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Multicomponent Immiscible flows within porous media are a pivotal concern in engineering applications, especially in contexts such as oil reservoirs, which exhibit a broad spectrum of properties, including varying viscosities. The precise characterization of flow dynamics, particularly when confronted with a dynamic contact interface within intricate and heterogeneous structures, has remained a significant challenge in the field. This study employs an enhanced Pseudo-potential Central Moment Lattice Boltzmann Method to simulate multicomponent immiscible flows within porous media. The model is implemented through an in-house CUDA code (called Dena) to leverage the parallel processing capabilities of the Lattice Boltzmann Method. In order to assess the accuracy and effectiveness of this method, several test cases are examined, including the Capillary Intrusion Test, the Fingering Process, and the Drainage Process within a real porous medium. Comparative analysis against analytical and experimental results substantiates the model's capabilities and accuracy. Furthermore, the impact of viscosity ratio variations among different flow components within porous media is investigated. With the developed approach, it is possible to span a range of viscosity ratios up to 2132. The findings underscore the model's stability and accuracy in simulating high-viscosity ratio multicomponent fluid flows within porous media. • A robust multicomponent lattice Boltzmann method to simulate flows in porous media. • Numerical stability and accuracy in high viscosity ratios ensured by the method. • Accurate capturing of capillary intrusion, fingering, oil displacement, saturation level. • Impact of viscosity ratio exceeding 2000 on drainage in porous media has been studied. [ABSTRACT FROM AUTHOR]

Flow regimes leading to clogging of pipes exist for most multiphase flows with cohesive particles. Although plugging is critical in many industrial and medical applications, there are few records describing the details of the process. To address the problem, we conduct a computed tomography (CT) study of plugging in a cohesive ice slurry. We run experiments for ice concentration of 15%, Re∼3500, particle size 0.2-0.4 mm, and their surface energy ∼150 mJ/m2. The CT scans, combined with experimental logs of the main flow parameters, revealed the formation of deposits around the orifice inserted into the pipe, with a complete blockage formed downflow the orifice. The deposition efficiency of ice was relatively low ∼ 10−3. Reproducing the experimental deposition efficiency with the Lagrangian CFD model, we extracted the probability of particle capture at the orifice, which was about 0.5%. The simulation results illustrated how inter-particle interactions hindered the plugging. • CT visualization of pipe plugging by cohesive slurry with 15% of particles. • The surface energy of particles was 150 mJ/m2. • Particle deposition efficiency was 0.1% at Re∼3500. • Lagrangian CFD model of the process developed. • Wall capture probability was 0.5%. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high accuracy CNN model was trained by 30,000 EHD spraying patterns images. • The CNN model recognized the patterns accurately across a wide range of conditions. • The generalized spraying pattern maps were drawn in terms of dimensionless groups. • A high accuracy DNN model was established with 11,650 experimental data points. • The DNN model can predict the EHD patterns under different conditions efficiently. Effective recognition and prediction of spraying patterns for electrohydrodynamic (EHD) process are extremely important for its applications in high quality micro/nanoparticles preparation, chip coating, droplet-reactor design, and high precision printing, etc. In this study, six distinct spray patterns, namely dripping, spindle, cone-jet, rotational jet, atomization, and skew jet-atomization, were classified through experiments. Subsequently, 30,000 images were obtained to train a convolutional neural network (CNN) model for recognizing EHD spraying patterns, which exhibited a remarkable accuracy of 99.80%. The CNN model was used to recognize the patterns across a range of experimental variables. Dimensionless groups were established and the generalized spraying pattern maps were drawn efficiently via the model. Finally, a database consisting of 11,650 experimental data points was constructed to train a deep neural network (DNN) model, aiming to reduce the number of experiments. The DNN model with an accuracy of 95.88% was employed to predict the spraying patterns, by which a rapid but comprehensive analysis of the impact of different conditions was achieved. [ABSTRACT FROM AUTHOR]

• Simulation of the multifilament spinning process with a modified Eulerian-Lagrange model. • Two dynamically unstable regions and one DMAC accumulation zone are quantitatively identified. • The hydrodynamic stability of spinning is intricately linked to the lateral and inversed stream. • The thermal stability of spinning can be efficiently regulated by the inlet air temperature. • The spinning safety can be efficiently regulated by the inlet DMAC fraction. The industrial multifilament spinning unit is plagued by intricate multiphase and multiscale interactions that remain insufficiently comprehended. A modified Euler-Lagrangian method is employed to scrutinize its dynamic field, taking the dry spinning of spandex as an illustrative case. This framework is first validated by industrial-obtained fiber behaviors. Thereafter, the interaction between 80 filaments and the surrounding airflow is comprehensively explored. Finally, two dynamically unstable regions at the channel upper and bottom sections, along with a solvent accumulation zone near outlet1 are quantitatively identified. The pivotal role of lateral and inverse streams in their formation is revealed. In addition, this work demonstrates an increase in hydrodynamic instability under elevated inlet velocities and outlet pressure conditions, and the efficient regulation of thermal and safety aspects by manipulating inlet air temperature and the dimethylacetamide fraction. The present study indicates that the Euler-Lagrangian model is a powerful tool for deeply exploring and optimizing the multifilament system. [ABSTRACT FROM AUTHOR]

• A multiphase reactive transport pore-scale model is improved. • Negative feedback between multiphase flow and solid dissolution is revealed. • Multiphase flow can promote the compact solid dissolution in porous media. • Structure heterogeneity effect is not intensified in the multiphase dissolution. • A new correlation between porosity, saturation and interfacial length is proposed. Fundamental understanding of the multiphase reactive transport with solid dissolution is crucial for a wide range of scientific and engineering problems. In this study, a pore-scale model is improved to study coupled processes of multiphase flow, mass transport, chemical reaction and solid dissolution in porous media with increasing structural heterogeneity. The results show that with the existence of multiphase flow, under the reactive transport conditions studied (Pe = 5, Da = 10; and Pe = 5, Da = 1), more compact dissolution pattern is generated due to the negative feedback between reactant transport and solid dissolution, while the feedback is positive in single-phase condition leading to wormhole dissolution. Besides, while it is found that the structural heterogeneity amplifies the wormhole dissolution in single-phase reactive transport processes or promotes the formation of fingering for multiphase flow, such heterogeneity effect is homogenized in the multiphase case. Finally, based on the pore-scale results, a new correlation between porosity, saturation and interfacial length is proposed which can be upscaled into the continuum-scale models. [ABSTRACT FROM AUTHOR]

• Deep neural networks are popular for fault detection and diagnosis; however, their results are not easy to interpret. • Multi-mode operations are prevalent in the chemical industry. • We propose a variable attribution method with mode-specific baselines for multi-mode operations. • The method correctly identifies the input variable attributions during normal or fault condition in multiple modes. • We illustrate the benefits of the method using two case studies – a CSTR process and the Tennessee Eastman challenge problem. Multi-mode operations are prevalent in the chemical industry. Various methods have been proposed for monitoring multi-mode operations. Of these, AI-based approaches such as Deep Neural Networks (DNN) are becoming popular due to their higher accuracy. However, the lack of transparency of DNNs hinders their widespread adoption in safety–critical applications such as process monitoring. This work addresses this limitation by proposing an Explainable AI (XAI) methodology for multi-mode operations. The proposed methodology encompasses a supervisory system that identifies the current operational mode. This information is used by an Integrated Gradient (IG) based XAI method to configure mode-specific baselines and thus generate DNN explanations corresponding to each operational mode. The ability of this methodology to generate reliable explanations to aid plant operators is illustrated through a simulated CSTR process, the Tennessee-Eastman process, and the pilot-scale Multiphase Flow Facility case study. [ABSTRACT FROM AUTHOR]

• Transient flows exhibit strong disturbances posing significant challenges. • The BSM considers the spatial distance and the background information factor. • The BSM achieves higher accuracy when simulating flow with sharp gradients. • Higher friction results in increased particle velocities, coefficients and mixing rate. It is of significance to numerically describe particle-flow interphase flow details at a feasible computational cost. Inspired by the semi-resolved Computational Fluid Dynamics-Discrete Element Method (CFD-DEM), an improved bilateral semi-resolved CFD-DEM approach (BSM) approach is developed in this work. Compared with the conventional divided particle volume method (DPVM) and recent semi-resolved CFD-DEM (SM) approach, the BSM approach allows a higher-resolution mesh and achieves higher accuracy as well as applicability when simulating the transient flow with sharp gradients of solid volume fraction and velocity etc. Then the BSM approach is applied to a rotary drum to demonstrate the effectiveness by investigating the internal hydrodynamics details. The typical flow behaviours are detailed; then the effects of the restitution and friction on the internal flow are analysed with details to demonstrate its effectiveness in terms of repose angle, active–passive zone, solid residence time, particle mixing and axial dispersion. The results show a positive correlation of the active depth, mixing degree, and particle dispersion with the friction, while restitution increasing depicts no significant effects on this particulate flow. This work provides an improved numerical tool for understanding the multiphase transient flows involving sharp gradients. [ABSTRACT FROM AUTHOR]

• Oil and brine relative permeabilities decreased with the decrease in average fracture aperture. • An increase in fracture aperture led to a decrease in the endpoint oil saturation post-waterflooding and the endpoint brine saturation post-oil flooding. • Relative permeability of mixed-wet fractures was lower than their oil-wet counterparts and both considerably lower than that of water-wet fractures. • The oil-brine flow in fractures with rough walls exhibited a significant phase interference. • Improved relative permeability models have been devised to describe the behavior of two-phase flow within rough-walled fractures with different wettability conditions. Tight subsurface geosystems provide significant prospects for the recovery and storage of mass and energy. Because of the tightness of these systems, natural and engineered fractures are the main conveyance conduits transporting the fluids from the tight rock matrix to the wellbore or vice versa. During the fracturing process, most of the newly induced fractures are considered water-wet, however during injection/production, the wettability of the fractures gradually changes. These changes are mainly due to the interactions between the resident and injected fluids, or the exposure of the virgin fracture surfaces to the resident fluids during production. This alteration in wettability can affect the trapping and flow dynamics, e.g., relative permeability, of the fluids flowing in the fracture. Furthermore, fluid injection and production into and from these systems impact the fractures pore pressure and hence the effective stress they are exposed to, resulting in variations in the fracture aperture. In this study, we present a comprehensive macro-scale experimental investigation focusing on the impact of wettability and aperture on steady-state two-phase relative permeability in rough-walled fractures. Using the stead-state measurement technique, we meticulously characterized oil-brine relative permeabilities and residual trapping in water-wet, oil-wet, and mixed-wet rough-walled fractures induced in Eagle Ford shale rock samples. Additionally, we assessed the influence of fracture aperture size on these properties during both drainage and imbibition flow processes. Our results indicate significant phase interference in oil-brine flow in non-water-wet rough-walled fractures, which renders the commonly used x-curve and Corey models inadequate to represent the steady-state oil-brine relative permeabilities measured in our study, leading to substantial overestimations. Mixed-wet fractures exhibited reduced relative permeabilities compared to oil-wet fractures, which in turn demonstrated lower relative permeabilities than water-wet counterparts. The observed trends stem from evolving fluid configuration and transport dynamics within the fractures as surface wettability transitions. Furthermore, an increase in fracture aperture corresponded with an increase in relative permeability. This was attributed to a broader flow area, diminished capillarity, attenuated impact of fracture wall roughness and tortuosity effects, and a reduction in bypassing and trapping events, all synergistically contributing to the mitigation of phase interference. Similarly, an increase in fracture aperture led to a marked decrease in post-waterflooding endpoint oil saturation and post-oil flooding endpoint brine saturation. Finally, we provided generalized correlation models based on experimental results from fractures with varying conductivities and wettability, yielding a more accurate representation of fracture relative permeabilities compared to traditional models. The data and correlation models produced in this study improve our understanding and prediction of multiphase flow in subsurface fractures and offer insights into rapid production decline in unconventional shale reservoirs. [ABSTRACT FROM AUTHOR]

Integration of physics principles with data-driven methods has attracted great attention in recent few years. In this study, a physics-informed dynamic mode decomposition (piDMD) method, where the mass conservation law is integrated with a purely data-driven DMD method, is developed for fast prediction of the spatiotemporal dynamics of solid volume fraction distribution in bubbling fluidized beds. Assessment of the prediction ability using both piDMD and DMD is performed using the CFD-DEM results as the benchmark: Both DMD and piDMD can predict the short-term behaviour of solid volume fraction reasonably well, but piDMD outperforms the DMD in both qualitative and quantitative comparisons; With respect to their long-term ability, the piDMD-based prediction of the instantaneous solid volume fraction distributions is qualitatively correct although the accuracy needs to be improved, and the predicted time-averaged radial and axial profiles are satisfactory; Whereas the DMD-based prediction of instantaneous snapshots and time-averaged results is completely nonphysical. Present study provides a fast and relatively accurate method for predicting the hydrodynamics of gas-solid flows. • Physical principle is integrated with data-driven method. • A physics-informed dynamic mode decomposition (piDMD) is proposed. • piDMD enables the long-term prediction of solid volume fractions. • piDMD outperforms purely data-driven DMD. [ABSTRACT FROM AUTHOR]

Polydisperse gas-solid flows, which is notoriously difficult to model due to the complex gas-particle and particle-particle interactions, are widely encountered in industry. In this article, a refined kinetic theory for polydisperse flow is developed, which features single-parameter Chapman-Enskog expansion (the Knudsen number) and exact calculation of the integrations related to pair distribution function of particle velocity without any mathematical approximations. The Navier-Stokes order constitutive relations for multifluid modeling of polydisperse gas-solid flow are then obtained analytically, including the solid stress tensor, the solid-solid drag force, the granular heat flux and the energy dissipation rate. Finally, the model is preliminarily validated by comparing to the discrete element simulation data of one-dimensional granular shear flow and by showing that the hydrodynamic characteristics of gas-solid flows in a bubbling fluidized bed containing bidisperse particles can be successfully predicted. • A refined kinetic theory with C-E expansion is developed for polydisperse flow. • The complex integrals related to particle collision are calculated accurately. • Precise constitutive relations at Navier-Stokes order for multifluid model are obtained. • The model is preliminarily validated for a bidisperse bubbling fluidized bed. [ABSTRACT FROM AUTHOR]

Overall process of the hybrid model for RF-ANN. [Display omitted] • A novel data-driven approach for solids velocity measurement. • A hybrid model of neural network and random forest developed. • The hybrid model achieves high accuracy and generalization performance. • Data-driven approach overcomes limitations of cross-correlation algorithm. Accurate measurement of solids velocity is crucial for fluidized bed reactor design, optimization, and scaling in chemical engineering. However, the cross-correlation calculation of dual-channel particle concentration signals has limitations in dense-phase fluidized systems. To address this, we propose a data-driven approach using machine learning algorithms in numerical simulations. Four popular algorithms (linear regression, random forest, support vector machine, and neural network) are evaluated. Individual models show poor generalization with a determinable coefficient below 0.2. To overcome this, a hybrid model combining a neural network and random forest is developed, improving data prediction and generalization. The determinable coefficient increases to 0.90, and the relative error in average particle velocity prediction reduces to less than 0.01. This hybrid machine learning model has the potential to overcome limitations of cross-correlation-based particle velocimetry, expanding its applications in multiphase flow systems. It offers a promising solution for accurate solids velocity measurement in fluidized beds. [ABSTRACT FROM AUTHOR]

• High-throughput microemulsion method of YSFs in microchannels is explored. • Effect of rheology of YSFs on fluid distribution is studied. • Prediction model of pressure drop in multiphase flow of YSFs is proposed. • Uniformity strategies of YSFs droplets are discussed. The microemulsion method is limited due to low productivity. Using Carbopol gel (0.05 %, 0.13 %, 0.2 %) and mineral oil as dispersed phase and continuous phase respectively (3 ≤ Q d ≤ 8, 2 ≤ Q c ≤ 350), the numbering-up of YSFs droplets in asymmetric parallel microchannels are experimentally studied. Ca *(10-3-10) and Ca c (10-4-10-2) are introduced to divide the two-dual droplet flow pattern which is conducive to production. It is found that yield stress mainly acts on the necking stage of droplet formation, so the continuous phase flow can be increased to shorten the necking time and improve the size uniformity. The influence of rheology on droplet morphology makes the existing multiphase flow pressure drop model no longer applicable. Therefore, a correction pressure drop model of Carbopol slugs and prediction models of droplet size and generation frequency are proposed. This study provides a reference for the high-throughput production of YSFs droplets in microchannels. [ABSTRACT FROM AUTHOR]

• Difference of flow pattern maps in short and long pipelines is revealed. • Influence of pipeline length and liquid viscosity on slug frequency is investigated. • Quantitative relation of slug frequency data with various viscosities is obtained. • Prediction correlation of slug frequency for different viscosities is established. The accurate prediction of slug frequency is critical for the construction of multiphase flow models and the flow assurance of oil and gas pipelines. In this paper, the slug frequency data are obtained by visualization method in short (65 mm ID, 215 D) and long (46 mm ID, 35957 D) pipelines. The slug frequency of horizontal pipeline is inversely proportional to pipeline diameter (26–300 mm) and proportional to the liquid viscosity (1.01–7500 mPa·s). The quasi-developed distance for the air–water slug flow at V SG ≤ 1.00 m/s is about 1200 D , and the frequency of the quasi-developed slug flow is less affected by the pipeline length. Based on the gas Strouhal number and the liquid viscosity ratio, the quantitative relation between the slug frequency data at different viscosities is constructed, and a new correlation is developed to predict both the slug frequency of water and viscous liquids. [ABSTRACT FROM AUTHOR]

This paper explores the through-/in-plane characteristics of water transport in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). Theoretical analysis is performed on the non-isothermal two-phase flow under flow channels. A dimensionless group Da (Damkohler number for PEFC operation), defined as the ratio of water generation rate to water vapor-phase removal rate, is formulated to characterize the flow regimes in a PEFC. This group, lumping geometrical parameters and physical properties, compares the water vapor-phase removal capability (via water diffusion and holding capacity) with the rate of water production by the oxygen reduction reaction. We find that this dimensionless group can be used to characterize the non-isothermal, two-phase phenomena: when Da→0, the fuel cell is subjected to single-phase operation; while as Da→ we have full two-phase operation. A more precise expression is explored for the dimensionless group at the channel central line, i.e. Da0: when Da0>1 the entire cathode GDL-CL (catalyst layer) interface is in two-phase region, whereas part of the interface is free of liquid water for Da0

• A closure model for bubbly flow is investigated. • Including bubble forces and bubble-induced turbulence. • Validation is performed for a time-dependent flow. • Specifically an oscillating bubble plume. • Good agreement is found for plume oscillation period, phase fraction and phasic velocities. For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. An ongoing effort at HZDR has led to a validated set of closures for adiabatic bubbly flows that is applicable under a rather broad range of conditions including flows in pipes and bubble columns. Up to now, however, only flows with stationary mean values have been considered. The present contribution extends the model validation to dynamic flow phenomena by considering a periodically oscillating bubble plume. Consequently, the turbulence model then runs in URANS mode. Literature data for a partially aerated flat rectangular bubble column are used for comparison. In particular, results for the plume oscillation period show good agreement between simulation and experiment. [ABSTRACT FROM AUTHOR]

• Mass transfer coefficient of oxygen can be measured by circulating bubble in 30 s. • The reactive mass transfer coefficient is of the order 10−4 m s−1 in turbulent flow. • The enhancement factor of the oxidation reaction is between 1.8 and 3. • The bubble and liquid Reynolds numbers in the mass transfer are elucidated. A non-intrusive measurement method was used to quantify the mass transfer between an oxygen bubble (with a spherical equivalent diameter in the range 2–4 mm) and the turbulent sodium sulfite solution in which the bubble was driven to circulate. The variations of the position, size, and velocity of the single bubble with time were derived from the images recorded by a high-speed camera, and the average reactive mass transfer coefficients were calculated from the reduction of the volume of the bubble. The enhancement factors under various flow conditions caused by the catalyzed chemical reaction were provided. The flow field in the chamber was measured by 2D particle image velocimetry (PIV). The single-phase instantaneous flow field was compared with the multi-phase flow field in terms of the effect of the single bubble. A correlation of the bubble Sherwood number with the bubble Reynolds number was obtained under different liquid Reynolds numbers. We found that the slip velocity has a high capacity to keep the bubble surface mobile. Both the bubble Reynolds number based on the bubble slip velocity and liquid Reynolds number contributed to the mass transfer in the turbulent chamber. [ABSTRACT FROM AUTHOR]

• Introduces a low cost and compact setup for measuring 3D bubble distribution. • Hybrid hologram processing approach resolves bubbles over a wide size range. • Performs accurate measurements of 3D bubble location and large bubble inclination. • Validated using synthetic bubble holograms, an oil droplet hologram, and a physical target. • Allows accurate measurement of the gas leakage rate from a ventilated supercavity. The paper presents a hybrid bubble hologram processing approach for measuring the size and 3D distribution of bubbles over a wide range of size and shape. The proposed method consists of five major steps, including image enhancement, digital reconstruction, small bubble segmentation, large bubble/cluster segmentation, and post-processing. Two different segmentation approaches are proposed to extract the size and the location of bubbles in different size ranges from the 3D reconstructed optical field. Specifically, a small bubble is segmented based on the presence of the prominent intensity minimum in its longitudinal intensity profile, and its depth is determined by the location of the minimum. In contrast, a large bubble/cluster is segmented using a modified watershed segmentation algorithm and its depth is measured through a wavelet-based focus metric. Our processing approach also determines the inclination angle of a large bubble with respect to the hologram recording plane based on the depth variation along its edge on the plane. The accuracy of our processing approach on the measurements of object size and 3D distributions are assessed through synthetic bubble holograms and oil droplet holograms from an experiment separately. In addition, we evaluate the ability of this algorithm to estimate the bubble inclination with respect to the hologram recording plane through measuring a 3D-printed physical target of pillars with different inclination angles. The holographic measurement technique is further implemented to capture the fluctuation of instantaneous gas leakage rate from a ventilated supercavity generated in a water tunnel experiment. Overall, our paper introduces an inexpensive and compact solution for high resolution characterization of bubbles and other particles in multiphase flows from a broad range of applications. [ABSTRACT FROM AUTHOR]

• FTLE and LCS reveal persistent vortical structure in wake of Taylor bubble. • Residence times in bubble wake peak for intermediate rise velocities of Taylor bubble. • Coherent structure can restrict availability of gas phase for chemical reaction. Timescales and residence times in reactive multiphase flows are essential for product selectivity. For instance when a gas species is consumed, e.g., by a competitive consecutive reaction with moderate reaction kinetics where reaction timescales are comparable to relevant mixing timescales. To point out the importance of the details of the fluid flow, we analyze experimental velocity data from a Taylor bubble wake by means of Lagrangian methods. By adjusting the channel diameter in which the Taylor bubble rises, and thus the rise velocity, we obtain three different wake regimes. Remarkably, the residence times of passive particles advected in the bubble wake's velocity field show a peak for intermediate rise velocities. This observation seems unintuitive at first glance because one expects a faster removal of passive tracers for a faster overall flow rate. However, the details of the flow topology analyzed using Finite Time Lyapunov Exponent (FTLE) fields and Lagrangian Coherent Structures (LCS) reveal the existence of a coherent vortical pattern in the bubble wake which explains the long residence times. The increased residence times within the vortical structure in combination with the close bubble interface acting as a constant gas species source could enhance side product generation of a hypothetical competitive consecutive reaction, where the first reaction with the gas species forms the desired product and the second the side product. [ABSTRACT FROM AUTHOR]

• Dynamic behaviors between Newtonian and viscoelastic droplets are compared. • Interfacial evolution of viscoelastic droplet with polymeric filament is displayed. • Effect of elasticity on shrinkage of droplet neck could be not prominent. • Elasticity plays an important role in stretching dynamic of polymeric filament. Dynamics of elastic droplet breakup and stretching of polymeric filaments in a microfluidic T-junction are investigated experimentally. Through comparisons between cases of Newtonian droplet and a series of viscoelastic droplets with similar shear viscosity, the effect of elasticity on breakup dynamic of droplet is especially focused. Four sequential stages of droplet breakup in a microfluidic T-junction are observed: (I) squeezing, (II) transition, (III) pinch-off and (IV) filament rupture stages. For former three stages (I–III), dynamic behaviors of viscoelastic droplets with lower molecular weight (M w = 1 × 105 g/mol and 3 × 105 g/mol) and Newtonian droplet are similar, while for viscoelastic droplet with higher molecular weight (M w = 1 × 106 g/mol), the spatial obstruction of previous filaments accelerates the shrinkage of droplet neck. Additionally, the transformation of dominant force from inertial to capillary force leads to the variation of scaling laws describing the neck evolution. For filament rupture stages (IV), with extension of polymer molecules chain, the elastocapillary balance contributes to the exponential thinning of the polymeric filament, while the width of thread neck decreases linearly with the time for Newtonian droplet. Furthermore, more effort has been devoted to investigate the stretching dynamic of filament. The stretching rate of filament is independent of elasticity, but proportional to two-phase flow rates. [ABSTRACT FROM AUTHOR]

• Fluid properties affect separation efficiency of inlet vane to a large extent. • Increasing the expansion factor of an inlet vane does not have a large effect upon separation efficiencies. • Increasing column diameter reduces separation efficiencies. • Inlet pipe diameter affect separation efficiency to a large extent. • Increasing liquid volume fraction in the inlet pipe increased separation efficiency at a given K-value. Separation efficiencies for a scrubber inlet vane section was investigated using a natural gas hydrocarbon system at 20, 50 and 85 bars. Several design features were investigated such as diameter of inlet pipe, vane design, separator vessel diameter. In addition the effect of liquid rate was examined. The study finds that pipe diameter, column diameter, liquid rate and fluid properties of the inlet vane affect separation efficiencies. This is a result of several different fluid mechanical processes which affect the droplet size distribution into the separation vessel. [ABSTRACT FROM AUTHOR]

• The variation of induction process was studied in hydrate formation in a visual flow loop. • The initial pressure is inversely proportional to the hydrate formation induction time and reaction time. • With the increase of the flow rate, the hydrate formation induction time and reaction time are shortened, but there is a flow rate threshold. • With the increase of inclination angle, the induction time tends to shorten and the reaction time generally prolongs. One of the primary issues with natural gas transportation assurance is pipeline obstruction due to the formation and deposition of gas hydrates. Thus it is crucial to study the prevention and control methods of natural gas hydrate formation. A high-pressure visual flow loop was established in this study to investigate the effects of pressure, liquid velocity, and loop inclination angle on the formation of natural gas hydrates, hydrate slurry flow and morphology. For the formation of hydrates, it was demonstrated that the pressure was inversely related to the induction time and formation time. As the initial pressure increases, the conversion rate of water increases, leading to poor fluidity. With the increase of liquid velocity, the conversion rate of water increases and there is a threshold liquid velocity. Compared with horizontal loop, the hydrate particles in the slope were repeatedly deposited and removed off the surface of the sedimentary layer by gravity, and some large hydrate particles in the slope section gathered near the bottom of the pipeline. The induction time shortens and the formation time prolongs as the inclination angle increases. The inclination angle shows little effect on the final conversion rate of water, but it can delay the growth of hydrates obviously. [ABSTRACT FROM AUTHOR]

• hp-adaptive quadrature increases the accuracy of numerical integration. • Better error control for the population balance source terms. • Irregular integrands are efficiently dealt with. • Combination of piece wise Gaussian quadrature with weighted residual methods. The solution of the population balance equation requires the integration of several source terms. In the numerical weighted residuals methods, Gaussian quadrature is a natural candidate for numerical integration. Previous works using the weighted residuals methods for solving the population balance equation did use a fixed grid of quadrature points. This work shows that the use of adaptive quadrature points for the numerical integration can lead to more efficient and accurate solutions of the equation. For cases where the integrand shows a high degree of irregularity, the hp-optimization method distributes the quadrature points such that the method becomes more efficient than with a fixed grid. An additional improvement is that the amount of quadrature points changes to fit the need for each integral present, rather than having one set of quadrature points for all cases. A simple population balance model demonstrates the use of the adaptive quadrature approach. [ABSTRACT FROM AUTHOR]

Highlights • Linear Stability Analysis is used to define the interface stability in two-layer Rayleigh-Bénard-Poiseuille convection. • Influence of thermocapillary, shear and buoyancy forces is considered. • Impact of interface deformation in critical Rayleigh and Marangoni numbers is evaluated. • The limits where the interface deformation can be neglected are defined. • Comparisons with CFD results shows the reliability of the linear analysis. Abstract Interface deformation is a common phenomenon in multi-layered systems that can significantly impact the velocity and temperature fields. In order to track the interface position in a two-layered system subjected to vertical temperature gradient and shear flow, techniques of linear stability analysis (LSA) and computational fluid dynamics (CFD) were applied. The LSA results show that the interface can be deformed for low Reynolds numbers if the fluids in each layer have different viscosity or thermal conductivity or if the thermocapillary effect is significant. The interface can be stabilized by increasing the ratio between the density of each fluid. The limits where the interface deformation can be neglected are defined for several cases. Comparisons with CFD results reveal that the linear analysis is consistent near the convection onset; however, as the Rayleigh number is increased and the non-linear terms become more significant, strong interface deformation can occur and the linear approximation no longer predicts the system behavior. [ABSTRACT FROM AUTHOR]

• Effects of flow rates and junction angle θ were investigated for 20° ≤ θ ≤ 160°. • Theoretical model to predict gas bubble and liquid slug sizes was established. • For θ = 20°, unit cell ↓ significantly with ↓ liquid or ↑ gas flow rate. • For 45° ≤ θ ≤ 160°, unit cell is less sensitive to flow rate change and < θ = 20°. Two-phase liquid-gas Taylor flow triggered by blocking-squeezing mechanism was studied with different junction angle θ microchannels, i.e. 20°, 45°, 90°, 135° and 160°, at various liquid (ethanol) and gas (He) flow rates. We experimentally investigated the effects of flow rates and θ on the gas bubble V B and liquid slug V S volumes. A theoretical model was formulated for the quantitative predictions of bubble and slug sizes for different θ and flow rates. Good agreements were obtained between theoretical predictions and experimental observations. The unit cell volume V U (V B + V S) decreased pronouncedly for the 20° channel with decreasing liquid or increasing gas flow rate, due to the slight increase in V B and large decrease in V S. In comparison, for the 45°, 90°, 135° and 160° channels with increasing liquid or decreasing gas flow rate, V U were less sensitive to fluid flow rate changes, due to the approximate cancellation between V B decrease and V S increase. For the 20° and 45° channels, it produced larger V U , due to larger V B and V S , when compared to the 90° channel. This is caused by the larger gas bubble throat width D N at the junction when θ < 90°. As for the 135° and 160° channels (θ > 90°), D N is approximately equal to the gas channel width, with V B , V S and V U approximately the same as the 90° channel. With θ ≥ 90° (i.e. 90°, 135° and 160° channels), as evident from the smaller V U , higher gas bubble density can be obtained when compared to θ < 90° (i.e. 20° and 45° channels). Hitherto, this observation has not been realized, and the mechanics is first investigated here with the employment of extreme θ (i.e. 20° and 160°). A thorough understanding of the underlying mechanics affecting Taylor flow can facilitate its exploitation for controlled gas bubble and liquid slug generation. Our theoretical model facilitates the tuning of the channel designs and fluid flow rates to achieve the desired gas bubble and liquid slug sizes for specific applications. [ABSTRACT FROM AUTHOR]

• Earth's field NMR flow meter used to simultaneously measure oil and water flowrates. • Dual polarisation mechanism introduced to allow T 1 phase differentiation. • 2D signal inversion method used to determine velocity- T 1 probability distributions. • Accurate flowrate measurements captured in three oil/water flow regimes. We present a novel multiphase flow metering technique for simultaneous measurement of oil and water volumetric flowrates. An Earth's field nuclear magnetic resonance (NMR) detection coil is applied to measure free induction decay (FID) signals of two-phase oil/water flows. A dual polarisation technique is introduced utilising an upstream permanent magnet as well as an electromagnetic pre-polarising coil. FID signals with variable pre-polarising conditions are acquired and fit with a model for the NMR fluid signal using a 2D Tikhonov regularisation algorithm, allowing determination of a joint 2D velocity- T 1 probability distribution. Appropriate analysis of the measured velocity- T 1 distributions allows calculation of individual phase flowrates. The performance of the NMR flow measurement technique is examined for oil/water flows which are visually observed to be in three different flow regimes: stratified flow with mixing, dispersion of oil-in-water and water, and full oil-in-water emulsions. Two-phase flow characteristic features such as velocity slip are examined for each flow regime. Finally the accuracy of the measurement system in each flow regime is validated against in-line rotameter measurements. [ABSTRACT FROM AUTHOR]

• G/L/L in Microfluidic system is reviewed. • Microfluidic device and microchannel type are comprehensively summarized. • Fluid mechanics and transport characteristic are classified and concerned. • Applications and scale-up of G/L/L are addressed. Gas-liquid-liquid (G/L/L) multiphase flow in microfluidic system has been a vital part of microfluidics, micro-chemical and micro-analysis in recent years. Microfluidics has emerged as a useful tool to prepare G/L/L that affords improved control over the micro-scale structure. With the aid of clever and efficient device designs, precise regulation of the size, shape and components can be realized. Existing results have shown that G/L/L multiphase micro-flow exhibits more complicated laws and unique characteristics in flow, transport and reactions compared with liquid-liquid or gas-liquid two-phase flow, allowing the optimal and more efficient control of the process. In this review, focused on the G/L/L multiphase flow in microfluidic systems, we recount the historical development of this system and approach, along with the state-of-the-art, including discussion of microfluidic devices (lithographically defined devices and capillary/needle-based devices) and microchannel type (cross-junction, flow-focusing, dual-coaxial, etc.) used to form and prepare G/L/L multiphase mixtures. Discussion is also extended to scaling laws and numerical simulations used to predict the size of microbubbles or droplets. In addition, flow and mass transfer characteristics, as well as applications and scale-up, are also discussed. Finally, the future trends in the development of G/L/L multiphase flow are addressed, emphasizing some directions worth detailed study and remaining challenges in the field. [ABSTRACT FROM AUTHOR]

Highlights • Observations of local saturations during two-phase flow in carbonate rocks. • A model is presented with property variations in the direction of displacement. • Parameters of the capillary pressure curve are found by bi-objective optimisation. • Estimation of both effective and relative capillary pressure curves. Abstract The heterogeneity of rocks represents a challenge for interpreting and using outcomes from multiphase-flow experiments carried out on laboratory samples. While the capillary pressure–saturation function, p c (S) , is known to vary spatially and cause local saturation development during immiscible displacements, its variation remains difficult to measure. This is particularly challenging for rocks with complex fabrics, such as carbonates. Here, we present a workflow for the dynamic measurement of core- and subcore-scale drainage p c (S) curves in heterogeneous porous media. Multi-rate, two-phase core-flooding tests are conducted on three carbonate rocks with direct observations of local saturation data. The interpretation of the experiments is done by fitting the parameters of the p c (S) curve, while describing both steady-state saturation and pressure profiles with a detailed one-dimensional model that accounts for the variation of subcore-scale properties in the direction of displacement. Workflow validation is achieved by means of synthetic data, thereby demonstrating the uniqueness of the solution of the resulting multi-objective optimisation problem. The model reproduces accurately experimental data on the three rocks and enables computing the effective core-scale p c (S) curve in the limit of zero velocity, as it would be expected during a porous-plate experiment. The output of the proposed technique is however much richer and includes the relative p c (S) curve that is universal and independent of the specific pattern of heterogeneity, in addition to a set of scaling factors. The latter describe the distribution of the p c (S) curves at the subcore-scale due to heterogeneity and form the statistical basis needed for upscaling studies. [ABSTRACT FROM AUTHOR]

Highlights • A novel continuum theory accurately predicts aggregation in a gas-solid flow. • The continuum theory accurately predicts entrainment of cohesive particles. • Aggregation leads to increased granular temperature and breakup of agglomerates. Abstract In this work, a continuum theory for cohesive particles developed recently (Kellogg et al., 2017) is applied to lightly-cohesive particles in an unbounded, gas-solid riser. The novelty of this recent theory is its fundamental incorporation of the effects of the granular temperature (i.e., continuum measure of impact velocity) and the material and cohesion properties on the rates of aggregation and breakage of agglomerates. Here, we extend this theory to multiphase systems and place particular emphasis on its ability to predict entrainment rate, as past empirical correlations vary by orders of magnitude when applied to the same system (Chew et al., 2015). Specifically, continuum predictions of entrainment rates and agglomerate fraction are compared with Discrete Element Method (DEM) simulations of lightly-cohesive particles in a gas-solid flow. The agreement obtained for these quantities provides preliminary validation for the use of the continuum theory for cohesive particles in gas-solid flows. [ABSTRACT FROM AUTHOR]

Highlights • First time use of moving overset meshes to simulate agitator motion. • Reynolds and Strouhal number equations account for non-linear impact of amplitude. • DSD comparison reveals a closer approximation using volume of fluid multiphase model. • User-defined functions are applied to model oscillatory translational velocity. Abstract This paper presents a CFD model and hydrodynamic study of a moving-baffle oscillatory baffled column (moving-baffle OBC). This work marks the first instance that moving overset meshing was used to simulate agitator motion in a fluid system. Population balance results are validated with experimental data for the inverse-suspension of non-reactive aqueous acrylamide in Isopar oil. A comparison of the droplet size distributions produced via various multiphase simulation methods was performed, resulting in a better overall agreement with the experimental literature for simulations applying the volume of fluid (VOF) multiphase method. Hydrodynamic studies reveal patterns of local flow circulations and centermost axial currents in relation to agitator position. Examination of the dimensionless groups traditionally used to describe flow conditions for moving-baffle OBCs reveal a considerable discrepancy between the previously-defined oscillatory Reynolds number and oscillatory Strouhal number with numbers derived from fluid flow within the column. A numerical correction has been presented to illustrate the nonlinear effect of oscillation amplitude on fluid flow through the system and to provide a more realistic estimation of the Reynolds number and Strouhal number for the modeled moving-baffle OBC. [ABSTRACT FROM AUTHOR]

Highlights • Mesoscale structures in fluid-particle systems were reviewed. • Multiscale simulation methods for fluid-particle systems were reviewed. • Formation mechanism, experiment and simulation of mesoscale structures were summarized. • Measurement and simulation methods of porous particles or reactive particles were introduced. Abstract This article reviews the general features of the multiscale structures in particle–fluid systems and the characterization, modeling, and simulation methods for these systems. The discussion focuses on the effects of mesoscale behavior, especially those present in process industries for materials and energy transformation and utilization. When there is substantial multiscale heterogeneity in these systems, local non-equilibrium and anisotropy generally lead to a lack of scale separation. Accurate and efficient simulation methods based on first principles and applied across different scales are highly desirable to reveal and quantify the complexities of these systems. Meanwhile, precisely designed experiments and exhaustive nonintrusive measurements are necessary to validate and expand the numerical findings. With this knowledge, rational mesoscale models can be established to provide multiscale simulation methods that do not need to fully reproduce the micro- and mesoscale details of the systems but can still take into account their effects on macroscales. Such multiscale methods are attractive for industrial applications but substantial effort in physical modeling and numerical implementation is still required before their widespread implementation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Real-time magnetic resonance imaging was used to study the dynamics of 3D fluidized beds with internals. • Below the minimum fluidization velocity (U mf), local bubbling was found adjacent to the insert. • Above U mf , a region of reduced bubbling and particle velocity was observed above the insert. Abstract The effect of internals on the fluidization dynamics in three-dimensional (3D) cylindrical fluidized beds was studied using real-time magnetic resonance imaging. Instantaneous snapshots of particle velocity and particle position were acquired for gas velocities U below and above the minimum fluidization velocity U mf. Below U mf , we found local fluidization and gas bubbling in areas adjacent to an inserted horizontal tube, likely caused by the gas locally exceeding U mf as it flows around the insert. Above U mf , the presence of the insert in the bed affected the fluidization dynamics. The wake region above the insert exhibited a lower average particle velocity and reduced velocity fluctuations as well as a substantially reduced number and size of gas bubbles as compared to a reference bed without internals. The extent of this wake region was found to be approximately as wide as the insert, and it extended from the top of the insert to the free surface of the bed. Moreover, the presence of internals also affected the regions below the insert by showing an increased rate of bubble formation directly below the inserted tube. The present work can provide relevant information on the design of fluidized beds with internals. Moreover, the data gathered in this work can be used to validate the accuracy of 3D numerical models of gas-solid systems. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Fully resolved simulations of heat transfer problems in tubular fluid-particle systems. • Handles mixed boundary conditions, i.e. isothermal and isoflux, consistently. • Investigation of the influence of particle sizes and passive particles. • Comparison between two classes of immersed boundary method, i.e. CFM and DFM. Abstract In this paper two immersed boundary methods (IBM), specifically a continuous forcing method (CFM) and a discrete forcing method (DFM), are applied to perform direct numerical simulations (DNSs) of heat transfer problems in tubular fluid-particle systems. Both IBM models are built on the well-developed models utilized in momentum transfer studies, and have the capability to handle mixed boundary conditions at the particle surface as encountered in industrial applications with both active and passive particles. Following a thorough verification of both models for the classical Graetz-Nusselt problem, we subsequently apply them to study a much more advanced Graetz-Nusselt problem of more practical importance with a dense stationary array consisting of hundreds of particles randomly positioned inside a tube with adiabatic wall. The influence of particle sizes and fractional amount of passive particles is analyzed at varying Reynolds numbers, and the simulation results are compared between the two IBM models, finding good agreement. Our results thus qualify the two employed IBM modules for more complex applications. [ABSTRACT FROM AUTHOR]

Highlights • Bubbles move behind the impeller blade due to pressure distribution. • Most bubbles in an unbaffled stirred vessel are fragmented in the trailing vortices. • The fragmented bubbles are transported by the trailing vortices, the core of which traps the bubble. • Smaller and more complicated bubbles are generated with increasing the impeller rotation rate. • More bubbles are agglomerated near the shaft with increasing the impeller rotation rate due to pressure distribution. Abstract The present study investigated the mechanism of small bubble breakup in an unbaffled vessel stirred by a 4-blade paddle impeller. Bubbles were injected underneath the rotating blades. Numerical simulation and experimental observations were performed to investigate the related phenomena. The Volume of Fluid (VOF) method was utilized to simulate a gas-liquid multiphase flow. The injected bubbles were broken behind the impeller blade, where they were transported due to a decreasing pressure gradient caused by the impeller rotation. At the behind of the blade, bubbles were elongated and fragmented due to the trailing vortices developing from the rear surface of blade. The fragmented bubbles were entrapped at the cores of trailing vortices, and then floated up in the space where the trailing vortices became weak. The size of the broken bubbles was dependent on the impeller rotation rate. [ABSTRACT FROM AUTHOR]

Highlights • The MD/COSMOmic method outperforms COSMOtherm and is only second to EPA. • MD/COSMOmic approach can be potentially applied to complex formulations. • Partitioning at different temperature and pH can be modelled with Replica exchange MD. Abstract Solute partition in multiphase fluids is an important thermodynamic phenomenon and performance attribute for a wide range of product formulations of foods, pharmaceuticals and cosmetics. Experimental evaluation of partition coefficients in complex product formulations is empirical, difficult and time consuming. In-silico methods such as fragment constant method and group contribution method require parameter fitting to the experimental data and are limited to relatively simple fluids. Recently, a method combining molecular dynamics (MD) and quantum chemical (QC) calculation of screening charge density function has been reported. The method does not only use fundamental properties of intermolecular force and charge density function, which does not require parameter fitting to the experimental data, but also applies to complex fluid structures such as micelles. In this work, the predictive accuracy of the combined method of MD and QC is evaluated. Using widely available octanol-water partition coefficients as a case study, the performance of the combined MD and COSMOmic for predicting octanol/water partition coefficients has been compared with those of the EPI Suite™ fragment constant method, UNIFAC group contribution method and COSMOtherm. The prediction of the combined MD/COSMOmic method is the closest to the best performing fragment constant method which was specifically designed for the octanol-water system. The combined MD/QC method proves to be the most promising and robust method applicable to a wide range of complex structures of multiphase fluid systems. [ABSTRACT FROM AUTHOR]

Highlights • Flow parameters effect on the stability of EHD-based droplet formation is investigated. • 3D computational analysis of the fluid flow and electrical phenomena is provided. • Effects of capillary number and permittivity ratio on the droplet size are studied. • A new double emulsion formation method based on EHD is suggested. Abstract The feasibility of droplet formation from the dispersion of one viscous fluid within another immiscible viscous fluid with low interfacial tension is shown to be very limited. In this work, the process of emulsion formation for low interfacial tension multiphase systems (e.g. aqueous two-phase systems (ATPSs)) was simulated, where the liquids were exposed to an electric field within a microfluidic device. For the first time, the formation of double emulsion via electrohydrodynamic (EHD) force within microfluidics was investigated. A three dimensional (3D) numerical model was developed based on finite-volume discretization of the governing equations to simulate the EHD-based single and double emulsion formation for ATPSs within microfluidics. The dispersed viscous phase moving toward the active electrode is subjected to shear stress, producing instability on the two-phase interface and causing the formation of a necking area. Upon removal of the electric pulse, the dispersed phase moves in the opposite direction resulting in the formation of the droplet. The volume-of-fluid numerical method was applied to trace the two-phase interface, and a height function was imposed to deal with the 3D contact angles. The effect of capillary number and permittivity ratio of the phases on the size and shape of the droplets was assessed and compared with experimental data. Through controlling the interface between the phases, pressure contours, and volumetric charge density contours, it is possible to generate EHD-based single and double emulsions from viscous fluids within microfluidics with applications in drug delivery, tissue engineering and chemical and biological processes. [ABSTRACT FROM AUTHOR]

Highlights • A two-fluid Eulerian-Eulerian CFD model is used to study bubbly flows. • Multiphase turbulence is modelled using an elliptic blending Reynolds- stress model. • Bubbly flows are studied in pipes, a square channel and a rod bundle. • Impact of the turbulence field and the lift on the lateral void distribution are comparable. • Void distribution is well-predicted without any wall force contribution. Abstract Eulerian-Eulerian two-fluid computational fluid dynamic (CFD) models are increasingly used to predict bubbly flows at an industrial scale. In these approaches, interface transfer is modelled with closure models and correlations. Normally, the lateral void fraction distribution is considered to mainly result from a balance between the lift and wall lubrication forces. However, and despite the numerous models available that achieve, at least in pipe flows, a reasonable predictive accuracy, agreement on a broadly applicable and accurate modelling approach has not yet been reached. Additionally, the impact of turbulence modelling on the lateral void fraction distribution has not, in general, been examined in detail. In this work, an elliptic blending Reynolds stress model (EB-RSM), capable of resolving the turbulence field in the near-wall region and improved to account for the contribution of bubble-induced turbulence, is evaluated against best-practice k - ε and high-Reynolds second-moment turbulence closures. Lift and wall lubrication forces are initially deliberately neglected in the EB-RSM. Comparisons for flows in pipes and a square duct show that the EB-RSM reproduces the lateral void fraction distribution, including the peak in the void fraction in the near-wall region, and reaches an accuracy comparable to the other two models noted above. In rod bundles, even if none of the models considered performs with sufficient accuracy, the EB-RSM detects features of the flow that are not predicted by the other two approaches. Overall, the results demonstrate a much more prominent role of the turbulence structure and the induced cross-sectional pressure field on the lateral void fraction distribution than is normally considered. These effects need to be accounted for if more physically-consistent modelling of bubbly flows is to be achieved. The lift force is added to the EB-RSM in the final part of the paper, to provide a two-fluid formulation that can be used as the basis for additional developments aimed at improving the accuracy and general applicability of two-fluid CFD models. [ABSTRACT FROM AUTHOR]

Highlights • A model was developed for compound droplet involving moving contact line problem. • We observed several interesting events of droplet sliding, detachment and pinch-off. • Capillary numbers of inner and outer droplet significantly affect droplet dynamics. • Effects of surface tension and inner droplet radius on droplet were studied. Abstract The dynamic behavior of compound droplets on the wall of a rectangle channel by the action of an imposed shear flow is simulated using our developed three-dimensional front-tracking method combined with generalized Navier boundary condition. The validity of the present method was confirmed by comparing results of the compound droplet spreading under gravity force with analytical solutions. To determine the physical condition required for detaching/pinching-off the compound droplet, we have performed a large number of simulations with varying capillary numbers of two interfaces and obtained a phase diagram of compound droplets on solid surface in shear flow. The deformation and motion of the compound droplet including its contact line motion are investigated. It is found that the behavior of the compound droplet is controlled by two dimensionless parameters, the capillary numbers of the outer interface and the inner interface. Moreover, we also analyze the deformation and migration of the inner droplet and discuss its effect on the compound droplet. The simulation demonstrate that the lateral migration of the small inner droplet could accelerates the pinch-off process and the large inner droplet could promote the detachment for a moderate capillary number of the outer interface. [ABSTRACT FROM AUTHOR]

Highlights • A novel fractal tree-like photobioreactor was designed and fabricated by 3D printer. • The fractal structure design generated good performances of multiphase flow. • Fractal tree-like photobioreactors had higher efficiency of bio-reaction. • Coupling of fractal geometry and 3D printing provide a potential development for PBR. Abstract Based on the bionic fractal theory, a fractal tree-like photobioreactor (PBR) with high surface area to volume ratio is designed on the basis of bifurcation tree algorithm and manufactured via 3D printing technology. Numerical simulation and experimental results show that the fractal structure has a good flow performance and can lead to secondary flow, which is beneficial to enhance the turbulence and produce smaller bubble sizes. Chlorella culture in the fractal tree-like PBR has a higher Fv / Fm (Chlorophyll fluorescence parameter), close to 0.767, and higher efficiency of photosynthetic growth as well as CO 2 capture, compared with multitubular PBR and conventional acrylic column reactors. Therefore, the fractal tree-like PBR can improve the efficiency of light energy utilization and bioreaction. Combined with 3D printing technology, fractal PBR blazes a new trail for process intensification on the microalgae cultivation. [ABSTRACT FROM AUTHOR]

Highlights • 3D fully resolved pore-scale simulations of multiphase flow using a VOF-IBM method. • Validation test cases for multiphase porous media flows with wettability effects. • Water flooding simulations through regular single and random multi-pore structures. • Effect of capillary number, contact angle and viscosity ratio on the mobility of flow. Abstract In this paper we quantify the effect of capillary number (Ca) , contact angle (θ) and viscosity ratio (M) on the mobility of multiphase flow through porous media. The focus is mainly on oil-water flows through porous rocks observed during the water flooding process. Simulations are performed using a finite volume method employing a staggered grid formulation. Interactions between fluids and complex solid boundaries are resolved by a direct forcing, implicit and sharp interface immersed boundary method (IBM). The fluid-fluid interface is tracked by a mass conservative sharp interface volume of fluid (VOF) method. IBM and VOF are coupled by imposing the contact angle as a boundary condition at the three phase contact line. Our methodology has been verified/validated for several test cases including multiphase Poiseuille flow in a channel, a viscous finger in a channel and mesh convergence of the contact force. Two types of porous structures are considered: (i) a repeated single pore and (ii) a random multi-pore arrangement. Temporal evolution of phase pressure difference and oil saturation have been studied as viscous fingers penetrate the pores. We observed that the residual oil saturation for different capillary numbers shows exactly the opposite trend for the single and multi pore arrangement. The residual oil saturation for multi-pore shows a well defined linear trend with log Ca , θ and log M. [ABSTRACT FROM AUTHOR]

Highlights • Mass transfer rates of hexadecane and oxygen were close to the stoichiometric. • Damköhler numbers suggested an enhancement of hexadecane mass transport. • Production of an oil-degrading consortium was enhanced with mass transfer. Abstract The production of oil-degrading bacteria in multiphase airlift reactors (ALBs) could be limited by the mass transport of both the gaseous and oil phases. In our study, the mass transfer rates of hexadecane and oxygen (HTR/OTR) were evaluated during the production of oil-degrading bacteria in a 3-L airlift reactor. To improve the HTR/OTR ratios during kinetics, a high initial concentration of hexadecane (77 g L−1) and constant superficial gas velocity (U G) in the range of 1.5–3.5 cm s−1 were used. Under these conditions, all initial HTR/OTR were close to the stoichiometric consumption ratio (SCR, ∼0.28), which in turn decreased at the end of the culture until 0.173 ± 0.013, 0.108 ± 0.006 and 0.123 ± 0.006 (g HXD) (g O 2)−1 for U G of 1.5, 2.5, 3.5 cm s−1, respectively. The evaluation of the Damköhler numbers suggested an enhancement of HXD mass transport that allowed for obtaining a maximum suspended solids (SS) production of 4.9–6.0 g SS (L h)−1. Since the operation of the ALB at high superficial gas velocities may lead to high power inputs, the variable U G technique was used for energy saving, finding similar maximum SS production (6.09 g SS (L h)−1) to that obtained at a constant U G of 2.5 cm s−1 and an energy saving of 33.4%. The improvement in the HTR/OTR ratio during ALB performance allowed us to enhance the production of an oil-degrading microbial consortium. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Dynamic coupling of two-fluid model and discrete particle model was achieved. • Hybrid discrete-continuum method was developed for gas-solid flow. • An inter-mapping method between discrete and continuum variables was proposed. • The inter-mapping method considers the effects of sub-grid mesoscale structures. • Hybrid multiscale method was nearly as accurate as discrete particle method. Abstract Multiscale methods have recently underpinned the successful simulation of gas-solid flow. In our prior study (Chen and Wang, AIChE Journal, 2017, 63: 3681–3691), a dynamic multiscale method (DMM) has been proposed to concurrently couple different simulation models in different simulation domains where discrete particle model (DPM) is used in the near wall regions and the rest of simulation domain is solved by two-fluid model (TFM). In this study, a mesoscale-structure-based mapping method was further proposed and implemented into the framework of DMM. The recently developed EMMS-based particle velocity distribution function (Wang et al., AIChE Journal, 2016, 62: 2649–2657), which was derived by assuming that there is a two-phase structure in a computational grid, was used for mapping between different models. In addition, the stability condition of the EMMS model was undertaken to locate the newly inserted particles during the boundary mapping process from the TFM to the DPM. The simulation results of gas-solid flow in a riser containing Geldart B particles using the proposed DMM have compared with those of using the full TFM and full DPM, which verifies its fidelities. [ABSTRACT FROM AUTHOR]

Highlights • Breakup rate model development using recent advances in theory of turbulence. • Validation of breakup rates with direct measurements. • Unique data for transition between the inertial and the viscous scale of turbulence. • Improved kernel prediction capabilities toward dissipation subrange. Abstract In this study, the role of turbulence on the formulation of breakup kernels for fluid particles in dispersed multiphase flows is demonstrated. Two pieces of information for model derivations including the turbulent energy spectrum and the second-order structure function are chosen as the main candidates to extend the models for the entire turbulent spectrum, contrary to the original expressions that are limited for the inertial subrange. Further, a two-step validation procedure is proposed to incorporate the effect of turbulence for model validations, that is, the original and the extended models are compared and validated against two sets of experimental data for breakup rates. The first set covers the inertial subrange, while the second set is a dataset that includes direct measurements toward the dissipation subrange of turbulence. The results show that the predictive abilities of breakup kernels can be enhanced by the model extension, when the droplet diameters are outside the inertial subrange of turbulence. This work, thus, answers how the entire spectrum of turbulence can improve the breakup kernels and proposes a validation method to include the effect of turbulence for the validation of breakup kernels. [ABSTRACT FROM AUTHOR]

Highlights • Non-invasive radioactive particle tracking technique was utilized. • Visualization of the hydrodynamics in airlift reactor was performed. • 3D Liquid velocity and turbulence kinetic energy were quantified. • Scenedesmus green microalgae was cultured. • Benchmark data for CFD validation was obtained. Abstract In this study, an advanced radioactive particle tracking (RPT) technique was used to investigate for the first time the details of the cells’ movements (trajectory) and multiphase flow hydrodynamics during microalgae culturing in a cylindrical split airlift photobioreactor. The cells’ trajectory, liquid velocity field, distributions of shear stresses, and the turbulent kinetic energy field were studied under superficial gas velocity of 1 and 3 cm/s. The structures of the flow in the whole reactor, the riser, the downcomer, as well as the structure above and below the split plate were characterized. The effects of the cells’ concentration and different aeration rate at different axial levels on the studied parameters were discussed. It has been found that the cells’ fluctuations reduced and its movement frequency between the light (wall) and dark zone decreased during the culturing particularly when the cells concentrations becomes large after 30 days of culturing. Distinguishing behaviors were observed for all the parameters, with a higher magnitude at the superficial gas velocity 3 cm/sec than at 1 cm/sec. This effect positively enhanced the liquid circulation and the movement between the reactor sides, the riser, and the downcomer. This circulation and good mixing phenomena had a large positive impact on the culture’s continuity. The obtained results are reliable as benchmark data to validate computational fluid dynamics (CFD) simulation and other models that can be later used to be integrated with dynamic growth and light intensity models for optimized. [ABSTRACT FROM AUTHOR]

It has been demonstrated that interstitial fluid (IF) flow can play a crucial role in tumor cell progression. In the seminal works by Swartz and collaborators (Fleury et al., 2006; Shields et al., 2007) it was discovered that due to this flow, chemokine ligands secreted by tumor cells selectively tend to bind to receptors (CCR7) on the downstream side of the cells that in turn stimulate cells to migrate in the direction of the flow. This migration process was denoted as autologous chemotaxis. Previous mathematical modeling of autologous chemotaxis apparently has been restricted to single-phase considerations. The purpose of this work is to explore how a multiphase approach can be used where the fluid and cancer cells are treated as two separate phases with their own momentum balance equations. A mathematical model is derived that sheds light on essential nonlinear coupling mechanisms and interactions that are involved. The role played by fluid-ECM (friction type of term) and cell-ECM interaction forces (adhesion forces) are demonstrated. In particular, a fluid generated stress term in the mathematical expression for the cell velocity is highlighted. This term reflects how the flowing fluid will try to push the cancer cells in the downstream direction whose effect must be counterbalanced by the cancer cells by creating a sufficiently strong cell-ECM resistance force. Moreover, in order to represent the autologous chemotaxis migration mechanism we include (i) a component to represent stagnant ECM concentration (collagen); (ii) a chemical component representing chemokine that can convect with the fluid; and (iii) a third chemical component to represent protease secreted by the cancer cells which is able to release ECM-bound chemokine through proteolytic activity. The resulting model allows us to demonstrate how the autologous chemotaxis transport mechanism is governed by formation of chemokine concentration gradients that are asymmetric and skewed in the flow direction. We test the model behavior for a flow system with an external imposed pressure gradient which is comparable with the laboratory experiments by Swartz and collaborators. Sensitivity to changes in circumstances like blocking of the CCR7 receptor needed for autologous chemotaxis and elimination of the pressure driven IF flow (i.e., no flow) are explored and discussed. We also illustrate the model behavior in an envisioned tumor setting where increased IF flow is produced from leaky blood vessels that sit on the inside of the tumor. An increased fluid flow towards the region on the outside of the tumor is then generated where it is adsorbed by lymphatic vessels and gives rise to a characteristic elevated IF pressure profile that decreases at the tumor periphery. In turn, this results in an autologous chemotactic driven migration of cancer cells at the rim of the tumor. The simulation illustrates how the autologous chemotactic cell migration mechanism discovered by Swartz and collaborators possibly can be used as a means for metastasis by generating aggressive cell migration towards lymphatic vessels. [ABSTRACT FROM AUTHOR]

Networks of microdevices can be used to form, sort, split and recombine droplets by varying the fluidic resistance of the channels. To facilitate design of such systems we propose two models to calculate pressure drop of liquid-liquid slug flow in square microchannels. By approximating a droplet surrounded by liquid film as annular flow, the moving film model includes the velocity profile in the lubricating layer. In the no-film model, the presence of liquid film is neglected. Pressure drop measurements of water-toluene and water-silicone oil slug flow generated in glass/silicon devices of 200 and 400  μ m width serve to validate these two models. We found that the droplet viscosity influences the applicability of the models. Good agreement is obtained for water-toluene slug flow, with the average error of 15–20% between the measured and calculated values for both models, proving that the presence of the lubricating film may be neglected for flows with similar viscosities of both phases. On the contrary, both predictions agree poorly with experiments for silicon oil-water flow which we attribute to the lower than expected liquid film thickness around the silicon oil droplets. Therefore we use the moving film model to estimate the thickness of the lubricating layer which we find to lie between 0.5% and 0.75% of the channel width, lower than the assumed 2%. Finally we compare the performance of our models against two correlations adapted from literature. We thus demonstrate that our approach allows reliable pressure drop prediction for liquids with similar viscosities and delivers important information on flow hydrodynamics. [ABSTRACT FROM AUTHOR]

A robust approach to access liquid residence time distribution (RTD) adapted to multiphase flow in porous media is presented. It is tailored to meet specific requirements of small scale systems (centimeter, millimeter or less) with Taylor segmented flow feed. The method involves direct visualization using fluorescence microscopy close to both extremities of a porous packing. Critical image treatment steps and optimization of a versatile discrete model with 4 parameters are detailed and discussed. They allow the precise and rapid determination of RTD curves and their 1st- and 2nd-order moments. The application of the method is successfully illustrated with dense micro-packed beds of sub-millimeter particles and highly porous media like open cell solid foams undergoing a preformed G-L segmented (Taylor) flow. Original results regarding the effect of fluid flowrates and different confined porous media are discussed and lead to a single two-parameter liquid hold up correlation, which is valid for both packings. As usual, RTD broadening is treated as a combination of convective dispersion and mass transfer to a fraction of immobile liquid. The predominant role of mass transfer is underlined with an analysis of characteristic times. [ABSTRACT FROM AUTHOR]

We present simulations showing the particulate flows passing through a single membrane pore under a dead-end and constant-pressure condition. We investigate the effects of the rolling friction acting on particles and the particle concentration on the pore clogging phenomena. A decrease in the rolling friction coefficient of particles shifts the clogging position toward the permeate side and decelerates the permeating flux decline. This effect of the rolling friction coefficient decreases with increasing particle concentration. Furthermore, we simulate the permeation of two-component suspensions, which include two types of particles with large and small rolling friction coefficients. The small number of particles with a large friction coefficient drastically accelerate the pore clogging because they first deposit near the pore entrance and trap subsequent particles. This result indicates that particles that are less accumulated on the membrane under a single-component condition may be primary foulants in a multicomponent system. [ABSTRACT FROM AUTHOR]

Improper sizing of pipelines and production tubings in the petroleum industry is often caused by lack of understanding of three-phase flow, which is characterized by gas flowing together with an immiscible water-oil mixture. There is the presence of a continuous liquid phase and a liquid dispersed phase, as observed in liquid-liquid flows, i.e., one can observe either a dispersion or emulsion of oil in water (o/w) or dispersion or emulsion of water in oil (w/o). The transition from o/w to w/o, or the other way around, is defined as phase-inversion. This phenomenon is characterized by a sharp increase in the pressure gradient, leading to significant pressure loss in the oil production system. The goal is to investigate the effects of oil viscosity, channel geometry (circular pipe or annular duct) and superficial gas velocity on the phenomenon of phase inversion in vertical liquid-liquid-gas flows, using oil with three different viscosities (ranging from 70 mPa s to 280 mPa s), tap water and compressed air as working fluids. The experiments were carried out in three different geometries: (i) glass pipe of 50 mm i.d., (ii) glass pipe of 95 mm i.d. and (iii) concentric annular duct with 95 mm of hydraulic diameter (glass outer pipe and PVC internal pipe). The experiments were performed under equivalent Reynolds number to evaluate the geometry effect. New data as total pressure gradient and volumetric fractions were obtained for all geometries. The results suggest that the extrapolation of results obtained in circular pipes with low viscosity oil and low gas flow rates to annular-duct flow with viscous oils and high gas flow rates can lead to significant errors. [ABSTRACT FROM AUTHOR]

We present a novel recurrence CFD (rCFD) method for the efficient simulation of passive scalar transport in pseudo-periodic flows. rCFD transfers full CFD(-DEM) simulations into a purely Lagrangian description of scalar transport by evaluating trajectories of fluid tracers and discrete particles. These trajectories are subsequently converted into cell to cell shift operations, resulting in data shift pattern on a computational grid. Finally, a recurrence process, based on the statistics of the full CFD(-DEM) simulation, controls the sequence of consecutive frames of data shift patterns. First, we applied rCFD to species transport in single-phase large eddy simulations, yielding excellent agreement with corresponding full CFD simulations. Second, we addressed heat transfer in a bubbling fluidized bed, yielding acceptable agreement with corresponding CFD-DEM simulations. In both cases, simulation times were reduced by more than four orders of magnitude without losing spatial resolution, resulting in faster than real-time simulations. Subsequently, we discuss existing model limitations such as (i) process periodicity, (ii) passiveness of transport, (iii) data storage requirements and (iv) physical diffusion and sketch possible future remedies. Concluding, we consider rCFD a promising bridging technology between full CFD simulations and online process prediction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Direct numerical simulation of bubbly flows and interfacial species transport. • Investigation of the effects of bubble-induced turbulence on the bubble dynamics. • Understanding the mechanism of interfacial species transport. • Analysis of the power spectra in the flow and species concentration fields. A direct numerical simulation (DNS) study is carried out to understand the effects of bubble-induced turbulence on the interfacial species transport. A volume-of-fluid (VOF) method is used in the DNS to simulate the multiphase flow in a box containing one or two deformable bubbles. The bubbly flows with Schmidt numbers 1 ≤ S c ≤ 64 , Reynolds numbers 100 ≤ Re B ≤ 750 , Eötvös number Eo = 1.21 and gas volume fractions 2.8 % ≤ α g ≤ 22.1 % have been investigated. The DNS results indicate that the one-dimensional energy spectra evolve as the power −3 of the wavenumber at large scales. At a high Schmidt number, an inertial subrange characterized by the - 5 / 3 slope can be found in the power spectra of species concentration. The power spectra of species concentration for different Schmidt numbers become close to each other when the wavenumber is scaled with Sc 0.5. The bubble-induced turbulence enhances the oscillation of the transient Sherwood number, however, it has marginal effects on the time-averaged value. By contrast, the time-averaged Sherwood number for a fixed Peclet number increases with an increase of α g , indicating that convection plays a more important role in species transport when the bubbles are more densely populated. A possible reason is that, the neighboring bubbles enhance the spatial fluctuations of the velocity, which favor the interfacial species transfer. The energy spectrum confirms that an increase of α g leads to stronger spatial fluctuations of the vertical velocity component at low wavenumbers. [ABSTRACT FROM AUTHOR]