Study on the wear characteristics of solid-liquid two-phase flow in centrifugal pumps based on CFD-DEM and support vector machine

A semi-analytical model for gas–water two-phase flow in deep shale gas formation considering partially-propped hydraulic fractures with stress-dependent conductivities

Effect of bend radius on gas slug formation mechanisms in air–water two-phase flow within a horizontal minichannel T-junction

In recent years, Shallow water Christmas trees have made a significant breakthrough internationally. It fills technological gaps, alleviates energy shortages, and offers innovative solutions for global shallow - water oil and gas development. However, this development faces challenges like special wellbore structures, complex temperature - pressure systems, and downhole operation uncertainties. These issues lead to poor wellbore pressure control and high well - control risks. Traditional steady - state models assume constant flow parameters. They fail to accurately depict wellbore dynamics, ignoring gas - liquid slippage and transient effects. As result, conventional commercial well control software exhibits significant calculation discrepancies, which hinders the design of effective well kill operations. This study introduces a semi-discrete relaxation strategy to address simulation challenges in shallow water environments. By reformulating gas-liquid two-phase flow equations into a semi-linear model with relaxation coefficients, numerical stability is enhanced. The system's dynamic evolution is analyzed using the Chapman-Enskog asymptotic expansion, while the FVS algorithm decomposes source terms to improve accuracy. Flow directions and boundary conditions are determined by solving the characteristic lines of the Jacobian matrix, enabling precise parameter calculation for the Driller’s Method. Practical applications confirm that this method significantly improves the stability and accuracy of transient wellbore simulations, offering an optimized strategy for well control operations. • Algorithmic Integration Innovation For the first time, the semi-discrete method is integrated with the FVS algorithm for solving gas-liquid two-phase flow models. The semi-discrete method transforms the nonlinear hyperbolic system into a semi-linear model, after which the FVS algorithm decomposes the source terms. This integration enables precise capture of the complex dynamic behaviors of fluid flow within the wellbore, significantly enhancing computational accuracy and numerical stability. It breaks through the limitations of traditional algorithms in resolving small-scale flow features. • Engineering Research Innovation This study conducts the first systematic research on well-killing operations in the development mode of shallow-water Christmas tree equipment, filling a gap in both theoretical and engineering practice. By thoroughly analyzing the unique wellbore structures, complex temperature-pressure systems, and operational uncertainties in shallow water, it proposes targeted well-killing strategies, providing a new technical approach and practical guidance for global shallow-water oil and gas development. • Boundary Condition Solution Innovation Through solving the characteristic lines of the Jacobian matrix to analyze the propagation of boundary physical quantities, this research achieves precise solutions for the boundary conditions during well-killing operations in shallow-water wellbores. Compared with the traditional first-order extrapolation method, which often causes numerical oscillations, this approach accurately determines the inflow and outflow directions of fluids and precisely calculates key parameters such as pressure and velocity. As a result, it significantly improves the reliability and engineering practicability of well-killing operation simulations.

A robust exact Riemann solver for a laminar two-phase flow model with two layers

This analysis's main purpose is to investigate the outcome of melting heating on microorganisms in a two-phase bioconvection flow of a dusty hybrid nanofluid via a sheet with Cattaneo-Christov flux model. Using an appropriate similarity transformation, constitutive partial differential equations are transformed into ordinary differential equations. Using reference datasets from numerical calculations, we train and assess the intelligent Bayesian regularized predictive neural network approach to forecast flow solutions under different physical parameter scenarios. This model is valuable in advanced thermal and environmental engineering systems that combine two-phase flows, particulate matter, and microorganism-induced bioconvection. It is used in melting and solidification processes, including phase-change materials, metal casting, and thermal energy storage systems, where dusty hybrid nanofluid improve heat transport. The Cattaneo-Christov flux model's addition makes it applicable to high-speed thermal transport and conduction of non-Fourier heat in micro- and nanoscale devices. When the thermal and solutal relaxation parameters' values rise, the solutal and thermal distribution improves. Histogram analysis, regression analysis, statistic transition, and Mean square error analysis all show that it is accurate when compared to reference data.

In tapered pipes commonly used in engineering applications, increasing the particle mass flux and reducing specific energy consumption are key to improving the energy efficiency of liquid-solid two-phase conveyance. This study introduces the Witoszynski curve as the profile for tapered pipes and analyzes its transport characteristics in two-phase liquid-solid flow. The contraction ratio, contraction angle, and profile type were selected as optimization parameters, and the back propagation neural network (BPNN) and the genetic algorithm (GA) were employed as the prediction model and optimization algorithm. An optimization framework was developed to determine the optimal structural parameters for tapered pipes. The results show that using the Witoszynski curve as a contour guide allows particles to follow a smoothly varying curvature trajectory through the transition zone, thereby increasing particle velocity and improving flow field uniformity. Compared to the tapered pipes before optimization, the particle mass flux increased by 11.85%, and specific energy consumption decreased by 9.90%. Validation simulations conducted under various flow rates and with fluids of different viscosities demonstrate that the optimized model exhibits good robustness.

The geometric and topological structures of fracture networks in unconventional reservoir fracturing are core factors controlling the transport of water-sand two-phase flow. At present, there is still a lack of clear understanding regarding the diversion and confluence laws of proppant within fracture networks. In this paper, numerical simulations are conducted to investigate the basic laws of proppant transport, diversion and confluence in fracture networks, as well as the influences of various parameters. The results show that the diversion process is characterized by inertia-dominated asymmetric distribution, and proppant transport exhibits path selectivity, with proppant preferentially entering main channels and eventually forming a stable stratified structure. During confluence, proppant converges and collides to form a high-concentration core zone, which propagates forward over time and tends to reach dynamic stability. For diversion, the slurry velocity is higher than 0.05m/s to overcome flow resistance and enter branch fractures, but a velocity exceeding 0.2m/s induces turbulent deposition. The proppant transport distance increases with rising concentration. When the concentration exceeds 0.3, proppant can be delivered deep into the fracture network. The optimal fracture height for diversion ranges from 2.5mm to 4.5mm. For confluence, proppant begins to deposit on fracture walls at a velocity of 0.2m/s, and backflow occurs at 0.3m/s. The optimal fracture height for confluence ranges from 1.5mm to 4.5mm. In complex fracture networks, high proppant concentration in main channels restricts effective diversion into branch fractures, while the confluence effect reduces transport efficiency in branch fractures near the high-concentration core zone. Proppant diversion follows an inertia-dominated asymmetric distribution with path selectivity during transport. Proppant confluence is characterized by collision and confluence at intersections to form a high-concentration core zone, which continuously migrates forward over time. This study provides theoretical guidance for the efficient development of unconventional oil and gas resources.

Due to its widespread geological distribution and substantial storage capacity, CO2 storage in saline aquifers is internationally recognized as one of the most effective methods for mitigating the greenhouse effect. The characteristics of the two-phase flow in porous media significantly affect the capacity and safety of CO2 storage. In this study, two structures at different locations of the Berea core were obtained and subsequently etched into two different micromodels to investigate the two-phase flow characteristics between CO2 and water. Using a microscopic visualization method, many experimental results have been obtained under different displacement patterns, including qualitative results of the displacement process, interface changes, and phase distributions and quantitative results of differential pressure, CO2 relative permeability, fractal dimension, and CO2 saturation. The results indicated that the maximum CO2 saturation, relative permeability, and fractal dimension were achieved when the displacement pattern was viscous fingering with CO2 predominantly existing in the micromodel as the main displacing channel. On the contrary, when the displacement pattern was capillary fingering, CO2 clusters showed the characteristics of large numbers and small areas, which led to the minimum CO2 saturation, relative permeability, and fractal dimension. Due to the simultaneous dominance of viscous and capillary forces, the flow characteristics under crossover fell between viscous fingering and capillary fingering, rendering them more complex. The phase states of CO2 and water exerted a profound influence on the differential pressure and displacement processes, primarily driven by the viscosity ratio at varying temperatures and pressures. The influence of the micromodel structure on the displacement process was mainly reflected in the local two-phase flow dynamics, resulting in numerical variations without significantly altering the general trend of change.

High-pressure gas intrusion during drilling operations poses significant well control challenges, heightening blowout risks. To address this critical safety concern, this paper proposes a real-time monitoring framework by characterizing gas-liquid flow pattern transitions through ultrasonic Doppler detection and time-frequency analysis. The proposed methodology systematically integrates three innovative processes: (1) gas-phase channel enumeration for spatial quantification of gas distribution patterns, (2) Doppler frequency shift range analysis enabling dynamic flow characteristic resolution, and (3) flow pattern threshold calibration to establish robust classification criteria. The thresholds of various flow patterns are obtained by the number of gas-phase channels and Doppler frequency shift range to achieve the purpose of real-time monitoring of gas intrusion status. To validate the methodology, an experimental gas intrusion simulation system was developed, comprising a wellbore pipeline integrated with a drilling fluid circulation pool and an ultrasound Doppler detection array. This system replicates downhole flow pattern transitions by injecting controlled gas velocities (0.1-5m/s) at multiple axial positions, enabling spatial-temporal analysis of gas-liquid phase redistribution under simulated drilling conditions. The results show that, our method effectively explain the dynamic evolution of two-phase flow under different flow regimes and achieved early detection of phase transitions. This method provide a non-invasive ultrasound-based pipeline, offering a high-responsiveness solution for gas kick monitoring in high-risk drilling.

This paper presents a comprehensive review of two-phase local pressure drop models in nuclear thermal-hydraulic systems, with a focus on pressure loss estimation arising from sudden flow area changes in two-phase flows. The abrupt area change models implemented in TRAC, TRACE, RELAP, and SPACE are examined, particularly for abrupt area expansions, contractions, and thin plate orifices. These models incorporate the concept of irrecoverable pressure losses (form losses) in the momentum conservation equations. In addition to the geometric considerations, the influence of the Reynolds number on form loss coefficients is comprehensively reviewed. An extended local pressure drop model is proposed to incorporate abrupt area changes, two-phase flow characteristics, and Reynolds number dependencies. The integration of two-phase multipliers and Reynolds number–based correlations is explored to enhance pressure loss predictions under complex flow conditions, which is relevant for modern reactor designs, as low pressure, low-flow velocity, and natural circulation conditions are considered highly important, especially in small modular reactors. To assess the influence of the local pressure drop models on pressure loss behavior and system performance, the models are implemented in SPACE and examined within the Bettis two-phase natural circulation loop and a conceptual reactor system. The simulation results demonstrated a notable deviation in the pressure drop predictions, and consequently, the mass flow estimations, depending on whether two-phase multipliers are applied. The proposed local pressure drop model exhibited improved consistency with the experimental data, particularly under conditions where the two-phase effects are significant. These findings emphasize the importance of incorporating abrupt geometry changes, two-phase dynamics, and Reynolds number effects for reliable thermal-hydraulic system analysis.

Induced two-phase air-water flows and droplet emissions after flushing a squat toilet.

Efficient gas transport and abundant triple-phase boundaries (TPBs) are vital for thick cathode catalyst layers (CCLs) in proton exchange membrane fuel cells (PEMFCs), yet remain challenging to realize. In this work, we introduce a carbon-based nanotrap architecture functionalized with pyrrolic-N groups, which reorganizes the Pt-carbon-ionomer interface to enhance local oxygen supply. These nanotraps simultaneously confine Pt nanoparticles and ionomer, forming continuous pathways for oxygen, protons, and electrons, thereby significantly increasing active TPB density. The underlying enhancement mechanism is validated by x-ray tomography and 3D two-phase flow simulations. Using a 15.5 µm-thick CCL, the optimized electrode achieves peak power densities of 1940 mW cm-2 in H2/O2 and 1410 mW cm-2 in H2/Air-improvements of ∼30% and ∼80%, respectively. Moreover, it exhibits a good stability, with a voltage decay rate of only 43.8 µV h-1 at 1.5 A cm-2 over 1000 h. This nanotrap concept offers a versatile interfacial design strategy for advanced gas-diffusion electrodes in energy conversion technologies.

We present an experimental dataset of focused dispersive wave groups, specifically designed to validate wave models and assess their capacity to propagate dispersive waves across significant distances in both deep- and shallow-water environments. The steepness of the wave groups varies from low to highly steep configurations, exhibiting pronounced nonlinear behaviours, including wave-breaking phenomena. The experiments were conducted in two distinct basin configurations: a constant-depth (deep water) set-up and a trapezoidal shoal, introducing inhomogeneity from deep- to shallow-water conditions. For selected tests, particle image velocimetry was used to capture kinematic measurements necessary for kinematics and energy assessment. Each test was performed with multiple repetitions to ensure data consistency and reliability. Furthermore, we utilised a Navier–Stokes two-phase flow model to demonstrate the reproducibility of wave groups in the numerical domain with a high degree of accuracy, employing the recorded wave paddle motion from the experiments as the boundary condition. The results were compared against linear wave theory where applicable, and we propose a benchmarking procedure for the systematic assessment and comparison of results across different wave models and varying levels of refinement.

Hydraulic fracturing is vital for enhancing oil and gas production. Proppant transport governs fracture conductivity and is therefore critical. Most studies simplify fractures as constant-width structures, inconsistent with real variable-width fractures.This paper establishes numerical models for proppant transport in variable-width fractures and networks via a solid-liquid two-phase flow method.The results show that, compared to constant-width fractures, variable-width fractures exhibit abrupt changes (reduction) in proppant bank height at width transition points, and the proppant bank trailing edge length is significantly shorter. Proppant particle size has a significant impact: smaller particle sizes increase the leading-edge length by up to 6.7 times and reduce the leading-edge inclination angle by up to 0.22 times. Perforation location greatly influences proppant vortices: when space near the fracture entrance is limited, only a counterclockwise vortex forms near the bottom perforation; if sufficient space exists between the proppant bank and the fracture entrance, besides counterclockwise vortices near the bottom and top perforations, a clockwise vortex forms slightly away from the entrance along the outer edge of the proppant bank; no vortices form in regions far from the fracture entrance. This study provides a new approach for researching proppant transport laws in irregularly shaped fractures.

Ultrasonic forward modeling of industrial oil-water two-phase flow.

Accurately reproducing and predicting transport behaviors inside spray towers still remain as a challenging issue. Most existing numerical results are validated only against outlet measurements. However, disagreements in internal multiphysics can prevent the results from accurately reflecting two-phase flow and transport within towers. In this work, a three-dimensional spray drying model was constructed using the Euler-Lagrange framework and validated in a pilot-scale centrifugal spray drying system with maltodextrin solution. The reaction engineering approach was adopted to describe the convection mass transfer via a user-defined function. Eighteen internal temperatures and outlet parameters were experimentally measured in validating numerical results. The results showed that the average relative error between the calculated temperatures and the experimental data was 1.76%. The relative errors between the predicted outlet air temperature, product water content, and average particle size and the experimental values were 0.06, 3.48, and 0.68%, respectively. The high-precision prediction of internal temperatures and outlet parameters demonstrated the model's reliability. The results also revealed a stronger evaporation around the tower centerline, where higher air velocity and temperature, as well as lower water vapor content, were observed. Droplet trajectories showed that large-size droplets required longer drying time, whereas small-size droplets dried rapidly but had longer residence time due to swirl and backflow. The effects of inlet air temperature, feed rate, disk rotational speed, and inlet air angle on droplet drying behaviors were further investigated. The research results are expected to provide industrialized guidance for designing a spray dryer and optimizing operating conditions.

Fractured caved carbonate condensate gas reservoirs (FCCCGRs) in northwestern China represent an important target for natural gas development, yet their highly heterogeneous structures and multiphase flow behaviors pose significant challenges for pressure transient analysis (PTA). Although several analytical and numerical models have been proposed for fractured caved reservoirs, they often fail to adequately capture the combined effects of condensate gas two-phase flow, laterally beaded large-scale cave geometry, and the diagnostic pressure transient features associated with multicave connectivity. To address these limitations, this study develops a novel analytical well test model for FCCCGRs with laterally beaded large-scale caves. First, the model integrates multiphase flow behavior and linearizes the governing equations through pseudopressure and pseudotime transformations. The governing equations are formulated and solved in the Laplace domain, and the corresponding solution methodology under infinite, closed, and constant pressure boundary conditions is described in detail. Subsequently, pseudopressure and derivative type curves are generated to delineate distinct flow regimes and to investigate the impacts of key parameters such as cave storage constants, fracture conductivity, mobility ratio, storage ratio, and region length on flow behavior. A major contribution of the proposed model is that it links the number and arrangement of laterally beaded caves to identifiable diagnostic features on the pressure derivative curves. Specifically, each additional cave introduces an additional concave feature in the derivative curve, providing a practical basis for cave number identification in well test interpretation. Furthermore, sensitivity analyses demonstrate that cave storage constants primarily control the depth and width of concave responses, while fracture conductivity and region length govern the duration and magnitude of linear-flow regimes. Higher mobility ratios result in delayed appearance and increased derivative responses of the corresponding linear- or boundary-flow regimes. Higher storage ratios lead to earlier termination of the corresponding cave-response regimes. Finally, the proposed model is validated using field data from a representative FCCCGR in Xinjiang, showing excellent agreement between the simulated and observed pressure responses. The interpretation results quantify cave volumes, separation distances, dynamic reserves, and production capacity, demonstrating the model's practical applicability for reservoir characterization and development planning.

To address the key issue that, during hydraulic fracturing, proppant deflects at the entrances of branch cracks due to inertial effects and that traditional models cannot accurately characterize proppant placement behavior, this study developed an improved Proppant transport model based on the Euler–Euler two-phase flow framework by incorporating a modified Bifurcation Force Term, thereby accurately describing the trajectory deviation of proppant at crack bifurcations. The model was validated through comparison between physical experiments and numerical simulations. After introducing the Bifurcation Force Term, the prediction error of the model for the proppant filling volume in secondary branch cracks was reduced by 3%, and the simulated crack morphology showed strong agreement with the experimental observations. Based on this model, a staged optimization strategy for dynamic and static parameters was proposed to achieve balanced propping of the crack network. This study quantitatively characterizes the inertial deflection behavior of proppant in branch cracks, providing a theoretical basis and methodological guidance for efficient hydraulic fracturing design in complex crack systems.

3D pore-scale digital twin for assessing thermal effects on two-phase flow and relative permeability in Bentheimer sandstone