phase flow was determined. The results showed that the gas phase separated from the side arm was more than the liquid phase. A uniform distribution could be achieved for the churn flow in water. Pressure drop occurred at the bifurcation of the side arm under the effect of the vortex in the liquid slug near the bubble nose; the pressure drop was much greater than that at the bifurcation of the run.

Numerical Investigation Into the Gas–Liquid Two-Phase Flow Regime and Heat Transfer Characteristics in a Gravity Heat Pipe

Abstract In order to reveal the gas–liquid distribution, heat and mass transfer characteristics inside a gravity heat pipe, the bubble behavior and the flow regime transition during the phase-change process were examined by employing a copper-water heat pipe, with the length of 500 mm and Φ22 × 1.5 mm. The results indicate that in the process of phase change, the typical flow regimes of bubble flow, slug flow, and churn flow can be observed in the evaporator, and the presence of bubbles has an obvious disturbance on the flow field. In addition, the discontinuous liquid film plays an important role in the heat transfer mechanism in the condenser, which allows the vapor to contact the wall directly and reduces the heat transfer resistance. The temperature difference between the evaporator and the condenser can be reduced by adjusting the saturation temperature, so as to effectively improve the heat transfer performance of the heat pipe and contribute to the practical engineering design.

Numerical simulation of boiling behavior in vertical microchannels

High heat flux electronic devices put forward new requirements for heat dissipation, and boiling heat transfer technology is widely used because of its higher heat dissipation capacity. In this study, the volume of fluid method was employed, along with the incorporation of the Lee phase-change mass transfer model, to investigate two-phase flow and heat transfer in vertical upward rectangular microchannels. The heat flux was varied within the range of 10–40 kW/m2, while the mass flux was varied within the range of 200–600 kg/m2 s. With the increase in heat flux, bubble flow, slug flow, churn flow, and annular flow were found successively. A phase diagram was established to predict the flow pattern transition during the boiling process. When the flow pattern changes to the churn and the annular flow, the active nucleation site density increases obviously with the Boiling number (Bo). A new correlation was proposed for two-phase flow boiling heat transfer, suitable for vertical upward channels in microscale fluids. The friction factor obtained using the Darcy friction factor equation agrees well with the simulation results at a high-pressure drop. The instability in microchannels increases with the increase in heat flux, particularly in annular flow, resulting in more severe wall temperature fluctuations.

Transition from bubbling to jetting in submerged gas-liquid jets through a minichannel

This paper provides a first insight into the transition from bubbling to jetting of submerged jets generated by the ejection of gas-liquid mixing flows through a minichannel into water. The ejections of rivulet, annular, churn, and Taylor-annular flows are found to generate jet behaviors of aperiodic bubbling, impact bubbling, chaotic bubbling, jetting-like jets, unstable jetting, and stable jetting. The correspondence relationship between the in-channel flows and submerged jets is revealed by establishing their flow regime maps, as well as the prediction models of transition boundaries. Compared to single-phase gas jets, the participation of liquid phase in mixing flows significantly promotes the transition from bubbling to jetting. Specifically, the increase of liquid phase velocity decreases the critical gas phase velocity for the transition from bubbling to jetting-like jets, as well as the transition from unstable jetting to stable jetting, characterized by the increase of liquid slug frequency and jet penetration length, as well as the decrease of liquid slug length, jet pitch-off frequency, and jet cone angles. As a result, via the in-channel mixing with a liquid phase of a Weber number of 110 prior to orifice ejection, the critical Mach number for the onset of stable jetting is significantly reduced from 3.76 to 1.25.

Local and global gas–liquid mass transfer in a micro‐packed bed reactor utilizing a noninvasive colorimetric technique

AbstractMicro‐packed bed reactor (μPBR) presents great potential in the field of multiphase reactions due to the features of safety and high efficiency. However, the deeper cognition of mass transfer needs to be taken into consideration that is the foundation of reactor design. In this work, local and global gas–liquid mass transfer in the μPBR were studied utilizing a noninvasive colorimetric technique. In reactor level, the qualitative and quantitative comparisons were conducted; in particle level, liquid flow and mass transfer textures were assessed for the first time. The diversities of local mass transfer characteristics from temporal and spatial dimensions were obtained, and the heterogeneity of local and global mass transfer was revealed. The predicted correlations of in μPBR with churn flow and pseudo‐static flow were established with deviations generally within ±18%. This study contributes to improve the understanding of mass transfer and points out the process intensification direction of μPBR.

Experimental study on the effect of liquid properties on fluid behavior and liquid loading in vertical natural gas wells

Liquid loading is one of the major challenges for natural gas wells, as it can decrease and eventually cease the production of hydrocarbons. Characterizing liquid loading in gas wells and quantifying flow dynamics throughout this process is crucial. The literature shows a lack of experiments for oil-air low liquid loading flow, especially in vertical pipes. This demonstrates a lack of experimental data to comprehend the effect of liquid properties on two-phase flow behavior. In order to simulate a vertical natural gas well, oil-air tests were carried out in this work in a vertical pipe with a 0.0508-m ID (Inner-Diameter) under low liquid loading conditions. The aim of this study is to better comprehend the effect of liquid characteristics on flow behavior and the onset of liquid loading.The results of the experiments reveal that changing the liquid phase from water to oil reduces pressure loss, liquid holdup, and the surface gas velocity (vSg) at which liquid loading occurs. Liquid holdup and pressure loss of the water-air and oil-air flow with medium gas rates show notable variances within the churn flow. Additionally, compared to the minimum-pressure drop technique, the positive pressure technique offers considerably more reliable predictions for the start of liquid loading.Two models—the unified Tulsa University Fluid Flow Projects (TUFFP) and OLGA—are used to investigate the flow pattern, liquid holdup, and pressure loss predictions. The liquid film reverse, liquid droplet models, and the inflection point technique were compared to experimental data for similar liquid loading onset models by Alsanea et al. (2022). For the data in this investigation, the OLGA model and Coleman's correlation perform the best at predicting the onset of liquid loading. Given that both the unified model and OLGA use slug flow models, the results show that a separate model must be created for churn flow to accurately estimate the pressure drop and liquid holdup.

Measurement of film fluctuations and aerated characteristics during gas-liquid slug-churn flow transition by wire-mesh sensor

Vertical upward gas-liquid slug flows are frequently encountered in chemical processes and petroleum industries. The measurement of the film fluctuations and the aerated characteristics is of great significance for uncovering the mechanism of slug-churn flow pattern transitions. In this study, a conductance wire-mesh sensor (WMS) measurement system is designed based on a Field Programmable Gate Array (FPGA) to visualize the structures of vertical gas-liquid flows. Liquid film flooding is a significant factor prompting the transition from slug to churn flow. Based on the WMS data, the 3D film structures are derived to indicate film instability during the flow pattern transition. Three types of film fluctuations in stable slug flow, unstable slug flow, and churn flow are presented. Liquid slug aeration is another important factor contributing to the slug-churn flow transition. The spatial distribution and the diameters of the gas bubbles in the liquid slug are detected by the WMS. The coalescence behavior of the bubbles is uncovered. Finally, mechanistic models based on the film flooding and slug aeration are constructed to predict the boundary of the flow pattern transition. The performance of the film flooding model and slug aeration model in predicting the onset of churn flow is evaluated.

Numerical modelling of multiphase flow hydrodynamics by CFD analysis methods in a double-elbow pipeline

Introduction. Prediction of multiphase flow patterns in pipelines of gas and oil industry is a complicated hydrodynamic process. Hydraulics of gas-liquid flows and erosion processes in pipelines with many bends in which gas, water, oil and air move are insufficiently studied. There are known studies of movement in single-phase flow conditions with one elbow, which is insufficient for design of modern pipeline systems. Therefore, there is a need for in-depth analysis of interaction of media in multiphase flow and transported sand particles. In this paper the effects of elbows on multiphase flow hydraulics and erosion of pipe sections are investigated using computational fluid dynamics (CFD) modelling tools for 100 seconds’ of process.
 
 Materials and methods. A liquid volume model (VOF) was used to simulate three-phase flow: air-water with solids in a pipe with two elbows. Turbulence effects have been accounted for with the RNG k–ε model. The model verification methods from previous studies have been used. For the numerical solution, the Ansys Fluent version 20.1 software package has been used. The results of CFD modelling of the volumetric gas content have shown a good agreement with the available experimental data.
 
 Results. The results showed that the change in the flow regime remains unchanged before the first elbow and after the se-cond elbow in the cork flow. However, for the initial churn flow regime, the flow regime varies at different segments of the flow area before and after each elbow.
 
 Conclusions. The preliminary churn flow in the upper vertical section was transformed to wavy stratified flow in the horizontal section between the two elbows and wavy annular flow in the vertical pipe after the second elbow. The flow pattern in slug flow maintained same after the first elbow, but the Taylor bubbles are lengthier in the horizontal section between the first and second elbows.

Achieving ultra-uniform temperature distribution with a heterogeneous wettability surface for two-phase flow in microchannels

Microchannel-based two-phase schemes have been proposed as an efficient solution for thermal management. However, the non-uniform temperature distribution in flow boiling limits phase-change performance and impedes commercial applications. In this study, we introduce a novel surface featuring heterogeneous wettability, comprising upstream superhydrophobic, middle plain, and downstream superhydrophilic regions. Hierarchical nanowires are employed to achieve the desired wettability, which can promote bubble departure and enhance capillary pumping. This wettability distribution facilitates upstream bubble nucleation and downstream liquid supply, significantly improving temperature uniformity. Moreover, surface contact angle variations effectively contribute to flow behavior improvement by restricting vapor reversal and fostering churn flow. Our results demonstrate that heat aggregation in the middle region and temperature restriction in the downstream region cause the high-temperature region to migrate upstream. This temperature redistribution stimulates axial heat transfer, substantially suppressing inlet subcooling and restricting temperature gradients. Compared to the plain surface, the heterogeneous wettability surface afforded an 87.8% reduction in temperature difference between Tw1 and Tw5 at approximately 120 °C, suggesting an ultra-uniform temperature distribution. Additionally, the average heat transfer coefficient showed a 35.1% enhancement rate at a wall heat flux of 100 W/cm2, and the performance evaluation criterion showed a 44.2% enhancement rate at an effective heat flux of 190 W/cm2. These results indicate that the proposed surface can efficiently regulate temperature distribution, maintain performance stability, and enhance heat transfer. The heterogeneous wettability surface has considerable potential for practical applications in high-power component heat dissipation.

Enhancement of flow boiling in the microchannel with a bionic gradient wetting surface

Flow boiling in microchannels is promising to enhance electronic heat dissipation (urgently required). However, vigorous boiling in a narrow space can trigger serious flow reversal and heat transfer deterioration, restraining further performance enhancement. In this work, a bionic gradient wetting surface was developed to overcome the challenge. The upstream hydrophobicity and surface variation induced flowing bubble expansion and frequent interface fluctuation, benefiting the backflow suppression and churn flow appearance. While the downstream hydrophilicity improved liquid supply and vapor venting, preventing partial dry-out and pressure drop increase. The flow regimes on the bionic surface were demonstrated by the quantitative analysis of two-phase flow, exhibiting the shortest backflow duration time and the second-high frequency of churn flow appearance. Moreover, the gradient wettability showed negligible oscillations in average wall temperature and pressure drop and achieved the maximum enhancement rate of 50.1% and 63.2% for the heat transfer coefficient and performance evaluation criterion, respectively. The surface combination scheme incorporated the merits of different wetting surfaces and significantly enhanced the integrated performance, showing immense potential in high-efficient thermal management applications.