Simulation Of Gas-liquid Flow Research Articles

Understanding the role of perforations on the local hydrodynamics of gas–liquid flows through structured packings

Structured packings are widely used to perform gas–liquid separation processes as they provide a large mass-transfer area and low-pressure drop. The overall performance of these packings is governed by the local liquid distribution/gas–liquid interfacial area. The local liquid distribution is substantially influenced by the arrangement and geometrical features of the structured packing. While the influence of arrangement and few geometrical features on the local liquid distribution has recently been investigated using the structure-resolved simulations, the perforations on the structured packings are usually ignored. In the present work, we have performed structure-resolved gas–liquid flow simulations, using the Volume-of-Fluid (VOF) method implemented in the open-source C++ library OpenFOAM, in a periodic domain of Mellapak.250 with and without resolving the perforations. We show that the presence of perforations results in flow separation as well as droplet formation leading to an increase in the liquid holdup, interfacial and wetted areas, irrespective of the fluid properties and wetting conditions (specified using static contact angle ‘θw’) considered in this work. We also show that at an inclination angle ‘β’ of 45° from horizontal, the location of the perforations governs the local liquid distribution and the resulting flow metrics. However, at a β of 90°, the number of perforations governs the local liquid distribution, irrespective of their location. Further, we also show that the predictions of structure-resolved VOF simulations, with perforations resolved, are in a relatively better agreement with the correlations in the literature at small values of θw in terms of liquid holdup and interfacial area.

Three-dimensional gas–liquid flow simulation of a rotating packed bed using Eulerian porous media models

The rotating packed bed (RPB) is a typical equipment in chemical process intensification technology due to its excellent mass transfer performance. In this paper, a three-dimensional full-scale model was established based on the Eulerian two-fluid method to study the gas–liquid two-phase flow in RPBs. Three different single-phase wire screen packing pressure drop models coupled with the interfacial area model were used to construct resistance calculation methods for porous media, respectively. The results show that simulation deviations of the liquid holdup and the pressure drop of the m-K model range from 0.92 % to 27.61 % and 1.63 % to 34.59 %, respectively. In addition, the simulation accuracy of the liquid holdup of three models was obviously influenced by the rotational speed (N). The m-K model has the highest prediction accuracy at N = 500 ∼ 1500 rpm. At N = 2000 ∼ 2500 rpm, the B model has the highest prediction accuracy. Characteristics of gas–liquid flow under different conditions and nozzle designs were obtained. In particular, the impact of different nozzle designs on liquid distribution has been investigated using a new method based on user-defined functions (UDFs). A more homogeneous distribution of liquid within the packing can be achieved by increasing nozzle height, decreasing nozzle size, and increasing the number of nozzles.

A generalized variational level set method without frequent reinitialization for simulations of gas-liquid flows

A generalized variational level set method without frequent reinitialization process is proposed to address the issue of the traditional level set method for detailed numerical simulations of gas-liquid flows. The gas-liquid interface is captured by the level set method and the discontinuity across the interface is discretized by the ghost fluid method. A penalty term is added in the classical level set advection equation to reduce the frequent reinitialization process. The effect of the frequency of the reinitialization step on the performance of the level set method is evaluated and the effect of the penalty factor on the interface evolution is investigated in the present work. Three typical benchmark cases, including rigid body rotation, two-dimensional shear motion, and three-dimensional shear motion, are used to validate the accuracy of the present variational level set method. It is found that the reinitialization process is not necessary for every time step with the penalty term. A spatially averaged parameter near the interface is proposed to quantitatively evaluate the necessity of reinitialization. The present method is also shown to have second-order accuracy. This work provides an accurate and efficient way to simulate the gas-liquid flows.

Bubble breakup criteria for the population balance model of gas–liquid flow simulations

This work presented a critical review of various literature models with focus on the bubble breakup criteria. A general formulation of critical energy for breakup criteria was derived. Based on the framework of Luo and Svendsen (1996), effects of breakup criteria and effective eddy scale on model outputs were examined. Results showed that a joint criterion consisting of surface energy criterion and force criterion (Cf + Wed', Wec = 2) exhibited both reasonable breakup frequency and daughter size distribution (M-shape), and an optimized kernel function was proposed. A correlation between fragmentation ratio and eddy scale was introduced, and a new breakup model with a simplified kernel function was obtained based on the model of Qi et al. (2022). Both kernel functions were implemented in CFD-PBM simulations, and the results agreed with bubble size distributions. The confusions about literature bubble breakup criteria were cleared and two bubble breakup models were suggested.

1D-3D coupled simulation method of hydraulic transients in ultra-long hydraulic systems based on OpenFOAM

Transients in hydraulic systems are normally simulated by one-dimensional (1D) method of characteristics (MOC). When local three-dimensional (3D) flow patterns have crucial impacts on the hydraulic system characteristics, 3D computational fluid dynamics (CFD) simulation should be incorporated. Since simulating an entire long system by the 3D CFD method is unrealistic, we have proposed several 1D-3D coupled simulation methods. However, the coupled methods are difficult to apply and popularise because most CFD codes are inaccessible and implementation details are unclear. Consequently, we utilised the open source toolbox OpenFOAM to develop a 1D-3D coupled simulation method and proved its feasibility by applying it to analysing practical problems. This paper describes the implementations of water compressibility, 1D-3D coupling, gas-liquid flow simulation, and dynamic mesh; shows their verifications of accuracy by benchmark cases; demonstrates the simulations of the closing and opening processes of a 194 km long water conveyance system. The gas-liquid flow patterns in the gate chamber and the maximum/minimum water head envelopes along the tunnels, which support the design optimisation of the project, are presented. It is shown that the method is computationally efficient and accurate, and can be applied to hydraulic transient analyses for water conveyance systems, pumped-storage power stations, etc.

A generalized coupled level set/volume-of-fluid/ghost fluid method for detailed simulation of gas-liquid flows

A generalized coupled level set/volume-of-fluid/ghost fluid method for the detailed simulation of gas-liquid flows is proposed in this paper. The interface is captured by the coupled level set and volume-of-fluid method, where the level set method is used to compute normal vector and curvature accurately, and the volume-of-fluid method is used to conserve the global volume or mass. The ghost fluid method is also used for discretization across the interface. The novelty of the present approach lies in that a generalized formulation for the conversion between the level set function and the volume-of-fluid function is proposed in a simple and efficient manner. Three benchmarks, including Zalesak's disk, two-dimensional deformation and three-dimensional deformation, are used for validation and verification. It shows that excellent agreement is achieved, and the present method has first-order accuracy. The current method is further applied to the simulations of droplet dynamics, rising bubbles, head-on droplet collision and liquid jet breakup, demonstrating the capability to accurately capture the interface.

Numerical simulation of gas-liquid flow in inclined shale gas pipelines

Corrosion and perforation accidents often occur in shale gas gathering pipelines, which causes serious economic losses. The accumulation laws and flow field of shale gas gathering pipelines are revealed by OLGA and ANSYS Fluent simulation. Under different working conditions, the gas entering the pipeline contains 1.3∼3.1% water, which will condense in the pipelines with the decrease of temperature and form effusion. The effusion is mostly distributed in low-lying places and climbing pipe sections, which is consistent with the location of corrosion perforation. Through the three-dimensional simulation of the local upward pipe section, the effusion pipe will form vortices to accelerate the corrosion mass transfer. Further combine the high-temperature and high-pressure reactor experiment, the flowing causes of corrosion failure of shale gas gathering pipelines in the lower part of upward inclined pipeline sections are determined. Therefore, the lower part of the upward inclined pipeline section is a high-risk corrosion area.

High-resolution model of complexly shaped bodies motion using an IBM-VOF-DEM coupling method

A new coupling model that focuses on the simulation of gas-liquid flow and irregular-shaped particulate flows was proposed based on the coupling of FD/IBM, VOF and DEM. A wide range of computing cases was presented for validation, including the spherical and cylindrical particle settling in fluid, where the particle Reynold's number is small, and the vortex shedding phenomenon could still be captured. Further, the simulations that the wooden blocks float upward and the cones fall into the water at a high Reynolds number were constructed. All these simulating results keep well consistent with the experiments. It turns out that the model is reliable for simulating the particulate flows as Reynold's number is up to 420,000. Besides, the model shows great strength of the solid-fluid motions capture capability, especially for the irregular-shaped objects moving trajectories at different scales from 0.00167 to 0.3 m, which is potentially helpful in industrial engineering. • A fully rsolved IB-VOF-DEM model is developed. • Typical and multi-scaling validating simulations are presented. • The model covers a wide range of Reynolds number from 400 to 420,000. • Multi-sphere model and Monte-Carlo method are employed.

Computational fluid dynamic simulation of gas-liquid flow in rotating packed bed: A review

The rotating packed bed (RPB) has been widely used in gas-liquid flow systems as a process intensification device, exhibiting excellent mass transfer enhancement characteristics. However, the complex internal structure and the high-speed rotation of the rotor in RPB bring significant challenges to study the intensification mechanism by experiment methods. In the past two decades, Computational fluid dynamics (CFD) has been gradually applied to simulate the hydrodynamics and mass transfer characteristics in RPB and instruct the reactor design. This article covers the development of the CFD simulation of gas-liquid flow in RPB. Firstly, the improvement of the simulation method in the aspect of mathematical models, geometric models, and solving methods is introduced. Secondly, new progress of CFD simulation about hydrodynamic and mass transfer characteristics in RPB is reviewed, including pressure drop, velocity distribution, flow pattern, and concentration distribution, etc. Some new phenomena such as the end effect area with the maximum turbulent have been revealed by this works. In addition, the exploration of developing new reactor structures by CFD simulation is introduced and it is proved that such new structures are competitive to different applications. The defects of current research and future development directions are also discussed at last.

Forecasting a bubbly-intermittent flow regime transition in helically coiled tubes

Simulations of gas–liquid turbulent flows in helically coiled tubes are conducted by a two-fluid hydrodynamic model coupled with the population balance equation. A model of bubble breakup in a turbulent flow, recently developed by the authors, is incorporated into the ANSYS Fluent CFD code employed as a computational tool. The population balance equation is solved by a discrete method. A realizable k-epsilon turbulence model is used for all computations. Numerous simulations of gas-liquid flows in vertically oriented coiled tubes are conducted. Three different coil diameters are employed for simulations. Computed bubble chord distributions are close to experimental data. Simulated dependencies of the superficial liquid velocity on the superficial gas velocity, corresponding the bubbly-intermittent flow regime transition, are in excelled agreement with measured ones. On the other hand, dependencies, obtained using standard bubble breakup models, significantly deviate from experimental results. Thus, it is demonstrated that employment of the novel bubble breakup model greatly enhances a computational accuracy of gas-liquid flows in helically coiled tubes.

Assessment of one-dimensional models used in the simulation of gas-liquid flows in vertical degassing columns

The present research aims to assess and analyze one-dimensional two-fluid models used in simulating gas-liquid dynamics and interphase transfers in degassing columns. The assessment of two-fluid models is based on benchmark measurement data carried out over a long period of time, both on dissolved gas concentrations in Lake Nyos at different depths and on the gas-liquid jet heights at the outlet of the degassing columns installed from 2001. The results of the numerical simulations with different two-fluid models were compared and their confrontation with the experimental data were discussed with respect to the sensitivity of the models to the different closures and hypotheses. The numerical analysis has led to a benchmark assessment of mono-dimensional two-fluid models in their capacity to account for the complexities associated with the different couplings between the dynamic aspects and interphase mass transfer phenomena that occur in degassing columns.

Estimation of Parameters for Non-Equilibrium Phase Transitions during the Flow of Oil and Gas Mixtures

Problems of unsteady gas-liquid flows in wellbores with phase transitions are common for hydrocarbon production and well drilling. Typically, flow in wellbores is sufficiently fast which requires taking into account the non-equilibrium nature of phase transitions. The set of equations describing conservation of mass for components and momentum conservation for the mixture is supplemented by the relaxation equation for concentration of gas dissolved in the liquid. It is known that the characteristic times of gas evolution from the liquid and gas dissolution in the liquid differ significantly and depend on fluid properties, thermobaric conditions, and the flow pattern. Therefore, obtaining estimates of relaxation times for real flows turns to be a difficult problem. In this study, we propose a method for estimating the characteristic relaxation times for gas evolution and dissolution during the gas-liquid flow in a well. The method combines the solution of the convective diffusion equation for the growth/collapse of a vapor bubble in a liquid with the current parameters of the gas-liquid flow. Estimates of the relaxation times for the bubbly flow (small bubbles, gas evolution predominates) and slug flow (large bubbles, dissolution predominates), as functions of time from the beginning of the process, are obtained for the parameters of a real flow in a wellbore. It is shown that the obtained dependencies are consistent with the typical scaling of the diffusion process with respect to the size of bubbles. The results are important for mathematical simulation of gas-liquid flows in wellbores during hydrocarbon production, as well as for calculation of the gas-kick process during well drilling with oil-based muds.

Downhole gas-kick transient simulation and detection with downhole dual-measurement points in water-based drilling fluid

Gas kick is generally difficult to discover in time using traditional surface detection methods, which results in a significant wastage of time and money. Owing to the restriction of the low data-transmission speed of measurement-while-drilling system, downhole measured data is usually ignored in gas-kick detection. Furthermore, surface detection methods comprising the use of pressure and flow-rate sensors require professional knowledge and many input parameters, some of which are required to be assumed. In this study, we used downhole dual measurement points for detecting gas kick without the use of other surface input parameters. Firstly, we developed an end-to-end supervised neural network to determine the still and circulation working conditions, which were used for calculating the drilling fluid density and viscosity. Secondly, an unscented Kalman filter was applied to perform a backward gas fraction calculation dynamically. However, this downhole calculation method cannot be used in highly deviated and horizontal wells. Because there is a downhole fluctuating pressure generated during the rock breaking, we proposed an auxiliary gas-kick detection method based on the theory of pressure wave attenuation. This method can be applied to all well types. To evaluate the proposed gas-kick detection method, we used a gas-liquid flow simulation model combined with a pump rate model, screw-drilling-tool pressure-consumption model, rock-breaking model, and formation permeability model to generate transient data with the highest possible accuracy. The advection upstream splitting model was used as the numerical scheme. The accuracy of the simulation model was successfully validated using two field experimental data sets. Finally, we generated a set of vertical and horizontal well data each with the simulation model to test the gas-kick detection method. The experiment results showed that the proposed gas-kick detection model was successful in detecting gas kick and obtaining the accurate gas fraction.

Numerical simulation of gas-liquid flows in a centrifugal rotor

Two-phase flows generally represent an adverse condition for centrifugal pumps. Research about this topic tends to be focused on performance evaluation through experimental approaches, while numerical works are quite scarce. In this paper, the numerical investigation of the gas-liquid flow in a centrifugal rotor is carried out. An Euler-Euler, polydispersed approach is adopted, together with several gas-liquid equations to model the relevant interphase interactions. The rotor geometry is a flat radial rotor, for which previously obtained experimental data to be used as input and for validation is available. Numerical results agree well with experimental ones for a range of operating conditions. They are further explored to investigate the effect of different interphase interactions on the results. Outcomes from this work can help with the understanding of the complex mechanisms associated with gas-liquid flows in centrifugal rotors, and contribute with the progress of numerical models for its solution.

Two-phase flow simulations at [formula omitted] inclination in an eccentric annulus

Co-current two-phase simulations of gas-liquid flow with mixture velocities from 1.2 to 4.2 m/s were run in a partially eccentric annulus and compared with entirely eccentric and concentric experimental data collected at the Institute for Energy Technology in Norway. The gas-phase was sulphur hexafluoride (SF6) for all cases, while the liquid-phase was Exxsol D60 for the horizontal cases and a mixture of Exxsol D60 and Marcol 82 for the inclined case. The outer diameter of the annulus was 0.1 m for all cases, while the inner diameter was 0.05 m in the horizontal configuration and 0.04 m for the inclined configuration. The purpose of this paper is to explore the effect of the holdup fraction, mixture velocity, and interior pipe’s position on the pressure gradient and flow regime, in effect a study of the pressure gradient and holdup fraction transients. The comparisons between simulations and experiments indicate that moving the pipe from an entirely eccentric to the partially eccentric configuration has a drastic impact on the pressure gradient. In all 4 cases where the inner pipe was changed from a completely eccentric geometry in the experiments to a less eccentric configuration in the simulations, we notice an increase of 48–303% of the mean pressure gradient. Comparatively, the 4 cases where the pipe was moved from a concentric experimental configuration to a more eccentric configuration in the simulations result in less drastic pressure gradient changes. Two cases were within 22% of the experimental results for mean, maximum, and minimum pressure gradient, while the last two cases exceeded the minimum and mean pressure gradients by 25–250%, respectively. The flow regime is rarely significantly affected by a change in eccentricity; 2 out of the 8 horizontal cases indicate either a transition from wavy flow to slug flow or significantly larger waves. The most prominent and frequent discrepancies identified were altered slug and wave frequencies. The last case, a 4o inclined, partially eccentric simulation was compared to an entirely eccentric experiment and results in a 0.2 Hz increase in wave frequency, up from the experimental 0.56 Hz and a 49% increase in the mean pressure gradient.

Numerical simulation of gas-liquid flows and boiling under effect of vibrations and gravity

In the paper a review of investigations related to a boiling process at normal conditions of microgravity and at a vibration forcing is presented. The effect of vibrations and a bubble boiling to heat transfer in water was studied. A decrease in temperature of heated wall in both cases as compared to the cases without boiling and vibrations has been shown. The results of modeling the problem on influence of the area of a vapor film on a heat flux of heated surface at various dimensionless governing parameters are presented. It has been shown the influence of the Grashof, Marangoni numbers and the contact angle on heat flux during formatting a bubble from air film.

Study on Heat Transfer and CFD in a SCR Reservoir

According to an industrial demand of the simulation of the heat transfer in a SCR reservoir by Plastic Omnium, we firstly developed a 3D numerical model written in C++. Subsequently, the computational performance of the model was analyzed with both laboratory and industrial experiments. Besides, it was optimized by implicating certain advanced numerical methods, for instance, a gas-liquid flow simulation based on three dimensional VOF method was implicated in order to simulate the phase change coupling sloshing condition.

Computational studies of gas-liquid flow in a multi-branch manifold

Three-dimensional, time-dependent numerical simulations of gas-liquid flow in a multi-branch manifold (an idealised model of the header/feeder system of a CANDU nuclear reactor) were carried out using the volume of fluid approach to separate the phases and the detached eddy simulation model to simulate turbulence. Interest was focusse n the distribution of the liquid to different feeders. Numerical results for a header connected to a small number of vertical feeders were in fair agreement with in-house experimental data. The rates of change of liquid discharge following changes of inlet conditions were estimated and found to depend on feeder location. The interface between an upper region of the header that was occupied by mostly air and a lower region that was occupied by an air-water mixture was found to rise with an increase in either air or liquid inlet flow rate. Simulations were performed to quantify the effects of differences in the values of fluid properties of air-water mixtures at approximately standard atmospheric pressure and temperature from those of saturated steam-water mixtures at significantly higher pressures (up to 10 MPa) and temperatures (up to 310 °C). The liquid flow rate through a feeder that was directly below the header inlet was found to decrease markedly with increasing mixture pressure and temperature. Pilot simulations of air-water flows in a header connected to multiple feeders with inlets at different elevations and orientations revealed that, under certain conditions, some of these feeders discharged little liquid.

GPU-accelerated transient lattice Boltzmann simulation of bubble column reactors

Design parameters for Bubble Column Reactors such as backmixing and light/dark cycles of microalgae cells are pertinent to transient flow dynamics and mesoscale coherent structures. Transient simulation is therefore of practical significance. Traditional CFD solvers are generally implemented on multi-core CPU workstations, which is time-consuming and difficult to meet the requirement of industry applications. We developed a GPU-accelerated transient LBM simulation of gas-liquid flow, achieving 5000 times acceleration in comparison with the CFD simulation. A notable feature of this method, which allows a tunable and smaller dimensionless relaxation time, is the remarkable decrease of required mesh number in LBM simulation by several orders of magnitude. The solver is validated against experimental data, resolving two mechanisms of mesoscale structure, i.e., vortex rotation and radial migration, in the intensification of macromixing. The computation acceleration and resolution of mesoscale structures demonstrate the potential of this approach for fast simulation of industrial applications.

General guideline for closure model development for gas-liquid flows in the multi-fluid framework

The two- or multi-fluid approach is frequently used for Nuclear Reactor Safety (NRS)-related simulations of gas-liquid flows. To enable reliable predictions the closure models have to reflect the involved local physical phenomena at the non-resolved scale properly. To consolidate the CFD-modelling in the frame of the multi-fluid approach the so-called baseline model strategy was recently proposed (Lucas et al., 2016). The present technical note discusses a long-term strategy for the baseline model development and ways to obtain or improve closure models. Guidelines for the model development are given by listing requirements for appropriate closure models as well as frequently made mistakes. This is illustrated by examples for recent developments done for HZDR baseline models for poly-disperse bubbly flows.