Multiphase Flow Research Articles

Investigation into flow-induced internal corrosion direct assessment in small-diameter dry gas fluctuating pipeline

Small-diameter undulating natural gas pipelines with low gas transmission capacity do not have internal inspection conditions to grasp the internal corrosion status of the pipeline. This study focuses on a small-diameter undulating dry natural gas gathering and transportation pipeline, the internal corrosion mechanism of the pipeline is studied through corrosion products, and the specific location of the internal corrosion sensitive pipe segment is determined based on multiphase flow simulation and PMDT(pipeline non-contact magnetic anomaly detection); the excavation inspection is ultimately used to evaluate the internal status of the pipeline. The results demonstrate that the internal corrosion mechanism of ZL (ZI Lai) pipeline is O2 and CO2 synergistic corrosion in which O2 plays a dominant role, while the increasing flow rate will aggravate corrosion; The maximum general corrosion rate and critical inclination along the pipeline are 0.0218 mm/a and 18.4°, respectively. Furthermore, twelve corrosion sensitive segments have been identified, including two II-level and six III-level magnetic anomaly segments. The internal corrosion defects are localized at the 3–9o’clock position of the pipeline, with a maximum general corrosion rate not exceeding 0.0228 mm/a. Furthermore, the pipeline failure pressure of 12.27 MPa surpasses the maximum allowable working pressure of 8.84 MPa, ensuring its continued operational safety. The corrosion protection measures of reducing the water content of natural gas, adding vapor corrosion inhibitor and regularly detecting magnetic anomaly pipeline are developed.

Characteristics of Methane Hydrate Formation in a Gas–Water–Silt Sand Three-Phase Flow System and Its Effect on Multiphase Flow Behavior

Characteristics of Methane Hydrate Formation in a Gas–Water–Silt Sand Three-Phase Flow System and Its Effect on Multiphase Flow Behavior

Three-Dimensional Lattice Boltzmann Simulations for Droplet Impact and Freezing on Cold Surfaces with a Large Density Ratio

Droplet impact and freezing on solid surfaces are ubiquitous in many natural and engineering processes. Simulating the impacting-freezing process of a droplet is still challenging because it involves the complex multiphase flow and the liquid-solid phase change. This paper establishes a three-dimensional lattice Boltzmann model that considers the effects of contact angle hysteresis and volume expansion to simulate this complex process under realistic conditions. We adopt an enhanced cascaded lattice Boltzmann method to calculate the flow field and a multiple-relaxation-time scheme to solve the liquid-solid phase change model. In addition, a new contact angle model based on the pseudopotential multiphase lattice Boltzmann model is proposed to mimic the contact angle hysteresis. The simulations of droplet impact and freezing on both hydrophobic and hydrophilic surfaces with different surface temperatures and Weber numbers are conducted, and the temporal droplet profile and dimensionless contact length agree well with the experiments, which effectively validates the accuracy and robustness of the present model. Finally, the effects of surface temperatures ( 0 , − 15 , − 30 ∘ C ) and Weber numbers (4.4, 19.2, 40.0, 71.1) on droplet dynamics are also examined.

MFiX-TFM simulation of hydrodynamics of a dual fluidized bed system

The abundance and replenishable nature of biomass make it a suitable fuel for power generation. Among the various technologies, dual fluidized bed gasification (DFBG) is a suitable technology to generate high-quality syngas from biomass. However, the complexity of hydrodynamics and heat transfer with bed geometry, flow conditions as well as feedstock demands effective research for the design of such system. This study, therefore, focuses on the simulation of hydrodynamics of a dual fluidized bed gasification system. The 2-D two-fluid model (TFM) simulations were performed using Multiphase Flow with Interphase eXchanges (MFiX) software by varying the superficial air velocities for both the gasifier and riser. The influence of superficial air velocity on static pressure, pressure drop, axial and radial voidage, solid velocities, and granular temperature was evaluated. From the simulations, it was observed that with the increase in superficial air velocities, there was an increase in the effective height of pressure drop (66%), voidage, and solid velocities of the gasifier. For the simulation of the riser, similar trends in the profile of hydrodynamic parameters were also observed. The optimum velocity for the gasifier and riser has been suggested to be between 0.15 and 0.35 m/s and 6–7 m/s, respectively.

Thermal-hydraulic performance evaluation of airside of wavy fin compact heat exchangers under wet conditions

This study presents a novel approach to evaluating the thermal-hydraulic performance of the airside of wavy-fin compact heat exchangers under wet conditions. While previous studies have predominantly focused on dry conditions, this paper extends this knowledge by exploring the effectiveness of wavy fin configurations in the presence of condensation film. Twenty configurations of wavy-finned geometries were evaluated, including 16 from the literature, and four were newly introduced. By examining the impact of condensation and geometric parameters on thermal-hydraulic performance, this research offers a deeper understanding of heat transfer behavior in wet environments. Species transport and volume of fluid (VOF) multiphase models were implemented to investigate Colburn “j” and Fanning friction coefficient “f” using ANSYS Fluent software. The results were validated against reported experimental data. Results showed that geometries G3 and G4 exhibited optimal “f” and “j” values, indicating reduced frictional losses and enhanced heat transfer performance. GF3, GF4, and G11 had higher performance if the effect of compactness was ignored, while G11, G12, and G13 did not compromise pumping power and maintained high performance. G12 outperformed other geometries at a pumping power limit of 1.35×1014(W/m2). The study also suggests new correlations to predict the j- and f-factor for wet conditions in terms of geometrical parameters or dry j- and f-factor.

A new model for predicting pressure traverse in two phase flow geothermal well

The complexity associated with the two phase or multiphase flow system have been a long-time challenge in the modelling of the flowing pressure in the production channel which includes geothermal well. The flow of hot water and its vapour ensued all throughout the geothermal system producing from the reservoir source to the wellbore and later to the surface. The performance of geothermal system is primarily dependent on the ability to accurately predict the flowing pressure in the production well. Several models derived from the fundamental thermodynamic energy equation to handle the complexity of two-phase flow in geothermal well have demonstrated diverse discrepancy when compared with real time measurement. It has been conceived in the study that the inclusion of pressure drop due to accumulation in the thermodynamic energy equation reduces the discrepancy between the predicted pressure and the field measurement. It is pertinent to the geothermal energy industry to assess the accurate model that consider all constituent terms that impact the two-phase flow behaviour in a geothermal production well. A more exact numerical model for evaluating the flowing pressure in geothermal has been derived in this study where the right constituent terms that practically impact the two-phase flow behaviour in a geothermal vertical well are considered. The present model has the capacity to predict flowing pressure accurately as the flow transit from one regime to another. Likewise, the present model was able to capture the transient period that usually occurs when the geothermal well is put to production. The present model was validated using data from KE1-22 and Mesa 6-1 wells reported in literature. The present model gave the least mean absolute relative error of 0.033 when applied to measured field data from KE1-22 Well while Hassan and Kabir, Ansari, Orkiszewski and Homogenous models gave errors of 0.12, 0.33, 0.41 and 0.38 respectively. Similarly, relative to data from Mesa 6-1 the present model gave a mean absolute relative error of 0.052 while Hassan and Kabir, Ansari, Orkiszewski and Homogenous models gave errors of 0.17, 1.46, 1.37 and 2.53 respectively. The newly derived model is reliable for assessing the performance of the geothermal system and evaluating flowing pressure at every difference transition period.

Mathematical modeling and numerical simulation of the N-component Cahn-Hilliard model on evolving surfaces

Establishing multi-component phase field models on dynamic surfaces, and exploring the similarities and differences in phase field evolution between evolving and static surfaces, are interesting studies in multi-phase flow problems. This paper focuses on mathematical modeling and numerical simulation of the N-component Cahn-Hilliard model on evolving surfaces. In the modeling process, the evolution of the energy functional, componential mass conservation, and point-wise mass conservation (hyperplane link condition) are considered. On an evolving surface, the energy dissipation law does not hold because the surface velocity can be viewed as an external force in the system. Meanwhile, due to the velocity, the surface area may change, the componential mass conservation property and the hyperplane link condition can not be satisfied simultaneously. From the point of view of preserving these two physical properties of mass conservation, three types of N-component Cahn-Hilliard model are established on the evolving surface: componential mass conservation, point-wise mass conservation, and both componential and point-wise mass conservation. For the numerical simulation, the evolving surface finite element method is considered for the space-time discretization of the proposed model. In order to obtain a linear, decoupled, high-accurate, and stable scheme for long time numerical simulations, the stabilized semi-implicit method is integrated into the framework of the evolving surface finite element method. Through several numerical examples, the rationality of the model and the efficiency of the numerical method are shown. Additionally, three- and four-component phase separation phenomena are shown to investigate the N-component Cahn-Hilliard dynamic on various evolving surfaces.

A high-efficient method to upscale H2 migration within heterogeneous saline aquifers

Drawing upon a range of energy storage methods that cover daily, weekly, and seasonal dynamics presents a route to reduce carbon dioxide emissions per unit of energy delivered. The utilization of renewable energy to generate, store, and recycle hydrogen stands out as a particularly promising strategy to address the seasonal fluctuations in energy production and usage. Deep saline aquifers offer a feasible solution for large-scale hydrogen storage, tailored to meet the demands of long-term storage requirements. This research introduces an upscaling method based on percolation theory, aiming to reduce computational costs in simulating H2 migration across diverse saline aquifers with different correlation lengths. Two geological models of distinct correlation lengths showcase the method's effectiveness. In the model with a 1.2-m correlation length, percolation-based upscaling yields final H2 saturation errors of 8.76 % in the main area and 3.7 % in the sink area, reducing runtime nearly sevenfold. Similarly, the model with a 4.0-m correlation length demonstrates final H2 saturation errors of 10.7 % in the main area and 1.27 % in the sink area, decreasing runtime almost fivefold. To bolster the credibility of the proposed upscaling method, parameters derived from the Brooks-Corey and van Genuchten models are calibrated to align with experimentally acquired H2-water multiphase flow properties. The resulting coarse-scale model accurately replicates primary permeability and H2 migration behavior, maintaining errors below 5 %. Importantly, dominant H2 migration mechanisms during underground hydrogen storage in saline aquifers are preserved in upscaled models, enabling efficient H2 saturation predictions beneath caprock. This study enhances our understanding of fine-scale H2 migration in complex geological systems and sheds light on integrating small-scale capillary barrier characteristics during upscaling.

Numerical investigation of mesoscale multiphase mass transport mechanism in fibrous porous media

At present, the proton exchange membrane fuel cell (PEMFC) is one of the most promising new energy solutions. The structure and material properties of the gas diffusion layer (GDL) are important factors that restrict the efficient water management and structural stability of PEMFCs. The complex mesoscopic fibrous porous structure of the GDL results in complex multiphase flow dynamics problems that have highly nonlinear characteristics. It is difficult to describe the details of mesoscopic multiphase coupled transport dynamics and numerically solve problems in which there is a two-phase flow with a high-density ratio. To solve these problems, a mesoscopic multiphase coupled transport model based on a lattice Boltzmann method and volume-of-fluid (LBM-VOF) model is proposed. Moreover, we also discuss the mechanism of the interaction between the fibrous porous structure and internal multiphase flow. The results obtained illustrate that the proposed method can obtain dynamic details of the flow field for fibrous porous media. The surface wettability of fibres strongly influences both the distribution and stability of liquid water clusters within porous materials. Concurrently, the fibre diameter assumes a pivotal role in governing lateral water diffusion and exclusion efficiency. This work lays a foundation for efficient water and thermal management of PEMFCs.

Modeling Pressure Gradient of Gas–Oil–Water Three-Phase Flow in Horizontal Pipes Downstream of Restrictions

Gas–oil–water three-phase slug flows in pipes commonly exist in the oil and gas industry as oil fields are becoming mature and water production is becoming inevitable. Although studies on multiphase flows in pipes have been ongoing for decades, most previous research has focused on gas–liquid or oil–water two-phase flows, with limited studies on gas–liquid–liquid flows. This leads to limited modeling studies on gas–liquid–liquid flows. One factor contributing to the complexity of the gas–liquid–liquid flow is the mixing between the oil and water phases, which have closer fluid properties and low interfacial tension. Restrictions or piping components play a crucial role in altering phase mixing. Unfortunately, modeling studies that consider the effects of these restrictions are limited due to the scarcity of experimental research. To address this gap, we conducted experimental studies on a gas–liquid–liquid flow downstream of a restriction and developed a new mechanistic modeling approach to predict the pressure gradient. Our model focuses on the flow pattern where the oil and water phases are partially mixed. This work emphasizes the modeling approach. The model evaluation results show that the model outperforms other existing models, with an average absolute relative error of 6.71%. Additionally, the parametric study shows that the new modeling approach effectively captures the effects of restriction size, water cut, and gas and liquid flow rates on the three-phase slug flow pressure gradient in horizontal pipes. Most previous slug flow modeling work assumes either a stratified flow or fully dispersed flow between the oil and water phases. This work provides a novel perspective in modeling a three-phase slug flow in which the oil and water phases are partially mixed. In addition, this novel approach to modeling the restriction effects on the pressure gradient paves the way for future modeling for different types of piping components or restrictions.

Comprehensive analysis and identification of energy performance and unsteady two-phase flow patterns based on experiments and comparison between two distinct multiphase flow models

ABSTRACT In the petroleum sector, electrical submersible pumps (ESP) face numerous challenges when handling multiphase flow of gas and liquid. The primary challenge is from the build-up of the gas-bubbles within the impellers of ESPs, leading from moderate to severe deterioration in pump efficiency. Consequently, a comprehensive investigation is conducted, involving a combination of experimental and numerical analyses, to thoroughly explore the effects of gas entrainment on the performance and intricate internal flow mechanisms of a five-stage mixed-flow ESP. All these analysis was carried out under both design (Qd ) and off-design conditions (0.8Qd , and 1.2Qd ). For unsteady numerical calculations, two widely used multiphase-models: The volume of fluid (VOF) and The Euler-Euler model are employed and compared to investigate the versatility/validity of these models in predicting multiphase performance of ESP. The comparison between tests, Eulerian, and VOF models demonstrated that the Eulerian model aligns well with the experimental results. and shows higher-adaptability pattern with the test results. This reveals its best capability/versatility in predicting two-phase performance and internal-flow results for ESP. Moreover, it can more accurately capture the phase slippage inside ESP under two-phase flow. Additionally, this work provides a vision to the broad-applicability of Eulerian-model for complicated machinery such as ESP.

Understanding cavitation bubble collapse and rebound near a solid wall

The collapse of cavitation bubbles is known for its intense and aggressive behavior, producing concentrated bursts of energy that can cause erosion, noise, and damage to metallic surfaces and mechanical equipment. However, this concentrated energy also offers significant potential for various applications in biomedical science, industrial engineering, and related technologies. This study presents a comprehensive numerical investigation of the collapse and rebound of cavitation bubbles near a wall using a conservative, compressible multiphase flow model. Laser-generated cavitation bubbles growing, collapsing, and rebounding in distilled water near a wall at three standoff distances were experimentally studied to validate the numerical method. The results show good agreement between the bubble shapes and radii from the numerical simulations and experiments. Additionally, velocity of microjets and thermodynamics of the bubble collapse were validated against the reference data in the literature. Subsequently, the pressure and temperature distributions and jet shapes were examined in detail, exploring the impact of standoff distances ranging from 0.2 to 1.8. A quantitative analysis of the pressure and temperature produced on the wall, as well as the jet velocity and bubble movement during the collapse, was systematically conducted. Jet velocities observed ranged from 30 m/s to 130 m/s, and numerical simulations were compared with experimental data from the literature, showing good agreement. Maximum temperature and pressure induced at the wall center can reach up to 616.2 K and 139.5 MPa, respectively. The detailed analyses in this study provide significant insights into the behavior of cavitation bubbles and the effect of standoff distance on their collapse and rebound near a wall.

PLIC-Net: A machine learning approach for 3D interface reconstruction in volume of fluid methods

The accurate reconstruction of immiscible fluid–fluid interfaces from the volume fraction field is a critical component of geometric Volume of Fluid methods. A common strategy is the Piecewise Linear Interface Calculation (PLIC), which fits a plane in each mixed-phase computational cell. However, recent work goes beyond PLIC by using two planes or even a paraboloid. To select such planes or paraboloids, complex optimization algorithms as well as carefully crafted heuristics are necessary. Yet, the potential exists for a well-trained machine learning model to efficiently provide broadly applicable solutions to the interface reconstruction problem at lower costs. In this work, the viability of a machine learning approach is demonstrated in the context of a single plane reconstruction. A feed-forward deep neural network is used to predict the normal vector of a PLIC plane given volume fraction and phasic barycenter data in a 3×3×3 stencil. The PLIC plane is then translated in its cell to ensure exact volume conservation. Our proposed neural network PLIC reconstruction (PLIC-Net) is equivariant to reflections about the Cartesian planes. Training data is analytically generated with O(106) randomized paraboloid surfaces, which allows for the sampling a broad range of interface shapes. PLIC-Net is tested in multiphase flow simulations where it is compared to standard LVIRA and ELVIRA reconstruction algorithms, and the impact of training data statistics on PLIC-Net’s performance is also explored. It is found that PLIC-Net greatly limits the formation of spurious planes and generates cleaner numerical break-up of the interface. Additionally, the computational cost of PLIC-Net is lower than that of LVIRA and ELVIRA. These results establish that machine learning is a viable approach to Volume of Fluid interface reconstruction and is superior to current reconstruction algorithms for some cases.

Investigation of free surface effect on the cavity expansion and contraction in high-speed water entry

The evolution of the water-entry cavity affects the impact load and the motion of the body. This paper adopts the Eulerian finite element method for multiphase flow for simulations of the high-speed water-entry process. The accuracy and convergence of the numerical method are verified by comparing it with the experimental data and the results of the transient cavity dynamics theory. Based on the results, the representative characteristics of the cavity are discussed from the perspective of the cavity cross-section. It is found that the asymmetry of the cavity expansion and contraction durations is related to the motion of the free surface and the closure of the cavity. The uplift of the free surface suppresses cavity expansion, while the jet generated from free surface closure accelerates cavity contraction. The duration of the contraction of the cavity near the free surface is shorter than the expansion duration due to the change in the velocity distribution caused by the free surface motion. The necking phenomenon during deep closure leads to an increase in the internal pressure of the cavity, prolonging cavity contraction near the deep closure area. This work provides new insights into the cavity dynamics in high-speed water entry.

A single mesh approximation for modeling multiphase flow in heterogeneous porous media

The control volume finite element (CVFE) approach is based on the discretization of primary flow and transport unknowns on two different meshes. The element mesh, used to represent the physical properties of the medium, differs from the control volume mesh necessary to ensure a mass conservative solution. The inherent two mesh feature of the CVFE approximation introduces inconsistency in the transport solution due to the averaging of physical and computed quantities between neighboring elements in the mesh. In this work, we present a consistent approach for modeling multiphase flow and transport in heterogeneous porous media. The approach is applied in the CVFE framework by enabling the discretization of primary unknowns on a single mesh. We combine the discretization of an element-wise, discontinuous pressure approximation with a first-order, discontinuous velocity approximation to resolve the elliptic or parabolic flow problem. The effectiveness of the formulation is achieved by exploiting the same finite element mesh as the flow problem, when updating the saturation solution. This direct mapping between the flow and transport mesh is simple yet effective for establishing a consistent solution in addition to circumventing the non-physical mass leakage exhibited in the classical CVFE method. We describe the interface approximations and the discontinuous terms needed for consistent solutions. The method is well suited to model flow in complex geometrical subsurface domains and is shown to be numerically stable while providing locally and globally mass conservative solutions. We apply the approach to several domains with complex geometrical features to emphasize the superiority of the approximation over conventional methods. The analysis shows over two orders of magnitude reduction in solution error compared to the classical CVFE. The new formulation effectively captures accurate transport solutions, even in the presence of varying material properties, without the need for mesh refinement.

High-resolution boundary variation diminishing scheme for two-phase compressible flow with cavitation and evaporation

We propose high-resolution numerical schemes for two-phase compressible flow simulations to reproduce dynamically created gas/vapor-liquid interfaces with phase change. In the Godunov-type finite volume framework, suppressing numerical dissipation errors in numerical schemes is crucial for capturing the discontinuous solutions. The MUSCL scheme has second-order accuracy for smooth solutions and non-oscillatory behavior near discontinuous solutions. However, the MUSCL scheme introduces excessive numerical dissipation and diffuses the discontinuities nonphysically, leading to difficulties in distinguishing gas/vapor and liquid phases, and thus causing a blur in the interfaces during the multi-phase flow simulations.The hybrid-type boundary variation diminishing (BVD) scheme in this paper combines the MUSCL scheme and the THINC scheme to reduce the numerical dissipation errors near the discontinuities. The MUSCL-THINC-BVD scheme applies the MUSCL scheme for smooth solutions and the THINC scheme for discontinuous solutions, resulting in the successful capture of the discontinuities including the dynamically created gas/vapor-liquid interfaces. The Adaptive THINC-BVD scheme, which switches two types of THINC schemes with different values of gradient parameter, also captures the discontinuities clearly. The numerical results of the benchmark tests show that the proposed BVD schemes can lucidly reproduce the vapor-liquid interfaces newly created during the dynamical process of phase change.

A 3-D extension of the Multiscale Control Volume method for the simulation of the single-phase flow in anisotropic and heterogeneous porous media

The level of detail on modern geological models requires higher resolution grids that may render the simulation of multiphase flow in porous media intractable. Moreover, these models may comprise highly heterogeneous media with phenomena taking place in different scales. Scale transferring techniques allow for the solution of such problems in a lower resolution scale at reduced computational cost. Among these techniques, the Multiscale Finite Volume (MsFV) method constructs a set of numerical operators in order to map quantities from the fine-scale mesh to a coarser one and vice-versa while maintaining flux conservation on both scales. However, the MsFV formulation, as originally stated, is only consistent on k-orthogonal grids since it uses a linear Two-point Flux Approximation (TPFA) method and may struggle to generate consistent primal-dual coarse grids pairs on unstructured grids. The Multiscale Restriction Smoothed-Basis method (MsRSB) improves on the MsFV by introducing a new iterative procedure to find the multiscale operators and the concept of support regions which reduces the method's complexity when applied to unstructured fine and coarse grids. The original version was only consistent on k-orthogonal fine grids due to the TPFA discretization, but filtering methods have been developed to also enable consistent multipoint schemes on the fine scale. Meanwhile, the Multiscale Control Volume method (MsCV) replaces the TPFA by the Multipoint Flux Approximation with a Diamond stencil (MPFA-D) scheme on the fine-scale while further enhancing the generation of the geometric entities to allow unstructured grids on the fine and coarse scales for two-dimensional simulations. In this work we propose an extension to three-dimensional geometries of both the MsCV and the algorithm to obtain the multiscale geometric entities based on the concept of a background grid, a coarser grid used as a proxy for the primal coarse grid. We modify the original MPFA-D method to use the very robust Global Least Squares (GLS) interpolation technique to obtain the required auxiliary nodal unknowns. We also introduce an enhanced version of the 3-D MsCV with the incorporation of the enhanced MsRSB (E-MsRSB) to enforce M-matrix properties and improve convergence. Finally, we employ the MsCV operators in a two-stage smoother to show how it can be used as a good iterative procedure to recover the fine-scale solution. We show that the 3-D MsCV method produces good results employing unstructured grids on both scales to handle the simulation of the single-phase flow in anisotropic, and heterogeneous porous media and that the smoothing procedure is able to accurately retrieve the fine-scale solution within a few iterations.

An efficient pressure-based multiphase finite volume method for interaction between compressible aerated water and moving bodies

Maritime structures in heavy seas can experience wave impact events with high loads. The loads can lead to structural failure and even loss of life. Wave breaking in said sea states causes air to be entrained in water as aeration cloads, remaining long enough to be transported and to play a role in the impulsive interaction with the structure. A small amount of air in water already forms a highly compressible mixture. Compressibility influences the magnitude of the impact loads.A new cartesian grid method for compressible multiphase flow is introduced to account for water, air and homogeneous mixtures of air and water. The method is designed to predict the hydrodynamic loads on moving bodies engaging with interfaces between fluids having large density ratios. An equation for conservation of energy is omitted by enforcing pressure-density relations. The interface between fluids is transported using a geometric Volume-of-Fluid method. The interface between fluids and structure is taken care of by a cut-cell method. An additional fraction field for the amount of air in water in combination with a new formulation for the multiphase speed of sound prevent overprediction of compressibility by artificial air entrainment.New experimental data of 2D wedge impacts with aerated water, made available as open data, are presented to demonstrate the validity of the numerical method. For low aeration levels, the simulation results in terms of the impact loads on the wedge and the frequencies of pressure waves generated upon impact are in good agreement with the experimental data. Increasing the level of aeration reduces the maximum impact load on the wedge. Reflected density waves lead to secondary loads on the wedge. The intensity of the secondary loads, relative to the primary load of impact, increases with the aeration level while the density wave frequency decreases.

Experimental and numerical investigations of flow behavior in an open falling film microreactor equipped with curved flow splitting elements

This work aims the experimental and numerical characterization of gas–liquid flow in an open multichannel falling film microreactor containing 64 coated microchannels, and a split & curve structure for the flow distribution. The operating flowrate range, the flow distribution, and the residence time of the liquid in the single channels were assessed via self-designed pulse input tracer experiments.3D simulations based on Volume of Fluid (VoF) multiphase model were developed in ANSYS Fluent considering a representative section of a single microchannel. Simulation results indicate that backflow phenomena and an increase in film thickness along the channel length are the main reasons for the high film thickness observed experimentally. While the flow rate has only a marginal effect on both processes, the plate inclination angle has considerable contribution in overflow and flow stability. Finally, the numerically calculated transversal wetted area is mainly determined by the defined GLS contact angle at the sidewalls.

CFD-PBM simulations the effect of aeration rates on hydrodynamics characteristics in a gas-liquid-solid aerobic fluidized bed biofilm reactor

A CFD-PBM coupling model was developed to simulate and calculate multiphase flow parameters, flow morphology, and bubble diameter in the aerobic fluidized bed biofilm reactor (AFBBR) under different aeration rates. The simulated radial solid volume fraction values were generally in agreement (within ±15%) with the experimental values. The gas phase predominantly occupied the central area of the reactor, with three distinct velocity peaks observed in the liquid and solid phases. Higher aeration rates improve the mixing of multiple phases by augmenting fluidization velocity, gas-phase volume fraction, eddies size, and turbulence characteristics, thereby leading to a rise in the average size of bubbles from 1.54 mm to 2.03 mm. However, the proportion of small diameter bubbles (0.27–1.03 mm) decreased from 69.4% to 59.6%. These studies concluded that the multiphase flow parameters under an aeration rate of 5.77 m3/(h·m3) were more favorable for improving oxygen mass transfer efficiency and reducing energy consumption.