Liquid Flow Patterns Research Articles

Bubble deformation characteristics and the effect on particle removal efficiency in wet scrubbers

Single-bubble formation and rise are fundamental to the prediction of decontamination factors (DF) under the complex hydrodynamics of bubble flow and the gas–liquid flow pattern. However, bubbles in the water for particle control are not always perfectly spherical or ellipsoidal. To date, studies of bubble washing for particle removal have mainly focused on models with simple spherical and ellipsoidal shapes or the impact of operating parameters on removal efficiency. No attempt has been reported in the literature to determine the effect of bubble shape on particle removal efficiency. An investigation of the influence of bubble deformation during the bubble rising period was carried out using a high-speed camera and image analysis techniques to study the bubble shape. The experimental results show that the deformation of a bubble is directly correlated with its rising velocity, rising tail, equivalent radius and residence time. These parameters are generally estimated using ideal values, which are crucial for the accuracy of efficiency calculation model results. SPARC-90 code is an important scrubbing modelling tool developed for prediction of bubble hydrodynamics and the corresponding aerosol retention behavior. The potential for particle removal with a single rising deformed bubble was recently determined using a prototype of the SPARC-90 code with the experimental results. The results of SPARC-90 calculations with various equivalent diameters obtained in this experiment have provided more accurate decontamination factors compared to those obtained with a round bubble and a default bubble diameter.

Gas liquid flow pattern prediction in horizontal and slightly inclined pipes: From mechanistic modelling to machine learning

This paper investigates the prediction of two-phase gas-liquid flow regimes in both horizontal and slightly inclined pipes. For this purpose, the mechanistic model of Taitel et al. (1976) and the machine learning approach have been adopted. First, the mechanistic model was implemented, tested and optimised by introducing factors in the transition equations to determine the configuration that gives the highest prediction accuracy for a specific two-phase system for which experimental data points are available. Second, several machine learning models are trained, tested and additionally validated. This is done by splitting the experimental data set corresponding to the pipe inclination range (−10∘ to 10∘) into training, test and validation sets. The best classifier achieved an accuracy of 95.5% after the test step and up to 98.9% after the validation step. Finally, the Taitel et al. model with the optimal configuration and the best machine learning classifier (XGB classifier) are used to generate the two-dimensional flow regime map.

Process Intensification of Gas–Liquid Separations Using Packed Beds: A Review

The gas–liquid multiphase process plays a crucial role in the chemical industry, and the utilization of packed beds enhances separation efficiency by increasing the contact area and promoting effective gas–liquid interaction during the separation process. This paper primarily reviews the progress from fundamental research to practical application of gas–liquid multiphase processes in packed bed reactors, focusing on advancements in fluid mechanics (flow patterns, liquid holdup, and pressure drop) and the mechanisms governing gas–liquid interactions within these reactors. Firstly, we present an overview of recent developments in understanding gas–liquid flow patterns; subsequently we summarize liquid holdup and pressure drop characteristics within packed beds. Furthermore, we analyze the underlying mechanisms involved in bubble breakup and coalescence phenomena occurring during continuous flow of gas–liquid dispersions, providing insights for reactor design and operation strategies. Finally, we summarize applications of packed bed reactors in carbon dioxide absorption, chemical reactions, and wastewater treatment while offering future perspectives. These findings serve as valuable references for optimizing gas–liquid separation processes.

Migration characteristics of bubbles moving in gas–liquid countercurrent two-phase flow in an inclined pipe

While exploring and developing oil and gas, well kick and overflow accidents are inevitable. In such an accident, if the drilling bit is not at the bottom of the well, the drilling tool is blocked, or the reservoir contains toxic gases such as hydrogen sulfide, the traditional technique for well control is no longer suitable, and the bullheading method must be adopted to kill the well. However, during bullheading, the flow patterns of gas and liquid are intricate, making gas velocity hard to predict. To solve these problems, a set of visual simulation experimental device for directional well bullheading was built to find out the effects of wellbore inclination, liquid viscosity, gas and liquid velocities, and bubble size on bubble migration characteristics in gas–liquid countercurrent (gas flowing in opposite direction to the liquid). Prediction models of bubble distribution coefficient and rising velocity considering liquid viscosity, bubble size, and wellbore inclination angle were worked out. The experimental results show that small bubbles are mainly located in the center of the wellbore and large bubbles tend to approach the wellbore wall in gas–liquid countercurrent. Increasing wellbore inclination, viscosity, and the velocity of the liquid flowing against the bubbles results in a gradual decrease in Taylor bubble migration speed, which promotes the bubbles' pressing-back, as inhibiting the upward movement of large bubbles is essential for effective bullheading operations. The prediction models of distribution coefficient and bubble migration velocity have an error of less than 10% and 9. 78%, respectively.

CFD assessment of internal Vapor/Liquid separator in an ebullated bed reactor (EBR) for heavy oil hydroprocessing

The ebullated-bed reactor (EBR) is an important system used in the upgrading of heavy oil residue into valuable light products in petroleum refinery operations. The assessment of the gas separation region hydrodynamics is very significant to investigate the performance of EBR. An advanced understanding of EBR fluid dynamics will help in improving the design of existing and future commercial units. For this reason, the development of a computational fluid dynamics (CFD) model is very challenging, where understanding the fundamentals of fluid dynamics in EBR is carried out using a three dimensional model and the turbulence model with a standard wall function in cup geometric design. The two models were used to analyze the influence of operational parameters such as recycle ratio, and inlet velocity on gas fraction recycled and separation efficiency. Moreover, the prediction of the regime transitions occurring in the freeboard region of the EBRs was achieved using the two aforementioned models. The results of the fluid dynamics behavior revealed that the inlet velocity has a substantial effect on gas fraction recycled and separation efficiency. The liquid mean residence time scale provided a valuable efficiency result for the separation within the range of expected mean residence times. This investigation, therefore, provided a good framework for the evaluation of future design and gave a better understanding of gas and liquid flow patterns in EBR.

The effect of swirling shear blade on gas-liquid flow pattern and mass transfer performance in Venturi injector

To address the challenge of low mass transfer efficiency of gas-liquid reaction in traditional reactors, this study proposes a new method to improve the gas-liquid mass transfer efficiency by integrating swirl shear blades (SSB) into Venturi injectors. The gas-liquid flow patterns in the mixing and diffusion sections between the Swirl Venturi Injector (SVI) and the Traditional Venturi Injector (TVI) was compared, and it was found that the SSB significantly reduced the proportion of annular flow while increased the proportion of mist flow. The enhancement factor αE and the acceleration factor αA are applied to evaluate the mass transfer performance. Compared to TVI, the maximum αA of SVI was 29%, and the maximum αE was 43%. This work shows great potential in efficiently capturing gas components with low solubility in the liquid phase, thereby helping to achieve the goal of green chemical engineering.

Numerical investigation of the sensible heat storage in novel electrostatic precipitators with liquid-filled collection electrodes

Heat recovery from flue gas holds significant potential for energy conservation. A strategy is proposed for recovering and storing heat in electrostatic precipitators by utilizing liquid-filled collection electrodes. In the prototype, the hollow collection electrode is connected to the heat storage tank. Convective heat transfer occurs between the gas stream and the liquid contained in the collection electrode. The heat storage mechanism is revealed by numerical simulation of corona discharge, flow and heat transfer processes in a simplified electrostatic precipitator. The results indicate that both the gas-side and liquid-side heat transfer coefficients reach steady values within approximately 100 s. The buoyancy-driven liquid flow results in a heat transfer coefficient that is 28 times higher than that for gas-side forced convection. Increasing the gas inlet temperature leads to a greater buoyancy force and, consequently, a higher heat transfer coefficient on the liquid side. Both ionic wind and inlet velocity affect the gas-side heat transfer. The ionic wind disturbs the thermal boundary layer, leading to a 27.9 % increase in the gas-side heat transfer coefficient at an inlet velocity of 0.5 m/s. Furthermore, this enhancement becomes more pronounced as the inlet velocity decreases. The flow pattern of liquid in the collection electrode and heat storage tank is crucial to the heat storage process. Additionally, installing the heat storage tank above the electrostatic precipitator provides added benefits. During the process of heat storage, the largest heat resistance is found on the gas side.

Operation of iron-based monolithic catalyst packing ozonation for industry wastewater advanced treatment: The importance of gas–liquid flow patterns and wastewater flow regimes

In this study, from the feasibility verification of the lab-scale test to the working condition study of the pilot-scale test the large-scale engineering application of the display manufacturing industry wastewater advanced treatment by ozonation with iron (Fe)-based monolithic catalyst packing was finally realized. Different from chemical packings, the catalyst packing has large porosity and specific surface area, while the pore size is small, which meets the requirements of •OH reaction, and these characteristics are necessary for engineering applications. Under the three scales, the reaction procedure and the corresponding reactor structure were introduced in detail. The importance of gas–liquid flow patterns and gas distribution device on treatment effect were proved in pilot-scale test. The treatment effect under gas–liquid counter-current flow was better than that of co-current flow. Through the analysis of the working conditions, the working parameters for high wastewater quantity and high organic loading were obtained. The large-scale test achieved the same excellent treatment effect as the lab/pilot-scale test, after 5 years of operation, the average chemical oxygen demand (COD) removal was about 72.0 %, and the COD concentrations after treatment were all lower than 30 mg/L. The biochemical oxygen demand (BOD5) decreased from 10.22 to 2.50 mg/L on average. Under the short-circuiting phenomenon, the wastewater through the catalyst area unevenly and the organic pollutants were not effectively oxidized and decomposed. This also proved the importance of Fe-based monolithic catalyst packing in advanced treatment. This work proved the importance of gas–liquid flow patterns and wastewater flow regimes in the reactor, which can provide reference for other catalytic ozonation technology in large-scale engineering applications.

Investigations on transport behaviours of rotating packed bed for CO2 capture by chemical absorption using CFD simulation

A rotating packed bed (RPB) has been proposed to overcome the limitations of high operating and capital costs involved in conventional columns which are used for chemical absorption-based carbon dioxide (CO2) capture. The design of large-scale RPBs depends on their transport characteristics. Owing to the difficulties in predicting the transport characteristics of RPBs experimentally, Computational Fluid Dynamics (CFD) simulation has been implemented. In this study, a two-dimensional (2D) volume of fluid (VOF) simulation is conducted to predict transport characteristics of RPB including, hydrodynamics, and physical and reactive mass transfers. To predict hydrodynamics of RPBs accurately, the liquid holdup by CFD simulation is compared against experimental prediction, showing a strong agreement between simulation and experimentation. Various liquid phase flow patterns within RPB are observed and these are cross-referenced with findings in the existing literature. Additionally, the impacts of rotational motion and flow rate are further assessed in the study. For the mass transfer performance, the prediction of the volumetric mass transfer coefficient, kLae of the air-water system from CFD simulation is studied. Two different mass transfer theories such as surface renewal theory and penetration theory are studied to predict kLae. It is observed that the kLae from the penetration theory closely follows the trend of the experimental data. Finally, a 2D simulation of the reactive absorption of CO2 by diethylenetriamine (DETA) in RPB is developed and compared with the existing available data in the literature. The present model underpredicts CO2 capture efficiency in RPB, which needs further improvement in reaction kinetics. In general, the present CFD model has the capability of predicting the transport characteristics of RPB.

Falling film hydrodynamics and heat transfer under vapor shearing from various orientations

Vapor shearing is a common issue encountered in the operations of falling film heat exchangers. The vapor stream effect depends on its orientation. This study investigates liquid film hydrodynamics and heat transfer performance under the influence of vapor streams from different orientations. The results indicate that both orientation and velocity of vapor determine the encountering time and position of the films on the tube's two sides. The liquid film thickness uniformity and the liquid column deflection vary significantly depending on the orientation and velocity of the vapor. Zones of accelerated liquid film, climbing liquid film, liquid stagnation, and transition of liquid film flow pattern are observed. The gradient of film thickness along the tube axis and the deflection in time-averaged peripheral film thickness increase as the vapor orientation varies from 0° to 90° and subsequently decrease as the vapor orientation varies from 90° to 180°. Vapor streams have more pronounced effects on time-averaged peripheral film thickness in regions close to the liquid inlet and outlet. Vapor streams result in changes in peripheral heat transfer coefficients toward the downstream side depending on the orientation and velocity of the vapor. The impact of vapor streams on the overall heat transfer coefficient does not directly correlate with the velocity of the vapor when maintaining the same orientation.

A real-time measurement and analysis method for gas holdup in a wet scrubber with the use of image information entropy

Wet scrubbers are often used in various types of industrial workshops to separate dust particles from the air. Non-uniform gas–liquid flow patterns above the sieve plate can result in significant losses in purification efficiency for particles. To improve the flow pattern via sieve plate design and to more accurately predict purification efficiency, a better understanding of the gas holdup is required. Various methods have been developed to measure and analyze the gas holdup from local and global perspectives. However, for guiding the operation and design of reactors, it is obviously insufficient to obtain the phase holdup characteristics under a steady state. The spatial and temporal characteristics of gas holdup in a wet scrubber are rather difficult to measure in real time with the current techniques. In this study, a fast real-time method for measurement of gas holdup characteristics was proposed, based on image information entropy analysis. The axial and radial profiles of gas holdup under different bubble washing operation statuses were obtained and are discussed here. More detailed information about the gas holdup above the sieve plate under various operation conditions has been attained. Sieve plate resistance and bubbling state were analyzed with the use of image information entropy.

Prediction of two-phase flow patterns based on machine learning

Due to the advantages of flexibility, security and economy, small modular reactor (SMR) has become a research hotspot in the field of nuclear energy. Gas liquid two-phase flow is one of the most common phenomena for the research and development of SMR. An effective two-phase flow pattern prediction model with high accuracy is very crucial since it will impact the thermal–hydraulic and heat transfer phenomena, and consequently, the safety of SMR. In this paper, support vector machine (SVM), Random Forest (RF) and K-Nearest Neighbor (KNN) algorithm were chosen as the candidates of machine learning (ML) models. we selected 12 databases to train and test ML models. Through the identification of flow pattern feature correlation and the preprocess of dataset, we proposed an ML model for gas–liquid flow pattern prediction based on the improved K-Nearest Neighbor (KNN). its accuracy can reach more than 99%, higher than the traditional methods.

Liquid Flow Patterns and Particle Settling Velocity in a Taylor-Couette Cell Using Particle Image Velocimetry and Particle Tracking Velocimetry

Summary Controlling the downhole pressure is an important parameter for successful and safe drilling operations. Several types of weighting agents (i.e., high-density particles), traditionally barite particles, are added to maintain the desired density of the drilling fluid (DF). The DF density is an important design parameter for preventing multiple drilling complications. These issues are caused by the settling of the dense particles, an undesired phenomenon also referred to as sagging. Therefore, there is a need to understand the settling characteristics of heavy particles in such scenarios. To this end, simultaneous measurements of liquid phase flow patterns and particle settling velocities have been conducted in a Taylor-Couette (TC) cell with a rotating inner cylinder and stationary outer cylinder separated by an annular gap of 9.0 mm. Liquid flow patterns and particle settling velocities have been measured using particle image velocimetry (PIV) and particle tracking velocimetry (PTV) techniques, respectively. Experiments have been performed by varying the rotational speed of the inner cylinder up to 200 rev/min, which is used in normal drilling operations. Spherical particles with diameters of 3.0 mm or 4.0 mm and densities between 1.2 g/cm3 and 3.95 g/cm3 were used. The liquid phases studied included deionized (DI) water and mineral oil, which are the basic components of a non-Newtonian DF with a shear-thinning viscosity. The DF is a mud-like emulsion of opaque appearance, which impedes the ability to observe the liquid flow field and particle settling in the TC cell. To address this issue, a solution of carboxymethyl cellulose (CMC) with a 6% weight concentration in DI water was used. This non-Newtonian solution displays shear-thinning rheological behavior and was used as a transparent alternative to the opaque DF. For water, PIV results have shown wavy vortex flow (WVF) to turbulent Taylor vortex flow (TTVF), which agrees with the flow patterns reported in the literature. For mineral oil, circular Couette flow (CCF) was observed at up to 100 rev/min and vortex formation at 200 rev/min. For CMC, no vortex formation was observed up to 200 rev/min, only CCF. The settling velocities for all particles in water matched with the particle settling velocities predicted using the Basset-Boussinesq-Oseen (BBO) equation of motion. For mineral oil and CMC, the results did not match well with the predicted settling velocities, especially for heavy particles due possibly to the radial particle migration and interactions with the outer cylinder wall.

Non‐invasive experiments on the fluid film behavior in a horizontal rotating cylinder

AbstractSubject of our investigations is the spatial distribution of a Newtonian liquid within a partially filled horizontal rotating hollow cylinder in dependence of the variables angular velocity and angular acceleration, cylinder filling and cylinder geometry as well as viscosity of the liquid. We focus on the development of a thin liquid film at the inner cylinder wall. The layer thickness was measured using a non‐invasive laser‐induced fluorescence measurement technique. In addition, the liquid distribution and flow topologies were observed and described using optical measurements.The occurring liquid distributions can be distinguished in three different states. At low angular velocities most of the liquid is located at the bottom area of the cylinder. However, a thin liquid film is always pulled out of the reservoir from the rotating cylinder wall. With increasing angular velocity more and more liquid is deflected and the locally measured film thickness increases. Exceeding a critical angular velocity, a centrifuged distribution of the whole liquid establishes. In this state the measured film thickness fits the theoretical calculated value quite well. Very complex liquid distributions and flow patterns develop in particular at critical angular velocities. In detail, at all investigated cylinder systems two critical angular velocities were verifiable, the so‐called transition points of liquid distribution. At the first critical velocity, the centrifuged state develops. With deceleration of the system a second critical angular velocity exists. Below this value the centrifuged distribution of the liquid collapses and moves back again to the bottom of the cylinder. A thin film is still pulled out of this reservoir. The second critical angular velocity of the break down is always smaller compared to the first one at which the centrifuged state develops. Both of them can be influenced using the investigated parameters. Eventually, we show that the locally measured film thickness also depends on these parameters.

Microfluidic systems with a pulsating heat pipe

This research addresses a critical issue in modern microelectronics, which arises from increased miniaturization and heat generation, necessitating effective temperature control. The study focuses on pulsatile heat pipes, offering a passive and highly efficient heat transfer solution by utilizing fluid and vapor phases within a closed capillary channel. To enhance temperature regulation, microfluidics are employed with integrated separation barriers to improve capacity and efficiency. Altering the flow pattern of liquid and vapor plugs through droplet generation may enhance thermal performance. The study demonstrates the accuracy of the heat transport model through mathematical and empirical data comparison, achieving a remarkable 90.9% accuracy and efficiency. Pulsatile flows, especially in microfluidic systems, exhibit advantages over steady flows, promising avenues for future physics-based research.

Numerical analysis of the behavior of molten pool and the suppression mechanism of undercut defect in TIG-MIG hybrid welding

In order to investigate the multi-coupling transport phenomena in TIG-MIG hybrid arc welding, a three-dimensional model including droplet and molten pool was established. An innovative distribution pattern of arc heat and force that adapted to the evolution of molten pool surface was proposed, achieving a unified distribution of "arc current density-arc pressure-electromagnetic force-arc heat". The effect of TIG arc on molten pool behavior and undercut defect was quantitatively analyzed by comparing TIG-MIG hybrid welding with traditional MIG welding. The results showed that the electromagnetic repulsion between the two arcs with opposite currents increased the aspect ratio of the hybrid arc heat and force distribution. It led to a long and narrow gouging region, where the promoting effect of inertial force on the undercut was weakened by arc pressure and hydrostatic pressure. The liquid metal with a lower cooling rate had sufficient time to fully fill the weld toe and suppressed undercut. Sensitivity and dimensional analysis illustrated that the TIG-MIG hybrid arc eliminated undercut by reducing the inertia force, adjusting the arc pressure distribution, and enhancing the hydrostatic pressure. The groove sizes was predicated based on molten pool characteristics, including the stress state of liquid metal, morphology, and fluid flow patterns. It revealed the quantitative relationships among welding parameters, behavior of molten pool, and weld bead formation, promoting the implementation of digital twinning technology in the manufacturing industries.

Interconnected ordinal pattern complex network for characterizing the spatial coupling behavior of gas-liquid two-phase flow.

The complex phase interactions of the two-phase flow are a key factor in understanding the flow pattern evolutional mechanisms, yet these complex flow behaviors have not been well understood. In this paper, we employ a series of gas-liquid two-phase flow multivariate fluctuation signals as observations and propose a novel interconnected ordinal pattern network to investigate the spatial coupling behaviors of the gas-liquid two-phase flow patterns. In addition, we use two network indices, which are the global subnetwork mutual information (I) and the global subnetwork clustering coefficient (C), to quantitatively measure the spatial coupling strength of different gas-liquid flow patterns. The gas-liquid two-phase flow pattern evolutionary behaviors are further characterized by calculating the two proposed coupling indices under different flow conditions. The proposed interconnected ordinal pattern network provides a novel tool for a deeper understanding of the evolutional mechanisms of the multi-phase flow system, and it can also be used to investigate the coupling behaviors of other complex systems with multiple observations.

Experimental investigation of oil film flow and droplets behavior in the annular channel of a cyclone separator

The separation of the gas and liquid in the gas-liquid cyclone separator is achieved through the swirling flow. The liquid film flow characteristics and the dynamics of droplets impacting the liquid film are very important for the separation performance, but these phenomena have not been well understood in the swirling flow. In this work, an experiment was conducted to investigate the liquid film flow and droplet impingement in the annular channel of the gas-liquid cyclone separator. Three regions of the annular channel could be divided based on the film flow patterns, which were the inlet region, the annular region, and the outlet region; and four typical droplet impact outcomes could be observed, which were splashing, coalescence, bouncing, and jet breakup. According to the characteristics of the liquid film and the outcome of droplet liquid film impingement, if the droplet splashing in the inlet region could be weakened and the length of the annular region was lengthened, it would be beneficial for gas-liquid separation. The impact outcomes were shown to undergo a transition from bouncing to coalescence as the droplet Weber number increased. Droplet coalescence was affected by the disturbance of gas flow and the evenness of the liquid film, so when the superficial velocity of the gas flow was fixed, the transition boundary was constant whatever the liquid volume fraction in the channel, and when the Reynolds number of the gas flow increased, the transition boundary of droplet Weber number increased first and then decreased. This work may provide a basis for a comprehensive understanding of the liquid film flow pattern and droplet behavior in the cyclone separator, and the results have the potential to be applied in other multiphase studies.

Experimental study of swirling flow pneumatic liquid-carrying characteristics in the vortex tool inserted tube under liquid loading conditions

Liquid unloading by vortex tool is one of the most important applications of swirling flow pneumatic conveying. However, due to swirl decay, the evolution of gas–liquid flow patterns and the dynamic characteristics of pressure drop downstream of the vortex tool are much more complex than those in non-swirling flow. In this study, the gas–liquid flow patterns and pressure drop inside the vortex tool inserted tube (ID = 60 mm) under liquid loading conditions were experimentally studied and compared with those of the plain tube. With the superficial gas velocities ranging from 0.5 to 6.0 m/s and superficial liquid velocities of 0.01, 0.02, and 0.04 m/s, the effects of the structural parameters and stages of vortex tools on the pressure drop were discussed. The experimental results reveal that three distinct swirling flow patterns can be identified downstream of the vortex tool, namely swirling gas column flow, swirling churn flow and swirling annular flow. The insertion of vortex tool facilitates an earlier transition of the churn flow to the annular flow, and the induced swirling flow can restrain the liquid from falling back. The helix angle of the corkscrew deflector has a more significant effect on the pressure drop than its length. By reducing the helix angle from 54° to 45°, the total pressure drop and downstream pressure gradient are significantly decreased, even lower than those of the plain tube. But the series combination of 54° and 45° vortex tools results in a significant increase in the downstream pressure gradient. Additionally, at low gas flow rate, negative frictional pressure drop occurs in both plain tube and vortex tool inserted tube. Hence, the new friction factor correlations were established respectively for the positive and negative friction regions in the cases of the tube with and without vortex tool, and most of the frictional pressure gradient predictions are within an error band less than 20%.

Liquid–liquid two-phase flow in a wire-embedded concentric microchannel: Flow pattern and mass transfer performance

In this work, flow pattern and mass transfer of liquid–liquid two-phase flow in a wire-embedded concentric microchannel are studied using toluene–water system. Droplet flow, slug flow, oval flow and annular flow are observed in the wire-embedded concentric microchannel. The effects of embedded wires and physical properties on flow patterns are investigated. The embedded wire insert is conducive to the formation of annular flow. The flow pattern distribution regions are distinguished by the Caaq (capillary number)–Weorg (Weber number) flow pattern map. When Weorg＜0.001, slug flow is the main flow pattern, and when Weorg＞0.1, annular flow is the main flow pattern. Oval flow and droplet flow are between Weorg=0.001–0.1, and oval flow is transformed into droplet flow with the increase of Caaq. The effect of flow rate, phase ratio, initial acetic acid concentration, insert shape and flow patterns on mass transfers are studied. Mass transfer process is enhanced under annular flow conditions, the volumetric mass transfer coefficient is up to 0.36 s–1 because of the high interfacial area and interface renewal rate of annular flow.