Gas-liquid Interaction Research Articles

Unsteady Mass Transfer in Bubble Wakes Analyzed by Lagrangian Coherent Structures in a Flat-Bed Reactor

To increase the yield and selectivity in reactive bubbly flows, the gas-liquid interactions have to be understood in depth. In the current fundamental study, flow and concentration data of the wakes of two-dimensional bubbles in an organic solvent are obtained experimentally in a flat-bed reactor. The unsteady mass transport phenomena in these turbulent wakes of two freely rising, two-dimensional bubbles with bubble Reynolds numbers Re=949 and Re=388 are evaluated by analyzing Lagrangian Coherent Structures (LCS). To reveal how LCS govern the transport of dissolved gas in bubble wakes, and therefore affect gas-liquid reactions, LCS in two-dimensional velocity fields are computed and compared with concentration fields of dissolved gas. The analysis of backward Finite Time Lyapunov Exponent (bFTLE) fields reveals coherent fluid dynamic structures for both bubble Reynolds numbers studied. In the higher bubble Reynolds number case, two types of coherent structures are found, which hinder the mixing of the dissolved gas and the liquid bulk. Repelling LCS are found to enclose parcels transported into the vortices, and indicate thus, which fluid parcels can possibly take part in chemical reactions. Due to higher mixing, unveiled by details from the LCS and FTLE analyses, and therefore increased contact area between dissolved gas and fresh liquid, higher yields of reaction products are suggested for the lower bubble Reynolds number case in this two-dimensional study. This is contradicting the rule of thumb that mixing increases for higher bubble Reynolds numbers.

Numerical Calculation of Slosh Dissipation

As part of the Sloshing Wing Dynamics H2020 EU project, an experimental campaign was conducted to study slosh-induced damping in a vertically excited tank filled with liquid water or oil and air. In this work, we simulate these experiments using two numerical approaches. First, a single-phase, weakly compressible liquid model is used, and the gas flow (air) is not modeled. For this approach, a proven Smoothed Particle Hydrodynamics (SPH) model is used. In the second approach, both phases are simulated with an incompressible liquid and weakly compressible gas model via a Finite Volume Method (FVM) using Volume-of-Fluid (VOF) to track the liquid phase. In both approaches, the energy distribution of the flow is calculated over time in two- and three-dimensional simulations. It is found that there is reasonable agreement on the energy dissipation evolution between the methods. Both approaches show converging results in 2D simulations, although the SPH simulations seem to have a faster convergence rate. In general, the SPH results tend to overpredict the total dissipation compared to the experiment, while the finite volume 2D results underpredict it. Time histories of the center of mass positions are also compared. The SPH results show a much larger vertical center of mass motion compared to the FVM results, which is more pronounced for the high Reynolds number (water) case, probably linked to the absence of the air phase. On the other hand, the limited center of mass motion of the FVM could be linked to the need for higher spatial resolutions in order to resolve the complex gas–liquid interactions, particularly in 3D.

Understanding keyhole induced-porosities in laser powder bed fusion of aluminum and elimination strategy

Laser powder bed fusion (LPBF) technology has the potential to revolutionize the fabrication of complex metal components in the aerospace, medical, and automotive industries. However, keyhole pores may be induced during the rapid laser-metal interaction (∼10−5 s) of the LPBF. These inner porosities can potentially affect the mechanical properties of the fabricated parts. Here, based on the experimentally observed keyhole-penetration pore (KP-pore) led by the keyhole splitting of the molten pool in LPBF, a multi-physics finite volume model was established to reveal this mechanism, where keyhole pores were formed under the direct contact of keyhole and solid metal substrate, which is different from the previously reported gas–liquid interaction. The formation mechanisms of the KP-pore, rear-front pore (RF-pore), and rear pore (R-pore) could be attributed to different keyhole fluctuation modes. The effects of the powder on the characteristics of the keyhole, molten pool, and pore formation were explored. The increased pore counts and decreased size were owing to the powder-promoting keyhole and molten pool oscillation. In addition, a relationship map between the input energy density and pore number was built via a high-throughput simulation, providing a strategy to reduce or remove the pores in laser powder bed fusion.

Constraint Handling and Flow Control in Stirred Tank Bioreactors with Magnetically Coupled Impellers

In this study, Computational Fluid Dynamics (CFD), applied to a non-Newtonian fluid, was developed to characterize gas-liquid interaction and mixing process in a 15 m3 (working volume) bioreactor. The bioreactor was equipped with four arrangements of standard Rushton, Pitch-blade and Scaba® impellers. Gas-liquid hydrodynamics was estimated based on CFD results. The chosen operating conditions were defined by the settings used for production of xanthan gum via fermentation route by Xanthomonas campestris. The mixing process was simulated by using the k-epsilon turbulence model, Multiple Reference Frame and Population Balance Model approaches. The simulation results have been compared and analyzed by isosurfaces, volume fractions, velocity graphs, torques and flow analysis calculations. Obtained results revealed that for the Pitched-Pitched-Pitched arrangement to avoid the constraint-imposed overload torque limitations impeller diameter size should be reduced by 10%. The use of Rushton-Rushton-Rushton impeller arrangement was discouraged for non-Newtonian pseudoplastic fluid mixing, whereas Pitched-Rushton-Scaba and Scaba-Rushton-Pitched impeller arrangements were both acceptable.

Gas–Liquid Interaction Characteristics in a Multiphase Pump under Different Working Conditions

In this study, we analyze gas–liquid interaction characteristics using a heterogeneous two-fluid model to investigate the influence of interphase force on multiphase pump performance. Two-phase transport platforms are used in oil and gas development to eliminate the need for separation equipment and reduce costs. Full-channel numerical calculations were conducted for an axial-flow multiphase pump based on different inlet gas void fractions (IGVFs) and flow rates. The results indicate that the interaction force of each phase is relatively large in the rotor–stator interference region, and the drag, lift, virtual mass, and turbulent dispersion forces increase with an increase in IGVF or when deviating from the design condition (Q = 50 m3/h). The interphase forces (resistance, lift, virtual mass force, and turbulent dispersion) increase considerably in the impeller passage and minimally in the guide blade passage. Under the conditions of small and high flows, the force of each phase changes considerably in the impeller and diffuser passages, respectively. Furthermore, the turbulent kinetic energy in the flow passage corresponds to the change trend of the interphase force, indicating that the interphase force causes energy loss inside a multiphase pump. These results provide essential information for the optimization of the hydraulic design of multiphase pumps.

Natural frequency discontinuity of vertical liquid sheet flows at transcritical threshold

The natural and forced dynamic response of a gravitational plane liquid sheet (curtain) of finite length interacting with an unconfined gaseous ambient is numerically and experimentally investigated. The global eigenvalue spectrum obtained by means of a linear inviscid one-dimensional model, accounting for the coupling between the curtain motion and the ambient pressure disturbances, clearly shows an abrupt increase (jump) in the characteristic natural frequency of the flow when the supercritical ( $We>1$ ) to subcritical ( $We<1$ ) transition occurs, with the Weber number $We$ defined as the ratio between inertia and capillary forces. On the other hand, the numerical simulation of the forced sheet response does not show any discontinuity between supercritical and subcritical conditions, as recently found by Torsey et al. (J. Fluid Mech., vol. 910, 2021, pp. 1–14) in the case of an infinite liquid sheet subjected to imposed ambient pressure disturbances not coupled with the curtain motion. It is argued that the forced liquid sheet behaviour varies continuously in shape and amplitude between the two regimes, not depending on the specific liquid–gas interaction model considered, whilst the natural frequency of the finite flow system does undergo a discontinuity, which can be theoretically predicted by the model of sheet–ambient interaction employed here. As a major result, the experimental evidence of the natural frequency jump is for the first time provided as well.

Comparative Study on Interphase Force Model of Gas-Liquid Two-Phase Bubbly Flow Based on OpenFOAM

It is essential to choose an appropriate interphase force model when studying gas-liquid two-phase bubbly flow by numerical calculation. Because of the complexity of gas-liquid interaction, researchers have developed many models, while there is still a lack of corresponding guidelines when selecting the combination of interphase force models. In the present study, taking the DEDALE experimental condition as the research object, the parameter distribution characteristics of void fraction and gas-liquid two-phase velocity under the experimental condition are simulated, and the calculation results of different interphase force models are analyzed and compared with the experimental results. The effects of different interphase force models on the local parameter distribution characteristics of the two phases are analyzed and discussed, and the optimal model combination under this experimental condition is obtained.

Experimental study on gas liquid interaction outside flow focusing/blurring nozzle

BackgroundAs two-phase flow nozzle, flow focusing/blurring nozzle has important application prospect in droplet generation and atomization fields. However, due to the incomplete understanding of the gas-liquid interaction, the application of this nozzle is limited. MethodsIn this paper, the relationship between gas-liquid interaction, flow modes and atomization ability of the flow focusing/blurring nozzle was studied by experimental method. Significant findingsThe results show that the flow modes of the nozzle is determined by the fluid inertial force. The gas and liquid inertia forces promote the flow mode to change from flow focusing to flow blurring. Gas fluid promotes the breakup of droplets, thus improving the atomization of liquid fluid, while the effect of liquid fluid is opposite. The introduction of gas fluid improves the atomization ability and the stability of the nozzle.

Flow-Independent Liquid Jet-in-Crossflow Injection Using Physical Obstructions

AbstractThe present work explores a novel flow-independent liquid injection scheme, incorporating solid obstructions to alter the key mechanisms controlling the liquid breakup and trajectory. These obstructions, designated pintiles, minimize the variability of fuel injection dynamics over a range of operational conditions. To better understand these mechanisms, a variety of solid pintile obstructions are designed and incorporated into a liquid jet in crossflow experiment. The design parameters of interest include the fraction of the liquid jet orifice blocked by the pintile (orifice coverage), the vertical height of the pintile in the liquid stream, and the angle of the obstruction with respect to the injection plate. All pintiles are tested at non-reacting ambient temperature and pressure conditions over a range of engine relevant Reynolds numbers (Re = 171,500–343,000), momentum flux ratios (Q = 4–45), and Weber numbers (We = 20–80) to understand the leading order effects the solid–liquid–gas interaction has on the liquid breakup and trajectory control. The results demonstrate that the most consistent jet trajectories are achieved with pintiles with a high orifice coverage, a large height, and an angle of 45 deg. Other parameters, such as the transverse spread of the liquid jet and droplet size distributions, are quantified to ensure that consistent jet trajectories can be achieved without imparting adverse effects on other relevant combustion characteristics. The results provide a foundational, first-order understanding on how to minimize variability of liquid injection across engine relevant Reynolds numbers, Weber numbers, and momentum flux ratios.

Solvent‐dependent gas‐driven fabrication of shape-controlled silica: insights into the active sites and catalytic mechanism of silica-catalyzed Baeyer-Villiger reaction

Silica nanomaterials have attracted widespread attention because of their various advantages. In this work, a solvent-dependent gas-driven mechanism is first demonstrated for manufacturing silica nanostructures with adjustable shell size and morphology under the gas-liquid interface interaction without the templating agent. The condensation rate of tetraethylorthosilicate in water and ethanol is found to play a decisive role in the gas-liquid interface inducing the morphological evolution of silicon nanosheets, hollow structures and nanospheres. The obtained silica show promise in the Baeyer-Villiger (B-V) reaction in the O2/aldehyde system. Detailed experimental results find that the radicals species in silica play a decisive effect in the excellent activity of catalyzing the B-V reaction. Meanwhile, a comparative experiment to further determine that the rate-determining step of the silica catalyzing the B-V reaction is that the catalyst accelerate the process of aldehyde generation peracid. This work provides a solvent-dependent gas-driven strategy to synthesize shape-controlled SiO2 for B-V reaction.

Investigation of Pobeda furnace bubbling zone physics using cold modeling method Part 2. Hydro-gas dynamics of liquid blowing with gas using bottom gas-protected lance

The cold flow simulation of the Pobeda furnace bubbled bath hydro-gas dynamics was performed using the bottom lance in a protective gas shell. It was shown that gas infusion into liquid at Ar = 5÷60 is carried out in pulse-coupled mode. The gas-liquid interaction area was investigated at Ar = idem for separate and joint air egress through ring and round nozzles. A two-phase zone was formed in liquid that consisted of a «leg» featuring different geometrical shape, a cavity and a gas-liquid layer over the bath surface at all considered Ar values. The most peculiar features of blowing zone formation, flame configuration and its structure depending on blow injection configuration and Ar values were found out. It was detected that ejected liquid prevails in the cavity structure at intensive blowing through the lance center and ring gap, and its content increases as gas flow rate rises in the shell, and the «leg» near the nozzle exit consists of the gas phase. An assumption was made that the presence of additional sulfide melt amount in the oxidative jet provides more complete magnetite destruction in the bath volume and protective skull formation in close proximity to the nozzle. Sizes of most indicative geometrical areas of flame were quantified, and they demonstrated periodical and extreme jet spread behavior in liquid. Empirical equations were obtained that describe the relation between maximum longitudinal and transverse «leg» sizes at dynamical conditions of blow injection into the shell (Ar shell ) and central tube (Ar center ) for two value ranges Ar shell ≥ Ar center and Ar shell ≤ Ar center . It was found that blow injection into the shell increases «leg» extension velocity on the nozzle exit up to 137 mm/s. The dependence of average splash lift height (H avg , m) above the calm bath surface was defined, which is H avg = 0.027(Ar shell + Ar center ) 0.27 within 25 ≥ Ar shell ≥ 5 and 60 ≥ Ar center ≥ 12 ranges. Schlichting equation was used to calculate the value of maximum offset from the nozzle surface where the joint axial movement of ring and round jets in liquid is maintained with equal velocities. It is assumed that the protective effect of the bottom lance with the shell appears in the lance belt area over a distance of 7–10 cm from the nozzle exit. It was noted that the cavity after separation from the nozzle moves down vertically, and the countercurrent liquid flow bounding on the cavity front moves in an opposite direction slipping the phase interface with comparable velocity. Due to more intensive changes in the interaction zone transverse size in the nozzle area and noticeable lateral liquid movement it was recommended to take corrective actions to decrease the erosive effect of melt in the Pobeda furnace lance belt at the initial jet development area.

Numerical simulation of primary atomization process of liquid jet in subsonic crossflow

Studies of primary atomization of liquid transverse jets in subsonic crossflow consider surface waves as the main cause of jet fragmentation. The characteristics of surface waves during jet fragmentation have been initially analyzed, but there is a lack of understanding of the mechanism of surface wave generation and development. This paper investigates the primary atomization of liquid transverse jets in subsonic crossflow based on the numerical method of Large Eddy Simulation (LES) with the coupled level set and volume of fluid method (CLSVOF) interface tracking, combined with adaptive mesh encryption techniques, where the liquid phase medium is water. This paper focuses on the fine structure of the primary atomization of the jet column, including the evolution of the jet column and the process of shedding the surface of the jet column, to clarify the physical process of primary fragmentation of the jet. The near-field flow structure and gas–liquid interaction are also analyzed to investigate the mechanism of primary atomization of liquid transverse jets and the mechanism of surface wave generation and development in subsonic flows. The results show that the shear action of gas and liquid leads to the generation of Kelvin–Helmholtz (KH) unstable wave, and KH surface wave dominates the surface breaking of jet column. The extrusion of gas and liquid results in the unstable fluctuation of Rayleigh–Taylor (RT), and the RT surface wave dominates the jet column, and finally the cylindrical fracture occurs. The development trend of RT surface wave is to increase the wavelength along the jet direction. When the wavelength of the RT surface wave develops from 0.12 mm to 1.2 mm, the jet column will be columnar broken at the trough of the last RT wave.

Центробежные тарелки — высокопроизводительные и эффективные контактные устройства для массообменных колонн в нефтепереработке и нефтехимииствольных зонах добывающих скважин

The article discusses the original design of a contact device - a centrifugal plate for heat and mass transfer processes, which implements the idea of gas-liquid interaction in a swirling gas flow and further separationof liquid from gas using centrifugal force. Numerous tests of centrifugal trays have confirmed their high efficiency, providing the lowest reduced costs and, accordingly, the maximum economic effect when used in pressurized fractionation plants.

Analysis of Gas-Liquid Interaction in the Ionic Liquid Compressor for Hydrogen Refuelling Stations: Effects of Liquid Density

Analysis of Gas-Liquid Interaction in the Ionic Liquid Compressor for Hydrogen Refuelling Stations: Effects of Liquid Density

Experimental and numerical investigation of Cross-Flow nebulizer for developing optimized suction pressure

A pneumatic nebulizer, a device that supplies the spray of the mist of liquid using pressurized air. A cross-flow nebulizer is a very popular pneumatic nebulizer due to its robust design. It consists of a partially filled liquid vessel and an orifice-capillary assembly through which pressurized gas is supplied. When air passes through the orifice, low pressure develops in the capillary, leading to the free aspiration of liquid in the nebulizer. It is expected that nebulizers must have controllable and reproducible output performance. In this paper, an experimental and numerical investigation of the orifice-capillary assembly of a nebulizer is presented. A cross-flow nebulizer is fabricated using 3D printing. In the experimental study, the vacuum pressure and the gas velocity developed in the cross-flow nebulizer are recorded. The steady-state numerical analysis of the three-dimensional nebulizer using Ansys Fluent R19 software and gas–liquid interaction inside the nebulizer is studied. The effect of supply inlet pressure on the performance of the nebulizer, i.e. generating the vacuum at capillary, is presented. It has been observed that for a certain range, with an increase in supply inlet air pressure till 2 bar, the vacuum developed inside the nebulizer, i.e. in the liquid capillary of the nebulizer increase. But with a further increase in supply inlet air pressure, a negative relationship is seen. Hence for a given geometry, there exists an optimized orifice-capillary assembly configuration.

Spontaneous liquid outflow from hydrophobic nanopores: Competing liquid–solid and liquid–gas interactions

Understanding liquid flow behavior in a nanoenvironment is of utmost importance for a vast array of biological and engineering applications. Both the liquid–solid interaction (LSI) and liquid–gas interaction (LGI) significantly affect the liquid outflow from hydrophobic nanopores in a liquid–gas–nanopore system. However, the individual contribution of these interactions on the spontaneous liquid outflow from the hydrophobic nanopores is not clear. To fill this scientific gap, we present an experimental study of the competition between the LSI and LGI on the nanoscale liquid outflow behavior in a liquid nanofoam (LN) system. LN samples, consisting of water and nanoporous silicas with similar pore size distribution but different average pore sizes, are subjected to cyclic pressure-induced liquid infiltration-outflow tests with or without the presence of a gas phase. Considerable difference in the liquid outflow behavior has been observed as pore size varies, indicating the size effect on the competition between the LSI and LGI. In smaller nanopores, the stronger LSI dominates the liquid outflow behavior as the LGI is diminished due to the nanoconfinement enhanced gas oversolubility. In contrast, in larger nanopores, LGI becomes a stronger driving force for the liquid outflow. These fundamental findings provide important insights on liquid flow behavior in a nanoenvironment and can facilitate a rational design of high performance nanofluidics-based systems.

Analysis of Theoretical and Experimental Research on Bubble Parameters and Gas-liquid Interaction in Bubble Flow

Bubble flow is a phenomenon in which gas flows with liquid in the form of bubbles, which widely exists in production and life. As an important part of fluid mechanics, bubble flow also has a certain impact on the actual production process. This work briefly summarizes the development of research on bubble flow in recent years. Firstly, a brief introduction to the development process and current situation of bubble flow in chronological order is presented, and the main difficulties related to the research and development of bubble flow are also pointed out, including the complicated gas-liquid distribution pattern and the exchange of materials and energy between gas and liquid phases, which slow down scholars’ research progress. Then, several theoretical models for bubble flow research are introduced. These models take bubble parameters into account, including the ultimate velocity of bubble rising, the transfer of energy and matter in the coalescence, and rupture of the bubble, the phase distribution of the bubble in the tube, and the interaction between the bubble and the liquid (the shear stress produced by bubbles affecting the turbulence field). This work briefly explains the ideas of each model and the results obtained, compares and analyzes their advantages, disadvantages and limitations, and predicts the theoretical and technical means required for subsequent theoretical model construction. Finally, part of the experimental research is summarized, along with the process and technical means of each experiment as well as the relationship between the experimental results and the theoretical research. It is hoped that this work could help to have a preliminary understanding of the research process and research methods of bubble flow, and provide some perspectives for incorporating bubble flow hydrodynamic theory into industrial applications and real life.

Surfactants protect the activities of endoglucanase and cellobiohydrolase from gas-liquid interface

The reasons for nonionic surfactants mitigated the cellulase deactivation were investigated from the points of lignocellulose-cellulase interaction and gas-liquid interface-cellulase interaction. Surfactants strengthened the interaction between substrate and cellulase, increasing the adsorption capacity by 19.0 %–45.8 % and glucose yield by 15.4 %–17.0 % respectively. Gas-liquid interface had a negative effect on the enzymatic hydrolysis with low enzyme loading at high shaking speed or large interfacial size. The enhancement in glucose yield by surfactants at 250 rpm or large interfacial size was greater than that at 0−150 rpm or small interfacial size. When cellulase solution was incubated at 250 rpm and large interface, the addition of Tween 80 increased the endoglucanase and cellobiohydrolase activities from 76.7 % and 63.0 % to 103.1 % and 123.2 %, respectively. Surfactants protected the endoglucanase and cellobiohydrolase from gas-liquid interface to enhance the enzymatic hydrolysis of hydrogen peroxide/acetic acid-pretreated poplar.

Bubble refinement by non-invasive rotating flow

Gas–liquid flow widely exists in industrial processes. Bubble refinement is of importance because smaller bubbles lead to higher efficiency of the gas–liquid interaction. Here, the novel rotating flow is designed for bubble refinement without using invasive parts. The drag force along the flow direction and the additional shear-lift force applied on the mother bubble allow it to detach from the orifice more easily with smaller size. In addition, the non-invasive rotating flow generates a large velocity gradient in both the shear and normal directions, resulting in turbulent shear and normal stress, causing the rising mother bubbles to break up in either the shear or normal direction. As a result, the number of bubbles increases to 408 compared to 9 under the static condition. Approximately 50% of the bubbles in the liquid are less than 3.60 mm in size and the Sauter mean bubble diameter is reduced from 10.45 to 4.77 mm, a decrease of 54.41%. The bubble refinement mechanism in the non-invasive rotating flow applies to other occasions where no invasive parts are needed.

Numerical investigation of unsteady cavitating turbulent flows around a three-dimensional hydrofoil using stress-blended eddy simulation

The mechanism of flow instability, which involves complex gas–liquid interactions and multiscale vortical structures, is one of the hot research areas in cavitating flow. The role of turbulence modeling is crucial in the numerical investigation of unsteady flow characteristics. Although large-eddy simulation (LES) has been used as a reliable numerical method, it is computationally costly. In this work, we used a hybrid Reynolds-averaged Navier–Stokes (RANS) and LES model, that is, stress-blended eddy simulation (SBES), to improve the prediction capability for the cloud cavitating flow. Our hybrid approach introduces a shielding function to integrate the RANS model with the LES applied only regionally, such as to large-scale separated flow regions. The results showed that the periodic shedding of cavity growth, break off, and collapse around a three-dimensional Clark-Y hydrofoil was reproduced in accordance with experimental observations. The lift/drag coefficients, streamwise velocity profiles, and cavity patterns obtained by the SBES model were in better agreement with the experimental data than those obtained by the modified RANS model. The re-entrant jet dynamics responsible for the break off of the attached cavity were discussed. Further analysis of vorticity transportation indicated that the stretching and dilatation terms dominated the development of vorticity around the hydrofoil. In conclusion, the SBES model can be used to predict cavitating turbulent flows in practical engineering applications.