Two-phase Flow Dynamics Research Articles

Examining the interfacial behavior of non-Newtonian gas-liquid two-phase flow in horizontal square microchannels

This study investigates the flow dynamics of a non-Newtonian two-phase flow within a horizontal square microchannel. The experimental apparatus employed an acrylic channel with a side length of 8 × 10−4 m. Nitrogen served as the test gas, and the test liquids consisted of water and CMC (Carboxymethylcellulose) aqueous solutions at concentrations of 0.2 and 0.4 %wt. The superficial velocity of working gas and liquids spanned ranges of 0.26–20 m/s and 0.05–1.0 m/s, respectively. A differential pressure transducer was used to measure pressure gradients, while a high-speed video camera captured the flow behavior for analysis with a custom image processing technique. Nonlinear regression statistical analysis was applied to establish the criteria for flow pattern transition. Furthermore, signal processing techniques such as PSD (Power Spectral Density), DWT (Discrete Wavelet Transform), ANN (Artificial Neural Network), and Kolmogorov entropy were employed to analyze the flow behavior based on the pressure gradient signals from the differential pressure transducers. Our findings reveal the occurrence of bubbly, slug, slug-annular, and churn flow patterns. The nonlinear regression statistical analysis offered ambiguous results for determining flow pattern transitions. However, an empirical coefficient was obtained for the nondimensional liquid height. Moreover, the empirical nondimensional liquid height aligned well with the experimental values. The PSD and DWT analysis corroborated each other in clearly characterizing the flow pattern based on pressure gradient fluctuation and wavelet energy. The Kolmogorov entropy effectively captured the chaotic flow pattern. Furthermore, the ANN analysis demonstrated a solid agreement between the predicted and actual flow patterns.

Numerical investigation of two-phase flow patterns and carbon deposition in a coaxial-type reactor for molten salt electrolysis

The electrodeposition process of carbon in molten lithium carbonate electrolysis and the associated gas-liquid flow hydrodynamics characteristics are for the first time investigated using computational fluid dynamics (CFD). The high-temperature (750 °C) process is challenging for conducting measurements, making CFD a valuable tool for providing insights into the novel coaxial-type cell design. The CFD simulation addresses the electric field distribution, oxygen gas evolution, and electrodeposition of carbon. The effect of gas bubble sizes (1, 0.8, and 0.6 mm) on the electrolysis process was examined at different electrical current densities (0.15 ± 0.01 A cm–2). The CFD results reveal that gas holdup increases by decreasing the bubble size and that the bubble size significantly impacts the current density distribution by affecting the two-phase flow dynamics. The study highlights the potential of CFD for optimization of molten salt processes, while also suggesting the need for further improvements in the model.

МАТЕМАТИЧЕСКОЕ ОПИСАНИЕ ДИНАМИКИ ЦЕНТРОБЕЖНОГО ДВУХФАЗНОГО ПОТОКА В ПОМОЛЬНОЙ КАМЕРЕ ДЕЗИНТЕГРАТОРА

Rational control of equipment operating modes in the production of building materials is possible only in the case of a mathematical description of various technological processes. The sequence of calculation methods for determining the design and technological parameters of grinding equipment makes it possible to numerically present the results of calculations of rational operating modes of the equipment. The study presents a mathematical description of the dynamics of a two-phase flow inside the grinding chamber of a disintegrator, with the help of which it is possible to determine the speed characteristics of its operating modes for materials with different physical and mechanical properties. The nature of the change in the tangential components of the velocities of the two-phase flow has been established: the range of the current radius of the grinding chamber Ri has been determined, at which the radial components of the velocities of the carrier flow and particles of the ground material continue to increase. As a result of mathematical modeling, it was confirmed that with an increase in the concentration of dust particles in the increasing volume of the grinding chamber, the value of the tangential component of the velocity of a dynamic two-phase flow decreases in relation to the maximum parameters at Ri = 0.15 m by an average of 15.5%. It has been determined that the maximum velocity values for the tangential component are in the limit of Ri = 0.1-0.15 m and are 131 m/s for air, and 127.5 m/s for an average suspended particle with dsr = 40 μm. In the process of developing a mathematical description, it was established that in the range Ri = 0.15 - 0.3 m the increase in the radial components of the velocities of the air carrier medium and the weighted average particle flow is about 14.5%, which, in turn, indicates an increase in the kinetic energy of the crushed particles during the movement of a dynamic two-phase flow from the center to the periphery of the grinding chamber of the disintegrator.

Two-phase flow dynamics study in the trapezoidal gas channel of PEM fuel cell based on lattice Boltzmann model

ABSTRACT Water management is a critical challenge in ensuring the performance and durability of low-temperature proton exchange membrane fuel cells (PEMFCs). This study utilizes the phase-field lattice Boltzmann method to conduct three-dimensional numerical simulations, investigating the dynamics of two-phase flow in the cathode gas channel (GC) of PEMFC with a trapezoidal cross-section. The effects of the water inlet location, the surface wettability of GC, the open angle of GC, and the air velocity on liquid water distribution and discharge are analyzed. The results indicate that positioning the water inlet in the middle of the GC significantly enhances PEMFC performance while having minimal impact on average pressure drop. A wall contact angle of 70° or 110°Can optimize fuel cell performance from different directions. Setting a wall contact angle at 70° optimizes gas flow stability and maintains a low-pressure drop value for the GC. A wall contact angle of 110° focuses on optimizing gas reactant diffusion ability into porous electrodes and GC drainage rate. An opening angle of 55° for the trapezoidal gas channel improves overall fuel cell performance. Increasing air velocity facilitates the film flow formation of liquid water on top wall surfaces within the GC.

Computational analysis of radon progeny deposition patterns in the human respiratory system

In the last year, the use of computational fluid dynamics (CFD) techniques has gained prominence as a powerful tool for modeling biological phenomena and influencing the design of biomedical devices. In this study, we utilized a computational fluid dynamics (CFD) model to simulate airflow and the deposition of aerosol particles within the human respiratory tract. To achieve this, we meticulously constructed a 3D model of the human tracheobronchial airways using SolidWorks software. Our computational analyses encompassed a range of breathing conditions, ranging from 15 to 60 (L/min). Through the application of discrete phase modeling (DPM), we investigate the behavior of two-phase flow dynamics. Our focus lies in the examination of aerosol particles, with diameters ranging from 1 to 10 (μm), in order to evaluate the influence of aerosol particle size on deposition rates. Our findings encompass velocity contour maps, deposition rates of aerosol particles, and insights into the process of aerosol particle entrapment at various locations within the respiratory tract. Our study reveals a direct correlation between higher inhalation rates and larger aerosol particle sizes, resulting in increased deposition rates. Additionally, we observe a heightened deposition of aerosol-particles at bronchi region. These computational results hold significant value in estimating the distribution of doses resulting from radon progeny exposure in distinct anatomical regions of the respiratory tract.

Numerical Simulation of the Two-Phase Flow Dynamics in an Alkaline Water Electrolyzer Considering Difference in Bubble Diameter

For more efficient hydrogen production, predicting the characteristics of bubble flow inside a water electrolyzer is critical since bubbles affect ion transport, and electrode coverage by bubbles influence overpotentials and the entire electrolysis performance. Transport of bubble significantly depends on its size. In this study, a CFD model of an alkaline water electrolyzer which considers difference in sizes of generated bubbles was developed. The model treats bubbles of different sizes as different gas phases, which are independent of each other. The total bubble mass source for a given current density is divided into phases of each bubble size according to experimental visualizations. Drag, virtual mass, lift, wall lubrication, and turbulent dispersion forces are considered as interaction between gas and liquid phase.The following three sizes of bubbles were considered: diameters d = 36 μm (small), 75 μm (medium), and 208 μm (large). The entire calculation domain represents the anode side of a zero-gap monopolar alkaline water electrolyzer. Figure 1 shows the volume fraction fields of the three gas phases (i.e., bubble sizes) at a constant current density of 0.6 A/cm2. The bubbles are generated on the electrode surface at the z=0 plane. As the liquid phase forms a circulating flow inside the electrolyzer, small bubbles are transported along the circulating downstream flow due to smaller buoyancy force compared to their viscous drag. In contrast, large bubbles flow out directly to the upper outlet because buoyancy force dominates. This result points out the need to consider the difference in bubble diameter for designing flow field inside alkaline water electrolyzer.[Acknowledgements]This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).Fig. 1. Total gas phase volume fraction field obtained from the sum of the volume fraction field for each size bubble, and its experimental visualization. Figure 1

Three-dimensional simulation of green soybean infrared-assisted spouted bed drying.

The current study introduces a novel infrared-assisted spouted bed drying technique for the dehydration of green soybeans, which aims to enhance the drying quality and efficiency. The investigation involves an examination of the flow pattern in the spouted bed to obtain relevant data, followed by an optimization of the entire drying process. The drying process of green soybeans was simulated using SolidWorks and ANSYS Fluent software, based on the principles of computational fluid dynamics. The simulation test results showed that the simulation outcomes were consistent with the experimental data. The optimal conditions for the process of green soybean infrared-assisted spouted bed drying were found to be an inlet speed of 8 m/s and a temperature of 50 °C with the wavelength and power settings of the infrared board at 10 μm and 500 W, respectively. The simulation method selected in this article, based on gas-solid two-phase flow dynamics, is feasible for green soybean infrared-assisted spouted bed drying process. © 2023 Society of Chemical Industry.

Analytic prediction of the effective reaction rate for methane cracking in molten catalysts: Transition from kinetics-dominated to diffusion-limited regimes

Molten catalytic media are increasingly attracting interest as a suitable reaction environment where cracking of hydrocarbons and separation of the solid carbon product can be achieved simultaneously, ideally avoiding catalyst regeneration. In conditions relevant to industrial production, multiscale approaches are needed to predict the reactor performance, where the macroscopic dynamics of two-phase flow is combined with the evolution of the reaction inside individual bubbles. We here develop a thermodynamically-consistent, analytically solvable model for predicting the effective reaction rate resulting from the interplay between diffusive transport within the bubble and the surface reaction at the gas/liquid interface. The analytical solution is based on a spectral (eigenvalue/eigenfunction) expansion of the concentration profiles. We show how in practically affordable conditions, the effective characteristic time of the reaction can be estimated based only on the dominant eigenvalue of the diffusion-reaction problem. The closed-form knowledge of the dominant eigenvalue provides key insight in establishing the range of existence of diffusion-limited, mixed, and kinetics-controlled regimes. Based on the limiting solutions of the model, an approximate model for the conversion, yielding the explicit dependence of conversion on the equilibrium, kinetics and transport parameters is derived. The approach proposed is validated by comparing its predictions with the solution of the fully-coupled mass/momentum local balance equations obtained through a finite-element commercial solver enforced on a moving boundary domain to account for the bubble expansion due to the increasing number of moles in the gas phase.

Influence and Optimization of Gas Diffusion Layer Porosity Distribution along the Flow Direction on the Performance of Proton Exchange Membrane Fuel Cells

Influence and Optimization of Gas Diffusion Layer Porosity Distribution along the Flow Direction on the Performance of Proton Exchange Membrane Fuel Cells

Foreword: Selected papers from the 12th Japan-U.S. Seminar on Two-Phase Flow Dynamics

Foreword: Selected papers from the 12th Japan-U.S. Seminar on Two-Phase Flow Dynamics

A mixed primary atomization model with quantification of aerodynamic, turbulence and cavitation effects

Spray atomization has a key impact on the combustion and emission performances of the engines. It involves a highly dynamic two-phase flow process consisting of two distinct stages: primary and secondary breakup. Due to their distinct physical characteristics, it is essential to model these processes separately using different numerical approaches within the spray breakup model. This study focuses on investigating the collective influence of aerodynamic force, cavitation, and turbulent fluctuations on primary breakup. To enhance the accuracy of spray simulations, a mixed primary atomization (MPA) model is proposed by integrating the Wu-Faeth theory along with the classical KH-RT model and the Sarre cavitation model. By comparing simulation results of both macroscopic and microscopic spray characteristics with experimental data under various conditions, the efficacy of the developed MPA model is validated. The sensitivity analyses of specific model parameters and the examination of the contribution ratios of different sub-models under various conditions enhance our understanding of the model calibration. Additionally, considering the complexity of near-nozzle sprays influenced by turbulent flows, cavitation, and interactions with the surrounding gas, a comparative analysis of the classical KH-RT model and the MPA model is conducted based on simulation results, specifically focusing on near-nozzle spray characteristics.

Validation of HiG-Flow Software for Simulating Two-Phase Flows with a 3D Geometric Volume of Fluid Algorithm

This study reports the development of a numerical method to simulate two-phase flows of Newtonian fluids that are incompressible, immiscible, and isothermal. The interface in the simulation is located and reconstructed using the geometric volume of fluid (VOF) method. The implementation of the piecewise-linear interface calculation (PLIC) scheme of the VOF method is performed to solve the three-dimensional (3D) interface transport during the dynamics of two-phase flows. In this method, the interface is approximated by a line segment in each interfacial cell. The balance of forces at the interface is accounted for using the continuum interfacial force (CSF) model. To solve the Navier–Stokes equations, meshless finite difference schemes from the HiG-Flow computational fluid dynamics software are employed. The 3D PLIC-VOF HiG-Flow algorithm is used to simulate several benchmark two-phase flows for the purpose of validating the numerical implementation. First, the performance of the PLIC implementation is evaluated by conducting two standard advection numerical tests: the 3D shearing flow test and the 3D deforming field test. Good agreement is obtained for the 3D interface shape using both the 3D PLIC-VOF HiG-Flow algorithm and those found in the scientific literature, specifically, the piecewise-constant flux surface calculation, the volume of fluid method implemented in OpenFOAM, and the high-order finite-element software FEEL. In addition, the absolute error of the volume tracking advection calculation obtained by our 3D PLIC-VOF HiG-Flow algorithm is found to be smaller than the one found in the scientific literature for both the 3D shearing and 3D deforming flow tests. The volume fraction conservation absolute errors obtained using our algorithm are 4.48×10−5 and 9.41×10−6 for both shearing and deforming flow tests, respectively, being two orders lower than the results presented in the scientific literature at the same level of mesh refinement. Lastly, the 3D bubble rising problem is simulated for different fluid densities (ρ1/ρ2=10 and ρ1/ρ2=1000) and viscosity ratios (μ1/μ2=10 and μ1/μ2=100). Again, good agreement is obtained for the 3D interface shape using both the newly implemented algorithm and OpenFOAM, DROPS, and NaSt3D software. The 3D PLIC-VOF HiG-Flow algorithm predicted a stable ellipsoidal droplet shape for ρ1/ρ2=10 and μ1/μ2=10, and a stable cap shape for ρ1/ρ2=1000 and μ1/μ2=100. The bubble’s rise velocity and evolution of the bubble’s center of mass are also computed with the 3D PLIC-VOF HiG-Flow algorithm and found to be in agreement with those software. The rise velocity of the droplet for both the ellipsoidal and cap flow regime’s is found, in the initial stages of the simulation, to gradually increase from its initial value of zero to a maximum magnitude; then, the steady-state velocity of the droplet decreases, being more accentuated for the cap regime.

Measurements of gas-liquid two-phase flow dynamics using high-speed neutron imaging

Gas-liquid two-phase flow appears in many heat-exchanging devices. The two-phase flow dynamics should be clarified to understand the phenomena in such devices. Although many measurement techniques have been applied to two-phase flow experiments, measuring the gas-liquid interfacial structure is difficult, which changes temporally and spatially. In this study, high-speed neutron imaging is used to measure two-phase flow dynamics, and the accuracy of the void fraction measurement is investigated. In high-speed neutron imaging, image blurring and distortion occur due to light and object motion intensifying. As a result, the quantitative accuracy might decrease. So, the rotating stainless-steel calibration disk, which simulates the bubble behavior in water, is observed by high-speed neutron imaging. Several noise reduction filters are tested to remove the blur and noise in the acquired images. Finally, the air-water two-phase flow is visualized by high-speed neutron imaging, and noise filtering is applied.

Modeling, Feedforward Control, and Constrained Trajectory Generation for a Concrete Conveyance System

Abstract Automated fabrication of concrete elements requires precise control of outgoing volume flow. Since measurements of the volume flow or the total extruded volume are challenging during production, a feedforward control is required, which in turn necessitates a model of the dynamics at hand. In this paper, a concrete conveyance system with two pumps is considered. These are mounted at the inlet and outlet of the hose, respectively. Based on previous work, a dynamical model with concentrated parameters is derived, which is motivated on the general distributed dynamics of two-phase flow. The model is validated by experiments, with parameters calculated by a tailored estimation approach. Based thereon, a feedforward control approach is presented and tested in simulation, exploiting the approximate flatness of the system. The flat parametrization is then used for constrained, smooth setpoint transition of the volume flow with minimal transition time.

Effect of thermal capacitance on microchannel heat sink response to pressure drop oscillations

The efficient heat transfer resulting from flow boiling in microchannel heat sinks can help dissipate high heat fluxes from high-density electronic devices across a small temperature difference. However, practical implementation challenges unique to two-phase flow boiling, as compared to single-phase liquid cooling, have prevented its widespread adoption. A primary challenge is the occurrence of dynamic two-phase flow instabilities, such as pressure drop oscillations (PDO), that have the potential to degrade heat transfer performance or trigger premature critical heat flux (CHF) under some conditions. Under other conditions, PDOs are observed to have little to no impact on performance. One factor proposed by modeling studies to be responsible for this discrepancy in observations of the effect of dynamic instabilities on performance is the thermal capacitance of the heat sink, though this has not been confirmed by experiments. In this study, the effect of thermal capacitance on the transient thermal response of a heat sink experiencing PDOs is examined through use of a dynamic two-phase flow model and experiments. Flow boiling experiments are performed with a controlled compressible volume upstream of parallel-microchannel heat sinks having either a large or a small thermal capacitance. In accordance with the behavior predicted by our model, when thermal capacitance is reduced, the pressure drop oscillation frequency is found to decrease and temperature swings in the heat sink become more severe. Additionally, the experimentally measured CHF limit is diminished in the heat sink at smaller thermal capacitance. These results reveal thermal capacitance as a critical parameter that determines how much dynamic instabilities degrade flow boiling performance in a microchannel heat sink.

Effects of macro-scale heterogeneity on the kinetic interface-sensitive tracer test for measuring the fluid–fluid interfacial area in dynamic two-phase flow in porous media

A novel reactive smart tracer method, termed the kinetic interface-sensitive (KIS) tracer test, has been demonstrated in laboratory column experiments to enable measurement of the specific capillary-associated fluid–fluid interfacial area in dynamic two-phase flow displacement processes in porous media. Development of the tracer method towards effective application in real field conditions requires investigation of the influence of the porous media heterogeneity on the front size and the specific interfacial area, and, consequently, in how far a kinetic interface-sensitive tracer experiment, and the corresponding breakthrough curves, are affected. This study employs a two-dimensional Darcy-scale two-phase flow reactive transport model to investigate numerically the KIS tracer transport in heterogeneous porous media. Simulations were carried out for the primary drainage process in a domain formed of fine and coarse porous media. Various heterogeneity patterns, having different numbers of inclusions and different geometrical distributions, were studied. It is shown that the shape of the breakthrough curves can be used as an indicator for quantifying the displacement front roughness, the specific interfacial area in the domain, and the domain heterogeneity, e.g., the existence of preferential flow pathways inside the porous media. The results indicate that when the displacement front roughness is small, the concentration breakthrough curves exhibit a linear increase. The slopes of the breakthrough curves linearly depend on the fraction of the bulk volume occupied by the low-permeability sand inclusions. The volume-averaged specific interfacial area and the size of the transition zone can be determined from the slopes of the breakthrough curves.

Dynamic mode decomposition for analysing multi-phase flow in porous media

For multi-phase flow through multi-scale heterogeneous porous media, such as the pore space of rocks, the interaction between multiple immiscible fluids and an intricate network of pores, creates a wide range of dynamic flow phenomena. At larger scales i.e. scales relevant for practical applications such as carbon sequestration, this interplay of dynamic phenomena is often referred to as “complexity”. However, it is important to describe the persistent features of the flow in an adequate manner, to represent the “complexity” of the system. Dynamic Mode Decomposition (DMD) is a dimensionality reduction algorithm that computes a set of modes associated with fixed oscillatory behaviours. In this work, saturation data extracted from dynamic two-phase flow experiments are analysed with DMD. We show that DMD can reproduce the data. Furthermore, not all dynamic modes are required to reproduce key dynamic features; this highlights the important spatial and temporal scales for flow. We show that DMD was able to identify localized regions important to flow. Overall, DMD is proven as a useful diagnostic tool for complex 4D flow dynamics for multi-phase flow.

Well-posedness of a Navier–Stokes–Cahn–Hilliard system for incompressible two-phase flows with surfactant

We investigate a diffuse-interface model that describes the dynamics of viscous incompressible two-phase flows with surfactant. The resulting system of partial differential equations consists of a sixth-order Cahn–Hilliard equation for the difference of local concentrations of the binary fluid mixture coupled with a fourth-order Cahn–Hilliard equation for the local concentration of the surfactant. The former has a smooth potential, while the latter has a singular potential. Both equations are coupled with a Navier–Stokes system for the (volume averaged) fluid velocity. The evolution system is endowed with suitable initial conditions, a no-slip boundary condition for the velocity field and homogeneous Neumann boundary conditions for the phase functions as well as for the chemical potentials. We first prove the existence of a global weak solution, which turns out to be unique in two dimensions. Stronger regularity assumptions on the initial data allow us to prove the existence of a unique global (respectively, local) strong solution in two (respectively, three) dimensions. In the two-dimensional case, we derive a continuous dependence estimate with respect to the norms controlled by the total energy. Moreover, we establish instantaneous regularization properties of global weak solutions for [Formula: see text]. In particular, we show that the surfactant concentration stays uniformly away from the pure states 0 and 1 after some positive time.

Impact of pressure drop oscillations and parallel channel instabilities on microchannel flow boiling and critical heat flux

Microchannel flow boiling heat sinks that leverage the highly efficient heat transfer mechanisms associated with phase change are a primary candidate for cooling next-generation electronics in electric vehicles. In order to design flow boiling heat sinks for such practical applications, one key obstacle is an understanding of the conditions for occurrence of dynamic two-phase flow instabilities, to which microscale flow boiling is particularly susceptible, as well as their impact on heat transfer performance. While mapping the operational regimes of these instabilities has been well-studied, with numerous stability criteria available, their impact on the heat transfer performance of heat sinks in practical applications is not understood. This work seeks to assess the impact of pressure drop oscillations and parallel channel instabilities on the surface temperature and critical heat flux in parallel microchannel heat sinks. This is achieved through measurement of time-averaged steady-state temperatures and pressures, combined with high-frequency pressure signals and high-speed flow visualization. These data are compared across three controlled flow configurations that comprise a condition of stable flow boiling, a condition where only parallel channel instabilities can occur, and a third where both pressure drop oscillations and parallel channel instabilities can occur. Experiments are performed using the dielectric refrigerant HFE-7100 in 2 cm long parallel microchannel heat sinks with square-cross-section channels (0.25, 0.5, 0.75, and 1 mm widths) at three mass fluxes (100, 400, and 1600 kg/m2s). Across this range of conditions, the time-averaged surface temperature and critical heat flux were remarkably insensitive to the occurrence of these instabilities despite the significant hydrodynamic events and transient flow patterns observed.

NOVEL MODEL FOR ESTIMATING GAS-SOLID TWO-PHASE FLOW RATE IN A HORIZONTAL PIPE

Dilute and dense conveying systems through pipelines are a common practice in our everyday life. It is used in many industries to convey a mixture of gas and solids from one location to another through pipes. Gas-solid transport is desirable in some industries but unwanted in others. Depending on the density, size, and shape, these solid particles may result in erosion and subsequent damage to piping and other equipment. Understanding the gas-solid two-phase flow dynamics can help develop efficient and cost-effective pipe transport systems, thereby mitigating the problems associated with the gas-solid two-phase flow. Models for estimating volumetric flow rates and other gas-solid two-phase flow properties are scarce as most are very complex, expensive, and unavailable proprietary commercial software. This study, therefore, developed a simple model using the general energy balance equation and relevant mixing theories for estimating the volumetric flow rate of natural gas-solid two-phase flow in horizontal pipes. The results from the model showed that the gas-solid flow rate is a function of pipe diameter, pressure drop, pipe length, solid volumetric concentration, solid-to-gas density ratio, and solid-to-gas friction factor ratio.