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Coalbed methane (CBM) is an increasingly important unconventional natural gas. Production logging can provide important information about the production status of each layer in a CBM well, which is crucial for developing and adjusting development plans. However, currently, only open-hole logging is done for CBM wells, and there is no mature technology for production testing of wells that produce low amounts of gas. To address this issue, a new method has been proposed in this paper for measuring the production profile of CBM wells. This method is based on the pressure difference method and measures the gas–liquid two-phase flow in a 125 mm vertical rising circular tube. The researchers established a simulation model of the CBM wellbore pressure difference method and obtained four flow patterns: bubble flow, slug flow, churn flow, and annular flow. We studied the relationship between the pressure difference and gas and water flow rates at different positions and spacing between measuring points in the wellbore. A differential pressure flowmeter without a throttling device was developed, and gas–liquid dynamic experiments were carried out through a simulation experiment platform to verify the feasibility of the flowmeter. Two well field tests were conducted in Shanxi CBM fields using differential pressure flowmeters, which accurately and quantitatively measured the stratified gas production of CBM wells. This technology can help improve the productivity and development efficiency of CBM wells. [ABSTRACT FROM AUTHOR]

In this paper, a homogenized multiphase lattice Boltzmann (LB) model is established for parallelly simulating immiscible two-phase flow in both solid-free regions (pore scale) and porous areas (continuum scale). It combines the color-gradient multiphase model with the Darcy–Brinkman–Stokes method by adding a term that includes surface force and drag force of porous matrix to multiple-relaxation-time LB equation in moment space. Moreover, an improved algorithm is proposed to characterize and implement the apparent wettability in the locally homogenized porosity field. Validations and test cases are given to demonstrate the accuracy and robustness of this new model, as well as its applicability for trans-scale fluid simulation of transport and sorption behavior from porous (Darcy flow) area to free (Stokes flow) area. For practicality, the two-phase seepage flow in a composite rock structure with multiscale pores is simulated by this new model, and the effects of viscosity ratio and wettability on the displacement process are discussed. [ABSTRACT FROM AUTHOR]

Accurate prediction of the entrained liquid droplet fraction in an annular two-phase flow regime plays a crucial role for estimating the dryout type critical heat flux to identify the optimized flow characteristics in the thermal systems across different industries. Existing studies have provided different correlations based on the limited experimental data. However, these correlations are applicable to certain operating conditions. Therefore, the present study aims at applying a deep learning method, specifically an artificial neural network (ANN), to enhance the prediction of the entrained liquid droplet fraction. Experimental data from various works on annular flow, covering a wide spectrum of pressure and flow conditions, are utilized for training the ANN model. Eight input variables, viz, superficial gas velocity (J S G ), superficial liquid velocity (J S L ), gas viscosity (μ G), liquid viscosity (μ L), gas density (ρ G), liquid density (ρ L), pipe diameter (d) and liquid surface tension (σ L V ) are considered as input features. The entrained liquid droplet fraction is the single output feature. The present model employs the Bayesian regularization backpropagation algorithm for training. The present ANN model is compared against the performance of linear regression, decision tree and support vector machine algorithms, and found that the performance of the present Bayesian regularization neural network (BRNN) model is superior within ∼ 7.5 % deviation. Further, the BRNN model is coupled with the film mass flow rate model to obtain the axial variation of the liquid film mass flow rate and good agreement is noticed when compared against the experimental data. [ABSTRACT FROM AUTHOR]

Gas–liquid two-phase stratified flow exists in many industrial processes. Although the flow pattern is simple, the interfacial shear prediction of stratified flow is still the focus of the study. The calculation of the shear stress at the gas–liquid interface is closely related to the measurement of the void fraction and pressure drop of the stratified flow. In this study, a new method for the calculation of interfacial shear stress of gas–liquid two-phase stratified flow is proposed. Differential pressure measurement and planar laser-induced fluorescence technology are combined to obtain important parameters for stratified flow under low-speed flow conditions (Ql = 0.10–0.25 m3/h, Qg = 0.35–1.00 m3/h). The interfacial shear stress is successfully calculated using macroparameters. The uncertainty associated with the calculated parameters using the proposed method is 2.67%, and this study verifies the accuracy of the linear relationship. The method provides a new way to obtain the interfacial shear stress of gas–liquid stratified flow. [ABSTRACT FROM AUTHOR]

[Display omitted] • PMOB is an economical solution to reduce landfill CH 4 emissions. • Both single- and two-phase flow models are used for calculating LUGM. • LUGM doesn't reflect gas flow rate into MOL. • A novel PMOB design is proposed with a trapezoidal MOL-GDL interface. • Trapezoidal MOL-GDL interface enhances total gas flow rate into MOL. Passive methane oxidation biosystems (PMOBs) are developed as an innovative and cost-effective solution to reduce methane (CH 4) emissions from municipal solid waste landfills. A PMOB consists of a methane oxidation layer (MOL) and an underlying gas distribution layer (GDL). The length of unrestricted gas migration (LUGM) has been recently proposed as the design criterion for PMOBs where the LUGM is calculated as the horizontal length along the MOL-GDL interface with the volumetric gas content (θ a) exceeding the threshold volumetric gas content (θ a,occ). This paper examined water and gas migration within three PMOBs with different MOL-GDL interfaces subject to precipitation and evaporation using verified numerical models. The results show that the use of a single-phase flow model underestimates the LUGM values of the PMOB for heavy precipitation events, and a two-phase flow model should be used to calculate both the LUGM and the total gas mass flow rate into the MOL when designing PMOBs. Both zig-zag and trapezoidal MOL-GDL interfaces can redistribute the gas mass flow rate at the MOL-GDL interface, while the trapezoidal MOL-GDL interface slightly outperforms the zig-zag MOL-GDL interface for enhancing the total gas mass flow rate into the MOL when comparing with the planar MOL-GDL interface. The zig-zag and trapezoidal MOL-GDL interfaces allow gas migration in the upper part of each PMOB segment even when the lower part of each PMOB segment was filled with water, and thus have a potential to minimize hotspot formation. [ABSTRACT FROM AUTHOR]

This paper deals with the existence of weak solutions of the system that describes the two‐phase two‐component fluid flow in porous media. Both two‐phase and possible one‐phase flow regions are taken into account. Our research is based on a global pressure, an artificial variable that allows us to partially decouple the original equations. As a second primary unknown for the system, we choose the gas pseudo‐pressure, a persistent variable which coincides with the gas pressure in the two‐phase regions while it does not have physical meaning in one‐phase flow regions, when only the liquid phase is present. This allows us to introduce an another persistent variable that is an artificial variable in one‐phase flow regions and a physical variable in two‐phase flow regions—the capillary pseudopressure. We rewrite the system's equations in a fully equivalent form in terms of the global pressure and the gas‐pseudo pressure. In order to prove the existence of weak solutions of obtained system, we also use the capillary pseudo‐pressure. By using it, we can decouple obtained equations on the discrete level. This allows us to derive the existence result for weak solutions in more tractable way. [ABSTRACT FROM AUTHOR]

Ionic liquid compressors are suitable for high-pressure hydrogen refuelling stations. The initial liquid piston height is a critical parameter in designing ionic liquid compressors. Sufficient initial liquid column height can effectively prevent hydrogen leakage and exposure of the solid piston. However, there is a lack of basis for selecting the initial ionic liquid column height in the compression cylinder. The gas-liquid interface in the multi-stage compression is investigated by an experimentally verified numerical simulation model. The results show that in the low-pressure stage of the ionic liquid compressor, the initial liquid piston height can equal to the piston stroke, but in the high-pressure stage, the solid piston could be exposed to the hydrogen, so it is necessary to increase the initial liquid piston height. By analyzing the fluctuation characteristics in the cylinder, it is found that there is a minimum initial liquid piston height in each stage to ensure effective sealing. The minimum liquid piston height for the first to the fifth stage is 52 mm, 40 mm, 44 mm, 51 mm, and 54 mm, respectively. • The compression cylinders of a five-stage ionic liquid compressor were designed. • A numerical method was established and verified by experiment data. • The characteristics of the gas-liquid interface were analyzed. • The minimum initial ionic liquid height in each stage was recommended. [ABSTRACT FROM AUTHOR]

Wireless sensor nodes (WSNs) play an important role in many fields, including environmental monitoring. However, unattended WSNs face challenges in consuming power continuously even in the absence of useful information, which makes energy supply the bottleneck of WSNs. Here, we realized zero-power infrared switches, which consist of a metasurface and two-phase microfluidic flow. The metasurface can recognize the infrared signal from the target and convert it into heat, which triggers the two-phase microfluidic flow switch. As the target is not present, the switch is turned off. The graphene/MoS2/graphene 2D material heterostructure (thickness <2 nm) demonstrates an exceptionally high thermal resistance of 4.2 K/W due to strong phonon scattering and reduces the heat flow from the metasurface to the supporting substrate, significantly increasing the device sensitivity (the displacement of the two-phase microfluidic flow increases from ~1500 to ~3000 µm). The infrared switch with a pair of symmetric two-phase microfluidic flows can avoid spurious triggering resulting from environmental temperature changes. We realized WSNs with near-zero standby power consumption by integrating the infrared switch, sensors, and wireless communication module. When the target infrared signal appears, the WSNs are woken and show superb visual/auditory sensing performance. This work provides a novel approach for greatly lengthening the lifespan of unattended WSNs. [ABSTRACT FROM AUTHOR]

• Boiling coefficient increased with nozzle inlet pressure and specific enthalpy. • Boiling coefficient ranged from 300 to 4000 in the investigated trans-critical region. • Modified HNB showed an accuracy of 3 % in predicting the nozzle flow rates. • Proposed method for determining saturation pressure was superior to constant value. A modified homogeneous non-equilibrium boiling approach (HNB) was proposed for high-fidelity modelling of the trans-critical flashing process in two-phase R744 ejector nozzles. In the modified approach, the method of determining the metastable liquid saturation pressure was improved by integrating the metastable liquid enthalpy. Experimental tests were conducted on two different nozzles to calibrate the lumped accommodation coefficient in the modified HNB. The calibration dataset consisted of 30 trans-critical test points, with the motive inlet pressure ranging from 7.5 MPa to 11.5 MPa and temperature varying from 21 °C to 45 °C. It was demonstrated that the boiling coefficient was strongly related to nozzle inlet pressure and specific enthalpy. The coefficient was therefore fitted as a function of the operating condition. The modified HNB with the fitted function was then validated against another set of test data composed of 29 test points. The results demonstrated that the relative errors of the nozzle mass-flow rates were within 3 %. Finally, the modified HNB with the improved metastable liquid saturation pressure was compared and discussed with the existing HNB approach in the literature. [ABSTRACT FROM AUTHOR]

• The two-phase distribution in the header of a microchannel heat exchanger was quantified by a flexible capacitance sensor. • Distribution of local vapor quality showed that gases were concentrated upstream of the header, while liquids were concentrated in the middle and lower reaches. • Compared with the downstream, the upstream flow had less stability with more discrete capacitance signals. • The increase of mass flux caused that both the local vapor quality maximum point and the minimum point in the header were shifted back toward the downstream. The two-phase distribution has always been one of the research focuses of microchannel heat exchangers, because the maldistribution could seriously affect the heat transfer performance. This paper developed a capacitive method to quantify the two-phase distribution of vapor-liquid flow in the aluminum header of a microchannel heat exchanger. A flexible capacitance sensor was used to quantify the two-phase distribution with R134a. The inlet mass fluxes vary from 17.47 kg m−2 s−1 to 52.42 kg m−2 s−1 and inlet vapor qualities range from 0.2 to 0.6. The normalized time-averaged capacitance signal was processed by a Gaussian function to obtain the mathematical expectation and the standard deviation. The local vapor quality in the header was solved for using a correlation derived from the pre-experiments. The distribution of local vapor quality showed that gases were concentrated upstream of the header, while liquids were concentrated in the middle and lower reaches. The local vapor quality reached a minimum and remained constant at 0.1 in the middle and lower reaches, unaffected by changes in inlet conditions. As the mass flux increased, both the local vapor quality maximum point and the minimum point in the header were shifted back toward the downstream. Additionally, the increase of mass flux caused the fluctuation of the standard deviation increased, which meant the stability of the flow decreased. The two-phase flow measurement technique based on flexible capacitance sensors proposed in this study realized the extension of the capacitive method from the experimental stage to the industrial application stage. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to analyze the mechanism of nanofluid enhanced heat transfer in microchannels and promote the application of nanofluids in industrial processes such as solar collectors, electronic cooling and automotive batteries. Design/methodology/approach: The two-phase lattice Boltzmann method was used to calculate the flow and heat transfer characteristics of Al2O3 nanofluids in a microchannel at Re = 50. By comparing the simulation results of pure water, nanofluids without calculated nanoparticle-fluid interaction forces and nanofluids with calculated nanoparticle-fluid interaction forces, the effects of physical properties improvement and interaction forces on flow and heat transfer are quantified. Findings: The findings show that the nanofluid (φ = 3%, R = 10 nm) increases the average Nusselt number by 22.40% at Re = 50. In particular, 16.16% of the improvement relates to nanoparticles optimizing the thermophysical parameters of the base fluid. The remaining 6.24% relates to the disturbance of the thermal boundary layer caused by the interaction between nanoparticles and the base fluid. Moreover, the nanoparticle has a negligible effect on the average Fanning friction factor. Ultimately, we conclude that the nanofluid is an excellent heat transfer working medium based on its performance evaluation criterion, PEC = 1.225. Originality/value: To the best of the authors' knowledge, this research quantifies for the first time the contribution of nanoparticle-liquid interactions and nanofluids physical properties to enhanced heat transfer, advancing the knowledge of the nanoparticle's behavior in liquid systems. [ABSTRACT FROM AUTHOR]

Solvent extraction using a microfluidic platform is one of the process intensification tools. It may involve different two-phase flow regimes that have different physical and mass transfer characteristics. Therefore, this study focuses on the selection of a better flow regime, flow conditions and cascade configuration (cross or counter-current) using mathematical modeling for a typical high-throughput application (1000 L/day). The mathematical model is based on a plug flow model. The liquid–liquid system considered is a water–acetone–toluene system. The different flow regimes such as slug flow (SF), slug-droplet flow (SDF) and core-annular flow (CAF) in different cascade configurations are compared on the basis of parameters like specific extraction rate (SER), solvent extraction process effectiveness (SEPE) and modified merit index (MMI). Among the different flow regimes and cases studied, CAF is found to offer lesser parallel paths, total extraction length, total pressure drop and residence time. The best case of CAF has higher SER (3.6 times), SEPE (3.6 times) and MMI (21.8 times) than the best case of SF in both cascades. SDF shows the results between SF and CAF. For a specific flow regime, higher values of parameters are obtained at higher flow rates. Counter-current cascade is found to be better than cross-current cascade. [ABSTRACT FROM AUTHOR]

Electrical submersible pump (ESP) is extensively utilized in industrial sectors such as petroleum, chemical, and nuclear energy. However, ESPs experience pressurization deterioration due to the high gas volume fraction (GVF), resulting in the pressurization failure. In this paper, a three-stage mixed-flow ESP with closed impeller structure is detailed analysis. The interstage hydraulic characteristics and pressurization deterioration mechanism of the mixed-flow ESP are investigated at various rotational speeds and inlet conditions by combining experimental and simulation. The population balance model (PBM) and renormalization group (RNG) κ-ε model are employed. As the liquid flowrate increases, the ESP experiences a "three-stage" downward trend in pressurization. It is discovered that the first booster stage has a lower inflow velocity and flow separation degree compared to the subsequent booster stages, resulting in a greater liquid-phase pressurization capacity. The gas-liquid pressurization exhibits a wave-shaped downward trend due to significant deterioration in stage-wise pressurization when the liquid flowrate is low. Once the inlet gas volume fraction (IGVF) reaches the first critical GVF, the gas aggregates on the impeller's suction surface are removed at the impeller outlet, creating an annular air mass, which creates a chaotic vortex absorbing the fluids' kinetic energy. [ABSTRACT FROM AUTHOR]

This study utilizes numerical simulations and dimensional analysis to investigate the impact of the two-phase outlet on flow field characteristics and separation efficiency of the separator. The study revealed a boundary layer separation at the water outlet, which was subsequently addressed to reduce energy losses in the separator. Dimensional analysis considered the influences of operational, structural, and physical parameters on the separator's performance. With other structural parameters held constant, separation efficiency is directly proportional to the ratio of inlet and oil-outlet diameter. Additionally, the separation efficiency is also associated with Re and the ratio of the inlet to the water-outlet diameter. When the diameter of the water outlet is constant, the axial vortex separator achieves optimal separation when the ratio of inlet and water-outlet diameter is 0.563, with a maximum separation efficiency of 97.00%. The optimal separation efficiency is reached at Re=22,908 under various operational conditions. Separation efficiency increases with water content, peaking at an inlet water content of 0.9 across different structural parameters. Separation efficiency shows an increase followed by a decrease with the rise in inlet flow rate(vi), achieving the best performance at vi=3m/s for the different separator structures studied. [ABSTRACT FROM AUTHOR]

Tight sandstone reservoirs are significant sources of natural gas reserves. As traditional reserves become increasingly scarce and costly, optimizing the development of these reservoirs becomes crucial. This study introduces a novel two-phase gas–water flow model for single wells, incorporating both Darcy and non-Darcy flow equations. These equations are derived from mass conservation and momentum principles for both gas and water phases. Using data from a real tight gas well, our model, which includes stress-sensitive phases for gas and water, outperforms traditional Darcy flow models. Specifically, the average relative deviations in daily production rates were 0.1815% for gas and − 0.2677% for water, which are significantly smaller compared to traditional Darcy flow models. Further application of the non-Darcy flow model reveals strategies to enhance well performance. For example, mitigating liquid lock damage within a 2 m radius near the well could restore the permeability from 0.045 to 0.143 mD, thereby tripling the daily gas production. This non-Darcy flow model is easy to implement and shows significant potential in forecasting production yields in tight sandstone reservoirs, highlighting its importance in the petroleum and natural gas industry. [ABSTRACT FROM AUTHOR]

To unravel the intricacies of two-phase gas-liquid flow characteristics and heat transfer behavior, an array mini-channel gravity plate heat pipe (AMGPHP) is proposed in this work, which allows for observing the internal changes in the state of the working fluids. The flow patterns such as pool flow, columnar flow, and slug flow, are experimentally explored and analyzed in detail. It is found that the optimal volume fill ratio is 20% by utilizing start-up time and thermal resistance as performance evaluation metrics. With this fill ratio, a medium optimization strategy by blending ethanol within R141b is proposed and evaluated. In comparison to pure working fluids, the heat transfer performance of AMGFHP in the binary fluid has been significantly augmented due to temperature and concentration shifts resulting from disparate boiling points. Under the 10% volume fraction ethanol blending condition, the equivalent thermal conductivity of the heat pipe is dramatically elevated, with a value of 3110 W/(m·°C), along with the reduction of the minimum start-up power to 4 W. In general, applying such a medium to heat pipes has considerable potential in practical applications. [ABSTRACT FROM AUTHOR]

In this paper, an efficient fully-decoupled and fully-discrete numerical scheme with second-order temporal accuracy is developed to solve the incompressible hydrodynamically coupled Cahn-Hilliard model for simulating the two-phase fluid flow system. The scheme is developed by combining the finite element method for spatial discretization and several effective time marching approaches, including the pressure-correction projection method for dealing with fluid equations and the explicit-invariant energy quadratization (explicit-IEQ) approach for dealing with coupled nonlinear terms. The obtained scheme is very efficient since it only needs to solve several decoupled, linear elliptic equations with constant coefficients at each time step. We also strictly prove the solvability and unconditional energy stability of the scheme, and verify the accuracy and stability of the scheme through plenty of numerical examples. [ABSTRACT FROM AUTHOR]

An accurate prediction of non-isothermal gas–liquid interfaces in cryogenic two-phase flows is crucial for the high-efficiency energy storage, transportation, and utilization of liquid hydrogen. However, temperature difference and interfacial mass and energy transport can change the thermodynamic state of gas–liquid interfaces and thereby impact the distribution. And the lower surface tension coefficient and viscosity of liquid hydrogen, compared to room-temperature fluids, increase the likelihood of the instability and breakage of non-isothermal interfaces. Conventional numerical methods suffer from a scarcity of precision and the propagation of spurious velocities in predicting such flows. In this study, a new numerical framework called cryoFoam was developed based on an open source CFD code OpenFOAM to address the issue of the inaccurate capture of non-isothermal cryogenic interfaces. A practical interface-capturing model involving phase change was implemented to achieve the uniform distribution of surface forces in both gas and liquid phases. The tangential surface force was incorporated into the governing equations to realize thermocapillary convection. The Schrage model, a widely-used phase change model, was employed to deal with condensation and evaporation. The performance of the solver was assessed using five benchmarks which involve thermocapillary flows and phase changes in liquid hydrogen, liquid oxygen, liquid nitrogen, and liquid methane. The results show that the new method can reduce large spurious velocities and prevent the distortion of isotherms near the curved interface in cryogenic fluids. It demonstrates higher precision than the traditional VOF method in predicting cryogenic thermocapillary convection and interfacial energy transport. • A new CFD code was developed to model the non-isothermal two-phase flows in liquid hydrogen. • A practical interface-capturing model involving phase change was implemented. • The tangential surface force was employed to realize thermocapillary convection. • Spurious velocities and the distortion of isotherms in liquid hydrogen were reduced. • The method presents high accuracy in predicting mass and energy transport at cryogenic interfaces. [ABSTRACT FROM AUTHOR]

As a promising green energy technology, low-temperature proton exchange membrane (PEM) electrolysis exhibits different reaction efficiencies and flow performances under various flow channel structures, but the specific impacts of these different layouts on performance are not well understood. To reveal the influence of the channel layouts, a two-phase PEM electrolysis model is established based on the experiment in this paper. Combing with flow characteristics, current density, and product distribution in the porous transport layers (PTLs) and catalyst layers (CLs), the results indicate that the flows from different directions have a significant impact on the electrolyzer. The vertical flow, perpendicular to the CLs, can greatly alleviate the product accumulation; meanwhile the transverse flow, parallel to the CLs, has a weaker but noticeable effect in gas ventilation. Partial gas will continue to accumulate in the region of weak vertical flow, especially at the end of the transverse flow. Except for the pin-type layout, other structures have a neat and orderly transverse flow within the porous medium, in the direction perpendicular to the flow channel's orientation. This flow pattern leads to product accumulation increasing along the exit direction, as well as product stagnation in the region of weak flow intensity. To facilitate the product discharge, a new flow channel layout, the pyramidal flow layout is proposed, which navigates the flow trend and enhances the convection near the exit. This new layout greatly evens out the current density and product concentration distribution. • Based on two-phase flow PEM electrolysis model of different flow channel layouts. • Finding a universal flow pattern within the porous medium among different layouts. • Proposed a new flow layout with better product distribution and discharge efficiency. [ABSTRACT FROM AUTHOR]

This paper is concerned with the nonlinear stability of planar Couette flow for the three‐dimensional NS‐NS equations, which are used to model the motion of two‐phase flow. Our result shows that the planar Couette flow is asymptotically stable for the initial perturbations sufficiently small in some Sobolev space if the background velocity and the Reynolds number are sufficiently small. Moreover, it is proved that the solution converges to the stationary state (ρ∗,us,n∗,ws)$$ \left({\rho}_{\ast },{u}_s,{n}_{\ast },{w}_s\right) $$ at an algebraic time decay rate, and we also give the decay rate of the relative velocity. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of snap-off during gas–liquid immiscible displacement is of great significance in the petroleum industry to enhance oil and gas recovery. In this work, based on the original pseudo-potential lattice Boltzmann method, we improved the fluid–fluid force and fluid–solid force scheme. Additionally, we integrated the Redlich–Kwong equation of state into the lattice Boltzmann model and employed the exact difference method to incorporate external forces within the lattice Boltzmann framework. Based on this model, a pore–throat–pore system was built, enabling gas–liquid to flow through it to investigate the snap-off phenomenon. The results showed the following: (1) The snap-off phenomenon is related to three key factors: the displacement pressure, the pore–throat length ratio, and the pore–throat width ratio. (2) The snap-off phenomenon occurs only when the displacement pressure is within a certain range. When the displacement pressure is larger than the upper limit, the snap-off will be inhibited, and when the pressure is less than the lower limit, the gas–liquid interface cannot overcome the pore–throat and results in a "pinning" effect. (3) The snap-off phenomenon is controlled using the pore–throat structures: e.g., length ratio and the width ratio between pore and throat. It is found that the snap-off phenomenon could easily occur in a "long-narrow" pore–throat system, and yet hardly in a "short-wide" pore–throat system. [ABSTRACT FROM AUTHOR]

Operating centrifugal pumps under two-phase flow conditions presents challenges such as phase separation, cavitation, and flow instabilities, compromising reliability and performance. A specialized design is crucial to mitigate these issues. This study utilized computational fluid dynamics (CFDs) to understand two-phase flow behavior and assess the impact of different blade geometries on pump performance under such conditions. For this purpose, the inhomogeneous multiphase model was employed, wherein the momentum and continuity flow equations were individually solved for each phase across three different impellers with varying blade angle distributions. The computational results indicated higher gas concentrations on the pressure side of the blade, with gas pocket size correlating with flow rate and inlet gas concentration. The blade angle distribution's effect was more pronounced with increased gas concentrations, while a tendency of gas bubbles to coalesce towards the impeller shroud was also observed. The presence of gas promoted flow recirculation and separation, substantially reducing impeller performance. Blade angle distribution critically influenced the flow field, affecting flow separation, stability, efficiency, and overall performance, highlighting the importance of optimized blade design for enhanced centrifugal pump performance in liquid–gas two-phase flow conditions. [ABSTRACT FROM AUTHOR]

The deposition of fly ash on the heat exchanger will reduce the heat transfer efficiency of the system. This article conducted experiments and simulations on the deposition, exploring the effects of velocity, particle size on the deposition position. In addition, deposition density distribution was demonstrated, the calculation method of fin thermal resistance was improved, and the efficiency of fins was also calculated. The results showed that deposition decreased with velocity increasing, and the simulation results were in good agreement with the experimental results. The deposition distribution of the first section of the fin is unimodal, and the maximum deposition value approaches the peak of the fin. The distribution of the second section of the fin becomes bimodal with increasing velocity. In addition, as the speed increases, due to the decrease in deposition mass, the thermal resistance decreases by 53.2% and the fin efficiency increases by 8.82%. [ABSTRACT FROM AUTHOR]

This study utilises computational fluid dynamics simulations with the OpenFOAM computational framework to investigate and compare the in-plane and through-plane permeability properties of four different gas diffusion layers (GDLs). Also the through-plane water and air relative permeability values and water saturations at different rates were simulated. Permeability analysis enhances our understanding of fluid flow, ways to decrease pressure loss in the GDL, and methods to enhance oxygen concentration at the catalyst layer interface through convection. The analysis reveals that the investigated GDL materials have spatial heterogeneity of porosity and permeability, especially in the Sigracet SGL 25 BA GDL. However, the porosity and permeability of the Toray TGP-H 060 and AvCarb 370 MGL GDLs exhibit less variations. The two-phase flow studies on GDL saturation show that at the same water injection flowrate, the AvCarb 370 MGL GDL has the largest remaining water saturation, with Sigracet SGL 25 BA GDL being the less saturated GDL among the four investigated GDLs. The compression from the ribs significantly affected the in-plane permeabilities of both Toray TGP-H 060 and especially impacted Sigracet SGL 25 BA GDL. This impact was expected as the pore size distribution varied significantly in the areas under the ribs versus the channel. [ABSTRACT FROM AUTHOR]

In this paper, we consider a singular limit problem for a diffuse interface model for two immiscible compressible viscous fluids. Via a relative entropy method, we obtain a convergence result for the low Mach number limit to a corresponding system for incompressible fluids in the case of well‐prepared initial data and same densities in the limit. [ABSTRACT FROM AUTHOR]

In order to solve the problem of the lack of maneuverability of the conventional underwater glider, this paper proposes a hybrid-driven underwater glider equipped with a Kappel tip rake propeller, analyzes the propulsion performance of different types of Kappel tip rake propellers in the wake field of the hybrid-driven underwater glider, optimizes the overall propulsion performance of the hybrid-driven underwater glider, and realizes self-propulsion and gliding with high efficiency and low energy consumption. In the research process, the Schnerr–Sauer cavitation model and the cavitation simulation strategy of VOF two-phase flow were adopted, coupled with the SST k-ω and γ transition turbulence model, and the control calculation error was not more than 3%. Based on the hydrodynamic performance study of the Kappel tip rake propeller, the self-propelled simulation was carried out under the working conditions of 6 kn, 5 kn, 4 kn, and 3 kn, and the gliding simulation was carried out under the working conditions of 1 kn, 0.5 kn, and a glide angle of 12°. The propulsion performance of the hybrid-driven underwater glider with different models of Kappel tip rake propellers was analyzed. It was found that the maximum open water propulsion efficiency of the propeller Kap05 had the largest improvement, which was 3.07% higher than that of the reference base propeller. Under the self-propelled condition, the hybrid-driven underwater glider with the propeller Kap05 had the lowest wake fraction, and the propellers Kap04 and Kap05 had the best propulsion performance in the wake field of the hybrid-driven underwater glider. In the gliding condition, the form of the folding paddle can reduce the gliding resistance generated by the propeller by more than 45% and the gliding negative lift by more than 68%. A moderate tip rake can effectively improve the propulsion efficiency of the Kappel tip rake propeller in the wake field of the hybrid-driven underwater glider, reduce energy loss, and improve the overall performance of the hybrid-driven underwater glider. [ABSTRACT FROM AUTHOR]

With the increasing demand for deep oil and gas exploration and CCUS (Carbon Capture, Utilization, and Storage) engineering, improving rock-crushing efficiency stands as a pivotal technology. Ultrasonic vibration-assisted drilling has emerged as a novel rock-breaking technology. The high-frequency vibrations of ultrasonic waves impact rocks, inducing resonance and accelerating their fragmentation. At the same time, ultrasonic waves generate cavitation bubbles in the liquid near rock surfaces; the expansion and collapse of these bubbles further contribute to rock damage, thereby improving crushing efficiency. Therefore, investigating the dynamics and failure characteristics of cavitation bubbles near rock surfaces under ultrasonic influence is crucial for advancing ultrasonic-assisted rock-breaking technology. This study treats the liquid as compressible flow and investigates the movement and rupture of bubbles near rock surfaces under varying ultrasonic parameters, rock properties, characteristics of the circulating medium, and other relevant factors. The findings show that ultrasonic waves induce the oscillation, translation, collapse, and rebound of bubbles near rock surfaces. Higher ultrasonic frequencies correspond to larger collapse pressures and amplitudes near surrounding rocks, as well as longer expansion times and shorter collapse durations. In addition, bubble movement and collapse lead to rock material deformation, influenced by the rheological properties of the liquid medium. The study outcomes serve as a foundation for optimizing engineering parameters in ultrasonic-assisted rock breaking and provide theoretical support for the advancement of this technology. [ABSTRACT FROM AUTHOR]

With the development of advanced pressurized water reactor technology, the thermal-hydraulic coupling effect between the containment and the primary system becomes increasingly tight. In order to meet the demand for integrated safety analysis between the containment and the primary system, this paper investigates a direct coupling method between the best-estimate system code Advanced Reactor Safety Analysis Code and the containment analysis program ATHROC (Analysis of Thermal Hydraulic Response Of Containment). The feasibility of this direct coupling method and the applicability of the coupled program for overall safety analysis are demonstrated using Marviken two-phase flow release experiments. The ATHROC/ARSAC coupled program is employed to analyze the impact of the pressure relief function of the CPR1000 nuclear power plant pressurizer on the behavior of the primary system and containment during the TMLB' accident. The calculation results indicate that these measures can reduce the pressure of the primary system to the level acceptable by the low-pressure injection system, but at the same time, they cause the pressure in the containment to rise to nearly 0.4 MPa. Therefore, to ensure the structural integrity of the containment, it is necessary for the non-passive hydrogen recombiner to effectively reduce the hydrogen concentration, thereby avoiding additional pressure increase in the containment due to hydrogen deflagration, which could lead to overpressure failure. The findings of this study are of significant reference value for improving the safety performance of thermal-hydraulic systems in operational Gen-II and advanced Gen-III pressurized water reactor nuclear power plants. [ABSTRACT FROM AUTHOR]

Critical heat flux (CHF) is one of the most concerned thermal hydraulic phenomena in reactor safety analysis. It involves complex two-phase flow heat transfer mechanism, and has not been fully understood, so the prediction of critical heat flux mainly depends on CHF correlations obtained under limited experimental conditions. At present, CHF correlations are generally developed with pressure, mass flux and quality as key independent variables. And correspondingly, the test matrix of a CHF test consists of the above parameters. However, it is impossible to perform CHF tests accurately according to the predetermined quality. In CIAE, a CHF experimental research of a 5 χ 5 uniformly heated rod bundle has been carried out. In the experiment, the inlet temperature of the test section was directly taken as a parameter in the test matrix. The CHF data were achieved by stepwise increasing the heating power. The test conditions covered the pressure of 2.8-15.5 MPa, the mass flux of 845-3533 kg/(m2-s), and the inlet temperature of 100°C-300°C. The test data have been analyzed to obtain the thermal-hydraulic parameter influences on CHF by taking the inlet temperature as a variable. The results indicated that, within the test condition range, under the same inlet temperatures, CHF was hardly affected by pressure, and linearly increased with the increasing mass flux. With the increase of inlet temperature, the enhancement of CHF with the increasing mass flux gradually weakens. And CHF was linearly decreased with the increasing inlet temperature under the same mass flux. By contrast, the parameter influences on CHF were more complex by taking the local quality as a variable. According to the research, it can be concluded that, it has an advantage of simplifying the CHF correlation form to take the inlet temperature of the test section as a variable parameter. The research can provide new ideas for CHF experiment, data analysis and correlation development. [ABSTRACT FROM AUTHOR]

Investigating the counter-current two-phase flow within the anodic porous transport layer (PTL) of polymer electrolyte membrane water electrolyzers (PEMWEs) is a complex yet intriguing challenge. Until now, the gas-liquid invasion processes inside PTLs are only to a limited extent accessible under operation conditions, usually using sophisticated and expensive optical approaches, i.e., neutron imaging. We propose a model-supported experimental method with a fully operating microfluidic PEMWE, that allows to examine pore-scale oxygen-water distributions at the anode with high spatial and temporal resolution. The microfluidic cell is made of transparent Poly-Methyl-Methacrylate (PMMA), and the PTL is simplified by a quasi-2D pore network (PN) with a uniform pore-throat structure in the first preliminary study. The proposed setup is a significant advancement over previous studies, where gas was only injected at a constant flow rate from a single point. Test cases with current densities of 0.1, 1, and 2 A/cm2 and water flow rates of 1, 3, 5, and 10 ml/min were realized in the novel setup. We found periodically alternating invasion of oxygen (drainage) and water (imbibition), which were analyzed based on image sequences as well as voltage measurements. The experimental data is additionally supported by pore-scale Lattice Boltzmann (LB) and PN simulations. The preliminary results with the simplified PN structure are used to study the dominating transport mechanisms, revealing that drainage and imbibition occur simultaneously and are affected by evaporation and wetting liquid films formed in sharp pore corners. These phenomena are also expected to occur in more complex PTL structures. The preliminary results can, therefore, be regarded as an important basis for PTL studies, which are structurally more complex. • Presentation of a novel PEMWE model cell for the study of two-phase flow inside the anode. • Visualization of dynamic drainage/imbibition cycles in anode at different current densities and water flow rates. • Analysis of the detailed invasion patterns by Pore Network and Lattice Boltzmann simulations. • Quantification of secondary transport through thick wetting capillary liquid films. [ABSTRACT FROM AUTHOR]

A theoretical analysis of a multi-phase fluid problem is presented in this paper. Electro-osmotic flow with heat transfer in a divergent channel is modeled. Jeffrey fluid is taken as the base liquid, which suspends with the spherical gold particles. Electromagnetohydrodynamic (EHD) of a two-phase fluid through a porous medium is influenced by thermal radiation. Cumbersome mathematical manipulations leads to yield an exact solution for the set of strenuous differential equations. A comprehensive parametric study validates the accuracy and formidability of this intuitive analysis, by confirming the corresponding boundary conditions. The investigation articulately describes that the momentum of two-phase flow is supported by the Jeffrey fluid parameter. Additional golden particles increase the velocity of the base liquid. However, more thermal energy has contributed to the variation of the Brinkman number B R M . Finally, thermal energy expunges from the diverse channel due to Jeffrey's fluid parameter. [ABSTRACT FROM AUTHOR]

Pulsating heat pipes (PHPs) employ to multiphase heat transfer between condensers and evaporators. The efficacy of PHP is predominantly contingent upon the thermos-physical property exhibited by its working fluid. The exergy analysis of evaporator, adiabatic and condenser system were performed to evaluate the efficiency and sustainability of energy conversion processes, it was also seen that exergy loss of condenser was 1.01% higher than evaporator. Further, 2-D numerical simulation of a cryogenic pulsating heat pipe (CPHP) was conducted and also numerical and experimental simulation was conducted, where simulation results agreed with experimental results with 10% similarity. The simulation employs the volume of fluid (VOF) model to capture the dynamics of two-phase liquid–vapor flow within the CPHP employing liquid acetone – Al2O3 as the working fluid. The diameter of the single turn is systematically varied, ranging from 1 mm to 2.5 mm, while maintaining the filling ratio (FR) within the range of 25% to 75%. The evaporator temperature is adjusted within the span of 85 K to 115 K. The PHP exhibited best thermal performance at inner diameter of 2 mm among (1, 1.5, 2, 2.5 mm) and filling ratio of 55% among (25%, 45%, 55%, 65% and 75%). [ABSTRACT FROM AUTHOR]

Particle distribution, wear failure, and particle passage performance in a two-stage mixed-transported pump are investigated by coupling computational fluid dynamic (CFD) and discrete element method (DEM). Results exhibit good agreement with the experimental data. The velocity and trajectory of a 10 mm particle are examined under three different concentrations. Consequently, the relationship between particle motion and the wear on the impeller and volute is revealed. The results indicate that low-speed particles lead to particle packing at the inlet of the first stage. The force variation of particles is closely related to the number of collisions with the wall. The wear on the suction side of the second-stage impeller and the second-volute wall are significantly less than that on the first-stage. Finally, the particle passage coefficient P is defined, demonstrating that the particle passage performance of the second-stage pump is better than that of the first-stage. [ABSTRACT FROM AUTHOR]

In this study, three types of flow channels including single serpentine, double serpentine, and parallel were compared to investigate the relationship between two-phase flows and the cell performance in the proton exchange membrane water electrolyzer. Pressure drop between the inlet and outlet was measured at the anode channel, and flow patterns affecting the cell performance were investigated using high-speed optical imaging. The single serpentine channel exhibited the best performance among the flow channels used in the experiment because an annular flow with a thin liquid film continuously provided water, preventing performance degradation. The parallel channel performed the worst owing to the slug flow accompanied by Taylor bubbles, which interrupted the water supply. [ABSTRACT FROM AUTHOR]

In this paper, a one-dimensional model of gas–water two-phase productivity for hydrate depressurization is established, which takes into account permeability variation and gas–water two-phase flow. By solving the coupled algebraic equations of dissociation front position, equilibrium temperature, and pressure in an iterative scheme, the movement law of the hydrate dissociation front and the evolution process of temperature and pressure near the well were obtained, and the effects of bottom hole pressure, reservoir temperature, and hydrate saturation on productivity were analyzed. The results show that the hydrate reservoir is divided into a decomposed zone and an undecomposed zone by the dissociation front, and the temperature and pressure gradients of the former are greater than those of the latter. Reducing bottom hole pressure, increasing reservoir temperature, and increasing hydrate saturation all lead to an increase in temperature and pressure gradient in the decomposed zone. Methane gas production is a sensitive function of bottom hole pressure, reservoir temperature, and hydrate saturation. The lower the bottom hole pressure, the higher the reservoir temperature, the lower the hydrate saturation (within a certain range), and the higher the gas production rate. The trend of the water production curve is the same as that of gas, but the value is 3–4 orders of magnitude smaller, which may be due to the large difference in the viscosity of gas and water, and the gas seepage speed is much larger than that of water. [ABSTRACT FROM AUTHOR]

This paper presents the effects of various properties on nanofluid flows and heat transfer over a permeable stretching sheet of variable thickness in the presence of a transverse magnetic field. Mathematically, the leading coupled partial differential equations are transformed into a self-similar system of ordinary differential equations through similarity variables, which are solved thereafter using Keller-box and Haar’s wavelet methods. Moreover, the impacts of various flow parameters involved in the physical problem are discussed thoroughly via tables and graphs. As findings, the analysis discloses that the nanofluid flow is significantly influenced by the physical parameters. Dynamically, the nanofluid flow is accelerated prominently with the strengthening in the injection process and decelerated in other situations. Furthermore, the obtained results are compared successfully with the earlier published findings. [ABSTRACT FROM AUTHOR]

We study linear models for the prediction of the initial guess for the nonlinear Newton-Raphson solver. These models use one or more of the previous simulation steps for prediction, and their parameters are estimated by the ordinary least-squares method. A key feature of the approach is that the parameter estimation is performed using data obtained directly during the simulation and the models are updated in real time. Thus we avoid the expensive process of dataset generation and the need for pre-trained models. We validate the workflow on a standard benchmark Egg dataset of two-phase flow in porous media and compare it to standard approaches for the estimation of initial guess. We demonstrate that the proposed approach leads to reduction in the number of iterations in the Newton-Raphson algorithm and speeds up simulation time. In particular, for the Egg dataset, we obtained a 30% reduction in the number of nonlinear iterations and a 20% reduction in the simulation time. [ABSTRACT FROM AUTHOR]

A wide range of flow-type mass movements occur in nature. Depending on the solid fraction of these flows, they can be characterized as stream flows (flash floods), hyper-concentrated flows (debris floods), debris flows, and dry debris avalanches. A key scientific challenge in mitigating these hazards is estimating the impact force that they exert on protection structures. In this study, a new framework (Nfric - Fr2 - α relationship) is proposed to characterize and unify the impact behavior for a wide spectrum of flow-type mass movements. The friction number Nfric characterizes the ratio of grain-contact to fluid-viscous stresses for the wide range of flow types. Solid–fluid interaction regulates the pore fluid pressure, thereby governing the rheology of the flows and the degree of static loading exerted on a barrier. The Froude number Fr2 (in squared form) macroscopically characterizes the flow inertia relative to the earth's gravitational field. Finally, the dynamic pressure coefficient α is used to quantify the impact force in a dimensionless manner. As compared to existing guidelines, which recommend a wide range of α without considering the flow composition, the newly proposed framework in this study estimates the dynamic impact force by considering the effects of solid–fluid interaction. Findings from this study could further enhance the design of flow-type mass movement mitigation structures. [ABSTRACT FROM AUTHOR]

• Ammonia condensation has been experimentally studied in 8 mm and 11 mm tubes. • A new phenomenological model has been proposed for ammonia condensation. • The lowest condensation HTCs characterise the downstream flow. The paper proposes the experimental study of ammonia condensation in aluminium tubes with 8 mm and 11 mm internal diameters. The new study aimed to compare and extend the existing ammonia in-tube condensation data. The lines were tested mainly in horizontal configuration at mass velocities of 20 to 160 kg·m−2s−1, saturation temperature of 35 to 65 °C and inlet vapour quality of 0.1 to 0.9. Shah (1979), laminar-laminar Dobson and Chato (1998), and Cavallini et al. (2001) models predict well ammonia condensation HTCs at mass velocities of 120 to 160 kg·m−2s−1. A new phenomenological model has been proposed for the mass velocities of 20 to 120 kg·m−2s−1, predicting the test data with an accuracy of ±20 %. Similar ammonia condensation HTCs have been obtained for horizontal and upstream flows at a mass velocity above 120 kg·m−2s−1. The lowest condensation HTCs at the considered boundary conditions characterise the downstream configuration of an in-tube condenser at a mass velocity below 120 kg·m−2s−1. However, inclining the ID 8 mm tube by 15° from the normal substantially increases the condensation HTCs by 10 to 30 %, depending on vapour quality. At the inclinations of 15 to 45° from the horizontal line toward the downstream flow, the condensation HTCs exceed the ones of horizontal flow by 10 to 15 % at the vapour quality of <0.5 and low mass velocity of 80 kg·m−2s−1. [ABSTRACT FROM AUTHOR]

Experiments on specimen cooling dynamics and possible film boiling around a body are very important in various industrial applications, such as nucleate boiling, to decrease drag reduction or achieve better surface properties in coating technologies. The objective of this study was to investigate the interaction between the heat transfer processes and cooling dynamics of a sample in different boundary conditions. This article presents new experimental data on specimens coated with Al–TiO2 film and Leidenfrost phenomenon (LP) formation on the film's surface. Furthermore, this manuscript presents numerical heat and mass transfer parameter results. The comparative analysis of new experiments on Al–TiO2 film specimens and other coatings such as polished aluminium, Al–MgO, Al–MgH2 and Al–TiH2 provides further detail on oxide and hydride materials. In the experimental cooling dynamics experiments, specimens were heated up to 450 °C, while the sub-cooling water temperatures were 14*‒20 °C (room temperature), 40 °C and 60 °C. The specimens' cooling dynamics were calculated by applying Newton's cooling law, and heat transfer was estimated by calculating the heat flux q transferred from the specimens' surface and the Bi parameter. The metadata results from the performed experiments were used to numerically model the cooling dynamics curves for different material specimens. Approximated polynomial equations are proposed for the polished aluminium, Al–TiO2, Al–MgO, Al–MgH2 and Al–TiH2 materials. The provided comparative analysis makes it possible to see the differences between oxides and hydrides and to choose materials for practical application in the industrial sector. The presented results could also be used in software packages to model heat transfer processes. [ABSTRACT FROM AUTHOR]

Ultrasonic flotation is widely used as an efficient mineral separation method. Its efficiency is related to the adhesion behavior between fine particles and flotation bubbles, which can be influenced by the bubbles' movement behavior. This paper used two immersed ultrasonic vibration plates to generate ultrasonic action and investigated the effect of ultrasonic action on the rising process of flotation bubbles. The distribution, aggregation and fusion, velocity, and other characteristics of bubbles generated by different needle apertures were studied by experimental and simulation methods. The results showed that a 0.4 mm needle produced bubbles that were more evenly spaced and more uniform in size and shape. The ultrasonic action can make the bubbles aggregate together and reduce the bubble rise velocity, as well as prolong their time in the flotation process at the same time. It is beneficial to the sufficient collision and adhesion behavior between flotation bubbles and particles, eventually improving the efficiency of mineral flotation. [ABSTRACT FROM AUTHOR]

To fill the research gaps in the study of flow boiling on composite surfaces, four heat exchange tubes with different structures were investigated: an enhanced tube with herringbone teeth (EHT_HB), a tube with a dimple structure (EHT_DIM), a tube with a composite herringbone tooth/dimple structure (EHT_HB/DIM), and a smooth tube as a baseline for comparison purposes. The experimental conditions were set as follows: saturation temperature 6 °C, mass flux 50-205 kg/(m²·s), and vapor quality 0.2-0.8. After confirming the validity of the experimental results, the effects of the mass flux on the flow boiling heat transfer and pressure drop characteristics were examined. Results showed that the flow boiling heat transfer coefficient and pressure drop increase with the increase of the mass flux and the vapor quality in the tested tubes. The EHT_HB/DIM tube was found to combine the advantages of the two structures and to have the highest heat transfer coefficient. The average value of the heat transfer coefficient was found to be 43.75% higher than that of the smooth tube. Also, the average flow boiling heat transfer coefficients of the EHT_HB and the EHT_DIM tubes were found to be 15% and 35% higher than that of the smooth tube, respectively. From the perspective of the frictional pressure drop, it was found that the EHT_HB/DIM tube exhibited the maximum frictional pressure drop. The optimum working conditions of the enhanced tubes were determined by introducing a performance factor that captures the combined effects of heat transfer and pressure drop. [ABSTRACT FROM AUTHOR]

Electric motors with high-power densities are required for the implementation of electromobility. To achieve this, direct liquid cooling methods are increasingly being considered, in which oil is injected into the motor compartment. This results in a two-phase flow that can be used for efficient cooling. However, the oil, which can also penetrate the air gap between the rotor and stator, can also lead to additional losses due to increased friction. Since little is known about the two-phase flow in such systems, especially in the air gap, it is investigated by means of simple optical visualizations and high-speed laser-induced fluorescence imaging as well as torque measurements. The measurements are carried out in the air gap of an optically accessible generic model of a directly cooled electric motor. Speed variations were performed from 100 to 2000 rpm, and three different two-phase flow regimes were observed. At low speeds (Flow Regime 1), the air gap is filled locally with oil in radial direction, in the medium speed range (Flow Regime 2) with foam, while at high speeds (Flow Regime 3) separated films were observed on the rotor and stator. The torque difference between the two-phase and single-phase operation, which quantifies the mechanical losses due to the injected oil, increased continuously due to the oil in the air gap until it reached a maximum in Flow Regime 2 due to foam formation. In Flow Regime 3, the torque difference was negative. This was attributed to the fact that the grooves in the stator were filled with oil, thus reducing the turbulence generation of the air flow. [ABSTRACT FROM AUTHOR]

Two-phase pipe flow occurs frequently in oil & gas industry, nuclear power plants, and CCUS. Reliable calculations of gas void fraction (or liquid holdup) play a central role in two-phase pipe flow models. In this paper we apply the fractional flow theory to multiphase flow in pipes and present a unified modeling framework for predicting the fluid phase volume fractions over a broad range of pipe flow conditions. Compared to existing methods and correlations, this new framework provides a simple, approximate, and efficient way to estimate the phase volume fraction in two-phase pipe flow without invoking flow patterns. Notably, existing correlations for estimating phase volume fraction can be transformed and expressed under this modeling framework. Different fractional flow models are applicable to different flow conditions, and they demonstrate good agreement against experimental data within 5% errors when compared with an experimental database comprising of 2754 data groups from 14 literature sources, covering various pipe geometries, flow patterns, fluid properties and flow inclinations. The gas void fraction predicted by the framework developed in this work can be used as inputs to reliably model the hydraulic and thermal behaviors of two-phase pipe flows. [ABSTRACT FROM AUTHOR]