Gas-liquid Mixing Research Articles

Numerical simulation of mixing effect of compressed air–foam gas–liquid mixer

This article investigated the effect of geometric structural parameters on flow patterns and pressure drops and gas–liquid mixing effects of gas–liquid mixing devices. The computational fluid dynamics software FLUENT was used to calculate the airflow inside the mixer of a compressed air–foam gas–liquid mixing device with different cone angles, foam flow rates, air inlet inclination angles, and pipeline diameters. The results obtained are the pressure distribution, the liquid volume fraction, and the liquid phase streamlines in the mixing device. The numerical simulation results showed that for a gas–liquid mixing device, the optimal inlet inclination angle was 60°–70°, and the mixing effect of an equal diameter mixer was better than that of a variable diameter mixer, but it would reduce the mixing efficiency of the air and foam. The optimal pipeline diameter of the conveying pipeline was 190 mm, and the optimal cone angle of the mixing device was 55°.

Study on spray characteristics of biodiesel alternative fuels for in-cylinder environment of diesel engine

This paper presents an experimental study of spray characterization of MD-NH (a blend of methyl decanoate and n-heptane in a molar ratio of 1:1 to characterize biodiesel) in an in-cylinder environment of diesel engines to provide a reference for the experimental study of engines in advanced combustion mode. Based on the Peng-Robinson state equation, the thermodynamic model of real fluid was established, and the influence law of ambient temperature and pressure on the diffusion characteristics of fuel flow was analyzed. Based on the constant volume combustion bomb experiments, the variations of spray penetration distance, spray cone angle, spray projection area, spray air entrainment mass, and spray fragmentation forms in different critical environment conditions were studied. The results show that the transport properties of the fuel change abruptly within the critical point neighborhood of the fuel. As the ambient temperature increases, near the critical temperature, the thermal conductivity of biodiesel decreases and then increases; density and kinematic viscosity decrease at an accelerated rate; and surface tension increases to a maximum and then disappears sharply. The diffusion coefficient decreases sharply when the ambient pressure reaches the critical pressure. The spray characteristics of biodiesel in sub/supercritical conditions were different. Compared with the subcritical environment, the biodiesel spray penetration distance decreases, the spray cone angle increases, the spray projection area decreases, and the air entrainment mass increases in the supercritical atmosphere, which induces a gas-liquid interface mixing layer and promotes the mixing of biodiesel with the atmosphere gas. The experimental data in this paper fill the gap in the study of biodiesel spray characteristics in supercritical environments and provide a basis for high-fidelity numerical simulation of the spray model.

Study of multiphase pump front homogenizer on the performance of fluctuating gas-liquid two-phase incoming flow reforming

As an important component of multiphase mixing technology in oilfield, the homogenizer plays the role of buffering the fluctuation of gas rate of incoming flow and gas-liquid homogenization, providing good inlet conditions for multiphase pumps. In this paper, the homogenizer designed and manufactured by ourselves is connected into the multiphase pump loop for experiment. The results show that the designed homogenizer can effectively improve the homogeneity of gas and liquid phases at the inlet of the multiphase pump, which in turn improves the pressurization capacity of the multiphase pump. The gas flow is buffered under slug flow condition, and the effective running time of multiphase pump is extended. The unsteady numerical simulation of the flow field in the homogenizer is carried out for three kinds of slug flow conditions. The results show that the homogenizer suppresses the fluctuation of gas content rate for the three blockage conditions. The gas content fluctuations of the outlet fluid were reduced by 71.3%, 64.7%, and 69.4%, respectively, compared with the incoming flow. In the homogenizer, the liquid phase entering the perforated pipe produced a significant jet phenomenon, which significantly enhanced the mixing with the gas phase. In the horizontal tube near the outlet, the gas phase floats due to gravity. The guide vane at the outlet effectively suppressed the gas-liquid stratification phenomenon that occurs here, which further improves the gas-liquid mixing at the outlet.

A unified heat transfer model for gas-liquid two-phase mixing process in a rectangular channel based on steady status identification

Gas-liquid two-phase flow in rectangular channels involves thermal energy, chemical industry, and other fields. However, it is difficult to identify steady flow status and unify heat transfer model owing to the changeable mixing process and the complex industrial environment. In this work, the time series decomposition technique (i.e., variational mode decomposition) and neural network algorithm (i.e., long short-term memory) are employed to identify the steady flow pattern of the gas-liquid mixing process in vertical rectangular channels. The heat transfer model of a single bubble in a rectangular channel is established based on the geometrical characteristics of the bubble. Results demonstrate that a 30-dimensional feature vector is extracted from the conductivity time series for flow pattern recognition. The feature parameters of each intrinsic mode function are period, minimum, maximum, standard deviation, skewness, and kurtosis. Average accuracy of the new model is 94.58% with the highest at 95.83% and the proposed new model improves the recognition accuracy of steady flow pattern by 2.54–6.93% compared with other models adopted in this work. The precision of the new hybrid model is the highest while the number of decomposition layers for the conductivity time series is 5 and the bubble flow exhibits the largest heat transfer area under the same conditions. The proposed hybrid model can be used to enhance the identification accuracy of bubble flow in rectangular channels, contributing to curtailing unneeded flow patterns in industrial processes. The heat transfer model of a single bubble can provide a unified and convenient method for calculating industrial heat transfer. These findings provide a useful guideline for engineering design and energy-saving in the fields of thermal energy and chemical industry.

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.

Effect of Y-jet nozzle geometry and operating conditions on spray characteristics and atomizer efficiency

The investigation and optimization of the atomizer nozzle design are paramount for an efficient atomization performance. Motivated by internal mixing atomizers used in FCC-reactors in the oil industry, the present work aims to improve the gas-liquid mixing process promoted by a specific design of the Y-jet nozzle by investigating the impact of key geometric parameters. The performance assessment is conducted by investigating the internal mixing chamber pressure, high-speed images of the spray, and the analysis of droplet size and velocity spatial distributions. The investigation considers industrially representative operating conditions as opposed to the lower mass flow rates typically employed in lab-scale investigations. The geometry variation considers the length and opening angle of the internal mixing chamber, as well as the impingement angle between the gas and the liquid jets inside the atomizer nozzle. A particular geometric characteristic of the utilized nozzles is the mixing-chamber conical geometry, distinguishing them from conventional cylindrical geometries. The impact of the nozzle geometry and operation parameters on atomization efficiency and spray homogeneity are the main outcomes of this approach. Overall, nozzles with shorter mixing chambers promote more efficient atomization combined with small droplet sizes and a more homogeneous spray.

Computational investigation on the flow and mass transfer properties inside ejector of loop reactor based on CFD-PBM simulation

Conventional stirred kettle reactors suffer from inadequate gas-liquid mixing in many production processes, and their reaction rates are greatly limited. The loop reactor can achieve high mass transfer rates with low energy consumption. It is well suited for multiphase reactions with limited mass transfer and has the advantage of being excellent sealing and low cost. In this paper, ejector as the core of the loop reactor was investigated. Combining the Computational Fluid Dynamics (CFD) and Population Balance Model (PBM), the industrial-scale ejector model was constructed. The detailed motion behavior of bubbles and bubble size distribution were predicted. Due to the entrainment of the liquid phase, the gas enters the suction chamber and throat of the ejector, where the gas is mainly sheared and broken, providing a large specific surface area of the gas-liquid interface. Moreover, the flow and transfer properties were closely related to parameters such as nozzle-throat diameter ratio and liquid inlet velocity. Based on the results of the simulation, the gas-liquid mass ratio and the volumetric mass transfer coefficient were correlated with the structure and process parameters, and the correlation model was obtained, which provides guidance for the design of the loop reactor.

Numerical study on spray characteristics of liquid jets in supersonic crossflow

The spray characteristics of liquid jets in supersonic crossflow at different injection jet-gas momentum ratios are investigated numerically. The compressible two-phase flow large eddy simulation (LES) method is based on the Eulerian-Lagrangian scheme. The average droplet volume fraction is defined to quantify spray concentration distribution, which can also reflect the oscillation boundary of the spray. The LES predicted the spray boundaries at different injection jet-gas momentum ratios in the central and cross-sectional planes, which agree reasonably well with the experiment. Two sets of counter-rotating vortex pair (CVP) are in the gas-liquid mixing region. As injection momentum ratio q increases, the upper CVP increases. Still, the absolute size of the wall CVP remains almost unchanged, which means that the relative size of the wall CVP to the upper CVP becomes smaller. As q increases, the spray's overall distribution position is generally upward, and the number of droplets entering the near-wall region becomes small. Thus, droplet-wall interactions are weakened. The spray body increases with the increase of q, while the spray foot decreases gradually. In the central plane, the coherent structures near the wall are mainly composed of splashed droplets, and this phenomenon gradually weakens as q increases. Although the increase of q can increase the total droplet mass flow rate, the proportion of the droplet mass flow rate in the near-wall region to the total mass flow rate decreases, and the droplet mass flow rate in the near-wall region decreases.

Numerical simulation and analysis of the 3D transient muzzle flow field of underwater artillery

The in-depth study of the muzzle flow field contributes to the improvement of the gun and the design of the projectile. This study establishes an unsteady muzzle multiphase flow model of the underwater sealed launch with a three-dimensional scale. Among that, the VOF model is employed to trace the two-phase interface and the gas-liquid turbulent mixing is described by the standard k-ε turbulence model. Also, the established numerical model was validated by comparing underwater sealed launching experimental results. On this basis, numerical analysis on the muzzle flow field of the 30 mm artillery under different launching conditions were carried out by coupling with revised interior ballistic equations. The results show that the “necking” phenomenon occurs during gas-expansion process due to the interaction between water and projectile. Then, a “bowl-shaped” shock area is obviously formed at the muzzle. In addition, the Mach disk diameter and the corresponding growth rate are closely related to the projectile head cavitation diameter. The growth rate of Mach disk diameter increases with an increase of the cavitation diameter. When the muzzle velocities are different, the positions of the Mach disk formed are also different, presenting that the Mach disk is farther away from the muzzle with the increase of muzzle velocity.

Mechanism of nanoparticle aggregation in gas-liquid microfluidic mixing

Using gas-liquid segmented micromixers to prepare nanoparticles that have a homogeneous particle size, controllable shape, and monodispersity advantages. Although nanoparticle aggregation within a microfluid has been shown to be affected by the shear effect, the shear effect triggering conditions in gas-liquid two-phase flow is unclear and the aggregation behavior of nanoparticles under the shear effect is difficult to predict, resulting in uncontrollable physical and chemical properties of nanoparticle aggregates. In this study, a numerical simulation of nanoparticle aggregation in gas-liquid two-phase flow under the shear effect is performed using the CFD-DEM method. Then, the effects of total flow rate, gas-liquid two-phase flow ratio, and particle volume fraction on particle aggregation were analyzed to achieve control of particle aggregation shape and size. Meanwhile, the triggering mechanism of the shear effect and the mechanism of the shear effect on the aggregation of nanoparticles were clarified. The results show that increasing the total flow rate or decreasing the gas-liquid two-phase flow rate ratio can induce the shear effect, which reduces the particle aggregation size and makes the morphology tend to be spherical. Moreover, increasing the particle volume fraction, and total flow rate or decreasing the gas-liquid two-phase flow rate ratio also increases the number of particle collisions and induce interparticle adhesion. Hence, particle adhesion and the shear effect compete with each other and together affect particle aggregation.

Experimental and Numerical Study on the Slug Characteristics and Flow-Induced Vibration of a Subsea Rigid M-Shaped Jumper

The subsea jumper has become an essential part of subsea production systems as a gas–liquid mixing pipeline connecting the pipeline end manifold (PLEM) to the Christmas tree. During oil and gas transportation, as a common flow pattern, the alternating flow characteristics of the slug flow easily cause pipeline vibration, resulting in pipeline instability or fatigue damage. The present study investigates experimentally and numerically the slug flow characteristics in the subsea M-shaped jumper and its induced vibrations of the jumper. The flow pattern evolution and slug characteristics of the inner slug flow under different gas–liquid velocities are obtained: the slug frequency and slug velocity, as well as the pressure fluctuation and vibration characteristics caused by the slug flow. The results show that the pressure fluctuations in the front and rear parts of the M-type jumper are obviously different. With the increase in the air–water mixing, the two characteristics, the slug frequency, and the slug velocity also increase. The gas velocity has a greater influence on the slug frequency than the liquid velocity. The slug length decreases as the slug frequency increases. Furthermore, numerical simulations under various experimental conditions are carried out. The results show that the simulation results of the pressure data, the slug characteristics, and the induced vibration amplitude are in good agreement with the experimental data.

Topological approach for the measurement of mixing state quality in a vertical rectangular channel

The phenomenon of gas-liquid two-phase mixing inside rectangular channels has been encountered in metallurgical and chemical industries. However, a large number of traditional measurement methods are unable to reliably characterize the degree of bubbles overlap in this sort of channel. In this work, the mixing state quality of the gas-liquid two-phase inside rectangular channels are accurately characterized with the help of the topological invariants (i.e., Betti numbers). Specifically, the indicator Betti numbers ratio is introduced to quantitatively describe the degree of bubbles overlap and the complexity of Betti numbers ratio time series of the gas-liquid mixing process is quantified by the permutation entropy and the modified 0-1 test for chaos for the first time. Experimental results show that the evolution of the flow pattern inside the rectangular channels is mainly caused by bubbles collision, coalescence and circling during the gas-liquid two-phase mixing process. The inexplicable mixing states were observed other than the identifiable flow pattern inside the rectangular channels. Betti numbers ratio as a novel topological indicator can be successfully used to distinguish quantitatively the various inexplicable mixing state with the same Betti number. In the context of considering the bubbles overlap, the presented working condition with the greatest Betti numbers ratio owns the lowest complexity and chaoticity.

Study on the Numerical Model of Gas–Liquid Dispersion Driven by a Coaxial Mixer

As the flow basis for gas–liquid mixing, turbulence plays an important role in the movement of bubbles in a stirred tank. Motivated by the fact that the current models in the framework of computational fluid dynamics-population balance model lack an adequate assessment of the turbulence effects, the coaxial mixer was chosen as the subject of study, and different turbulence models, drag models, and breakup and coalescence models were compared and optimized. The results showed that the RNG k-ε model better characterized the turbulent scale and achieved a higher exactness for the gas-phase concentration in the axial direction. The Luo–Luo model modified based on the eddy capture mechanism could effectively describe the coalescence and breakup processes of bubbles. Additionally, in the presence of strong turbulence, the Ishii & Zuber model and the Brucato model outperformed other models in predicting gas dispersion and flow structure but still failed to capture the peak gas holdup. By analyzing the available data, a new correlation was proposed to elucidate the increase in drag coefficient caused by turbulence, which significantly improved the prediction accuracy of gas holdup.

Hydrodynamics, power consumption and bubble size distribution in gas-liquid stirred tanks

In this work, we present the results collected in a gas-liquid stirred tank by a combination of experimental and computational methods, with the aim of presenting original data on the bubbles size distribution and contributing to the development of fully predictive methods for the design and the scale-up of chemical and biochemical gas-liquid reactors. Basic variables which affect mass transfer and consequently the performances of industrial aerobic fermentations are discussed, with special focus on the bubble size distribution, the gassed power consumption and the gas cavities. The current developments of Two Fluid and Population Balance models for obtaining fully predictive results on gas-liquid mixing in stirred tanks are discussed. The results confirm that the correct prediction of the bubble size in the impeller zone is a crucial prerequisite for obtaining reliable results of the hydrodynamics of aerated stirred tanks.

Design and Experiment of Ecological Plant Protection UAV Based on Ozonated Water Spraying

With the development of pesticide substitution technology, ozonated water has been gradually applied in agricultural plant protection. This paper describes our development of an ecological plant protection unmanned aerial vehicle (UAV) that can produce and spray ozonated water while flying. Firstly, this paper carries out the design of the ozonated water system, including the selection of the ozone generator and the gas-liquid mixing method. Secondly, the conceptual design method of the ecological plant protection UAV is introduced, including total weight estimation, propulsion system selection, layout and structure design, battery modeling, center of gravity evaluation, and control system. Then, static analysis was computed in ANSYS Workbench on the UAV fuselage. Finally, the field test verified that the hovering time of the UAV could reach the design requirement of 10 min when it was fully loaded. The effective spraying width (with a height of 2 m and a speed of 3 m/s) is 5.25 m. The UAV was used to spray ozonated water with a concentration of 17 ppm continuously once a day; on day 7, the control effect could reach 76.4% and the reduction rate of the larvae population was 59.3%. Therefore, spraying ozonated water with a concentration of 17 ppm every day by using the ecological plant protection UAV can effectively control broccoli diamondback moth larvae and achieve the control effect of traditional pesticides (Chlorantraniliprole SC).

The characteristics of gas-liquid dispersive mixing and microbubble generation in turbulent adjustable jet flow field

In this study, the gas-liquid two-phase mixing process and the microbubbles formation process in a jet flow field has been investigated by using a self-designed on-line measurement system for measuring bubble generation characteristics and the Volume of Fluid (VOF) model in numerical simulation methods for analyzing flow field distribution characteristics. The effect of turbulence intensity on the dynamic size distribution of microbubble has been considered. The characteristics and duration of the three stages during the bubble breaking process, namely, surface oscillation stage, surface tension stage and fracture stage, were analyzed. The results show that the increase of turbulence intensity in jet flow will further promote the imbalance between the external deformation force and the surface tension resisting the deformation of the bubble, and promote the breaking probability of bubble. However, when the bubble breaks to a sufficiently small size, the surface tension against bubble deformation will increase sharply, the surface free energy needed to overcome for bubble breakage is very large, and the breakage probability of bubble will significantly decrease. Compared with the breaking process of bubbles, the increase in turbulence intensity will greatly promote the bubble coalescence process, which will ultimately become the main reason for affecting the bubble size distribution. Moreover, the influence of flow field distribution characteristics on bubble size distribution and average bubble size change is analyzed by using Population Balance Model.

Morphology Study of Hydrate Shell Crystal Growth on a Microbubble Interface in the Presence of Additives

Bubble dispersions in water can be observed in both wellbore or subsea piping as well as subsea gas seepages. The hydrate risk in subsea pipelines or methane leaks from the cold spring into seawater can be strongly influenced by the hydrate crystal growth on bubbles. In addition, the bubbling method has been proven to be an effective method to enhance the gas–liquid mixing pathway and promote hydrate’s rapid formation in the application of hydrate-based technologies, yet the microscopic mechanism of hydrate film growth on the bubbles still needs to be further clarified. In this study, the hydrate crystal growth morphology evolution at the microbubble interface was investigated by a high-resolution microscope combined with the temperature-controlled stage. The results showed that the hydrate crystals nucleated rapidly at the bubble interface to form a hydrate shell-coated structure in a pure water system. The defect growth mechanism dominated the hydrate crystals growth at the bubble interface in additive solutions. Hydrate did not nucleate directly on the surface of bubbles but by trapping guest molecules around the shrinking bubbles to form aggregated hydrate agglomeration in the presence of surfactants. In addition, the bubbles tend to provide a steady stream of gas source for hydrate formation. The growth of hydrate shells contributed to a normal distribution of bubble shrinking rates, with an average rate of 9 μm/s in 0.5 wt % NaCl solution. The existence of a high concentration of ions or organic molecules at the microbubbles’ interface and the exclusive effect played a dominant role in the process of hydrate formation. In addition, it was found that the repulsive effect of ions at the bubble interface on hydrate formation was weak under a high subcooling degree. However, other organic molecule promoters still accelerated the hydrate’s formation rate because they increased the dissolution and diffusion rate of gas in solution. The results are expected to strengthen further the applications relating to hydrate-based phase transition promotion technology in the industry in energy storage, gas separation, or inhibition techniques in flow assurance of the offshore industry.

An improved thermal jet for the propellant launching system

This work is focused to study the energy release and flow behavior of liquid propellant during internal ballistics cycle of liquid launching system on the base of the thermal gas jet. Especially, an improved thermal jet is proposed via new type of stepped-wall chamber structure and thus the energy release efficiency is also enhanced with a decrease of pressure oscillation. The combustion of the liquid propellant in this system with a base ignition strongly depends on hydrodynamic instability of gas-liquid mixing process with high temperature and high pressure. The chamber structure has been verified to be as a means for controlling the instability problem in this propulsion process and three types of stepped-wall chambers are investigated to account for the effect of the stage on the flow and energy release behavior of liquid propellant based on this improved thermal jet. For the stepped-wall structure with three stages, the local liquid can be entrained into the Taylor cavity with more intense turbulent mixture at the corner of steps because of the existence of vortices under Taylor-Helmholtz effect. The corresponding propulsion efficiency γ only reaches to 1.003 mm−2 ms−1 and the muzzle velocity of the vehicle is 911 m/s with the maximum pressure of 317 MPa. Consequently, the heat transfer process from the high-temperature combustion-gas to the liquid propellant is also enhanced for the chamber with three stages, and more liquid propellant can be involved into the chemical reaction with providing more energy for the propulsion process of the launching system.

Investigation of boiling hydrogen heat transfer characteristics under low-pressure conditions

Understanding the heat transfer characteristics of boiling hydrogen is a critical issue in developing of liquid hydrogen system. However, there has been insufficient systematic research on boiling hydrogen flow characteristics. This report investigates the heat transfer characteristics of boiling hydrogen, following our previously reported gas-liquid mixing characteristics and flow regime transition characteristics. This study generated an arbitrary gas-liquid two-phase flow state in 15 mm tube by experimentally heating liquid hydrogen with an electric current. The experimental conditions were a pressure of 250 – 300 ▪, a mass flux of 50 – 110 ▪, and a heat flux of 0 – 12 ▪. Based on the experimentally obtained heat transfer coefficients, a heat transfer prediction model for boiling hydrogen was constructed, considering the change in the heat transfer process from liquid single-phase to saturated boiling. A one-dimensional flow simulator was also constructed that applies the proposed model and confirms that the model can be reduced the wall temperature error to about 1/10 against the conventional models.

Influence of Bionic Waveform Leading Edge Blade on Drag Reduction Characteristics of Mixed Pump

Because the helical axial flow gas-liquid mixing pump has the great advantage of conveying gas-liquid two-phase mixed medium, it has become the main core equipment for deep-sea oil and natural gas exploitation. The gas phase aggregation and bubble movement trajectory in the impeller channel have been widely studied, but the increase of medium flow resistance caused by flow separation has not been deeply discussed. Combined with the Euler multiphase flow model and the SST k-ω turbulence model, the numerical calculation of the helical axial flow gas-liquid mixed pump is carried out. Under design flow conditions Q = 100 m3/h, head H = 30 m, speed n = 4500 r/min, specific speed ns =213.6 r/min, and under different inlet gas content conditions, the influence of the bionic waveform leading edge blade on drag reduction characteristics of the helical axial flow gas-liquid mixed pump was investigated. By designing the blade with a leading-edge structure with different heights and pitches, the separation of the mixed medium and the suction surface is effectively suppressed, and the flow resistance of the medium in the 1/10 area of the inlet end of the blade is reduced. The results show that when the height A is 0.25%L and the pitch λ is 12.5%h, the maximum drag reduction rate in this region is 52.6%, the maximum increase in efficiency of the mixed pump is 2.2%, and the maximum increase in head is 4.8%. This study can provide technical support for flow drag reduction in gas-liquid mixed pump.