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Hydrate formation in foam drainage gas recovery wells and the shut in accidents caused by plugging have become an important problem that restricts the safe production of natural gas. The blockage and accumulation of hydrates is a gradual problem. This research goes beyond predicting the formation of hydrates and delves deeper into examining the rate of hydrate formation and the degree of pipeline blockage at different wellbore locations. First, the temperature model, pressure model, multiphase flow model, and hydrate plugging model of hydrate formation process are established from the equations of mass conservation, energy conservation, and momentum conservation. Second, an iterative approach is employed to solve the model, with a maximum error of 6.86% in model validation. Finally, sensitivity analysis shows that wellhead temperature, wellhead pressure, and foam viscosity have different effects on hydrate formation, maximum plugging position, and plugging degree. At the same time, combined with the actual drainage and gas production process, and the characteristics of hydrate blockage, proposed hydrate prevention measures can be taken to achieve safe production of natural gas. The research results indicate that a decrease in temperature signifies an increase in undercooling, resulting in an accelerated rate of hydrate formation and an elevated risk of hydrate blockage. The decrease in wellhead pressure leads to a decrease in the rate of hydrate formation and an increase in production, which is beneficial for the hydrate prevention. However, larger pressure differences and gas production rates will put higher requirements on equipment such as well control devices. An increase in foam viscosity will lead to increased pressure, foam compression, reduced drainage capacity, and intensified hydrate generation. Therefore, foam viscosity should be kept as small as possible to keep the foam stable. [ABSTRACT FROM AUTHOR]

[Display omitted] Water wetting induced corrosion is the core issue for uncovering the corrosion mechanism in multiphase flow environments, relevant to many industrial applications. Here, we experimentally investigated the dynamic failure of an oil film attached on the pre-wetted model surfaces by the electrochemical current detection using an "Alternate Wetting Cell" and the direct visualization of near-wall fluid states. The oil pre-wetted surface performed a superior corrosion mitigation efficiency, exhibiting a protective oil film with a duration time at least 5 times longer than the water pre-wetted surface. It confirms that the oil film rupture is a combined process of the local penetration and pinning of micro-droplets and the phase redistribution of the near-wall fluids. Corrosion finally initiates and propagates on the surface once the droplets pin there or damage the oil film. The result suggests new control strategies for materials corrosion in complex systems by surface modification and fluid management. [ABSTRACT FROM AUTHOR]

Cementing technology is crucial to the development of oil and gas resources, and the quality of cement slurry required is an important factor affecting the cementing effect. Previous studies ignored mixing speed effect on cement slurry quality. CFD numerical model is established to simulate the flow filed of the agitated slurry tank under various operation and structural parameters. The multiphase flow model and the k-ε turbulence model are used to describe the turbulence characteristics in the agitated slurry tank. The multiple reference frame (MRF) model is used to realize the rotation of the area near the stirring blade. The results indicate that the density of the cement slurry in the agitated slurry tank can finally reach a stable state, and the concentration distribution is uniform. Increasing the rotational speed, the stirring time needed to achieve stability becomes shorter, and the uniformity of the cement slurry will also be improved. Reducing the distance between the impeller and the bottom of the agitated slurry tank, the mixing effect can be improved. It provides certain theoretical guidance for the practical application of this agitated slurry tank and has certain reference significance for research on improving the quality of cement slurry required for cementing. [ABSTRACT FROM AUTHOR]

The catastrophic effects of climate change can be mitigated by transitioning to renewable energy sources such as wind, solar, and hydropower while utilizing hydrogen (H 2) as an energy carrier. As renewable fuel sources are intermittent and location-specific, large-scale, long-term storage options for H 2 must be explored with high necessity. Subsurface hydrogen storage in saline aquifers provides a vital scope to store H 2 gas in available pore voids with minimal environmental risk. In this work, a highly heterogeneous porous micromodel was used to study the immiscible two-phase dynamics at high-temperature, high-pressure saline aquifer conditions using computational fluid dynamics (CFD) simulation based on volume of fluid (VOF) method. A set of microfluidic experiments were carried out under atmospheric conditions to validate the numerical model. The VOF model was observed to show good agreement with microfluidic experiments. An unstable displacement pattern with viscous fingering was observed during various flow conditions that captured high pressure (15 and 25 MPa) and temperature conditions (323 and 343 K). It was observed that fingering displacement of brine limits the storage spaces for hydrogen, which consequently follows the high permeable path. As a result, only 0.272 fraction of brine was invaded by the H 2 at a temperature of 323 K and pressure of 15 MPa. A comparison between H 2 -brine and nitrogen (N 2)-brine flow dynamics revealed a 46% less storage capacity of porous media for H 2. Formations bearing high temperature (343 K) showed an 11.27% increase in H 2 storage capacity, while pressure increase had negligible effect. At low capillary number (Ca), more snap-off effects resulted in higher trapping of H 2 gas. This study aims to provide meaningful insights into the complexities of flow dynamics and displacement patterns that are crucial for optimizing hydrogen storage efficiency in saline aquifers and for potential 'white' hydrogen production. [Display omitted] • Hydrogen-brine two-phase flow was simulated in a heterogeneous porous media. • Simulation captures pressure and temperature conditions of geological aquifers. • Microfluidic experiments were carried out to validate the numerical model. • Viscous fingering under high-pressure and temperature limits hydrogen storage. • More snap-off effects lead to increased hydrogen trapping in porous media. [ABSTRACT FROM AUTHOR]

This paper presents and discusses the results obtained by the participants to the benchmark described in de Hoop et al, Comput. Geosci. (2024). The benchmark uses a model for CO2 geological storage and focuses on the coupling between two-phase flow and geochemistry. Several test cases of various levels of difficulty are proposed, both in one and two spatial dimensions. Six teams participated in the benchmark, each with their own simulation code, though not all teams attempted all the cases. The codes used by the participants are described, and the results obtained on the various test cases are compared, as well as the performance of the codes. It is shown that the results obtained are widely consistent, giving a good level of confidence in the outcome of the benchmark. The general complexity of two-phase flow coupled with chemical reactions altering porous media means that some differences between the codes remain. Besides, from the convergence study, it is clear that the two-dimensional problem has a relatively high sensitivity to a spatial resolution which adds to the complexity. [ABSTRACT FROM AUTHOR]

Gas conditioning towers (GCTs) or cooling towers have broad industrial applicability, especially in the cement industry. Most cement factories deal with the same problems faced by other factories. However, the solutions to these problems are barely internationally published and have not received much attention, meaning a lot of time and money is spent on researching previous solutions. Iran is among the top ten cement manufacturing countries in the world. Therefore, many of these problems have occurred in Iranian cement factories. The purpose of this paper is to provide a review of studies in this field over the last couple of decades, with a particular focus on advances in Iran. The most important findings in the literature are summarised in order to suggest the best possible solutions for improving the performance and lifetime of GCTs and decreasing common problems such as dust build-up and wet bottom. Numerical methods for modelling different aspects of GCTs are reviewed. The results can be used to reduce water and energy consumption, air pollution and the repair and maintenance costs of cement factories. [ABSTRACT FROM AUTHOR]

This article discusses the use of distributed acoustic sensing (DAS) for monitoring gas–liquid two-phase slug flow in horizontal pipes, using standard telecommunication fiber optics connected to a DAS integrator for data acquisition. The experiments were performed in a 14 m long, 5 cm diameter transparent PVC pipe with a fiber cable helically wrapped around the pipe. Using mineral oil and compressed air, the system captured various flow rates and gas–oil ratios. New algorithms were developed to characterize slug flow using DAS data, including slug frequency, translational velocity, and the lengths of slug body, slug unit, and the liquid film region that had never been discussed previously. This study employed a high-speed camera next to the fiber cable sensing section for validation purposes and achieved a good correlation among the measurements under all conditions tested. Compared to traditional multiphase flow sensors, this technology is non-intrusive and offers continuous, real-time measurement across long distances and in harsh environments, such as subsurface or downhole conditions. It is cost-effective, particularly where multiple measurement points are required. Characterizing slug flow in real time is crucial to many industries that suffer slug-flow-related issues. This research demonstrated the DAS's potential to characterize slug flow quantitively. It will offer the industry a more optimal solution for facility design and operation and ensure safer operational practices. [ABSTRACT FROM AUTHOR]

Artificial lift systems, such as electrical submersible pumps and sucker rod pumps, frequently encounter operational challenges due to high gas–oil ratios, leading to premature tool failure and increased downtime. Effective upstream gas separation is critical to maintain continuous operation. This study aims to predict the efficiency of downhole gas separator using machine learning models trained on data from a centrifugal separator and tested on data from a gravity separator (blind test). A comprehensive experimental setup included a multiphase flow system with horizontal (31 ft. (9.4 m)) and vertical (27 ft. (8.2 m)) sections to facilitate the tests. Seven regression models—multilinear regression, random forest, support vector machine, ridge, lasso, k-nearest neighbor, and XGBoost—were evaluated using performance metrics like RMSE, MAPE, and R-squared. In-depth exploratory data analysis and data preprocessing identified inlet liquid and gas volume flows as key predictors for gas volume flow per minute at the outlet (GVFO). Among the models, random forest was most effective, exhibiting an R-squared of 96% and an RMSE of 112. This model, followed by KNN, showed great promise in accurately predicting gas separation efficiency, aided by rigorous hyperparameter tuning and cross-validation to prevent overfitting. This research offers a robust machine learning workflow for predicting gas separation efficiency across different types of downhole gas separators, providing valuable insights for optimizing the performance of artificial lift systems. [ABSTRACT FROM AUTHOR]

Numerical modeling of the high-speed flow of a multicomponent dissociated gas around a blunt body was carried out for the flow regime corresponding to the thermally stressed point of the gliding trajectory of entry into the Earth's atmosphere in the surface temperature range of 800–2000 K. As boundary conditions, a stage-by-stage model of heterogeneous catalysis of the interaction of dissociated air with the thermal protection material SiO 2 was used, previously developed by the authors on the basis of transition state theory and quantum mechanical calculations. The dependence of the modes of heterogeneous chemical reactions on the surface temperature and the density of surface adsorption centers and their influence on the chemical composition of the shock layer and the convective heat flux to the streamlined surface are analyzed. The contributions of individual mechanisms of heterogeneous recombination to the total rate of formation of molecules on the surface are estimated. The possibility of using the density of adsorption sites as an effective parameter when setting boundary conditions on a real thermal protection surface in flow problems is shown. • The influence of heterogeneous processes on the structure and chemical composition of the shock layer was studied. • The contribution to surface recombination of different mechanisms of heterogeneous catalysis was analyzed. • A significant influence of the number of adsorption sites on the regime of surface reactions has been shown. [ABSTRACT FROM AUTHOR]

CO2 geosequestration is an important contributor to United Nations Sustainable Development Goal 13, i.e., Climate Action, which states a global Net-Zero CO2 emissions by 2050. A potential impact of CO2 geosequestration in depleted oil and gas reservoirs is the variations in induced pressure across the caprocks, which can lead to significant local variations in CO2 saturation. A detailed understanding of the relationship between the pressure gradient across the caprock and local CO2 concentration is of utmost importance for assessing the potential of CO2 geosequestration. Achieving this through experimental techniques is extremely difficult, and thus, we employ a coupled Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) based solver to mimic sub-critical CO2 injection in Opalinus Clay under various pressure gradients across the sample. The geomechanical and multiphase flow modelling utilising Darcy Law helps evaluate local variations in CO2 concentration in Opalinus Clay. Well-validated numerical results indicate favourable sub-critical CO2 geosequestration under a positive pressure gradient across Opalinus Clay. In the absence of a positive pressure gradient, a peak CO2 concentration of 5% has been recorded, which increases substantially (above 90%) as the pressure gradient across the sample increases. [ABSTRACT FROM AUTHOR]

Accurate measurement of complicated multiphase flow is crucial to the safety and efficiency of petroleum and chemical industrial facilities. However, the existing multiphase flow detection techniques are not applicable to pipelines in remote regions including deserts or deep seas, due to the high cost of providing a stable power supply. Herein, a self‐powered multiphase flow sensor, composed of a liquid‐driven triboelectric nanogenerator (TENG) ‐based signal generator, a ring‐type transmitter, and a string‐type receiver, is proposed. Theoretical modeling of displacement current between transmitter and receiver implies that the received current signal can accurately reflect the wetting state of the receiver, validated by a combined experimental (accuracy above 97%) and simulation study. Coupling with a quantitative analysis algorithm, a multiphase flow detection system with numerous receiver measurement points is developed to precisely monitor various flow parameters, including slug frequency (one point), slug length (two points), and flow pattern (four points), which is verified by spontaneous high‐speed camera recordings of water–air flow. The present work provides a paradigm‐shift way to develop a self‐powered, inexpensive, and accurate technique to detect multiphase flow at remote industrial facilities. [ABSTRACT FROM AUTHOR]

In this computational study, we investigate the gravity and pressure-driven electroosmotic multiphase flow of third-grade fluid through steep microchannel by using the semi-analytical technique. A two-dimensional mathematical model is proposed here for the supercritical bi-phase flow with the suspension of the nanometallic particles. A special type of non-Newtonian fluid (third-grade) is selected as a base fluid. The governing equations for the current flow problem are obtained through Poisson–Boltzmann equations, continuity equations, and Cauchy's momentum equations. The Poisson–Boltzmann equation is simplified by using the Debye–Hückel approximation. The symbolic software MATHEMATICATM is used to obtain the closed-form expression of electric potential, fluid and particle velocities, pressure gradient, and volumetric flow rate, respectively. The computational results are discussed qualitatively under the impact of the physical parameters embedded in the study. The graphical plots of fluid and particle-phase velocities are generated against the different parameters used in this study by adopting the same software as discussed earlier. The electrokinetic forces are responsible for electroosmotic flow which is modeled through the Laplace and Poisson–Boltzmann equations. The externally applied potential and electrical double-layer potential is governed by the Laplace and Poisson–Boltzmann equations, respectively. [ABSTRACT FROM AUTHOR]

3D simulations have been achieved on a flow‐focusing geometry employing the VOF method to study the consequence of viscosity, surface tension, wettability, and geometry on drop generation for the dripping regime. Here the dispersed phase is the PDMS oil (polydimethylsiloxane), and the continuous phase is the water. Simulations were performed at different oil‐to‐water viscosity ratios μoμw of 3, 12, 27, and 50. The interfacial tension between PDMS oil and water is 0.0118 N/m. It has been abridged to 0.008 N/m, 0.005 N/m, and 0.002 N/m, and simulations were performed. The walls of the microchannel are considered to be PMMA surfaces. The contact angle of an oil droplet on the PMMA surface in the presence of water is 140°. The effect of wettability was shown at various contact angles (angle created by water droplet on the PMMA surface in the presence of oil) of 0°, 40°, 90°, 135° and 180°. The frequency of droplet generation (1/s), non‐dimensional droplet length (L/Wc), droplet volume (nl), and droplet velocity (m/s) have been calculated for each of the cases. A flow pattern map has been industrialized classifying the dripping and jetting regimes. A comparison between normal geometry and two constricted geometries (having different orifice lengths) based on the frequency of droplet, non‐dimensional drop length, drop volume, and drop velocity has been made for both dripping and jetting regimes. Prediction of simulated non‐dimensional droplet length has also been made using dimensional analysis. [ABSTRACT FROM AUTHOR]

Multiphase flow with boiling in parallel channels is often an efficient approach to managing heat and energy distribution in several engineering systems. However, two-phase flow with heating in parallel channels is prone to maldistribution, which can result in sub-optimal performance and, in some cases, permanent damage to the system. This challenge requires accurate flow modeling in parallel channels to mitigate or design against the adverse effect of two-phase flow maldistribution. The nonlinear nature of the multiphase flow model can yield multiple solutions for the same operating condition, creating significant challenges in predicting flow distribution. This study addresses this challenge by applying the entropy balance analysis and the conservation of mass, momentum, and energy to predict two-phase flow distribution in two thermally isolated parallel channels with a numerical model. Our model predictions and experiments show that equally distributed flow can become severely maldistributed with a decrease in flow rate, accompanied by a significant (>30%) change in the entropy generation rate. We show that the entropy balance analysis can distinguish between stable and unstable flows and identify the most feasible flow distribution in thermally decoupled parallel channels. [ABSTRACT FROM AUTHOR]

The tailrace tunnel system, as a core component of hydroelectric power stations, directly influences the stability and efficiency of the power generation process. Transient conditions often lead to the occurrence of complex unsteady flow phenomena in the tailrace tunnel. In this study, numerical methods integrating open channel flow, multiphase flow, and compressible models were combined to conduct hydraulic analysis of the tailrace system in large hydroelectric power stations. Under specific conditions, periodic jet phenomena were observed, corroborating field observations. The research revealed that the proximity of downstream water levels to the crest level of the tailrace outlet is a prerequisite for the periodic jetting phenomenon, with a sudden rise in water level serving as a triggering condition. Although the surge shaft effectively mitigates wave action, it fails to entirely eliminate the influence of pressure pulsations, resulting in a 23.2% increase in pressure pulsation amplitude in the turbine area. However, the efficiency of the turbine unit is hardly affected; only a slight loss of energy occurs due to the increase in local turbulent entropy production, deemed inconsequential for the overall system. This study aims to investigate the complex response of tailrace tunnel systems in hydroelectric power generation amidst abrupt changes in downstream river, providing crucial insights for the engineering design and operation of large-scale power stations. [ABSTRACT FROM AUTHOR]

A high-fidelity multiphase flow computational model is utilized to investigate the interaction mechanism between anti-phase tandem bubbles and tissue materials in a free-field environment. The formation of liquid jets generated by tandem bubble coupling and its effects on tissue deformation are analyzed. Parametric studies are conducted to explore the impacts of bubble–bubble distance ( γ b b ), bubble size ratio ( S b b ), and bubble–tissue distance ( γ t b ). The results indicate that the regime of tissue penetration varies under different γ b b . For small γ b b , the tissue deformation is mainly attributed to the stretching of upper bubbles and liquid jets; whereas for large γ b b , tissue deformation is primarily induced by the jets themselves; and for moderate γ b b values, it is caused by a combined effect involving both jets and the evolution of toroidal bubbles. Comparative analysis shows the significant impact of varying Sbb on bubble coupling dynamics, with larger Sbb values correlating with more potent tissue penetration. Furthermore, the study also reveals that, beyond γtb exceeding 3, penetration ceases to manifest, advocating for the maintenance of γtb below 1.4 for practical applications. [ABSTRACT FROM AUTHOR]

Constrained by economic development and geographical features, numerous railway lines remain unelectrified, underscoring the expansive potential of diesel trains. Diesel engine emissions discharged from the roof of trains pose a challenge as some of the smoke infiltrates the cabin through the intake of roof-mounted air-conditioning units (ACUs). This intrusion diminishes the indoor air quality, posing health risks to passengers and potentially jeopardizing their safety. This study employs the shear stress transport k-omega turbulence model to formulate a multiphase flow model for simulating smoke diffusion in diesel trains. Additionally, we conducted an optimization design to minimize smoke entry into the ACUs. This study defined six cases based on variations in the shape and height of the cover and the spacing of the smoke vents. The results show that the effect of the diffusion characteristics decreased with the cover height. With the progression of airflow diffusion, the effect of the smoke vent structure on the concentration diminished farther from the vents. The minimum smoke mass flow rate into the intake occurred with the vent spacing of 2.14 m and without a cover, resulting in a 57.0% decrease compared with the maximum. Thus, a smoke vent spacing of 2.14 m without a cover was deemed to be the optimal configuration. The research results provide certain engineering guidance significance for the design and operation of train-smoke vent structures. [ABSTRACT FROM AUTHOR]

The reduction of carbon emissions has become a critical global issue, and the use of monoethanolamine (MEA) solution for CO2 absorption is prevalent in industry. To elucidate the mass transfer mechanisms in reactive multiphase flow, we employed high-speed photography and digital image processing to examine the dynamics and mass transfer behavior of CO2 bubbles in a Hele-Shaw cell. The results indicate that as the MEA solution concentration increases, oscillations during bubble ascent diminish, and the terminal velocity decreases. Based on changes in the mass transfer coefficient, the reaction process can be segmented into a phase of intensified mass transfer, marked by a rapid decrease in bubble equivalent diameter, and a phase of deteriorating mass transfer, where the diameter stabilizes. Additionally, we introduced a dimensionless mathematical model for the Sherwood number based on experimental findings, and its reliability was confirmed. [ABSTRACT FROM AUTHOR]

The multiphase fluid flow and heat transfer behavior in the steelmaking converter are essential for efficient and stable smelting. Herein, a mathematical model of heat transfer for the hot spot zone of the converter is established. The temperature distribution of the molten bath is clarified, and the effects of operating parameters and the exothermic rate of hot spot zone on the heat transfer behavior of the molten bath are investigated. The results show that the temperature gradient between the hot spot zone and the liquid steel as well as the circulation of liquid steel will lead to the nonuniform distribution of temperature. Both the direction of flow field and the mixing characteristics of molten bath influence the heating rate of molten bath, whereas the direction of the flow field plays a dominant role. In addition, the oxygen lance height has a significant influence on the heat transfer behavior; as the lance height increases from 1.35 to 1.65 m, the heating rate increases by 68.32%. The increase of exothermic rate will remarkably increase the temperature gradient and the heating rate increases by 65.84% and 114.28% when the exothermic rate increases by 1.5 and 2 times, respectively. [ABSTRACT FROM AUTHOR]

In this work, the droplet impact and rebound behaviors on a flat substrate are comprehensively investigated by using the consistent and conservative phase-field based lattice Boltzmann method, which is robust for the multiphase flow problems with the large density ratios and long-time dynamics. The dynamic behavior of the droplet considered here is governed by five key factors: the contact angle, droplet size, the Bond number, the Reynolds number and the density ratio. The effects of these parameters on the barycenter motion trajectory, contact time, the maximum spreading factor and rebound height are studied, and the results show that the Bond number and the density ratio play the critical roles in the droplet morphology when it impacts the substrate. After the impact process, there are three typical patterns: fragmentation, deposition and rebound, which are mainly controlled by the wettability, the size of droplet and the Bond number. In the rebound process, we focus on the rebound height and the number of rebound, and also give the distribution of pressure inside the droplet and the evolution of pressure before fragmentation. Finally, it is also found that under some certain conditions, the air density has a positive effect on the droplet rebound behavior and a large density ratio of 6400 can be achieved. [ABSTRACT FROM AUTHOR]

Thermodynamic consistency is a key factor in heat and mass transfer simulation. A modified lattice Boltzmann pseudopotential model with the ability to simulate multiphase and multicomponent flow with a large density and viscosity ratio is proposed. Relative to a model using the exact difference method, a better thermodynamic consistency is obtained through introducing an improved external force term, a multi-relaxation-time collision operator, and a scaling coefficient k of the equation of state. The coefficient of scale k = 0.1 is preferred due to its better thermodynamic consistency, lower spurious current and a smaller surface tension. The inter-particle interaction strength has little influence over the thermodynamic consistency due to its limited contributions to the surface tension. With the model, the bubble dissolution under pressure is investigated and Henry's law is validated. • A lattice Boltzmann pseudopotential multiphase-multicomponent model is developed. • Improved source term achieves thermodynamic consistency with large density ratio. • Effect of the inter- and intra-particle forces on the surface tension is investigated. [ABSTRACT FROM AUTHOR]

• A fully coupled three-dimensional THMC model (DEHydrate) is developed for simulating hydrate dissociation. • The numerical results obtained from the proposed model are in good agreement with those from other simulations. • Only a small fraction of gas produced from radial hydrate dissociation is collected from the wellbore. • The model provides an effective tool to predict the mechanical behavior during hydrate dissociation. Due to high energy density and huge reserves, many trial projects worldwide have been conducted to exploit natural gas hydrates (NGH). However, most of them did not meet the commercialization requirements because of submarine hazards, low gas production and sand production. Therefore, it is important to investigate the NGH dissociation process. In this paper, a fully coupled multiphase, strongly nonlinear three-dimensional (3D) thermal–hydro–mechanical–chemical model (DEHydrate) is developed to consider the multiphysics behaviours including solid-liquid-gas multiphase flow, heat transfer, NGH phase transition and solid deformation during hydrate dissociation. The model is solved using a fully implicit finite element method. The gas-liquid flow and heat transfer are simulated by low-order elements while the solid deformation is calculated by high- or low-order elements. The behaviours of the multiphase seepage and geomechanics are fully coupled and the physical properties of the reservoir are updated iteratively based on changes in pressure, temperature and displacement. The DEHydrate simulator provides an effective tool to predict the evolution of reservoir mechanical behavior during hydrate dissociation, including transient pressure, temperature, displacement and stress in the reservoir, as well as multiphase saturation, hydrate dissociation rate/mass and gas production rate/mass. During the NGH dissociation, the initial stage exhibits a rapid dissociation rate of up to 206.23 kg/(d·m) for NGH layer with a length of 600 m and a thickness of 22 m, which subsequently decreases to 11.64 kg/(d·m). Only a small portion of the gas generated during NGH dissociation is collected at the wellbore (approximately 35.6 % after 100 days), while the majority remains trapped in the reservoir. In addition, throughout NGH dissociation, the reservoir matrix continues to move toward the wellbore in the horizontal direction. While in the vertical direction, the reservoir matrix below the wellbore moves upwards, with decreasing displacement due to low-pressure diffusion, while the reservoir matrix above the wellbore moves downwards, with increasing displacement. The largest displacements occur near the wellbore during the early stage of NGH dissociation, while in the late stage, the largest displacements occur above the reservoir. [ABSTRACT FROM AUTHOR]

The hydrodynamics of a conical spouted bed was simulated utilizing the Eulerian–Eulerian Two-Fluid Model (TFM) incorporating a kinetic theory of granular flows. The simulations were confirmed with experimental data. To accurately examine the pyrolysis process, the hydrodynamics of the solid bed as well as the heat transfer inside it were analysed separately by considering a precise synthetic model. The effects of gas velocity, particle size, bed length, and temperature were thoroughly investigated. The results indicated that the amount of relative standard deviation increases with an increase in the inlet velocity into the bed. This amount of deviation at the inlet velocity (0.6 m/s for tar and gas flow to its maximum value of 9.1 and 9.4) is not desirable in product production and should be modified so that the amount of gas flow increases and the tar produced reaches the minimum possible amount. Also, the graphs of the relative standard deviation in terms of temperature indicate that the increase in temperature from 730 to 950 K is associated with a relatively smaller fluctuation of the relative standard deviation so that at the temperature of 730 K, it is 7.2 % for tar and 6.4 % for gas flow, while at temperature of 950 K, it is 6.5 % for wire and 6.8 % for gas flow. Finally, the results determined that small-diameter particles have a more significant fountain height and also higher velocity in the spout section. [ABSTRACT FROM AUTHOR]

When the airlift bioreactor is applied to the field of industrial fermentation, there is a common problem of low mixing and flow efficiency due to its simple structure. In order to expand the application of airlift bioreactor in the field of industrial fermentation, a new type of airlift bioreactor with three-dimensional bumps in the draft tube has been designed to enhance the mixing and flow of gas-liquid two-phase in the reactor. In order to determine the specific influence of the three-dimensional bumps on the internal flow field of the reactor, and to provide technical reference for the improvement of the structure of the airlift bioreactor, in this paper, the CFD simulation of this type of bioreactor is carried out. Based on the Euler multiphase flow, the Realizable k-ε model was used to analyze the flow field of the reactor with average gas-liquid flow linear velocity and temperature as parameters. The results show that under certain conditions, the three-dimensional bumps inside the draft tube can effectively accelerate the gas-liquid two-phase flow and better promotes the mixing of pig manure fermentation broth and air. [ABSTRACT FROM AUTHOR]

The application of a two-phase ejector allows for the mixing of liquid and gas and provides effective heat transfer between phases. The aim of the study is a numerical investigation of the performance of a water-driven, condensing two-phase ejector. The research was performed using CFD methods, which can provide an opportunity to analyze this complex phenomenon in 2D or 3D. The 2D axisymmetric model was developed using CFD software Siemens StarCCM+ 2022.1.1. The Reynolds-Averaged Navier–Stokes (RANS) approach with the Realisable k-ε turbulence model was applied. The multiphase flow was calculated using the mixture model. The boiling/condensation model, where the condensation rate is limited by thermal diffusion, was applied to take into account direct contact condensation. Based on the mass balance calculations and developed pressure and steam volume fraction distributions, the ejector performance was analyzed for various boundary conditions. The influence of the suction pressure (range between 0.812 and 0.90) and the steam mass flow rate (range between 10 g/s and 25 g/s) is presented to investigate the steam condensation phenomenon inside the ejector condenser. The provided mixture of inert gas (CO2) with steam (H2O) in the ejector condenser was investigated also. The weakening of the steam condensation process by adding CO2 gas was observed, but it is still possible to achieve effective condensation despite the presence of inert gas. [ABSTRACT FROM AUTHOR]

Indirect thermal desorption process of petroleum hydrocarbon contaminated soil is very complex and difficult to be analyzed by engineering full-scale numerical simulation considering multi-phase flow and interphase heat as well as mass transfer. Therefore, it is urgent to develop a simple and rapid calculation method to guide technology development and engineering applications. In this paper, the method of equivalent specific heat approximation was proposed to simplify the mass transfer process on the material side to the heat transfer process under variable specific heat conditions, and the numerical simulation of engineering scale indirect thermal desorption equipment was studied by coupling the diffusion flame combustion model, weighted-sum-of-gray-gases model, and discrete ordinates model. The heating process of soil in thermal desorption chamber was simulated, and the influence of soil residence time and designed feed rate on process parameters was obtained. The research results showed that soil residence time should be extended appropriately under the condition of less than 1.75 hours and designed feed rate be limited within 4 t/h to ensure reasonable soil discharge temperature that was directly related to the removal efficiency of petroleum hydrocarbons in contaminated soil. Meanwhile, the modification scheme of power distribution of combustion system was further studied to improve the heating uniformity of tubes. [ABSTRACT FROM AUTHOR]

In this study, we present a novel interpolation scheme for chimera simulations in CFD that treats flows with discontinuities. This scheme is suitable for interpolation over polyhedral meshes using only scattered data and without the use of stencils. During the interpolation data transfer among overset meshes, both solution variables and their gradients are communicated and then used for the interpolation process. First, the overset topology problem in partitioned polyhedral meshes is addressed, and then a new interpolation algorithm for generally discontinuous fields is introduced. Then, we describe how the gradient approximation of the Finite Volume (FV) method is utilized in order to construct bounded approximations on values on the direction of discontinuities and enhance the accuracy of the low order Nearest Neighbor value (NNV) algorithm. The performance of the proposed algorithm is quantified and validated in various test cases, together with a comparison with NNV. Finally, scalability tests are presented to prove computational efficiency. The method is proved to be highly accurate in propagation cases and performs well in unsteady two-phase problems executed using parallel architectures. [ABSTRACT FROM AUTHOR]

The Richards equation is commonly used to model the flow of water and air through soil, and it serves as a gateway equation for multiphase flows through porous media. It is a nonlinear advection–reaction–diffusion equation that exhibits both parabolic–hyperbolic and parabolic–elliptic kind of degeneracies. In this study, we provide reliable, fully computable, and locally space–time efficient a posteriori error bounds for numerical approximations of the fully degenerate Richards equation. For showing global reliability, a nonlocal-in-time error estimate is derived individually for the time-integrated H^1(H^{-1}), L^2(L^2), and the L^2(H^1) errors. A maximum principle and a degeneracy estimator are employed for the last one. Global and local space–time efficiency error bounds are then obtained in a standard H^1(H^{-1})\cap L^2(H^1) norm. The reliability and efficiency norms employed coincide when there is no nonlinearity. Moreover, error contributors such as space discretization, time discretization, quadrature, linearization, and data oscillation are identified and separated. The estimates are also valid in a setting where iterative linearization with inexact solvers is considered. Numerical tests are conducted for nondegenerate and degenerate cases having exact solutions, as well as for a realistic case and a benchmark case. It is shown that the estimators correctly identify the errors up to a factor of the order of unity. [ABSTRACT FROM AUTHOR]

Sudden displacement of large volumes of liquid–granular mixtures in nature (dam-breaks, landslides, floods, etc.) are often reported to be deadly and destructive. The flow behavior of those mixtures is complex and depends on a large variety of parameters, e.g., size distribution of the solid phase, viscosity of the fluid, predisplacement packing conditions, ratio of solid to liquid phase, and geometry of the domain. Because of the multitude of parameters and the large displacements involved, the numerical modeling of these phenomena is complex. A two-phase double-point material point method formulation in Anura3D, a particle-based continuum numerical method, was tested against two experimental cases. Model simulations showed that simple constitutive models such as Mohr-Coulomb (MC) with perfect plasticity can be sufficient to accurately model bulk granular flow behavior. However, with slightly different initial conditions, these flows can exhibit more complex features such as progressive block failures, which necessitates a more advanced solid constitutive model such as MC strain softening. Further, other simulation parameters like wall friction boundary conditions and fluidization threshold are also crucial in these types of numerical simulations. The ability of such models to capture complex failure modes is critical to assess dam safety. The sudden release of a mixture of granular materials and water, for example, after failure of a tailings dam, can have devastating consequences on downstream infrastructure and communities. We investigated how such flows can be accurately predicted using the computer model Anura3D, which uses a special technique, where material points separately represent the water and the grains because those points can efficiently represent the large deformations that these types of granular flows exhibit. We found that, at higher water content, a simple model of the mechanical properties of the granular and water mixture suffices. However, at lower water content, the more complex behavior of the granular flow requires a specific model that takes into account the local history of deformations. This study is relevant to the analyses of dam safety, post-wild fire hillslope debris flows, and landslides. [ABSTRACT FROM AUTHOR]

Control of phonon transport in solid devices is important for thermoelectric energy conversion and phononic crystal technology, and much attention has been paid to sub-micrometer or nanometer scale structures for that purpose. In order to investigate how various nano-structures affect the phonon transport, we have developed a numerical simulation code based on the Boltzmann transport equation of phonon distribution function in the reciprocal space. To appropriately treat the phonon transport at interface of an arbitrary shape, we newly introduced a volume of fluid like scheme, which was originally developed for multi-phase flow simulation. As a test of the developed simulation code, we investigated two-dimensional thin silicon films with two types of hole shape and two types of hole arrangement. The results essentially agree with recent experiments. [ABSTRACT FROM AUTHOR]

Unlike conventional single-phase seepage monitoring methods, monitoring multiphase flow in porous media is more complex. This paper addresses this complexity by analyzing the heat transfer in porous media models under multiphase seepage conditions. It introduces a set of theories, methods, and devices to effectively monitor the flow velocity in multiphase seepage processes. Utilizing a self-developed single-point self-heating temperature-sensing device combined with saturation testing at monitoring points, we establish a method to determine the relationship between different saturation and resistivity, as well as the saturation and thermal conductivity of the reservoir model, which provides essential parameter support for the calculation of results during flow velocity monitoring. The effectiveness of the flow velocity monitoring method was confirmed through a one-dimensional constant velocity multiphase seepage experiment. Furthermore, oil-water two-phase seepage simulation experiments were conducted based on the sandpack model. By comparing the real oil-water flow velocity with the monitored velocity, the accuracy can reach over 95%, validating the accuracy and reliability of the method proposed in this paper. The seepage flow velocity monitoring theory and technology established herein offer corresponding theories and methods for obtaining fluid seepage velocity in porous media with multiphase fluids. [ABSTRACT FROM AUTHOR]

We present a modular and cost-effective gamma ray computed tomography system for multiphase flow investigations in industrial apparatuses. It mainly comprises a 137Cs isotopic source and an in-house-assembled detector arc, with a total of 16 scintillation detectors, offering a quantum efficiency of approximately 75% and an active area of 10 × 10 mm2 each. The detectors are operated in pulse mode to exclude scattered gamma photons from counting by using a dual-energy discrimination stage. Flexible application of the computed tomography system, i.e., for various object sizes and densities, is provided by an elaborated detector arc design, in combination with a scanning procedure that allows for simultaneous parallel beam projection acquisition. This allows the scan time to be scaled down with the number of individual detectors. Eventually, the developed scanner successfully upgrades the existing tomography setup in the industry. Here, single pencil beam gamma ray computed tomography is already used to study hydraulics in gas–liquid contactors, with inner diameters of up to 440 mm. We demonstrate the functionality of the new system for radiographic and computed tomographic scans of DN110 and DN440 columns that are operated at varying iso-hexane/nitrogen liquid–gas flow rates. [ABSTRACT FROM AUTHOR]

In this study, three-dimensional modeling of a pulsating heat pipe is carried out, and the effect of physical and geometrical parameters such as filling ratio (FR), transverse distance (Z), and the number of loops (N) on its performance is investigated. In this study, it is assumed that the heat pipe is embedded in the microchannel heat sink, and its boundary condition is the thermal condition in the microchannel heat sink. The volume of fluid (VOF) multiphase flow model is used in the current numerical analysis. For the PHP, four different filling ratios (FR = 40, 50, 60, 70%), four transverse distances (Z = 2, 5, 8, 18 mm), and four numbers of loops (N = 1, 2, 3, 4) are considered, and the results will be compared with each other. It is shown that PHP with FR = 60% has the best performance. Also, comparing different values of transverse distance, Z = 18 mm has the lowest thermal resistance. The results show that by embedding a 4-loop PHP, the thermal resistance of MCHS decrease from 0.0268 to 0.0221 K/W, which indicates a 21.27% increase in the thermal performance of the microchannel heat sink compared to the basic design (without PHP). [ABSTRACT FROM AUTHOR]

Velocity string (VS) is one of the most common methods to unload water in gas-producing field. In order to understand the behavior affecting production rate, we obtained several parameters including well completion, gas well production data, gas liquid ratio (GLR) and pressure data at tubing and casing head pressure, flowing bottom hole pressure. We then explore the relationship between these parameters against reservoir pressure and perform sensitivity analysis using multiphase steady-state flow simulator to analyze the parameters are the most sensitive to gas production rate. The results show that: (1) at larger inner diameter of the VS, there is a certain increase trend of gas production of gas wells. However, the production rate does not show a linear increase relationship with the larger internal diameter. It will reach certain inflection point before it decreases; (2) the gas production of the VS well is mainly driven by the reservoir pressure, the higher the reservoir pressure, the greater the gas production; (3) the root cause of relatively low initial production rate after small inner diameter coiled tubing VS installation is categorized as an abnormal well startup. This study provides theoretical support for selecting the optimum size and depth of VS to maintain well productivity. [ABSTRACT FROM AUTHOR]

Multiphase flow entrainment in natural gas engineering significantly influences the safety and efficiency of oil companies since it affects both the flow and the heat transfer process, but its mechanisms are not fully understood. Additionally, current computational fluid dynamics (CFD) methodologies seldom consider entrainment behavioral changes in pipe elbows. In this article, a verified CFD method is used to study the entrainment behavior, mechanism, and changes in an elbow. The results show that droplet diameter in a developed annular flow follows a negative skewness distribution; as the radial distance (from the wall) increases, the fluctuation in the droplets becomes stronger, and the velocity difference between the gas and the droplets increases linearly. Turbulence bursts and vortices sucking near the wall jointly contribute to droplet entrainment. As the annular flow enters the elbow, the secondary flow promotes the film expansion to the upper and lower parts of the pipe. Droplets re-occur near the elbow exit intrados, and their size is much smaller than those in the upstream pipe. Vortices sucking under low gas velocity play an important role in this process. These findings provide guidelines for safety and flow assurance issues in natural gas production and transportation and bridge the gap between multiphase flow theory and natural gas engineering. [ABSTRACT FROM AUTHOR]

A numerical method for describing droplet-driven particle motion at low Weber numbers in fluids is proposed. A coupling strategy combining the Shan–Chen (SC) model and the smoothed profile method (SPM) is employed. The proposed scheme correctly resolves the momentum transfer between solid particles and fluid phases, while effectively controlling the wetting condition. An interaction zone where three phases coexist is introduced to solve the contradiction between the SC model and SPM (i.e. whether fluid particles are allowed at the solid nodes). In the interaction zone, partial solid particles are entrapped in the fluids owing to the coexistence of solid and fluid particles, causing solid particles to exchange momentum with fluid particles. Furthermore, the interaction forces between fluid and solid particles near the solid surface are considered at nodes near pure solid particles within this region. Based on the proposed scheme, the interactions between freely moving particles and freely moving droplets were investigated, along with the effects of wettability (Gads) and volume forces (Fp*) on particle–droplet interactions. When a liquid droplet comes into contact with a solid particle, the adhesion force between the droplet and the solid surface promotes the movement of solid particles toward the droplet. When a double emulsion comes into contact with solid particles, the adhesion force between the emulsion film and solid surface causes the double emulsion to break at the connecting point, and the volume force of the emulsion film Fd* causes the solid particles to penetrate the emulsion. [ABSTRACT FROM AUTHOR]

We develop a numerically stable sequential formulation of thermoporomechanics for largely deformable gas hydrate deposits, extended from the fixed stress split of infinitesimal transformation. Constitutive equations are based on the total Lagrangian approach for both flow and geomechanics, including dynamic full tensor permeability and thermal conductivity updated from the deformation gradient. For space discretization, we take the cell‐centered finite volume and node‐based finite element method for flow and geomechanics, respectively. Then, we propose a sequential implicit method for all‐way coupled thermoporomechanics, where the nonisothermal multiphase flow problem of gas hydrates is solved implicitly first and then the geomechanics problem is solved implicitly at the next step. During solution of the flow problem, we fix the rate of first Pioal total stress for numerical stability as well as apply porosity correction and entropy correction to account for geomechanical effects. We test numerical examples where flow and geomechanics parameters are based on deep oceanic gas hydrate deposits. When applying depressurization, even though the results between the infinitesimal transformation and finite strain geomechanics are similar in the early stages due to small deformation, we find differences between them in the late times as deformation becomes large. Accordingly, permeability and thermal conductivity tensors become nonisotropic full tensors although they are initially isotropic. We identify numerical stability of the developed sequential method from the test cases that exhibit the highly complex coupled gas hydrate systems with large deformation. Thus, the proposed sequential formulation can be applied in largely deformable gas hydrate systems. [ABSTRACT FROM AUTHOR]

A robust finite volume framework for solving incompressible two-phase flow problems based on an explicit dual-time stepping based artificial compressibility formulation has been developed by Parameswaran and Mandal (2019) for structured meshes. This artificial compressibility framework is extended to unstructured meshes in the present paper. In order to further enhance the applicability to real life engineering problems, the surface tension effect is also modeled here. To deal with arbitrary unstructured mesh topology, least square and Green-Gauss integral based methods are used. The efficacy of the proposed method is demonstrated using a set of scalar advection based test problems and a set of standard incompressible two-phase flow test problems involving gravitational, viscous and surface tension forces. The numerical results show improvement in accuracy compared to the results of the structured mesh formulation. [ABSTRACT FROM AUTHOR]

Smoothed particle hydrodynamics (SPH) is a meshless, particle-based approach that has been increasingly applied for modelling of various fluid-flow phenomena. Concerning multiphase flow computations, an advantage of the Lagrangian SPH over Eulerian approaches is that the advection step is straightforward. Consequently, the interphasial surface can be explicitly determined from the positions of particles representing different phases; therefore, there is no need for the interface reconstruction step. In this review paper, we briefly recall the basics of the SPH approach, and in particular the physical modelling and numerical implementation issues. We also mention the weaknesses of the approach and some remedies to overcome them. Then, we demonstrate the applicability of SPH to selected interfacial flow cases, including the liquid column break-up, gas–liquid flow regimes in a channel capturing the transitions between them and the wetting phenomena. Concerning the two-fluid modelling, it is illustrated with sediment transport in the presence of surface waves. Various other applications are briefly recalled from the rich and growing literature on the subject, followed by a tentative list of challenges in multiphase SPH. [ABSTRACT FROM AUTHOR]

The air-lift reverse circulation drilling method enables efficient and continuous core extraction. However, the flow characteristics of gas–liquid–solid mixtures during core mass transport are complex, and developing a model to predict performance remains challenging. The flow characteristics of gas–liquid–solid mixtures inside the drill pipe are numerically analyzed by calculating the mixing transport of the core during the airlift process. By solving the momentum equations for multiphase flow, the distribution of physical quantities of three phases and pressure along the depth was calculated, and the laws of influence of the operating parameters on the transport characteristics of the core were analyzed. The results show that the drilling performance is related to the geometric parameters of the pipe and core, drilling speed, and depth. When the submergence ratio is increased to 0.9 , the maximum liquid-phase superficial velocity is increased by 109 % compared with that when the submergence ratio is 0.6. The size of the annular space gap 67 formed between the core and the pipe wall is the key to the core's mechanical properties, and the differential pressure gradient force increases with increasing core diameter. An increase in well depth reduces the fluid flow. In addition, increasing the pipe diameter improves drilling performance due to reduced friction losses, which elevates the air flow rate required for air-lift reverse circulation operation. [ABSTRACT FROM AUTHOR]

The interaction between liquid spray and the surrounding air is crucial in fluid research, especially in the study of fuel spray and combustion. However, the fuel spray–air interaction is a complex process influenced by multiple factors, including fuel type, fuel injection pressure, and fuel temperature. These factors are coupled together, making it challenging and time-consuming to accurately capture the spray–air data using traditional experimental methods alone. The current study proposes a hybrid physics-based and machine learning model for utilizing spray images to reconstruct ambient flow fields. The novelty of this work lies in leveraging the spatial characteristics of spray and airflow data to optimize feature extraction and reduce unnecessary nonlinearity in the model. Consequently, the model offers complementary advantages, improving model interpretability and reducing its reliance on massive data. The training dataset is collected using a combined diagnostic approach, utilizing Mie-scattering imaging and fluorescence particle image velocimetry. The liquid spray and the ambient air velocity field are measured simultaneously under a wide range of experimental conditions, including different fuel types, fuel injection pressures, and fuel temperatures. The reconstruction results are validated against unseen experimental data. In general, the reconstruction results indicate that the model is accurate, fast, and robust for different fuel conditions and injector types. It provides an innovative way to reconstruct airflow fields based on spray images (spray density distribution). These findings highlight the potential of integrating physics-based and machine learning methods for multiphase flow diagnostics, paving the way for broader data-driven applications in fluid research. [ABSTRACT FROM AUTHOR]

The hydrodynamic and stirring characteristics of gas-slag-copper matte three-phase in side-blowing melt pool melting were numerically simulated using a combination of the volume of fluid (VOF) model in computational fluid dynamics and the realizable k-ε turbulence model. The study obtained macroscopic flow and gas-liquid two-phase distribution information of the flow field in the melting process. It also examined the effects of isokinetic blowing and nonlinear blowing on the fluid velocity, penetration depth, gas content, and turbulent eddy volume of the flow field, and compared the results. The results indicate that, for the same total gas volume, constant velocity blowing (CVS) inadequately agitates the molten pool, resulting in a large stirring dead zone within the flow field. In contrast, nonlinear blowing enhances the fluid velocity overall. Specifically, sinusoidal variable speed blowing (SWS) and rectangular variable speed blowing (RWS) reduce the stirring dead zone area by 79 and 73.5 %, respectively. This is attributed to the increase in maximum penetration depth and slag phase gas content, as well as the decrease in gas escape during nonlinear blowing. The vortex volume over the total calculated time for the three conditions is enhanced by 6.7 and 1.1 % for SWS and RWS, respectively. Additionally, the turbulent kinetic energy of the fluids is increased by 18.7 and 17 %, respectively. [ABSTRACT FROM AUTHOR]

As Pelton turbines are increasingly used in high mountain regions because of their unique advantage of high-water head adaptability, the hydraulic characteristics and multi-phase flow behaviour in Pelton turbines have attracted the attention of many scholars. Most notably, the presence of solid particles such as sand exists in natural river systems, which end up in the turbines, causing erosion. This has become an international academic issue which has not been fully developed yet. In this study, three-phase simulations based on Eulerian–Lagrangian methodology are conducted to investigate the erosion phenomenon, especially in the bucket region. Sediment particle characteristics such as size and concentration in both the distribution system and buckets region are analysed. The innovation of this study is that, unlike other erosion investigations, it focuses on the impact angle of the jet flow as this is a unique characteristic of Pelton turbines. Furthermore, the sediment particle's flow characteristics at different bucket rotating angles and how they influence the erosion mechanism are also investigated. Results reveal that larger particles cause greater erosion on the bucket. In small particle and standard diameter conditions, the impact angle is mostly below 5 $ ^\circ $ ∘ . Finally, this study presents the first successful attempt in using rotating angle to describe the erosion in a Pelton turbine. A corrected erosion model adapted to the Pelton turbine is given through regression and proves effective in predicting erosion. [ABSTRACT FROM AUTHOR]

Velocity string (VS) is one of the most common methods to unload water in gas-producing field. In order to understand the behavior affecting production rate, we obtained several parameters including well completion, gas well production data, gas liquid ratio (GLR) and pressure data at tubing and casing head pressure, flowing bottom hole pressure. We then explore the relationship between these parameters against reservoir pressure and perform sensitivity analysis using multiphase steady-state flow simulator to analyze the parameters are the most sensitive to gas production rate. The results show that: (1) at larger inner diameter of the VS, there is a certain increase trend of gas production of gas wells. However, the production rate does not show a linear increase relationship with the larger internal diameter. It will reach certain inflection point before it decreases; (2) the gas production of the VS well is mainly driven by the reservoir pressure, the higher the reservoir pressure, the greater the gas production; (3) the root cause of relatively low initial production rate after small inner diameter coiled tubing VS installation is categorized as an abnormal well startup. This study provides theoretical support for selecting the optimum size and depth of VS to maintain well productivity. [ABSTRACT FROM AUTHOR]

In numerical linear stability investigations, the rates of change of the kinetic and thermal energy of the perturbation flow are often used to identify the dominant mechanisms by which kinetic or thermal energy is exchanged between the basic and the perturbation flow. Extending the conventional energy analysis for a single-phase Boussinesq fluid, the energy budgets of arbitrary infinitesimal perturbations to the basic two-phase liquid–gas flow are derived for an axisymmetric thermocapillary bridge when the material parameters in both phases depend on the temperature. This allows identifying individual transport terms and assessing their contributions to the instability if the basic flow and the critical mode are evaluated at criticality. The full closed-form energy budgets of linear modes have been derived for thermocapillary two-phase flow taking into account the temperature dependence of all thermophysical parameters. The influence of different approximations to the temperature dependence on the linear stability boundary of the axisymmetric flow in thermocapillary liquid bridges is tested regarding their accuracy. The general mechanism of symmetry breaking turns out to be very robust. [ABSTRACT FROM AUTHOR]

Surfactants are widely used in the fracturing fluid to enhance the imbibition and thus the oil recovery rate. However, current numerical models cannot capture the physics behind capillary imbibition during the wettability alteration by surfactants. Although the interacting capillary bundle (ICB) model shows potential in characterizing imbibition rates in different pores during wettability alteration, the existing ICB models neglect the influence of wettability and viscosity ratio on the imbibition behavior, making it difficult to accurately describe the oilewater imbibition behavior within the porous media. In this work, a new ICB mathematical model is established by introducing pressure balance without assuming the position of the leading front to comprehensively describe the imbibition behavior in a porous medium under different conditions, including gaseliquid spontaneous imbibition and oilewater imbibition. When the pore size distribution of a tight rock is known, this new model can predict the changes of water saturation during the displacement process in the tight rock, and also determine the imbibition rate in pores of different sizes. The water saturation profiles obtained from the new model are validated against the waterflooding simulation results from the CMG, while the imbibition rates calculated by the model are validated against the experimental observations of gaseliquid spontaneous imbibition. The good match above indicates the newly proposed model can show the water saturation profile at a macroscopic scale while capture the underlying physics of the multiphase flow in a porous medium at a microscopic scale. Simulation results obtained from this model indicate that both wettability and viscosity ratio can affect the sequence of fluid imbibition into pores of different sizes during the multiphase flow, where less-viscous wetting fluid is preferentially imbibed into larger pores while more-viscous wetting fluid tends to be imbibed into smaller pores. Furthermore, this model provides an avenue to calculate the imbibition rate in pores of different sizes during wettability alteration and capture the non-Darcy effect in micro- and nano-scale pores. [ABSTRACT FROM AUTHOR]

In recent years, the pseudopotential multiphase lattice Boltzmann method (LBM) has been widely applied in the numerical simulations of complex multiphase flow. However, numerical stability at high Weber (We) and Reynolds (Re) numbers seriously restricts its application. In the present work, the pseudopotential multiphase LBM is developed by introducing the entropic stabilizers to the cascaded collision operator, and thus, the numerical stability is effectively enhanced. The relaxation rates for different order moments are all determined by fluid viscosities and the maximum entropy condition instead of being user-defined. Furthermore, the surface tension and contact angle can be adjusted in a wide range, which extends the application of the pseudopotential multiphase model. The accuracy and capability of the present model to simulate the complex multiphase flow are validated by reproducing the droplet impact on the flat or textured superhydrophobic surfaces. In addition, a droplet impact on the superhydrophobic surface at We = 1280 and Re = 18000 is simulated, in which the Weber and Reynolds numbers have significantly increased. This strongly demonstrates that the present model can enhance the numerical stability in the simulation of large density ratio multiphase flows at simultaneously high Weber and Reynolds numbers, which means the present model can further extend the pseudopotential multiphase LBM to more realistic scientific and technical applications. [ABSTRACT FROM AUTHOR]

This work proposes an original preconditioner that couples the Constrained Pressure Residual (CPR) method with block preconditioning for the efficient solution of the linearized systems of equations arising from fully implicit multiphase flow models. This preconditioner, denoted as Block CPR (BCPR), is specifically designed for Lagrange multipliers-based flow models, such as those generated by Mixed Hybrid Finite Element (MHFE) approximations. An original MHFE-based formulation of the two-phase flow model is taken as a reference for the development of the BCPR preconditioner, in which the set of system unknowns comprises both element and face pressures, in addition to the cell saturations, resulting in a 3 × 3 block-structured Jacobian matrix with a 2 × 2 inner pressure problem. The CPR method is one of the most established techniques for reservoir simulations, but most research focused on solutions for Two-Point Flux Approximation (TPFA)-based discretizations that do not readily extend to our problem formulation. Therefore, we designed a dedicated two-stage strategy, inspired by the CPR algorithm, where a block preconditioner is used for the pressure part with the aim at exploiting the inner 2 × 2 structure. The proposed preconditioning framework is tested by an extensive experimentation, comprising both synthetic and realistic applications in Cartesian and non-Cartesian domains. [ABSTRACT FROM AUTHOR]

We consider a reactive multiphase multicomponent Darcy flow in a porous medium while taking into account the effects of temperature. This flow model is coupled to an energy balance equation and ordinary and/or algebraic differential equations to model the chemical reactions. The model is discretized using a cell-centered finite volume method with implicit Euler or second order backward differential formula time discretization. Both sequential and fully coupled fully implicit strategies are considered. Two new DuMu X modules are developed based on the above schemes. Two numerical examples are presented to validate the implementation of the two methods and the capability of the code to solve CO 2 sequestration scenarios. The first test addresses a one-dimensional radial problem to study thermal effects on injectivity during CO 2 storage. For this purpose, isothermal/nonisothermal comparisons are carried out to highlight these differences, which can modify the flow. The second test is chosen to test the code to approximate solutions for a three-dimensional benchmark based on the Johansen CO 2 storage operation. Then, we compare the efficiency, performance in terms of computation time, and parallel scalability of the sequential and implicit methods. In conclusion, both modules demonstrate accuracy, numerical robustness, and the potential to solve realistic problems. With an equal time step, the sequential scheme can be faster than the implicit scheme, but the splitting can present a loss of accuracy, particularly concerning the conservation of mass of the injected CO 2 . [ABSTRACT FROM AUTHOR]