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Reservoir modeling consists of two key components: the reproduction of the historical performance and the prediction of the future reservoir performance. Industry-standard reservoir simulators must run fast on enormous and possibly unstructured grids while yet guaranteeing a reasonable representation of physical and chemical processes. However, computational demands limit simulators in capturing involved physical and geochemical mechanisms, especially when chemical reactions interfere with reservoir flow. This paper presents a mathematical workflow, implemented in IORSim, that makes it possible to add geochemical calculations to porous media flow simulators without access to the source code of the original host simulator. An industry-standard reservoir simulator calculates velocity fields of the fluid phases (e.g., water, oil, and gas), while IORSim calculates the transport and reaction of geochemical components. Depending on the simulation mode, the geochemical solver estimates updated relative and/or capillary pressure curves to modify the global fluid flow. As one of the key innovations of the coupling mechanism, IORSim uses a sorting algorithm to permute the grid cells along flow directions. Instead of solving an over-dimensionalized global matrix calling a Newton–Raphson solver, the geochemical software tool treats the species balance as a set of local nonlinear problems. Moreover, IORSim applies basis swapping and splay tree techniques to accelerate geochemical computations in complex full-field reservoir models. The presented work introduces the mathematical IORSim concept, verifies the chemical species advection, and demonstrates the IORSim computation efficiency. After validating the geochemical solver against reference software, IORSim is used to investigate the impact of seawater injection on the NCS Ekofisk reservoir chemistry. Article Highlights: The IORSim sorting algorithm decouples the nonlinear geochemical reaction calculations into recurring one-dimensional problems to assure numerical stability and computation efficiency. To the best of our knowledge, this work presents the mathematical concept, implementation, and application of topological sorting for the first time on (industry) field-scale problems. IORSim combines topological sorting with basis swapping and splay trees to significantly reduce computation times. Moreover, a high-speed forward simulation mode was developed to allow the post-advection of chemical components to visualize species distribution, water chemistry, and mineral interactions. If the geochemical reactions interfere with the fluid flow, the IORSim backward mode uses relative permeability curves to update the global fluid flow at each time step. We validate the implemented topological scheme on a reservoir grid, show the computation efficiency, and compare the impact of explicit, implicit, and grid refinement on numerical dispersion. The decoupled flow simulator and geochemical reaction calculations allow seamless integration of full-field reservoir models that contain complex geological structures, a large number of wells, and long production histories. The computation capabilities of IORSim are demonstrated by simulating and reproducing the impact of seawater injection in the southern segment of the giant Ekofisk field (more than 50 years of injection and production history). IORSim shows that seawater injection changed the Ekofisk mineralogy and impacted the produced water chemistry. In the investigated Ekofisk case, seawater promoted calcite dissolution and led to the precipitation of magnesite and anhydrite. Moreover, surface complexation modeling revealed that sulfate is adsorbed on the calcite surface. [ABSTRACT FROM AUTHOR]

This paper presents and discusses the results obtained by the participants to the benchmark described in de Hoop et al, Comput. Geosci. (2024). The benchmark uses a model for CO2 geological storage and focuses on the coupling between two-phase flow and geochemistry. Several test cases of various levels of difficulty are proposed, both in one and two spatial dimensions. Six teams participated in the benchmark, each with their own simulation code, though not all teams attempted all the cases. The codes used by the participants are described, and the results obtained on the various test cases are compared, as well as the performance of the codes. It is shown that the results obtained are widely consistent, giving a good level of confidence in the outcome of the benchmark. The general complexity of two-phase flow coupled with chemical reactions altering porous media means that some differences between the codes remain. Besides, from the convergence study, it is clear that the two-dimensional problem has a relatively high sensitivity to a spatial resolution which adds to the complexity. [ABSTRACT FROM AUTHOR]

One of the most significant techniques of heat exchange in manufacturing appliances is convective heat transfer which can be enhanced by porous media and magnetic fields in various applications such as improving dramatically the different thermal equipment performance. This study investigates magnetohydrodynamic Maxwell nanofluid saturated in a porous medium towards convectively heated extending cylinder with higher-order chemical reactions. The ordinary differential equations resolved by using the optimal homotopy analysis method. The impact of various relevant factors on the schemes of velocity, energy, and concentration is drawn via diagrams and discussed physically through graphs, and discussions. The correlation between current and previously published findings is noted for accuracy. It is found that the heat transfer enhances when the Biot number and order of chemical reaction increase. When, the parameter of reaction, magnetic field, permeability and Eckert number increase, the heat transfer diminishes. The rising values of Joule heating, chemical reaction and Biot number rises the mass transfer, but in the opposite direction the mass transfer is reduced as the magnetic parameter, permeability and the order of chemical reaction grow. This study will be helpful in studying the movement of water or oil and gas through the cylindrical tanks. [ABSTRACT FROM AUTHOR]

Large eddy simulation (LES) coupled with Lagrangian particle simulation (LPS) is applied to investigate high‐speed turbulent reacting flows. Here, LES solves a velocity field while LPS solves scalar transport equations with notional particles. Although LPS does not require sub‐grid scale models for chemical source terms, molecular diffusion has to be modeled by a so‐called mixing model, for which a mixing volume model (MVM), that is originally proposed for an inert scalar in incompressible flow, is extended to reactive scalars in compressible flows. The extended model is based on a relaxation process toward the average of nearby notional particles and assumes a common mixing timescale for all species. LES/LPS with the MVM is applied to a temporally‐evolving compressible turbulent planar jet with an isothermal reaction and is tested by comparing the results with direct numerical simulation (DNS). The results show that LES/LPS well predicts the statistics of mass fractions. As the jet Mach number increases, the reaction progress delays due to the delayed jet development. This Mach number dependence is also well reproduced in LES/LPS. The mean molecular diffusion term of the product calculated as a function of its mass fraction also agrees well between LES/LPS and DNS. An important parameter for the MVM is the distance among particles, for which the requirement for accurate prediction is presented for the present test case. LES/LPS with the MVM is expected to be a promising method for investigating compressible turbulent reactive flows at a moderate computational cost. [ABSTRACT FROM AUTHOR]

This study presents a mathematical investigation into the phenomena of radiative heat with an unsteady MHD electrically conducting boundary layer of chemically reactive Casson nanofluid flow due to a pored stretchable sheet immersed in a porous medium in the presence of heat generation, thermophoretic force, and Brownian motion. The surface is assumed to be not flat, and has variable thickness. The magnetic field is time-dependent, and the chemical reaction coefficient is inversely varied with the distance. The nanofluid's velocity, heat, and concentration at the surface are nonlinearly varied. A similarity transformation is introduced, and the controlling equations are converted into nondimensional forms involving many significant physical factors. The transformed forms are analyzed numerically using a computational method based on the finite difference scheme and Newton's linearization procedure. The impact of the involved physical parameters is performed in graphical and tabular forms. Some special cases of the current work are compared with published studies, and an excellent agreement is obtained. The main results of the present work indicate that the higher values of the Casson parameter cause an increase in both the shear stress and heat flux, but a decrease in the mass flux. Also, it is noted that the chemical reaction, the nanoparticles' volume, and the permeability factor enhance the effect the of Casson parameter on both the shear stress and heat flux, while the variable thickness and thermal radiation field reduce it; on the other hand, the variable thickness and nanoparticles' volume enforce the influence of the Casson parameter on mass flux, but thermal radiation, the permeability factor, and chemical reaction decrease it. The present study has important applications in mechanical engineering and natural sciences. In addition, it has significant applications in devices used for blood transfusion, dialysis and cancer therapy. [ABSTRACT FROM AUTHOR]

The occurrence of buoyancy-driven flow and reactive solute transport in a fluid-saturated porous medium can be induced by either natural processes or human activities. Typical examples include the groundwater salinization in carbonate-rock aquifers and the acid treatment of oil wells in petroleum drilling industry. In this paper, the classical Elder problem of buoyancy-driven convection in two-dimensional porous media is extended to include the local chemical interactions between the solute in the pore liquid (e.g. salt such as NaCl or acids such as HCl and HCl/HF mixtures) and the solid space of the porous medium (e.g. minerals such as calcite and dolomite). Effects of the geochemical processes on the flow and mass transport are investigated. For the reactive, strongly solute-driven case in the regime dominated by the diffusive mass transport, a decrease in the net solute concentration is found as compared to the non-reactive case. This decrease is pronounced at higher values of the Damköhler number when the solute reaction rate becomes larger than the solute diffusion rate. Furthermore, the flow structure is affected by products generated by the chemical reaction when the Rayleigh number for the products is sufficiently high. In that case, numerical simulations show the formation of diluted fluid tongues exhibiting damped periodic oscillations about a nonzero mean. The results are obtained using the pseudospectral numerical method, verified against the analytical solution for the non-reactive, purely diffusive case. [ABSTRACT FROM AUTHOR]

Nanolubricants fall among the newly evolved and emerged technologies used in lubrication and heat transfer systems due to their unique thermo-physical properties. They are crucial to the industry because they enhance surface performance, reduce maintenance and fuel costs and boost engine efficiency. They are also used in mechanical systems to efficiently minimize friction and surplus heat. The present investigation focuses to analyze Darcy–Forchheimer flow of magnetized ZnO-SAE50 nanolubricant across Riga plate. Riga plate is poised of an electromagnetic equator that consists of an everlasting magnet and a span-wise collection of irregular electrodes mounted over a planner surface and is utilized in achieving proficient flow. The flow takes place in the presence of viscous dissipation, heat source–sink and chemical reaction of higher order. Newtonian heating and thermophoretic particle deposition effects are also investigated in this study. The role of viscosity is quite important and dynamical in various engineering and industrial fields. The viscosity variation highly fluctuates the thermal systems. The present work also highlights the role of variable viscosity, owing to its importance. A novel micro-nano-convection model called the Patel model is invoked in perspective of the enhancement in thermal conductivity of nanolubricant. The use of ZnO-SAE50 nanolubricant (a brand-new form of nanolubricant) over Riga plate, variable viscosity effects and the application of Patel model are novel features of this study. The application of selected transformations causes the modeled PDEs to change into ODEs. The modeled problem is executed numerically with MATLAB bvp-4c solver. The alterations in the concerned profiles corresponding to various emerging parameters of interest are presented graphically in order to develop better understanding and make analysis. The outcomes reveal that larger modified Hartmann number significantly favors the velocity of nanolubricant ZnO-SAE50, while solid volume fraction, magnetic parameter and variable viscosity parameter halt it. The heat source–sink parameter, Eckert number and solid volume fraction are found to be helpful agents in improving temperature of nanolubricant ZnO-SAE50. In comparison with Newtonian heating (NH), common wall temperature condition (CWT) yields better thermal enhancement. The enhancing chemical reaction order ameliorates the concentration profile but it gets minified for chemical reaction parameter and thermophoresis parameter. The increasing values of magnetic parameter, variable viscosity parameter and inertial parameter tend to enhance the skin friction, while the modified Hartman number reduces it. The enhancing values of Eckert number, magnetic parameter and heat source–sink parameter increase the value of Nusselt number. [ABSTRACT FROM AUTHOR]

Turbulent reactive flows laden with droplets appear in various energy systems but are difficult to understand and parametrize. Such flows involve interactions of turbulent fluctuations, phase changes, and chemical reactions that give rise to complex phenomena. To improve our knowledge, we performed direct numerical simulations of a canonical shear flow. It is composed of a hot, quiescent outer layer and a cold, turbulent inner layer that is laden with droplets. Due to the turbulent fluctuations, the droplets form clusters. Due to the high temperatures, the droplets evaporate quickly and flames emerge spontaneously at the interface of the two layers. We observed premixed flames that enclose droplet clusters and diffusion flames that enclose vapor pockets or single droplets. To examine these flame structures in more detail, we varied the droplet size, droplet loading, and shear rate. We found that the droplet size and droplet loading have significant effects, whereas the shear rate has only subtle effects. [ABSTRACT FROM AUTHOR]

Convection, diffusion, and reaction dynamics of radial displacement of reactive fluids undergoing second-order chemical reaction in a porous medium are modeled and understood numerically. In the case of iso-viscous reactants and products, reaction dynamics are examined to understand the effect of reaction rate after solving a system of convection–diffusion–reaction equations using a method of lines. Various temporal scalings for reaction characteristics like the total amount of product and width of reaction front are obtained in terms of the Damköhler number (Da) for the first time in this work. The generation of the product having different viscosity than the reactants results in a hydrodynamic instability called viscous fingering. The numerical technique based on hybrids of compact finite difference and pseudo-spectral methods is utilized, for the first time, for the linear stability analysis (LSA) of miscible viscous fingering induced by chemical reaction. The onset time of instability (ton) is found to depend on the reaction rate, and we obtain a stable zone sandwiched between two unstable zones in the M c , t o n plane for a fixed Péclet number and Damköhler number, where Mc is the log-mobility ratio. The results agree with existing numerical studies validating the novel LSA technique utilized. [ABSTRACT FROM AUTHOR]

The emergence of the "mush paradigm" has raised several questions for conventional models of magma storage and extraction: how are melts extracted to form eruptible liquid-rich domains? What mechanism controls melt transport in mush-rich systems? Recently, reactive flow has been proposed as a major contributing factor in the formation of high porosity, melt-rich regions. Yet, owing to the absence of accurate geochemical simulations, the influence of reactive flow on the porosity of natural mush systems remains under-constrained. Here, we use a thermodynamically constrained model of melt-mush reaction to simulate the chemical, mineralogical, and physical consequences of reactive flow in a multi-component mush system. Our results demonstrate that reactive flow within troctolitic to gabbroic mushes can drive large changes in mush porosity. For example, primitive magma recharge causes an increase in the system porosity and could trigger melt channelization or mush destabilization, aiding rapid melt transfer through low-porosity mush reservoirs. In this study, the authors use a thermodynamically constrained model of melt-mush reaction to simulate the chemical, mineralogical, and physical consequences of reactive flow in a multi-component mush system. [ABSTRACT FROM AUTHOR]

The impacts of viscous dissipation, Brownian motion, and the thermophoresis caused by temperature gradient on the steady two‐dimensional incompressible chemically reactive and radiative flow of traditional fluid through an exponentially stretched sheet embedded in a Darcy porous media are explored by approaching boundary layer analysis. A magnetic field effect is also addressed along the transverse direction of the horizontal stretched sheet. With the implementation of some suitable nondimensional quantities, the regulating nonlinear partial differential equations, which represent the flow geometry, are transformed into coupled nonlinear ordinary differential equations. To acquire the numerical findings from this set of equations, a three‐stage Lobatto IIIa, in‐built MATLAB scheme named, Bvp4c is used. The effects of the dimensionless physical factors on the flow, heat, and concentration profile, as well as on the coefficient of drag force and the rate of thermal and mass transit at the surface, are graphically and numerically depicted. The thermal profile, as well as the magnitude of the coefficient of the drag force and the Sherwood number, is found to be escalated with the Darcy–Forchheimer factor, but the depreciation in the value of temperature gradient at the wall is noticed for the same. [ABSTRACT FROM AUTHOR]

We study mixing-controlled chemical reactions in unsaturated porous media from a pore-scale perspective. The spatial heterogeneity induced by the presence of two immiscible phases, here water and air, in the pore space generates complex flow patterns that dominate reactive mixing across scales. To assess the impact of different macroscopic saturation states (the fraction of pore volume occupied by water) on mixing-controlled chemical reactions, we consider a fast irreversible reaction between two initially segregated dissolved species that mix as one solution displaces the other in the heterogeneous flow field of the water phase. We use the pore-scale geometry and water distributions from the laboratory experiments reported by Jiménez-Martínez et al. (Geophys. Res. Lett. 42: 5316–5324, 2015). We analyze reactive mixing in three complementary ways. Firstly, we post-process experimentally observed spatially distributed concentration data; secondly, we perform numerical simulations of flow and reactive transport in the heterogeneous water phase, and thirdly, we use an upscaled mixing model. The first approach relies on an exact algebraic map between conservative and reactive species for an instantaneous irreversible bimolecular reaction that allows to estimate reactive mixing based on experimental conservative transport data. The second approach is based on reactive random walk particle tracking simulations in the numerically determined flow field in the water phase. The third approach uses a dispersive lamella approach that accounts for the impact of flow heterogeneity on mixing in terms of effective dispersion coefficients, which are estimated from both experimental data and numerical random walk particle tracking simulations. We observe a significant increase in reactive mixing for decreasing saturation, which is caused by the stronger heterogeneity of the water phase and thus of the flow field. This is consistently observed in the experimental data and the direct numerical simulations. The dispersive lamella model, parameterized by the effective interface width, provides robust estimates of the evolution of the product mass obtained from the experimental and numerical data. [ABSTRACT FROM AUTHOR]

This work comprehensively reviews the equations governing multicomponent flow and reactive transport in porous media on the pore-scale, mesoscale and continuum scale. For each of these approaches, the different numerical schemes for solving the coupled advection–diffusion-reactions equations are presented. The parameters influenced by coupled biological and chemical reactions in evolving porous media are emphasised and defined from a pore-scale perspective. Recent pore-scale studies, which have enhanced the basic understanding of processes that affect and control porous media parameters, are discussed. Subsequently, a summary of the common methods used to describe the transport process, fluid flow, reactive surface area and reaction parameters such as porosity, permeability and tortuosity are reviewed. [ABSTRACT FROM AUTHOR]

The reduction of emissions from large industrial furnaces critically relies on insights gained from numerical models of turbulent non-premixed combustion. In the article Mitigating Thermal NOx by Changing the Secondary Air Injection Channel: A Case Study in the Cement Industry, the authors present the use of the open-source OpenFoam software environment for the modeling of the combustion of Dutch natural gas in a cement kiln operated by our industrial partner. In this paper, various model enhancements are discussed. The steady-state Reynolds-Averaged Navier-Stokes formulation is replaced by an unsteady variant to capture the time variation of the averaged quantities. The infinitely fast eddy-dissipation combustion model is exchanged with the eddy-dissipation concept for combustion to account for the finite-rate chemistry of the combustion reactions. The injection of the gaseous fuel through the nozzles occurs at such a high velocity that a comprehensive flow formulation is required. Unlike in Mitigating Thermal NOx by Changing the Secondary Air Injection Channel: A Case Study in the Cement Industry, wave transmissive boundary conditions are imposed to avoid spurious reflections from the outlet patch. These model enhancements result in stable convergence of the time-stepping iteration. This in turn increases the resolution of the flow, combustion, and radiative heat transfer in the kiln. This resolution allows for a more accurate assessment of the thermal NO-formation in the kiln. Results of a test case of academic interest are presented. In this test case, the combustion air is injected at a low-mass flow rate. Numerical results show that the flow in the vicinity of the hot end of the kiln is unsteady. A vortex intermittently transports a fraction of methane into the air stream and a spurious reaction front is formed. This front causes a transient peak in the top wall temperature. The simulated combustion process is fuel-rich. All the oxygen is depleted after traveling a few diameters into the kiln. The thermal nitric oxide is formed near the burner and diluted before reaching the outlet. At the outlet, the simulated thermal NO concentration is equal to 1 ppm. The model is shown to be sufficiently mature to capture a more realistic mass inflow rate in the next stage of the work. [ABSTRACT FROM AUTHOR]

Geothermal reservoir scaling controlled by reactive flow is a common phenomenon during geothermal development, which might lead to the decline of geothermal productivity and abandonment of geothermal projects. It is significant to reveal chemical influence on the geothermal reservoir characteristics and production performance to provide the reference for geothermal sustainable development. In this work, a thermal-hydraulic-chemical coupling model is developed for a triple-well fractured enhanced geothermal system considering the silica dissolution and precipitation at the fracture surface. It is focused on the evolution of fracture aperture and geothermal productivity. The results indicate that undersaturated injection will cause mineral dissolution which leads to the rise of fracture transmissibility and a thermal break. The fracture width is enhanced by 0.093 mm, and the permeability is 8 times the initial value after 20-year production. The oversaturated injection will cause mineral precipitation which leads to the reduction of fracture aperture and the increase of pressure difference. The opening is reduced by 0.041 mm and the permeability goes down by 2 orders of magnitude. The maximum increases of average production temperature and differential pressure are 10 °C and 13.5 MPa respectively in the 20th year from undersaturation to supersaturation. Besides, it is figured out that reaction rate denotes the evolution of fracture aperture. Both of them are distributed as a band at a fracture plane, which is determined by saturation index and temperature together. The former controls the reaction pattern (dissolution/precipitation) while the latter controls the reaction speed. Furthermore, the evolution of opening is uneven around the production well at different exploitation stages. Fracture width is higher on the strong side in the first 8.7 years but is higher on the weak side in later development when undersaturated water (0 mol/kg) is injected. The phenomenon can be employed to judge the production status, guide the descaling, etc. Production analysis indicates that oversaturation delays the heat breakthrough and undersaturation reduces the surface pump input. This study will provide a significant reference for the geothermal sustainable production influenced by chemical reactions in an enhanced geothermal system. [ABSTRACT FROM AUTHOR]

The chemical time scale can be used to characterize a reactive system('s behavior). In addition, various dimensionless numbers (e.g. Damköhler number) rely on a characteristic chemical time scale. The inverse eigenvalues of a system are regarded as the system's time scales. This means, the number of time scales is equal the numbers of eigenvalues. A formulation for a single characteristic time scale is required for the system characterization and to calculate dimensionless numbers. Recently proposed modifications of the Eddy Dissipation Concept (a turbulence-chemistry interaction model) also incorporate the Damköhler number in their formulation. Besides accuracy, the numerical efficiency is important, since the chemical time scale needs to be computed in each cell at every time step. We present different chemical time scale definitions found in literature, evaluate them on simple test problems and use them for flame simulations in conjunction with the modified Eddy Dissipation Concept. For the simple test case, most formulations give satisfactory results. The complexity of the chemical reaction mechanism greatly impacts the calculated time scale values. Therefore, we suggest to use a simple global mechanism for the calculation of chemical time scales to ensure reproducibility and consistency of the results. [ABSTRACT FROM AUTHOR]

The prime objective of binary chemical reaction (BCR) is concentrated on the study and optimization of chemical reaction to accomplish finest reactor design and performance, which elaborated the interfaces of flow phenomena, reaction kinetics and heat and mass transport. The reactor performance is likely to be linked to the reaction operating constraints and feed composition through the aforementioned factors. The applications of BCR are generally in the petroleum and petrochemical regions, but with the help of chemical engineering and reaction chemistry concepts, it could be used in different areas, like waste treatment, chemical pharmaceuticals, nanoparticles in advanced materials, microelectronics, enzyme technology, biochemical engineering, living systems, renewable energy systems, sustainable development, environment/pollution prevention, as well as to optimize a different reaction framework via simulation and modeling methodology. Owing such physical applications in mind, this research deals with the binary chemical reactive flow of non-Newtonian fluid (Walter's B) subject to activation energy. Stagnation point is accounted. Radiative flux and ohmic heating effects are considered in the development of energy expression. Concentration and microorganism equations are considered. The governing system is altered to ordinary one through the important similarity variables. Results are obtained through bvp4c technique. All results are discussed graphically. Furthermore, surface drag force (skin friction) and heat and mass transfer (Nusselt and Sherwood) rates are calculated and displayed graphically. Significant results are listed in conclusion. [ABSTRACT FROM AUTHOR]

A new lattice Boltzmann model for reactive ideal gas mixtures is presented. The model is an extension to reactive flows of the recently proposed multi-component lattice Boltzmann model for compressible ideal gas mixtures with Stefan–Maxwell diffusion for species interaction. First, the kinetic model for the Stefan–Maxwell diffusion is enhanced to accommodate a source term accounting for the change in the mixture composition due to chemical reaction. Second, by including the heat of formation in the energy equation, the thermodynamic consistency of the underlying compressible lattice Boltzmann model for momentum and energy allows a realization of the energy and temperature change due to chemical reactions. This obviates the need for ad-hoc modelling with source terms for temperature or heat. Both parts remain consistently coupled through mixture composition, momentum, pressure, energy and enthalpy. The proposed model uses the standard three-dimensional lattices and is validated with a set of benchmarks including laminar burning speed in the hydrogen–air mixture and circular expanding premixed flame. This article is part of the theme issue 'Progress in mesoscale methods for fluid dynamics simulation'. [ABSTRACT FROM AUTHOR]

We analyze the dynamics of solute mixing and reaction in a mixing-limited reactive flow by considering the transport of a tracer in a linear shear flow and in a Rankine vortex. The action of a shear flow, in general, achieves stretching of fluid elements due to the heterogeneous nature of the flow. A vortex flow exhibits not only stretching but also folding of fluid elements in a way that brings adjacent fluid elements closer at every turn. A strong stretching along the tangential direction is accompanied by a concomitant thinning in the radial direction leading to a strong diffusive flux, which may cause the material from neighboring regions of the mixing interface to aggregate. Through a Lagrangian concentration evolution technique, the diffusive strip method, we obtain the concentration field and pinpoint the signature of coalescence of two neighboring concentration regions by analyzing the concentration distribution profiles. The role of substrate deformation on the reaction kinetics of a classical heterogeneous chemical reaction is also studied where we derive analytical expressions for the coupling between the rate of product formation and the Péclet number in different time limits. Finally, the impact of coalescence on reaction rates is studied for a Rankine vortex, a result that holds important implications for simple bimolecular reactions. This analysis is useful to understand scalar dispersion in vortical flow structures and the consequences of stretching-enhanced diffusion in mixing-limited reactive flows. [ABSTRACT FROM AUTHOR]

In this paper, the sintering behavior of the lanthanum-borate (B 2 O 3 -La 2 O 3 -MgO-TiO 2 ,BLMT) glass-ceramic with BaTi 4 O 9 filler composite was investigated in terms of the wetting behavior, interfacial reaction, sinter-shrinkage process, sintering activation energy, as well as phase and microstructure evolution with change in filler contents and sintering temperature. Our research suggested that the glass is unable to wet the filler material within a temperature up to 1000 °C, indicating that the densification process of composites is dominated by viscous flow of glass matrix. The increase in filler content that performs as a rigid particle in composite causes the rise in the sinter-shrinkage-onset and -end temperature, thereby proving that the viscous-flow densification of the composites with x≤ 30 wt% filler content is accomplished before the crystallization of BLMT glass, whereas the composites with x≥ 40 wt% cannot. After densification, a chemical reaction that almost synchronizes with the glass crystallization occurred between glass and ceramic, which not only imposes significant influence on the crystallization behavior, but eradicates the closed pore formed by the viscous flow and the induced crystallization porosity. The densification process of the BaTi 4 O 9 filler-BLMT glass composite was referred to as two-stage reactive assisted viscous flow sintering process which consists of viscous flow of glass, of the crystallization process of glass, and/or of the chemical reaction between glass and filler. [ABSTRACT FROM AUTHOR]

During the last years, several thrust control systems of aerospace rocket engines have been developed. The fluidic thrust vectoring is one of them; it is simple in design and offers a substantial gain in weight and in performance. Most of the studies related to this device were carried out with cold gas. It is quite legitimate to expect that the thermophysical properties of the gases may affect considerably the flow behavior. Besides, the effects of reacting gases at high temperatures, under their effects all flow parameters like to vary. This study aims to develop a new methodology that allows studying and analyzing the fluidic thrust vectoring for a perfect gas, by taking into account the effects chemical reactions on the flow parameters, such as separation point, reattachment point downstream and pressure distribution upstream the injection port. In this study, the thrust vectorization implying frozen reacting hot gases was carried out by considering a chemical reaction mechanism. The thermodynamic parameters of the flow are calculated within the combustion chamber and different sections of the supersonic part of the nozzle. The results show a good agreement for cold gas, and as expected a slight difference for hot reacting gases. In parallel, in order to give more credibility to our work a study was carried out by numerical simulation for supersonic reactive and perfect flows in order to analyze the results of the method developed. In this work, the CFD performance of the fluidic thrust vectoring has been qualitatively and quantitatively analyzed. The Schlieren visualization and the wall pressure results are compared to analytical and experimental findings. Performance analysis is conducted, and basic conclusions are drawn in terms of thermodynamic gas properties effect on the fluidic thrust vector system. The primary effect was related to the gas molecular weight and its specific heat ratio. It is observed that for fixed injection conditions, the vectoring angle is different when the injected gas molecular weight and specific heat ratio are different. For a given mission of the launcher, it can be concluded that the mass of the embedded gas, used for the fluidic vectorization system, can be significantly reduced, depending on its molecular weight and specific heat ratio. [ABSTRACT FROM AUTHOR]

This article reports a revised relation of nanofluid considering the properties of activation energy in mixed convection Carreau nanofluid, The Brownian and thermophrotic diffusions are incorporated. The aspects of convective heat transport, viscous dissipation, Joule heating and chemical reaction are also reported. The numerically bvp4c scheme has been established for the solutions of nonlinear ODEs. The local Weissenberg number and magnetic parameter decline the velocity field. The radiation and thermophoretic parameters enhance the temperature of Carreau fluid. Furthermore, on both Bejan number and entropy generation, the impact of radiation and magnetic parameter have been studied. [ABSTRACT FROM AUTHOR]

Large eddy simulations (LES) of non reactive and reactive flows in a cavity-based scramjet combustor configuration from the U.S Air Force Research Laboratory (AFRL) are performed. These simulations feature a 22 species and 206 reactions chemical scheme for ethylene/air. The ability of LES to reproduce the main features found in the experiment is first emphasised such as the average velocity field and the stability of the combustion for the case studied. The influence of the mesh resolution and of the thermal wall condition on the simulation results is also investigated along with the soundness of the use of a laminar model for the filtered source terms. The results of the simulations with the finest grid (resolution of 100 micrometers in the flame region) are then employed to gain understanding in the flame dynamics. This reactive simulation shows the persistence of the two recirculation zones already present in the non reactive flow. The globally high temperature into the cavity helps to sustain a reactive zone located in the mixing layer above the cavity. Combustion first occurs in a diffusion dominated regime followed by the efficient burning of a well stirred mixture (rich then lean). A significant diffusion dominated burning is also found inside the cavity. The links between the residence time inside the cavity and the efficiency of the combustion are explored along with the velocity/heat release correlation. [ABSTRACT FROM AUTHOR]

• Buchwald–Hartwig reaction as a case study to investigate crystal growth in shear flow. • Wall deposition and crystal formation under flow in situ within glass microchannels. • Tuning shear rate leads to dramatic changes in crystal morphology and composition. In many industrial applications, ranging from chemical reactions to transport of suspensions, colloids can be produced and deposited within the processing equipment leading to significant fouling and clogging issues. Here, a continuous-flow reactor for the production of pharmaceutically relevant arylamines through the Buchwald-Hartwig synthesis is coupled to a microfluidic channel to investigate the complex interplay among fluid dynamics, crystallization, reaction and surface chemistry. The process of wall deposition and crystal formation under flow is studied in situ by fragmenting to the micron-scale the particles coming from the reactor and using glass microchannels. Tuning the flow rate, a dramatic change in crystal morphology and composition is found, from dendritic needle-like potassium tert-pentoxide structures to irregular colloidal clusters mainly made of potassium bromide. The results are characterized in terms of dimensionless parameters and provide novel insights for an improved understanding and control of fouling and crystal growth under flow. [ABSTRACT FROM AUTHOR]

Our main focus here is to analyze the chemically reactive flow of Prandtl–Eyring nanofluid. Flow is caused by linear stretching of sheet. Heat transfer characteristics are examined subject to nonlinear radiative flux and heat source/sink. Moreover Joule heating and dissipation effects are considered. Entropy optimization is expressed as a function of temperature, velocity and concentration. Total entropy has been calculated. Buongiorno nanofluid model which incorporates important slip mechanisms like Brownian motion and thermophoresis diffusion is used. Chemical reaction is considered along with activation energy. Suitable transformations are implemented to convert the governing expressions into ordinary one. Built-in-shooting technique is used for the solution development. Results for the velocity, entropy, temperature, Bejan number and concentration are presented graphically. Particular attention is given to quantities of engineering interests such as skin friction coefficient and Nusselt and Sherwood numbers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Magnetized water-based carbon nanotubes flow is investigated. • Chemical reactive flow is flowing through Darcy-Forchheimer porous space. • Entropy generation volumetric rate relation is modeled. • The numeric solutions through shooting scheme are executed. This investigation described the features of magnetized water-based carbon nanotubes in slip flow saturated through Darcy-Forchheimer porous space. Cattaneo and Christov heat diffusion relation is used for the modeling of energy equation. Chemical reaction and heat generation influences are accounted. The entropy generation (EG) volumetric rate relation is modeled. The Fehlberg numerical scheme is implemented for the construction of the solutions. The results revealed that the EG is augmented in the presence of magnetic field and porosity parameter but decays against solid volume fraction of nanoparticles for both SWCNTs (single-wall carbon nanotubes) and MWCNTs (multi-wall carbon nanotubes). [ABSTRACT FROM AUTHOR]

Conventionally, a finite element framework for coupled hydro-mechanical-chemical processes in porous media adopts simplified chemical reactions, which consider superficial chemical effects of complicated multiphysics mechanisms. This paper presents a novel computational framework for geochemistry of reactive multi-component systems to explicitly capture the mineral dissolution/precipitation of saturated porous media. The resultant of this framework can be applied in oil recovery engineering and used to simulate the production scenarios. The model is also fundamental for studying on creep behaviors from the view of the coupling effects between hydro-geochemistry. In particular, a complete chemistry system of ▪ is considered, including intra-aqueous chemical reactions and kinetic rate-limiting chemical reactions. Besides, an algorithm is proposed such that the complete chemistry system is scalable for various chemical reactions and is easily incorporated into existing finite element frameworks for hydro-mechanical processes of porous media. This complete chemistry system is implemented to establish a local chemical equilibrium. The geochemical reactive transport equations are then sequentially coupled with the balance laws such that coupling among fluid advection-diffusion, solid deformation, chemical concentration advection-diffusion, intra-aqueous chemical reaction, and kinetic rate-limiting chemical reaction can be simulated. Phenomenological relations for porosity and permeability changes with mineral saturation in solutions are employed. We first verify the proposed framework to capture the advection-diffusion of different chemical species under steady-state and transient conditions. Then a consolidation problem under the chemical reactions is presented to further demonstrate the capabilities of the proposed computational framework. [ABSTRACT FROM AUTHOR]

CFD-based optimization provides an efficient tool to improve systems in which conversion processes depend on a strong interaction between flow field and chemical reactions. The present work develops an improved multi-parameter and multi-objective optimization concept for reactive flow systems and demonstrates this concept for a new quench reactor. Response surface methods (metamodels) are used within the metamodel-based optimization process to accelerate the optimization rapidly. Different metamodels such as polynomials, K-nearest, radial basis functions, anisotropic Kriging, smoothing spline analysis of variance, and artificial neural networks are applied and carefully analyzed. It can be shown that radial basis function metamodels in combination with a certain number of CFD calculations provide a robust and efficient optimization scheme. The computational effort can be reduced by a factor of 17, which provides a reliable basis to optimize more complex reactive flow systems, e.g. the high pressure partial oxidation of natural gas or crude oil. [ABSTRACT FROM AUTHOR]

[Display omitted] • Here Darcy-Forchheimer relation is accounted in flow of viscous fluid. • Soret and Dufour effects are considered. • Chemical reaction is addressed in concentration equation for the mass transfer analysis. • Numerical results are obtained via Shooting method. The main purpose of this work is to analyze chemically reactive Darcy-Forchheimer nanoliquid flow towards a stretched surface. Buongiorno's model is utilized for the nanoliquid importance. Additionally, Soret and Dufour characteristics are also considered. Gyrotactic microorganisms with chemically reactive flow are considered. The given partial differential systems are converted into dimensionless ordinary expressions with the implementation of suitable transformation. Non-dimensional systems are solved through Newton built in-shooting technique. Graphical outcomes for temperature, microorganisms' field, velocity and concentration versus secondary variable are discussed. Numerical outcomes of drag force, density number and heat transport rate for sundry parameters are examined. A reduction occurs in velocity for higher porosity variable. Higher estimation of Dufour number upsurges the temperature. Similar impact for temperature is seen for random motion and thermophoresis variables. Concentration upsurges for higher Soret number, while reverse effect holds for Schmidt number. An increment in heat transport rate occurs for higher Dufour number. Microorganisms' fluid diminishes for higher Peclet number, while reverse impact seen for density number. [ABSTRACT FROM AUTHOR]

The design of reactors with a dispersed gas in a liquid phase, e.g., bubble columns, is often based on rather roughly estimated parameters. To obtain a better understanding of the influence and interaction of the fluid dynamics and the mass transfer in the presence of a chemical reaction of NO and Fe(EDTA) in the liquid phase, the complex system of a bubbly flow is here reduced to single-bubble investigations. For this purpose, mass transfer is investigated with and without chemical reaction to be able to differentiate between various influencing factors and determined enhancement caused by the chemical reaction. Two experimental setups are applied, namely, the first one with two moving cameras where the velocity is adapted to the rising velocity of the bubble, and the second one is a countercurrent-flow cell. [ABSTRACT FROM AUTHOR]

This attempt reports the influence of variable thermal conductivity over an impermeable surface stretching in a nonlinear manner. Flow formulation is developed considering stagnation point and rheological expressions of second grade liquid. Different from the traditional literature, a new concept of heat flux covering paradox of heat conduction is imposed. Such concept has been used in view of Cattaneo-Christov theory. Besides this first order chemical reaction and double stratification are also considered. The subjected problems are modeled first and then non-dimensionalized. Computations for highly nonlinear problems are presented. The derived expressions are acceptable for convergence. Velocity, temperature, concentration, skin friction and Sherwood number are described through graphs for meaningful discussion considering important variables. Our computed analysis reveals that impacts of local second grade parameter and ratio of velocities have similar behavior on velocity distribution. Moreover the consideration of variable thermal conductivity improves the temperature and associated thermal boundary layer thickness. [ABSTRACT FROM AUTHOR]

Several assumptions of atmospheric-pressure (atmospheric- p ) single-phase turbulent reaction rate models are examined for high- p reactive flows having turbulent characteristics. The study uses a Direct Numerical Simulation (DNS) database described elsewhere (Bellan, 2017). This database was obtained with a model combining multi-species mixing under high- p conditions, a real-gas equation of state (EOS) and a single-step chemical reaction. The database, created in the configuration of a temporal mixing layer, probes the effect of the initial Reynolds number, Re 0 , of the initial pressure, p 0 , and of the initial composition of the two mixing-layer streams. The reaction is initiated in a turbulent flow and in each simulation the computations are pursued past a time when a maximum average-volumetric p is attained, t p p * . The examination of the vorticity and enstrophy equations at a time before reaction initiation and also at t p p * highlights the pivotal role of the high density-gradient magnitude regions (Bellan, 2017) in producing turbulence and the crucial role at t p p * of the baroclinic effect representing the misalignments of gradients of thermodynamic variables. Compared to the classical mixture fraction equation, the results show that the mixture fraction obeys an equation in which there is an additional diffusion term having a larger r.m.s. magnitude than that of the mixture-fraction typical diffusion term. An assessment of the Conditional Source-term Estimation (CSE) model assumptions found that, using an accurate mixture fraction probability density function (PDF), one can obtain a very good representation of the turbulent reaction rate in the most intense reaction regions, however the quality of the predictions of CSE deteriorated significantly when a common model for the PDF, the β -PDF, was used despite the β -PDF being constructed with the accurate moments extracted from the DNS. In the regions of minimal reaction, the CSE model using the exact PDF extracted from the DNS does not provide an accurate representation of the turbulent reaction rate, a fact which is attributed to the combined effect of lack of correlation between fluctuations of the reaction rate and of the mixture fraction, and to the strong correlation of the thermodynamic variables through the real-gas EOS in regions of colder and denser fluid. [ABSTRACT FROM AUTHOR]

Reactive transport modelling (RTM) is a powerful tool for understanding subsurface systems where fluid flow and chemical reactions occur simultaneously. RTM has been widely used to understand the formation of dolomite by replacement of calcite, which can be an important control on carbonate reservoir quality. Dolomitisation is a reactive transport process governed by slow dolomite precipitation and cannot be correctly simulated without a kinetic rate model. The new CSMP++GEM coupled RTM code uses the GEMS3K kernel for solving geochemical equilibria by the Gibbs energy minimisation method with the CSMP++ framework that implements a hybrid finite element-finite volume method to solve partial differential equations. The unique feature of the new coupling is the mineral reaction kinetics, implemented via additional metastability constraints. CSMP++GEM is able to simulate single-phase flow and solute transport in porous media together with chemical reactions at different pressure, temperature, and water salinity conditions. This RTM assures mass conservation which is crucial when simulating transport of solutes with low concentrations over geological time. A full feedback of mineral dissolution/precipitation on the fluid flow is provided via corresponding porosity/permeability evolution and two source terms in the pressure equation. First, the mass source term accounts for the mass of solutes released during mineral dissolution or taken from the solution by mineral precipitation. The second source term attributes to the fact that the solution density is affected by mineral dissolution/precipitation, too. This effect is included through the equivalent water salinity, which is calculated from the total amount of dissolved solutes and is used to update the properties of saline water from the H $$_2$$ O-NaCl equation of state. This paper puts emphasis on the thorough mathematical derivation of the governing equations and a detailed description of the numerical solution procedure. Two sets of benchmarking results are presented. The first benchmark is a well-known 1D model of dolomitisation by MgCl $$_2$$ solution with thermodynamic reactions. In the second benchmark, CSMP++GEM is compared with TOUGHREACT on a 1D model of dolomitisation by sea water taking into account mineral reaction kinetics. The results presented in this paper demonstrate the ability of the CSMP++GEM code to correctly reproduce dolomitisation effects. [ABSTRACT FROM AUTHOR]

This paper examined the capabilities of computational fluid dynamics (CFD) techniques in modeling the transport and chemical transformation of power plant plumes. Based on turbulence characteristics, we divided the plume evolution into two stages. The first stage is referred to as the jet-dominated region (JDR), characterized by a high momentum jet flow of flue gas. The second stage is referred to as the ambient-dominated region (ADR), driven by atmospheric boundary layer turbulence. Then, we compared the three methods in simulating plume transport in the JDR, i.e., Reynolds-averaged Navier–Stokes (RANS) model with velocity inlet (RANS-VI), RANS with volume source (RANS-VS) and Large-Eddy Simulation (LES). The VI method treats the stack exit as a surface inlet to the simulation domain, while the VS method defines a volume region containing the source with a specific emission rate. Our evaluation against a relevant wind tunnel experiment suggested that RANS-VI is most appropriate for power plant plume transport in the JDR. LES can achieve more accurate results, but the improvement in accuracy over RANS-VI may not justify its high computational costs. Nevertheless, LES is still preferable for JDR simulations if computational costs are not a constraint. The VS method requires refined mesh in the source region in order to achieve accurate results, making it no different from the VI method in the JDR. Next, for our ADR evaluation, we simulated plume chemical evolution in a well-characterized 1999 TVA Cumberland aircraft plume transect field study. RANS-VS was adopted, as proper RANS-VI and LES simulations would be exceedingly expensive in terms of computational costs. The overall model performance was satisfactory, evinced by the predicted concentrations of SO 2 , O 3 , NOx as well as NO 2 /NOx ratios fell within the variations in the observed values for large portions of the plume distributions. An indirect JDR evaluation by comparing the predicted plume centerline trajectory with that estimated using a semi-empirical equation and Cumberland-specific parameters indicated that RANS-VS can reasonably predict plume evolution in the JDR as well. Our study suggested that properly configured CFD simulations (e.g., turbulence model, source representation and mesh sensitivity) were able to capture the evolution of chemical reactive plumes from power plants in high accuracy, however, with high computational cost and thus limited applicable spatial range. [ABSTRACT FROM AUTHOR]

In this work, we develop a non-isothermal model for diesel particulate filters including exothermic and competing chemical reactions. We begin with an isothermal, single-reaction model and we gradually increase its complexity. By comparing various models, we aim at establishing the minimum degree of complexity required to effectively model the system under investigation. Based on the numerical simulations, we conclude that isothermal models are adequate only if the temperature of the catalyst is, at all times, completely below or completely above a critical temperature. However, if the goal is to predict the critical temperature, only non-isothermal models should be used. The results with competing reactions, on the other hand, show that the presence of competing reactions does not affect significantly the overall conversion in the filter. [ABSTRACT FROM AUTHOR]

An in-line mixing system mainly consists of an injecting part and a mixing part. We consider that the injecting part will be more important for highly reactive species, because some reactions terminate before the mixture reaches the static mixer. This issue has limited the applications of in-line mixing. In this study, we developed an improved injecting system to resolve this issue. We used a swirl f low ejector (SFE) in which a swirl driving f low is supplied from the entire inner circumferential surface and a suction f low is injected at the center of the channel. Through CFD simulations, we revealed that the suction f low is diffused by the swirl driving f low, and mixing proceeded rapidly. In the early step of mixing, the mixing time of the new system was around four times shorter than that of the conventional system. We also performed an experiment using reactive f luids that gel upon poor mixing, and we clearly demonstrated the effectiveness of the SFE. Finally, we found that the combined use of the SFE and the static mixer is the most effective approach. [ABSTRACT FROM AUTHOR]

We consider a model for reactive flow in a fractured formation. The main aim is to study the complex interplay of advection–diffusion flow mechanisms in a fracture–matrix system combined with different chemical reactions taking place. In particular we wish to estimate how a core flooding experiment might behave on larger scale. Brine is injected through a fracture network and ions diffuse into a surrounding low permeable matrix rock where reactions occur. We formulate the interaction between fractures and matrix in the form of transfer functions. The model takes the form of a transport-reaction PDE system for the fracture coupled to an ODE system for the matrix. The chemistry we consider is represented by the interaction of MgCl 2 brine with chalk rock. The involved chemistry bears essential features of the interactions between more complex brines such as seawater and carbonate. This is of high interest since chemistry-driven processes can aid to improved oil recovery from fractured carbonate reservoirs. The injected brine dissolves calcite mineral and precipitates magnesite. Cations ( Ca 2 + and Mg 2 + ) are exchanged on the mineral surface by a substitution mechanism. Reaction kinetic parameters are obtained from experimental data. The numerical code is verified against analytical solutions for the case where reactions do not occur and for linear adsorption of species. First, the flow along a single fracture is analyzed by a parameter study. The behavior can be categorized into regimes determined by the efficiency of species transfer between fracture and matrix and by the efficiency of the dissolution/precipitation reactions. This is further dependent on the magnitude of two characteristic dimensionless numbers alone and the behavior can be translated from one scale to another. The one-fracture model is generalized to study flow through a network of fractures and we relate our previous conclusions to the more complex system. The behavior along individual flow paths is characterized by their dimensionless numbers. The fracture geometry determines the flow distribution (which regions receive the most brine) and the interaction efficiency (whether ions diffuse effectively into the matrix and react). Early injectant breakthrough implies the existence of a zone with low matrix-fracture interaction. [ABSTRACT FROM AUTHOR]

In this paper we analyse, numerically and experimentally, the laminar reactive flow in a cylindrical cavity with a rotating end wall. A basic solution is initially in the cavity and an acid solution is introduced at very low velocity through the center of the stationary endwall when the flow in the cavity is at the steady state. The effect of the different flow structures obtained at different Reynolds numbers on the irreversible fast acid–base neutralization is measured with a simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) technique and simulated numerically with a finite volume code. The observed flow structure, the recirculation bubbles in the vortex breakdown regions as well as the numerical velocity profiles are in agreement with the measurements and with previous studies. The range of measured concentrations is limited to regions where the molar fraction of the base ( x B ) is larger than 0.57. The comparison between the experimental and numerical contours of concentration of base solution at Re = 1000 and 1500 are in general agreement. At larger Reynolds numbers ( Re = 1700, 2000 and 2300), the experimental and numerical contours of concentration of base solution inside the vortex breakdown bubbles differ because of the relatively large concentration of product (i.e. x B < 0.57) in these regions, which is predicted by the numerical simulations. The effects of small lateral displacements of the axis of rotation with respect to the axis of the cylindrical cavity on the flow and the chemical reaction are analyzed. It has been found that for the fast irreversible reaction considered the small displacements do not increase significantly the reaction rate but improve the mixing of the product of the reaction. [ABSTRACT FROM AUTHOR]

One important strategy for process intensification is the enhancement of yield and selectivity in fast gas–liquid reactions, like oxidations, hydrogenations or halogenations. However, the interplay between fluid dynamics and competitive chemical reactions has not yet been understood to an extent that allows tailoring the flow and concentration fields for intensified reactions. To understand the interplay, the fluid dynamic conditions surrounding Taylor bubbles rising in an organic solvent are studied and compared to data of aqueous systems from the literature. The local flow fields are measured using Particle Image Velocimetry (PIV) and compared to spectroscopically derived selectivity data of a competitive consecutive gas–liquid reaction. The general rising behavior of Taylor bubbles in methanol is confirmed to be similar to those of bubbles in aqueous systems. However, as surface active agents do not affect the interface mobility in organic solvents, the local flow structures in the bubble wake differ significantly from those of bubbles rising in water, impacting the mixing behavior. Finally, the flow fields are compared to the concentration fields of the main and side products. Thereby, a decisive influence of the fluid dynamics on yield and selectivity becomes apparent, unveiling the potential for process intensification. [Display omitted] • Local flow and concentration fields around Taylor bubbles in methanol. • Visualization of the selectivity of a competitive consecutive reaction. • Influence of flow field on yield and selectivity for process intensification. [ABSTRACT FROM AUTHOR]

Vortices generation and flow dynamics are investigated by a numerical calculation with LES methodology on the evaporative surface including chemical reactions. For simplicity, fuel is radially injected from the surface in order to decouple pyrolysis of solid fuel from the governing equation and consideration of heat transfer balance. Nevertheless its simple treatment of chemical reactions and fuel pyrolysis, numerical results captured very fundamental understandings in terms of averaged temperature, velocity profile, and mixture fraction distribution. Results showed that a well-defined turbulent velocity profile at the inlet becomes twisted and highly wrinkled in the downstream reaching the maximum velocity at far above the surface, where the flame is located. And the thickness of boundary layer increases in the downstream due to the enhanced interaction of axial flow and mass injection from the surface. Also, chemical reaction appears highly active and partially concentrated along the plane where flow condition is in stoichiometric. In particular, flame front locates at the surface where mixture fraction Z equals to 0.07. Flame front severely wrinkles in the downstream by the interaction with turbulences in the flow. Partial reactions on the flame front contribute to produce hot spots periodically in the downstream attaining the max temperature at the center of each spot. This may take the role of additional unsteady heat generations and pressure perturbations in the downstream. Future study will focus on the evolution of hot spots and pressure perturbations in the post chamber of lab scale hybrid rocket motors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reduced order modeling of non-catalytic partial oxidation of natural gas. • Low computational effort through a physics-based and compact model. • Validation against semi-industrial test plant experiments and CFD. • Demonstrated exibility and reliability of the model for a broad spectrum of operating parameters. • Analysis of conversion processes in different reactor zones. A reduced order model (ROM) for the non-catalytic partial oxidation (POX) of natural gas was developed and validated against large-scale numerical and experimental results. The ROM utilizes a network of perfectly stirred reactors, each describing a distinctive reactor zone and corresponding conversion processes. The zone definition is based on the CFD calculation of reactive flow, resulting in a compact, physics-based model that is valid for a broad range of POX reactors. The ROM is capable of predicting global reactor characteristics and flow field pattern within a short period of time, enabling the optimization of reactor geometry and the boundary and operating conditions. Additionally, the ROM can be used to evaluate detailed chemical reactions mechanisms. The ROM is validated against semi-industrial process data, and used to analyze the influence of each reactor zone on the overall species conversion. A new correlation between the fuel slip from the burner to the downstream reactor zones, the steam injection, and the λ value is built. [ABSTRACT FROM AUTHOR]

We provide empirical evidence that the eddy diffusivity $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}D_{{t}\alpha }$ and the turbulent Schmidt number ${\mathit{Sc}}_{{t}\alpha }$ of species $\alpha $ ($\alpha =\mathrm{A}, \mathrm{B}$ or $\mathrm{R}$) change with a second-order chemical reaction ($\mathrm{A} + \mathrm{B} \rightarrow \mathrm{R}$). In this study, concentrations of the reactive species and axial velocity are simultaneously measured in a planar liquid jet. Reactant A is premixed into the jet flow and reactant B is premixed into the ambient flow. An optical fibre probe based on light absorption spectrometry is combined with I-type hot-film anemometry to simultaneously measure concentration and velocity in the reactive flow. The eddy diffusivities and the turbulent Schmidt numbers are estimated from the simultaneous measurement results. The results show that the chemical reaction increases ${\mathit{Sc}}_{t\mathrm{A}}$; ${\mathit{Sc}}_{t\mathrm{B}}$ is negative in the region where the mean concentration of reactant B decreases in the downstream direction, and is positive in the non-reactive flow in the entire region on the jet centreline. It is also shown that ${\mathit{Sc}}_{t\mathrm{R}}$ is positive in the upstream region whereas it is negative in the downstream region. The production terms of axial turbulent mass fluxes of reactant B and product R can produce axial turbulent mass fluxes opposite to the axial gradients of the mean concentrations. The changes in the production terms due to the chemical reaction result in the negative turbulent Schmidt number of these species. These results imply that the gradient diffusion model using a global constant turbulent Schmidt number poorly predicts turbulent mass fluxes in reactive flows. [ABSTRACT FROM AUTHOR]

Abstract: A numerical technique that uses dynamic adaptive chemistry (DAC) with operator splitting schemes to solve the equations governing reactive flows is developed and demonstrated. Strang-based splitting schemes are used to separate the governing equations into transport fractional substeps and chemical reaction fractional substeps. The DAC method expedites the numerical integration of reaction fractional substeps by using locally valid skeletal mechanisms that are obtained using the directed relation graph (DRG) reduction method to eliminate unimportant species and reactions from the full mechanism. Second-order temporal accuracy of the Strang-based splitting schemes with DAC is demonstrated on one-dimensional, unsteady, freely-propagating, premixed methane/air laminar flames with detailed chemical kinetics and realistic transport. The use of DAC dramatically reduces the CPU time required to perform the simulation, and there is minimal impact on solution accuracy. It is shown that with DAC the starting species and resulting skeletal mechanisms strongly depend on the local composition in the flames. In addition, the number of retained species may be significant only near the flame front region where chemical reactions are significant. For the one-dimensional methane/air flame considered, speed-up factors of three and five are achieved over the entire simulation for GRI-Mech 3.0 and USC-Mech II, respectively. Greater speed-up factors are expected for larger chemical kinetics mechanisms. [Copyright &y& Elsevier]

• A three-dimensional discrete Boltzmann model for simulation of detonations is developed using a unified formulation. • The proposed model fully couples the compressible flow, temperature field, and chemical reactions. • An improved discrete velocity model D3V30 is constructed with excellent symmetry. • Rectangular and diagonal detonation modes are successfully reproduced, showing effects of initial conditions. A discrete Boltzmann model (DBM) for compressible reactive flows, with a two-step reaction scheme is presented. The discrete velocity model is modified using the characteristic points of the platonic solids, which leads to excellent spatial symmetry. In the continuum limit, the reactive Navier-Stokes (NS) equations are recovered. This DBM is validated by classic one-dimensional (1D) Riemann problems and 1D detonation. The numerical results agree well with the analytical solutions. Using this model, we simulate three-dimensional (3D) detonations in a rectangular tube. The characteristic features of the 3D detonation are well captured. Two types of experimentally observed detonation modes, namely rectangular mode and diagonal mode are reproduced by the DBM. It is found that the final structures of the detonation are related to the initial perturbation and the width of the tube. The similarity between the diagonal mode and the rectangular in-phase mode is obtained. The predictions of the DBM are in excellent qualitative agreement with the previous studies. Our simulation results indicate a great potential of the DBM to simulate complex reactive flows. [ABSTRACT FROM AUTHOR]

The present work focuses on the large coherent structures of a turbulent, reacting and imperfectly-expanded supersonic jet. These have been extracted from a Large Eddy Simulation (LES) including chemical reactions by Spectral Proper Orthogonal Decomposition (SPOD). While SPOD is now a standard tool for non-reactive flows, very few studies have dealt with reactive jets. The article shows that the pressure and axial velocity fields exhibit coherent wave-packets with a well-defined wavelength and amplitude envelope. The shock/recompression cells have a strong effect on the amplitude of the wave-packet, but a weak effect on the wavelength. The temperature field exhibits a lower self-coherence and exhibits small scale structures upstream, generated within the mixing layer, and an irregular pattern of larger structures downstream in agreement with Prasad and Morris (2020) [65]. A high-energy coherent structure has been observed at a Strouhal number of S t = 0.4 (normalized by the jet diameter and the jet exit velocity), which appears to result from a mutual reinforcement between the main shear layer instability and the vortex shedding from the normal shock. An attempt is made to model the wave-packets using the parabolized stability equations (PSE) about the mean flow, ignoring the chemical reactions. The PSE solution fails to model the temperature fluctuations, but shows rather good agreement with the leading SPOD modes of pressure and axial velocity downstream. This reveals that the flame impacts the pressure and velocity wave-packets in a weak manner: the coherent structures in the pressure and velocity field are generated by hydrodynamic convective instability, without being significantly altered by the reactive nature of the flow. [ABSTRACT FROM AUTHOR]

We investigate the irreversible evolution of a small system in which a chemical reaction takes place. We have two main goals: the first requires to find an equation to produce a time-irreversible behavior, the second consists in introducing a simple exactly solvable model in order to understand basic facts in chemical kinetics. Our basic tool is the transition function counting the number of paths joining two points in the reactive coordinates system. An exact quantum Smoluchowski equation is derived for the reactive system in vacuum, in the presence of a solvent in equilibrium at any time with the reactive system a new Smoluchowski equation is obtained. The transition from a quantum regime to a classical one is discussed. The case of a reactive system not in equilibrium with its neighborhood is investigated in terms of path integral and via a partial differential function. Memory effects and closure assumptions are discussed. Using a simple potential model, the chemical rate constant is exactly calculated and questions such as the meaning of the activation energy or the physical content of the so-called prefactorare investigated. [ABSTRACT FROM AUTHOR]