Multicomponent Flow Research Articles

Visualisation of [11C]CO2 storage in coal with positron emission tomography imaging

Positron Emission Tomography (PET) imaging has demonstrated its capability in providing real-time visualisation of fluids flow in geological materials. However, it has not been used for the study of CO2 injection and storage in coal for the application of CO2 geo-sequestration. To observe the processes directly, [11C]CO2 is the most optimal radiotracer, which is rarely used due to its short half-life (20.4 min) and handling safety issues as a gaseous tracer. In this work, a novel laboratory protocol is developed to use gaseous [11C]CO2 as the radiolabelled tracer to visualise and quantify dynamic processes of gas spreading, adsorption, diffusion, and advection flow in coal under in-situ conditions. The experimental setup integrates core flooding setup with PET scanning. Coal samples are pre-treated to mimic different injection conditions, including coal seam gas reservoirs in early production stage, gas depleted stage and CO2 storage stage. Due to high temporal resolution of PET imaging, time-lapse CO2 gas concentration map of each test is acquired by converting the PET intensity values to gas concentrations. Impacting factors on storage capacity and efficiency are also studied, including permeability, gas adsorption, gas exchange, and initial storage conditions. This work introduces a new laboratory protocol and analysing framework to quantify sub-core scale multiphysics CO2 flow in coal, which provides a foundation for future across-scale theoretical and experimental study of multiphase and multicomponent flow behaviours in coal for the application of CO2 geo-sequestration.

Pseudopotential-based multiple-relaxation-time lattice Boltzmann model for multicomponent and multiphase slip flow

Pseudopotential-based multiple-relaxation-time lattice Boltzmann model for multicomponent and multiphase slip flow

Nonlinear domain-decomposition preconditioning for robust and efficient field-scale simulation of subsurface flow

We discuss a nonlinear domain-decomposition preconditioning method for fully implicit simulations of multicomponent porous media flow based on the additive Schwarz preconditioned exact Newton method (ASPEN). The method efficiently accelerates nonlinear convergence by resolving unbalanced nonlinearities in a local stage and long-range interactions in a global stage. ASPEN can improve robustness and significantly reduce the number of global iterations compared with standard Newton, but extra work introduced in the local steps makes each global iteration more expensive. We discuss implementation aspects for the local and global stages. We show how the global-stage Jacobian can be transformed to the same form as the fully implicit system, so that one can use standard linear preconditioners and solvers. We compare the computational performance of ASPEN to standard Newton on a series of test cases, ranging from conceptual cases with simplified geometry or flow physics to cases representative of real assets. Our overall conclusion is that ASPEN is outperformed by Newton when this method works well and converges in a few iterations. On the other hand, ASPEN avoids time-step cuts and has significantly lower runtimes in time steps where Newton struggles. A good approach to computational speedup is therefore to adaptively switch between Newton and ASPEN throughout a simulation. A few examples of switching strategies are outlined.

DetonationFoam: An open-source solver for simulation of gaseous detonation based on OpenFOAM

Detonation has promising applications in advanced propulsion systems, and numerical simulation is widely used to gain insights into the complex interaction between the hydrodynamic flow and chemical reactions involved in detonation. In this work, detonationFoam, an open-source solver for accurate and efficient simulation of compressible reactive flow and detonation are developed based on OpenFOAM. detonationFoam can simulate compressible, multi-component, reactive flow and it can accurately evaluate the detailed transport coefficients using the mixture-averaged transport model. Compared to rhoCentralFoam, the improved HLLC-P approximate Riemann solver is used in detonationFoam and it helps to accurately resolve shock waves appearing in detonation. Besides, the adaptive mesh refinement and dynamic load balancing algorithms are used in detonationFoam, which greatly improves the computational efficiency. Validation tests including homogenous ignition, unsteady diffusion, shock tube problem, premixed flame, planar detonation, double Mach reflection, detonation cellular structure and oblique detonation wave are conducted. These tests demonstrate that detonationFoam can be used to accurately and efficiently to simulate the compressible, multi-component reactive flow and detonation processes. Program summaryProgram Title: detonationFoamCPC Library link to program files:https://doi.org/10.17632/x45zh4nz28.1Developer's repository link:https://github.com/JieSun-pku/detonationFoamLicensing provisions: GPLv3Programming language: C++Nature of problem: Gaseous detonation involves different length scales and complicated chemistry. To accurately and efficiently simulate the gaseous detonation, adaptive mesh refinement needs to be conducted and detailed chemistry should be considered. Besides, the severe load imbalance caused by the chemical source term evaluation may greatly reduce the computation efficiency.Solution method: An open-source solver, detonationFoam is developed based on OpenFOAM. The species equations considering detailed chemistry are solved in detonationFoam and thereby detonation in a compressible, multi-component, reactive flow can be simulated. The adaptive mesh refinement technique and the dynamic load balancing algorithm are incorporated into detonationFoam. It is demonstrated that detonationFoam can accurately and efficiently simulate gaseous detonation.

Microchannel reactors for Fischer-Tropsch synthesis: Experimental investigation and mathematical modeling

The Fischer-Tropsch synthesis is a significant technology for converting coal, natural gas, and biomass into synthetic fuels. In recent years, the use of microchannel reactors for the Fischer-Tropsch synthesis has attracted significant attention. Fischer-Tropsch synthesis experiments were carried out in a microchannel reactor and the influences of reaction conditions on the experimental results were investigated in this study. Based on the experimental data, a dynamic multi-component pseudo-homogeneous variable-volume flow model of microchannel reactors for the Fischer-Tropsch synthesis was built to determine the pressure-, velocity-, conversion- and (component-wise) concentration-distributions in reaction channels. The model takes into account the combined effects of gas volume expansion caused by the frictional pressure drop and gas volume contraction caused by reaction consumption. A novel effective method for calculating the pressure and superficial gas velocity values in microchannel reactors was proposed in the model. Besides that, two sets of experimental data were selected from references to evaluate the validity and accuracy of the model. The reaction performances in the microchannels were analyzed carefully based on the calculated results.

Experiments and modeling of fluidized bed steam-biomass char gasification with a red-mud oxygen carrier at particle scale for chemical looping

Chemical Looping Combustion (CLC) of biomass provides a low-cost way for CO2 negative emission. It creates complex multi-component flows including solids of oxygen carrier and fuel, and gasses of steam and/or CO2 as well as other gasification products. Experiments and modeling of steam-gasification of biomass char were investigated using a low-cost red mud as oxygen carrier materials. Effects of temperature, steam concentration, H2 inhibition on chemical reaction kinetics and mass transfer were experimentally investigated and modeled. A self-designed macro-TGA was used to detect its oxidization kinetics under isothermal conditions. The red mud oxygen carrier reduced inhibitory effect of H2 on carbon reaction, thus enhancing char conversion remarkably. With the neglect of the external mass limitation on char conversion, the reaction kinetics during reduction process was calculated by an experimentally-fitted function, expressing the char conversion. Pore structure evolution during the char conversion on kinetics was considered and its function was obtained based on the experimental results. The radial gas profiles under the bed of red mud particles by the solution of interparticle and external mass transfer coupled with the kinetics of char gasification were obtained, revealing the whole process of char conversion in CLC process. A semi-empirical kinetic model, including both of chemical and diffusion processes, provided a good insight of oxidation reaction kinetics, which was proven to be better than the classic models. The experimental data and modeling results got high agreement in both reduction and oxidation reactions.

Mass transfer of the multicomponent free jet and one numerical implementation on a graphic processing unit platform

Jet flows are ubiquitous in nature and laboratories. For example, helium and argon jets into ambient air are commonly used to produce atmospheric plasma jets. The jets before and after discharge both are typical multicomponent flows. This study reports on the implementation of a numerical solver based on the graphic processing units to model multicomponent mixture gas flows. To this end, two- and three-dimensional Jacobian matrices for the multicomponent Euler equations were obtained to reconstruct numerical fluxes and build a total variation diminishing scheme. The two-dimensional early-stage mass transfer of gas jets was studied for three mixture gases: He/air, Ar/air, and N2/air to numerically verify the steady functioning of the numerical solver despite the high mass fraction gradients. The mass fraction distribution of helium in ambient air exhibited more complex substructures than those of argon and nitrogen in ambient air. Using the watershed method, self-generated bullets were extracted from the mass fraction distributions of the helium jet. The proposed numerical solver implemented in this study is expected to provide a better understanding of gas jet dynamics, and the Jacobian matrices can provide a mathematical foundation for constructing potential higher schemes.

Modeling of the flow measurement system of multicomponent flows based on the method of differential pressure

The paper presents a generalized method for measuring the flow rate of multicomponent flows, which is based on a combination of the method of differential pressure and the principle of multichannelling of the invariance theory. The paper proposes a generalized structure of such an invariant system for measuring the flow rate of multicomponent flows and analytical expressions for the implementation of algorithms for measuring the flow rate of substances are obtained. The uncertainty of the measurement results of the flow rate of individual components of the flow is estimated. The results of modeling a flow measurement system on a flow that consists of a mixture in the form of natural gas with a high content of hydrogen sulfide are presented. Metrological characteristics of the invariant system are investigated, and further ways are proposed for the development of invariant methods of flow measurement and improvement of systems based on them.

Pore scale study of heat and mass transfer in ice-containing gas diffusion layer of polymer electrolyte membrane fuel cells

The liquid water transport and ice melting process in gas diffusion layer (GDL) are studied using the enthalpy-based multi-component multiphase flow lattice Boltzmann model. Then the heat and mass transfer process under different inlet heating temperatures, inlet flow velocities, rib-channel width ratios and contact angles of carbon fibers are discussed. The results show that heat convection and heat conduction areas are formed in the GDL, and the increase of the inlet heating temperature promotes ice melting, the heating temperature needs to be high enough to promote the reduction of the mixture content of water and ice. The inlet flow velocity has a great influence on both the ice melting efficiency and the discharge of liquid water. The reduction ratio of melting time from 0.5 m/s to 1.0 m/s is larger than that from 1.0 m/s to 1.5 m/s. The wider rib structure reduces the range of heat conduction region, so it has higher ice melting efficiency. The surface wettability of carbon fibers has no significant effect on ice melting rate in the heat convection area. Overall, the more hydrophilic the surface, the sooner the ice melts, but the more hydrophobic the surface, the more favorable the discharge of liquid water.

Photocatalytic degradation of ethylene in tubular microreactor coated with thin-film of TiO2: Mathematical modeling with experimental validation and geometry analysis using computational fluid dynamics simulations

The study aimed to establish a comprehensive understanding of the photocatalytic process and optimize the reactor design for efficient ethylene regulation to improve the shelf-life of fruits and vegetables. For this, it was performed 2D computational fluid dynamics modeling at two different reactor geometry (conventional cylindric reactor and annular cylindric reactor) using the conservation equations combined with Langmuir-Hinshelwood mechanism. A continuous single-phase multicomponent fluid flow with the reactor surface supported with a thin-film catalyst under UV-A light irradiation was simulated for initial ethylene concentration at 0.479–4.234 × 10−3 molC2H4 m−3 and inlet axial velocity at 0.0085–0.1019 m s−1. In the 2D CFD results, it was observed that the difference in ethylene concentration between the microreactor bulk and surface is only significant for high initial concentrations and axial velocities. Furthermore, it was found that the parabolic conversion profile remains unchanged for lengths greater than 10% of the reactor length across all geometries studied. The variation in reactor diameters resulted in a substantial reduction in ethylene conversion; however, the incorporation of an annular cylinder coated with a catalyst led to an enhancement in conversion rates, with improvements of approximately 28%, 17%, and 6% observed for diameters of 5 mm, 10 mm, and 20 mm, respectively. This reduction in improvement as diameter increase can be attributed to the laminar flow dynamics that impede the diffusion of ethylene molecules from the bulk to the catalytic surface. Consequently, the simulated data highlight the potential of employing a catalyst-doped annular cylinder as a promising strategy to increase ethylene conversion and extend the shelf life of fruits. However, it should be noted that the addition of an annular cylinder, while enhancing conversion, also introduces operational complexities and cost implications due to the significant increase in pressure drop associated with lower diameters.

A one-stage high-order gas-kinetic scheme for multi-component flows with interface-sharpening technique

We propose a one-stage high-order gas-kinetic scheme (GKS) with interface-sharpening technique for the 4-equations model of compressible multi-component stiffened-gas flows. The scheme is constructed based on the framework of a one-stage efficient high-order GKS (EHGKS), which can achieve uniform high-order accuracy in both space and time. The main idea in the construction of the new scheme consists of three parts. Firstly, different from the original EHGKS, the non-oscillatory kinetic (NOK) flux is introduced to compute the leading term and the related flux evaluations, which enables the modified EHGKS suitable for stiffened gases, together with no pressure and velocity oscillations across the contact discontinuities. Then the modified scheme is utilized to discrete the conservative parts of the 4-equations model. Secondly, in order to avoid the oscillations across material interfaces, a high-order GKS is derived to solve the non-conservative parts of the 4-equations model following the idea of Abgrall [1]. Finally, to further reduce the over diffusion near a material interface, a simple interface-sharpening technique is developed, which combines the idea of interface construction and downwind scheme. The numerical results demonstrate that the proposed scheme can not only achieve the designed uniform accuracy in both space and time, but also sharply capture material interfaces.

Effects of Salty Additives in Drilling Fluids on Hydrate Formation Dynamics and Phase Equilibrium

In the drilling process for deepwater and hydrate formations, adding salty components to drilling fluids is an important way to avoid secondary generation of hydrates in the annulus, and the effect of salt solutions on the hydrate generation lays a basis for drilling fluid design. In this study, an evaluation device for the effect of drilling fluid additives on hydrate formation and phase equilibrium is designed based on their interaction characteristics. In addition, hydrate generation experiments were carried out for pure water and three commonly used salty additives for drilling fluids. As such, the hydrate phase equilibrium equations under different conditions are established, and the hydrate phase change latent heat is further calculated. The results show that hydrate formation can be divided into four stages, i.e., gas dissolution, hydrate crystal nucleation, hydrate particle mass aggregation, and stabilization. Compared with pure water, sodium chloride and potassium formate solutions can effectively inhibit hydrate formation. At lower ambient temperature, the higher the concentration of potassium formate, the lower the phase equilibrium pressure. On the contrary, at higher ambient temperature, the higher the concentration of potassium formate, the higher the phase equilibrium pressure. The incomplete presence of sodium silicate in water in the form of ions is found to promote methane hydrate formation. Based on the experimental results of methane hydrate generation in potassium formate and sodium silicate solutions with different mass concentrations, the phase equilibrium calculation models for methane hydrate in both salt solutions were finally established. The latent heat of the phase change distribution of hydrate under different conditions was further calculated. The results of this paper can provide a theoretical basis for the study of deepwater drilling fluid systems and multicomponent annular flow.

A new family of downwind-limited, scale-invariant WENO schemes with optimal accuracy

Despite improvement over decades, there are still at least two key issues not fully solved in Weighted Essentially Non-oscillatory (WENO) schemes. Firstly, most WENO schemes hardly satisfy the scale-invariant property, which undermines their robustness and accuracy when simulating flows involving different scales such as reactive multi-component flows and plasma. Secondly, most of existing Essentially Non-oscillatory (ENO) constraints are not sufficient and necessary conditions to achieve optimal accuracy. Therefore, in this work, we design a new family of WENO schemes based on a three-cell stencil to address these two issues. The new WENO non-linear weights are designed as bounded asymptotic functions which are dependent on cell Normalised Volume Integrated Average (NVIA) values and a shape parameter θ. Thus, the new WENO weighting functions are scale-independent. The shape parameter θ controls the errors between the nonlinear weight and the ideal weight. As the value of θ increases, the new weighting functions become more accurate but also become more likely to produce numerical oscillations. Thus, we propose a downwind limiting method as a supplementary constraint of ENO property. The maximum value of θ which corresponds to the optimal accuracy of a weighting function can then be determined. The accuracy analysis via the standard Taylor expansion at critical points reveals that the proposed weighting functions outperform classical WENO schemes. The accuracy, scale-invariant property and ENO property of proposed schemes are further validated through benchmark tests, which shows the superior performance of the new schemes in comparison with existing three-cell-based WENO schemes. Thus, this work proposes a new direction to construct scale-invariant WENO weighting functions with optimal accuracy, which can potentially be extended to higher-order WENO schemes.

Pore scale study of ice melting and multiphase flow in gas diffusion layer with porosity gradient in PEMFC

An enthalpy-based multi-component multiphase flow model is established by using the lattice Boltzmann method (LBM), and the ice melting and liquid water flow behavior during cold start process in gas diffusion layers (GDLs) with porosity gradients of proton exchange membrane fuel cell (PEMFC) are captured. GDLs with five porosity gradients are considered to explore the ice melting efficiency, temperature distribution characteristics and liquid water transport. The results show that the ice melting rate is significantly affected by the porosity distribution. The model of porosity decreasing gradually from near catalyst layer to near channel side (M4) greatly improves ice melt efficiency by up to 61.44%, while the 'V' porosity gradient (M2) and the model of porosity increasing gradually from near catalyst layer to near channel side (M3) prolong the heating and melting time of 15.6% and 25.56% respectively. The arrangement of small porosity structure near the channel side enhance the convective and conduction heat transfer. The hydrophilicity of the surface of fibers is beneficial to ice melting but hinders the discharge of liquid water. Considering the ice melting efficiency and drainage performance, the GDL with porosity gradient can be used when selecting the auxiliary measure of inlet preheating.

Phase Equilibrium Studies in the Geothermal Energy Development: The Effect of Hydrogen Bond on the Multi-Component Fluid.

Geothermal energy has become an emerging resource with both large reserves and environmental friendliness and is playing an increasingly important role in the current energy transition progress. In this paper, a thermodynamically consistent NVT flash model is developed to consider the effect of hydrogen bond on the phase equilibrium states of multi-component fluid to resolve the challenges of the special thermodynamic characteristic of water as the main working fluid. In order to provide practical suggestions to the industry, a number of possible effects have been investigated on the phase equilibrium states, including the hydrogen bond, environmental temperature, and fluid compositions. The calculated phase stability and phase splitting results can provide thermodynamic foundations for the establishment of the multi-component multi-phase flow model and also help optimize the development process to control the phase transitions for a number of engineering purposes.

Compositional noise in nozzles with dissipation

We propose a physical model to predict indirect noise generated by the acceleration of compositional inhomogeneities in nozzles with viscous dissipation (non-isentropic nozzles). First, we derive the quasi-one-dimensional equations from the conservation laws of multicomponent flows. Second, we validate the proposed model with the experimental data available in the literature for binary mixtures of four gases. Third, we calculate the nozzle transfer functions for different Helmholtz numbers and friction factors, in both subsonic and supersonic flows with/without shock waves. We show that friction and dissipation have a significant effect on the generation of indirect noise, for which the physical mechanism is identified and explained. Fourth, we find a semi-analytical solution with path integrals, which provides an asymptotic expansion with respect to the Helmholtz number. Fifth, we introduce the compositional-noise scaling factor, which is applied to quickly estimate compositional noise from the knowledge of only one single-component gas transfer function. The approximation error is less than $1\,\%$ . The proposed low-order model provides accurate estimates of the transfer functions and physical insight into indirect noise for multicomponent gases. This opens up new possibilities to accurately predict, and understand, sound generation in gas turbines.

Hydrogen tightness evaluation in bedded salt rock cavern: A case study of Jintan, China

Hydrogen is regarded as one of the most important energy sources for the future. Safe, large-scale storage of hydrogen contributes to the commercial development of the hydrogen industry. Use of bedded salt caverns for natural gas storage in China provides a new option for underground hydrogen storage (UHS). In this study, the physical properties of multicomponent gases in UHS and salt rock are reviewed and discussed, along with the flow of hydrogen in the surrounding salt rock. Mathematical models of the two-phase multicomponent flow of the gas–brine system in the UHS were established. A numerical model of a simplified elliptical salt cavern was built to simulate the migration of the gas–brine system in the UHS. The hydrogen tightness of the UHS was evaluated through simulation with different storage strategies, salt rock and interlayer permeabilities, and gas components. The results indicate that: (1) Cyclic injection and withdrawal facilitate hydrogen leakage, which is accelerated by increasing the frequency. (2) The huff-n-puff of hydrogen gas in the injection and withdrawal cycles forces the gas into pore space and enhances the relative permeability of the gas phase. The migration of hydrogen and brine weakens the hydrogen tightness. Brine saturation is an important index for evaluating the hydrogen tightness of UHS. (3) The leakage rate of UHS increases with an increase in the permeability of the salt rock and interlayer and the total thickness of the interlayers. The average permeability Kwa weighted by the thickness of layers for the bedded salt formation is proposed to integrate three variables to facilitate field application of the simulation results. The critical Kwa is less than 3.02 × 10−17 m2 if the recommended annual hydrogen leakage rate is less than 1%. (4) The difference between hydrogen and other gas species is another important factor in the leakage rate and should be considered. This study provides theoretical guidance for evaluating the feasibility of UHS in salt caverns and site selection in China.

Space-Time Adaptive ADER-DG Finite Element Method with LST-DG Predictor and a posteriori Sub-cell WENO Finite-Volume Limiting for Simulation of Non-stationary Compressible Multicomponent Reactive Flows

Space-Time Adaptive ADER-DG Finite Element Method with LST-DG Predictor and a posteriori Sub-cell WENO Finite-Volume Limiting for Simulation of Non-stationary Compressible Multicomponent Reactive Flows

Gas condensate well productivity in fractured vuggy carbonate reservoirs: A numerical modeling study

The spatial distribution of fractures and cavities may generate important impact on the fluid flow behavior in fractured vuggy carbonate reservoirs. However, the recovery mechanism of gas condensate wells is not well understood due to the lack of effective reservoir simulation methods that coupled porous-medium and free flows occurring in fractured vuggy carbonate reservoirs. In this work, a novel compositional reservoir model is developed for modeling the production dynamics of gas-condensate well in complex fractured vuggy reservoirs. The compositional multiphase fluid flow through rock matrix and fractures is assumed to follow Darcy's law, while the free flow in cavities is modeled based on the assumptions of instantaneous thermodynamic equilibrium and phase segregation controlled by gravity. An advanced numerical calculation method combining finite volume method (FVM) and embedded discrete fracture-vug model (EDFVM) is developed to efficiently solve the multi-component multiphase flow problem. Case studies are conducted to investigate the gas-condensate flow behavior and well production performance under various configurations of fracture-cavity patterns. Two scenarios are considered by placing the production well at the top and bottom of the models, which aim to mimic different locations of directional well target. The results indicate that when cavities are present, condensate oil accumulates mainly beneath the cavities due to the effect of gravity segregation. Thus, more condensate oil may be produced with depletion at the bottom of the reservoir. However, condensate oil distributes surrounding the production well when cavities are absent, and the production performance of gas-condensate well is less affected by depletion location. Furthermore, the cumulative condensate oil and gas production are higher when cavities are present because of the continuous supplement of condensate gas by cavities. Our research findings have important implication for the design of directional well planning in the fractured vuggy gas condensate reservoirs.

Hydrate Reservoir Stimulation and Sand Control by Liquid-Solid Phase Change Proppant Filled in Radial Well

Summary The depressurization method for natural gas hydrate exploitation encounters the difficulties of low productivity and sand production. Enhancing hydrate production efficiency and reducing massive sand production are the key issues to be solved in hydrate development. This paper proposes a new approach to hydrate reservoir stimulation and sand control by liquid-solid phase change proppant (LSP) filled in radial well (SCRP). A multicomponent flow model of sand-water-gas-hydrate is established and applied to evaluate the effect of SCRP on hydrate development. The results obtained show that the application of SCRP realizes an integrative effect of both reservoir stimulation and sand control. Radial wells increase the sweep area of pressure drop and promote hydrate decomposition. Solid particles, which are formed by LSP, not only fill and support radial wells but also act as sand control medium, preventing sand from flowing into the production well. It is found that reducing the production pressure difference can effectively reduce sand production. To achieve a large-scale stimulated reservoir volume, it is necessary to increase the length of a single radial well, the number of radial wells in the same layer, and the number of radial well layers. The spiral layout of radial wells has a better effect on improving gas production. A single radial well achieves good sand control effect with the application of the LSP system, but an increase in radial well number leads to an increase in sand production, resulting in massive amounts of sand gathered in the production well. As a result, in the case of multiple radial wells, other sand control technologies, such as mechanical sand screening, should be used along with SCRP to further reduce sand production.