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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]

Carbonatites, carbon-rich magmatic rocks, are thought to form by low-degree partial melting of a relatively carbon-poor mantle followed by protracted differentiation and immiscibility. However, the nature of parental magmas and the characteristics of the early stages of differentiation that shape the subsequent crystal and liquid lines of descent remain poorly constrained. To provide new constraints, deep crustal cumulative xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatite magmas, were studied. We use major and volatile elements in primitive olivine-hosted melt inclusions, as well as major and trace elements in crystals, to reconstruct the conditions of formation and evolution of cumulates (pressure, temperature, composition). Xenoliths are composed of olivine, diopside, phlogopite, amphibole and accessory minerals. One remarkable feature is the presence of diopside and phlogopite oikocrysts enclosing roundish olivine chadacrysts. Melt inclusions do not have vapor bubble and have major element compositions resembling olivine nephelinite (7–10 wt % MgO after corrections for post-entrapment crystallization). The absence of vapor bubbles implies that the concentrations of volatile components (i.e. CO2, H2O, S) were not compromised by well-known post-entrapment volatile loss into the vapor bubble. Based on the melt inclusion study by SIMS, the volatile concentrations in olivine nephelinite magmas (early stage of differentiation) at Oldoinyo Lengai were 20–130 ppm S, 390–4500 ppm F, 50–540 ppm Cl, up to 6074 ppm CO2 and up to 1.5 wt % H2O. According to the calculated CO2-H2O saturation pressures and geophysical data, xenoliths from Embalulu Oltatwa document a mushy reservoir in the lower crust. Primitive olivine nephelinite melt inclusions have higher H2O contents than olivine nephelinite lavas from other further South volcanoes from the North Tanzanian Divergence (0.2–0.5 wt % H2O), suggesting that the lithospheric mantle source beneath the Oldoinyo Lengai is more hydrated than the mantle beneath the rest of North Tanzanian Divergence. We present a model in which resorption features observed in olivine chadacrysts, together with the LREE enrichments in olivine grains, are the consequences of reactive porous flows in a deep crustal mushy reservoir. We provide constraints on the major, trace and volatile element composition of the parental magmas of carbonatite series and demonstrate with Rhyolite-MELTS models that phonolites and related natrocarbonatites from Oldoinyo Lengai can be produced by protracted differentiation of olivine nephelinite melts. [ABSTRACT FROM AUTHOR]

This paper is concerned with the analysis of the mixed convective magnetohydrodynamic (MHD) flow of a reactive couple stress multi-walled carbon nanotube − Ag / C 2 H 6 O 2 hybrid nanofluid in a porous vertical channel subjected to quadratic thermal radiation along with a uniform inclined magnetic field applied to the channel walls. The flow is driven by the pressure gradient force and the buoyancy force, which is modeled based on the nonlinear Boussinesq approximation. The temperature-dependent reaction rate of the reactant molecule is derived using the Arrhenius law. The momentum and energy equations that govern the system are modeled in consideration of slip and convective conditions. The governing equations are non-dimensionalized by applying relevant dimensionless parameters and are solved using the homotopy analysis method (HAM). To analyze the irreversibilities in the system, the entropy generation number and the Bejan number are defined. Different important physical parameters developing in the system are considered for analysis, and their effects are scrutinized on the velocity and temperature profiles along with entropy generation. The emphasis is given to the concentration of nanoparticles along with the parameters arising due to the reactions of the fluid, buoyancy force, inclined magnetic field, thermal radiation, and porous material. The analysis reveals that the velocity and temperature of the fluid lowers with a higher concentration of nanoparticles, radiation parameter, and Hartmann number, whereas develops for the higher slip parameters and inclination of the magnetic field. The entropy generation rate increases with rising slip parameters and depletes for higher nanoparticle concentration, radiation parameter, Hartmann number, and inclination angle. The irreversibility in the system remains dominant due to heat transfer with higher Frank-Kameneskii and activation energy parameters, Hartmann number, and angle of inclination. [ABSTRACT FROM AUTHOR]

This study presents a new single-phase transformer-less grid-connected inverter based on a six-phase interleaved dc/dc converter as a suitable topology for PV applications. The proposed topology consists of a dc input and multi-output in the dc-link side which results in production of six levels per half cycle. The voltage of the inverter at output side is 7-level that is injected into the network. The voltage of PV panels is low and this problem is solved by increasing the voltage level in the interleaved converter. Besides, the input current ripple of the interleaved dc/dc converter is very low which causes to improve the quality of the injected current into the grid through a PV panel. For control of the power switches and active/reactive power flows, the model predictive control (MPC) method is applied. The proposed system is capable of creating different voltage levels in step-up/down at the dc-link side and this will make it suitable for working in a wide range of power in the grid-tied. Besides, the total voltage blocking (TVB) of the power switches at the inverter side is greatly decreased. Consequently, the efficiency of the proposed system is high. To prove the accuracy of theoretical calculations, the proposed topology for a 900 W prototype at an operation of 50 Hz is built and tested in the laboratory. [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]

A novel set of experiments and reactive flow modeling of pentaerythritol tetranitrate (PETN) is presented. Here, the specific phenomenon of shock to detonation transition is examined, where an initial, relatively weak shock is propagated into pressed PETN powder at 1.65 g/cm 3 and the subsequent buildup to detonation is observed experimentally. These experiments, in conjunction with reactant and products' equations of state, are utilized for building reactive flow models. [ABSTRACT FROM AUTHOR]

Due to their simplicity, cheapness, and ease of maintenance, induction motors (IMs) are the most widely used motors in the industry. However, if they are not properly controlled, the load torque and motor speed will fluctuate in an unsatisfactory fashion. To effectively control the load torque and speed of these IMs, it is necessary to use specialized drives. The entire system (IMs + Drives) will experience uncertainty, nonlinearities, and disruptions, which calls for an outstanding performance control structure. The sensorless sliding mode predictive torque control (SSM-PTC) for both AC-DC converter and DC-AC inverter, which are utilized for feeding the IM, is investigated in this work. The AC-DC converter is controlled using the SSM-PTC method in order to follow the DC-link reference voltage throughout any changes in the operating point of the IM. While the DC-AC inverter is controlled using a sensorless predictive power control (SPPC). Within a unity power factor, this SPPC regulates the reactive power flow between the motor and the supply to account for the undesirable harmonic components of the grid current. In addition, an experimental performance improvement of SSM-PTC of IM supplied by a 5-leg AC-DC-AC power converter using extended Kalman filter (EKF) without weighting factor (WF) is also studied in this work. Design and implantation of the suggested control systems are performed using a dSPACE 1104 card. The experimental results of the proposed converter control demonstrate that the suggested approach effectively regulated the DC link, reducing load torque and speed fluctuations. In the context of inverter control, a prompt active power response yields a motor current waveform that resembles a sinusoidal pattern, exhibiting minimal levels of harmonic distortion. [ABSTRACT FROM AUTHOR]

The flow‐induced dissolution of porous rocks governs many important subsurface processes and applications. Solute mixing, which determines pore‐scale concentration fields, is a key process that affects dissolution. Despite its importance, the effects of pore‐scale mixing on large‐scale dissolution patterns have not been investigated. Here, we use a pore network model to elucidate the mixing effects on macroscopic dissolution patterns and solute transport. We consider two mixing rules at pore intersections that represent two end members in terms of the mixing intensity. We observe that the mixing effect on dissolution is the strongest at moderate Damköhler number, when the reactive and advective time scales are comparable. This is the regime where wormholes spontaneously appear. Incomplete mixing is shown to enhance flow focusing at the tips of the dissolution channels, which results in thinner wormholes and shorter breakthrough times. These effects on passive solute transport are evident independent of initial network heterogeneity. Plain Language Summary: When a reactive fluid infiltrates the rock, the dissolution channels (wormholes) can spontaneously form, in which the flow and transport of reactant focus. The formation and growth of such channels is a complex phenomenon in which the processes taking place at the micro‐scale are strongly coupled with the macro‐scale patterns. One of these processes is the mixing of reactant‐saturated water at pore intersections. In this paper, we study how the intensity of the mixing process impacts the shapes and growth velocities of the dissolution channels. We find that when the mixing at pore intersections is relatively weak, the flow focuses more strongly in front of the wormhole tip, which reduces the width of the wormhole and leads to its faster propagation and early breakthrough. These effects are also evident from tracer breakthrough curves. Our findings contribute to the understanding of dissolution‐induced patterns, with implications to subsurface flow‐related processes such as karst formation and contaminant migration. Key Points: Mixing at pore intersections can have a major impact on macroscopic dissolution patterns and solute transportMixing effect is the strongest when reactive and advective time scales in the system are comparableMixing effect on dissolution increases as network heterogeneity decreases [ABSTRACT FROM AUTHOR]

Regional paleoregolith is found to exist immediately below unconformities separating basin fills from basement rocks in sedimentary basins. However, the controlling role of paleoregolith on unconformity-type uranium mineralization has not been quantitatively addressed before. Coupled hydrothermal fluid flow and reactive mass transport modeling are therefore performed in this study by using the software TOUGHREACT. The modeling results reveal that preferential flow occurs in the regolith due to its relatively high permeability in comparison with that of the host rocks. The thicker the regolith is, the more concentrated the fluids in the footwall of a fault zone are, leading to more compact and higher-grade deposits therein, and vice versa. Also, displacement of the regolith caused by fault offset plays an important role, as it appears to control the shape of uranium deposits. When the displacement is less than 30 m, the deposits are characterized by a more compact shape. When the displacement is over 60 m, the deposits extend more laterally and even exhibit a 'discrete' shape due to the expelling effect of downslope flow that occurs at the fault offset site. [ABSTRACT FROM AUTHOR]

In this article, the magnetohydrodynamic flow of a chemically reactive blood-gold nanofluid between two rotating disks is examined. At the lower disk surface, the thermal convective and zero mass flux conditions are considered, while the upper disk is kept at a constant temperature and concentration. The mathematical formulation of this analysis is presented in the form of PDEs. By means of proper similarity variables, PDEs are transformed into ODEs. The perseverance of this research is to investigate the influences of different entrenched factors, which are established during the transformation procedure, on the blood-gold nanofluid flow. The numerical solution of the modeled problem is established using the bvp4c MATLAB function. The correctness of the present model is confirmed by a comparison between the outcomes of the current numerical solution and those from previously published studies. The outcomes exhibit that the solid volume fraction increases both the axial and tangential velocities of the blood-gold nanofluid flow while decreasing its temperature. It is originated that the solid volume fraction has a dual effect on radial velocity of the blood-gold nanofluid flow. Also, we have seen that the axial velocity of the lower disk is greater for blood-gold nanofluid flow, while at the upper disk the axial velocity is lesser for blood-gold nanofluid flow. In addition, the pure blood has maximum temperature. It is observed that the axial, radial, and tangential velocities of the blood-gold nanofluid flow increase while the thermal profile reduces with the increasing Casson factor. [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]

The purpose of the current study is to develop numerical capability to analyze the flow structures of the scramjet engine in which many complex physical phenomena are involved, such as shock waves, breakup, atomization, and chemical reactions. To understand these complex physical phenomena, we first proposed the five-equation multiphase flow model coupling with the Lagrangian method to reproduce the process of fuel atomization and evaporation in a flow over a side jet problem. Shock waves, recirculation zones, and breakup processes of droplet particles were well captured in the computational works. It was shown that the five-equation multiphase model achieved better resolution of the shock-capturing comparing with the single-phase Navier–Stokes equation coupling with the Lagrangian approach. In addition, the single-step reaction model was performed with the current five-equation multiphase model to simulate the detonative cell in the detonation flow problem. The detonation waves under various operating conditions were discussed. Finally, a preliminary simulation is applied to the flow phenomena through DLR scramjet. The current works have achieved satisfactory agreement compared to the experimental data no matter in reacting flow case or nonreacting flow case. [ABSTRACT FROM AUTHOR]

In this work, the influence of gas–solid drag and heat transfer coefficient models on the prediction capacity of the Euler–Euler approach to simulate reactive bubbling fluidized bed flows is studied. Three different cases are considered, a non-reactive bidisperse bubbling fluidized bed flow (Case 1), and two reactive polydisperse flows in bubbling fluidized beds, one for biomass gasification (Case 2), and the other for biomass pyrolysis (Case 3). The Gidaspow, Syamlal–O'Brien, and BVK gas–solid drag models and the Gunn, Ranz–Marshall, and Li–Mason gas–solid heat transfer correlations are investigated. A Eulerian multiphase approach in a two-dimensional Cartesian domain is employed for the simulations. Computational results for the three cases are compared with experimental data from the literature. The results obtained here contribute to a better understanding of the impacts of such closure models on the prediction ability of the Euler–Euler approach to simulate reactive flows. The results indicate that, for the simulation of reactive flows in bubbling fluidized bed reactors, the kinetic modeling of the reactions has a global effect, which superposes with the influence of the drag and heat transfer coefficient models. Nevertheless, local parameters can be noticeably affected by the choice of the interface closure models. Finally, this work also identifies the models that lead to the best results for the cases analyzed here, and thus proposes the use of such selected models for gasification and pyrolysis processes occurring in bubbling fluidized bed reactors. [ABSTRACT FROM AUTHOR]

This study numerically investigated the combustion instability and characteristics of a laboratory-scale gaseous hydrogen-fueled scramjet combustor. For this purpose, a numerical simulation with an improved detached eddy simulation and a detailed hydrogen/oxygen reaction mechanism was performed. The numerical framework used high-resolution schemes with high-order accuracy to ensure high resolution and fidelity. A total of five fuel injection pressures were considered to characterize the combustion instability as a function of the equivalence ratio. A sampling time of up to 100 ms was considered to sufficiently accumulate several cycles of low-frequency combustion instability dynamics with a period in the order of 100 Hz. Numerical results revealed the repetitive formation/dissipation dynamics of the upstream-traveling shock wave, and it acts as a key factor of combustion instability. The period and derived principal frequency of these upstream-traveling shock waves is several ms. The frequency analysis showed that the instability frequency increased in the low-frequency range as the combustion mode transitioned from the cavity shear-layer to the jet-wake type. This characteristic was derived from the transition in combustion mode at the same equivalence ratio. Therefore, it suggests that the instability frequency shifting is governed by the combustion mode rather than the equivalence ratio. These comprehensive numerical results demonstrated not only the effect of the equivalence ratio but also the important role of the combustion mode on the low-frequency combustion instability. [ABSTRACT FROM AUTHOR]

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Matrix acidizing is one of carbonate reservoirs' most efficient and widely implemented stimulation techniques. It improves productivity and flow capacity by creating new conductive flow channels called wormholes. The propagation of these channels has been a topic of interest as many researchers tried to investigate this phenomenon experimentally, theoretically, and numerically. Among various models, the two-scale continuum (TSC) model is the most common and reliable model due to its ability to predict better results as it combines Darcy and pore scales to capture the phenomenon. However, the main disadvantage of using the TSC model is its high computational cost. This highlights the need for a computationally efficient model that reduces that cost while maintaining solution accuracy. Also, examining wormhole propagation in 3D perforation is untouched yet. In this paper, we developed a numerical model in-house using MATLAB® software to simulate the wormhole generation considering the perforation in three-dimensional space based on the two-scale continuum mathematical model. The model performance is optimized to be a time-efficient simulation model that considers thermal energy transfer beside flowing and reactive mass transfer. Computation efficiency is achieved using the Darcy equation, vectorizing code operations, and implementing a proposed iterative algorithm that is based on the GMRES method. The associated tuning parameters and a proper preconditioner are obtained, which improved the model efficiency by more than 90%. The model used typical data reported in experimental acidizing work. [ABSTRACT FROM AUTHOR]

Physical barrier has been proven to be one of the most effective measures to prevent and control seawater intrusion (SWI) in coastal areas. Mixed physical barrier (MPB), a new type of physical barrier, has been shown to have higher efficiency in SWI control. As with conventional subsurface dam and cutoff wall, the construction of MPB may lead to the accumulation of nitrate contaminants in coastal aquifers. We investigated the SWI control capacity and nitrate accumulation in the MPB using a numerical model of variable density flow coupling with reactive transport, and performed sensitivity analysis on the subsurface dam height, cutoff wall depth and opening spacing in the MPB. The differences in SWI control and nitrate accumulation between MPB and conventional subsurface dam and cutoff wall were compared to assess the applicability of different physical barrier. The numerical results show that the construction of MPB will increase the nitrate concentration and contaminated area in the aquifer. The prevention and control efficiency of MPB against SWI is positively correlated with the depth of the cutoff wall, reaching the highest efficiency at the minimum effective dam height, and the retreat distance of the saltwater wedge is positively correlated with the opening spacing. We found a non-monotonic relationship between the change in subsurface dam height and the extent of nitrate accumulation, with total nitrate mass and contaminated area increasing and then decreasing as the height of the subsurface dam increased. The degree of nitrate accumulation increased linearly with increasing the height of the cutoff wall and the opening spacing. Under certain conditions, MPB is 46–53% and 16–57% more efficient in preventing and controlling SWI than conventional subsurface dam and cutoff wall, respectively. However, MPB caused 14–27% and 2–12% more nitrate accumulation than subsurface dam and cutoff wall, respectively. The findings of this study are of great value for the protection of coastal groundwater resources and will help decision makers to select appropriate engineering measures and designs to reduce the accumulation of nitrate pollutants while improving the efficiency of SWI control. [ABSTRACT FROM AUTHOR]

This model is designed to provide clarity on how blood travels through tiny veins in physiological systems with heat and mass transfer characteristics. Further, the purpose of this paper is to examine the Ohmic heating and heat source/sink effects on peristaltic transport of radiative Casson nanofluid in a nonuniform porous inclined channel in the presence of a normal/inclined magnetic field. We also considered the sway of chemical reaction, Soret and Dufour effects. The momentum, temperature and mass equations for Casson fluid model are obtained with the utilization of the lubrication approach. The exact solutions have been acquired for stream function and axial velocity. Further, the temperature and concentration equations are solved numerically by using the R–K based shooting method. We also tabulated the Nusselt and Sherwood numbers for various relevant parameters. Finally, the impacts of all major factors on the physical properties of the flow for both normal and inclined magnetic fields are explored and discussed in depth using graphs. The Casson fluid velocity is more for an inclined magnetic field than a normal magnetic field. The nonuniform parameter of the channel boosts the trapped fluid bolus size. The heat source/sink parameter improves the temperature field but the opposite trend is observed in the field of concentration. Moreover, the findings are validated with the existing works for some special circumstances. [ABSTRACT FROM AUTHOR]

Restricted by the development of the transient flow and solute reactive transport models for unsaturated soil, empirical functions have been used previously to calculate the mass of dissolved or precipitated salt when they have to be taken into account. Besides, the solute reactive transport process has often been inferred based on measurements that cost lots of time and manpower. HP1 model coupled with PHREEQC provides a suitable tool to improve the estimation of salt distribution during evaporation in saline soil, where the salt dissolution and precipitation cannot be ignored. In this study, we compare the performance of a standard solute transport (SST) model and the HP1 model to examine the improvement of salt distribution estimation. Model results are compared with experimental data sets from four field lysimeters. These columns were exposed to NaCl solution with different concentrations (3, 30, 100, and 250 g/L) and were undergoing the same strong evaporation boundary condition. The pre-existing CaSO4, NaCl and Na2SO4 loads were 1.15, 0.47 and 0.23 g/(100 g of soil), respectively. Simulation results show that HP1 ameliorates the overestimation of salt content by SST in deeper soil due to the absence of dissolution of pre-existing soluble salts, and prevents the concentration of the solute from exceeding the solubilities which would occur in SST-result. Additionally, HP1-predicted results can help trace the transport process of each solute. Based on the results, we strongly suggest that the management of fields sensitive to salt content should make use of a coupled flow and chemical reaction model. [ABSTRACT FROM AUTHOR]

It is often highly difficult to predict the main flow path of reactive fluids in porous media with complexly distributed fractures and/or caves. Based on Darcy's law, this research defines the control domain of fractures/caves that represents the interference range of fractures/caves. This control domain can be used to identify the connectivity possibility between fractures/caves and predict the flow paths of reactive fluids at the optimal flow rate. Furthermore, after simplifying the geometry of fractures/caves, a threshold geometric aspect ratio of 20 is set to distinguish fractures and caves, concerning the flow mechanisms, by clarifying the ranges of control domains. Moreover, the control domain theory is combined with the two-scale continuum model for acidizing carbonate rocks to estimate the flow paths of acid in fractured-vuggy carbonate rocks at an optimal flow rate, thereby validating the accuracy of the reactive fluid main flow path estimation based on the control domain theory. The primary criterion to determine the reactive transport in porous media with complex fracture/cave distribution is the overlap degrees of control domains of adjacent isobaric bodies along their width and length directions, while the directions of isobaric bodies offer supplementary material. If the control domains of two isobaric bodies overlap with each other perpendicular to the flow direction, these isobaric bodies have higher odds of connected fluid flow. [ABSTRACT FROM AUTHOR]

The present study investigates the combustion performance of pure ammonia in a stratified vortex-tube reactive flow (SVRF) concerning stability limits, flame topology, pressure fluctuations, and emissions. The results demonstrate that the SVRF enables efficient and stable combustion of ammonia, characterized by uniform flame topology, low NO emissions, and high combustion efficiency. The lean φg stability limits consistently remain below 0.32 within the qf range of 5.0–30.0 l/min. Moreover, the flame topology remains consistently smooth and uniform throughout the process while maintaining a peak heat release above 5.0 × 107 W/m3. Additionally, pressure fluctuation amplitude generally stays within 100 Pa, indicating a remarkably steady combustion process for ammonia burning in the SVRF. The investigation focuses on the multi-field cooperative coupling, which enhances species and enthalpy transport to increase combustion strength, thereby contributing to a larger stability limit. Various criterion numbers are calculated to quantify the aero-/thermo/flame- dynamic stability. It is found that excellent flame-dynamic/thermo-acoustic stability plays a crucial role in achieving steady combustion of pure ammonia, which can be measured by Ra(x) and the "Gain" of the flame transfer function. The degree of synergy between flame disturbance and fluid disturbance, as well as the response of flame disturbance to fluid disturbance in SVRF, is identified as the primary factor influencing different levels of combustion stability performance. Furthermore, a relationship between aero-/thermo-dynamic stability and flame stability has also been discovered. Favorable aero-/thermo-dynamic stability promotes excellent flame-dynamic behavior by suppressing normal direction fluid fluctuation and resulting in more stable intensity and spatial location fluctuations of the flame. Additionally, momentum flux decreases within the interior region, enhancing good flame-dynamic stability when using pure ammonia as fuel. [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]

Optimal reactive power flow (ORPF) is of great importance for the electrical reliability and economic operation of modern power systems. The integration of distributed generations (DGs) and two-terminal high voltage direct current (HVDC) systems into electrical networks has further complicated the ORPF problem. Due to the high computational complexity of the ORPF problem, a powerful and robust optimization algorithm is required to solve it. This paper proposes a powerful metaheuristic algorithm namely fitness-distance balance-based adaptive gaining-sharing knowledge (FDBAGSK). In the performance evaluation, 39 IEEE CEC benchmark functions are used to compare FDBAGSK with the original AGSK algorithm. Moreover, the proposed algorithm is applied to perform the ORPF task in modified IEEE 30- and IEEE 57-bus test systems. The effectiveness of the FDBAGSK method was tested for the optimization of three non-convex objectives: active power loss, voltage deviation and voltage stability index. The ORPF results obtained from the FDBAGSK algorithm are compared with other optimization algorithms in the literature. Given that all results are together, it has been observed that FDBAGSK is an effective method that can be used in solving global optimization and constrained real-world engineering problems. [ABSTRACT FROM AUTHOR]

Present work is concerned with hydromagnetic bioconvective chemically reactive flow of Reiner-Rivlin nanoliquid. Analysis is constructed for entropy generation. Thermal relation consists of Joule heating, radiation and dissipation. Soret effect for chemically reactive flow is examined. Nonlinear governing systems after adequate transformations are solved by ND-solve technique. Graphical analysis for velocity, microorganism field, entropy rate, thermal field and concentration is analyzed. Graphical description for coefficient of skin friction, microorganism density number, heat transport rate and concentration gradient are studied. Entropy rate increase is detected for higher magnetic parameter while reverse trend holds for velocity. Clearly temperature augments against thermophoresis and radiation. Radiation intensifies entropy rate and heat transport rate. Similar impact of drag force and temperature for magnetic parameter is noticed. Concentration and mass transport rate rise against higher Soret number. Brownian motion variation results in concentration decays. Large Peclet number leads to decrease of microorganism field whereas it intensifies the microorganism density number. [ABSTRACT FROM AUTHOR]

In this paper, we deal with the existence of local strong solution for a perfect compressible viscous fluid, heat conductive and self-gravitating, coupled with a first-order kinetics used in astrophysical hydrodynamical models. In our setting, the vacuum is allowed and as a byproduct of the existence result we get a blow-up criterion for the local strong solution. Moreover we prove a blow-up criterion for the local strong solutions in terms of the velocity gradient, the mass fraction gradient and the temperature similar to the well-known Beale–Kato–Majda criterion for ideal incompressible flows. [ABSTRACT FROM AUTHOR]

We study the General Equations of Non-Equilibrium Reversible–Irreversible Coupling (GENERIC) structure of models for reactive two-phase flows and their connection to a porous-media model for a reactive fluid–rock interaction used in geosciences. For this, we discuss the equilibration of fast dissipative processes in the GENERIC framework. Mathematical properties of the porous-media model and first results on its mathematical analysis are provided. The mathematical assumptions imposed for the analysis are critically validated with the thermodynamical rock datasets. [ABSTRACT FROM AUTHOR]

This study experimentally and numerically investigates the applicability of the DaI and Re criteria for scaling the geometry of a lean premixed swirl combustor during a reaction and in the absence of it. We first set up an experimental system to test the loss of pressure, the flow field, and NOx emissions in a prototype combustor and two models of it scaled to 3/5 of its size. The results showed that the friction in the flow in the prototype decreased with an increase in its intensity, and the corresponding constant DaI model (M-D) exhibited a similar trend, while the constant Re model (M-R) exhibited an adverse trend to that of the prototype. The results of particle image velocimetry (PIV) of the flow field in the non-reactive state showed that regardless of the criterion used and the state of the reaction, the flow fields of the prototype and the models were similar under flows of different strengths. However, a quantitative comparison of their distributions of velocity showed that the peak velocity of the rotating jet of M-R was significantly lower than that of the prototype. PIV results of the flow field in the reactive state exhibited similar phenomena. Moreover, the NOx emissions of M-D were consistent with those of the prototype, while emissions from M-R were significantly higher. The numerical results also showed that the shape of the flame and the pattern of flow of M-R were significantly different from those of the prototype. [ABSTRACT FROM AUTHOR]

Power flow calculation is the basis of power grid planning and many system analysis tasks require convergent power flow conditions. To address the unsolvable power flow problem caused by the reactive power imbalance, a method for adjusting reactive power flow convergence based on deep reinforcement learning is proposed. The deep reinforcement learning method takes switching parallel reactive compensation as the action space and sets the reward value based on the power flow convergence and reactive power adjustment. For the non-convergence power flow, the 500 kV nodes with reactive power compensation devices on the low-voltage side are converted into PV nodes by node type switching. And the quantified reactive power non-convergence index is acquired. Then, the action space and reward value of deep reinforcement learning are reasonably designed and the adjustment strategy is obtained by taking the reactive power non-convergence index as the algorithm state space. Finally, the effectiveness of the power flow convergence adjustment algorithm is verified by an actual power grid system in a province. [ABSTRACT FROM AUTHOR]

Nanofluid lubrication and machining are challenging and significant tasks in manufacturing industries that are used to control the removal of a material from a surface by using a cutting tool. The introduction of a nanofluid to the cutting zone provides cooling, lubricating, and chip-cleaning benefits that improve machining productivity. A nanofluid is a cutting fluid that is able to remove excessive friction and heat generation. Chemical reactions and temperature-dependent density are essential in the thermal behavior of a nanofluid. The present study presents a careful inspection of the chemical reactions, temperature-dependent density, viscous dissipation, and thermophoresis during the heat and mass transfer of a nanofluid along a magnetically driven sheet. The physical attitude of viscous dissipation and the chemical reaction improvement rate in magneto-nanofluid flow is the primary focus of the present research. By applying the proper transformation, nonlinear partial differential expressions are introduced to the structure of the ordinary differential framework. The flow equations are simplified into nonlinear differential equations, and these equations are then computationally resolved via an efficient computational technique known as the Keller box technique. Flow factors like the Eckert number, reaction rate, density parameter, magnetic force parameter, thermophoretic number, buoyancy number, and Prandtl parameter governing the velocity, temperature distribution, and concentration distribution are evaluated prominently via tables and graphs. The novelty of the current study is in computing a heat transfer assessment of the magneto-nanofluid flow with chemical reactions and temperature-dependent density to remove excessive friction and heating in cutting zones. Nanofluids play significant roles in minimum quantity lubrication (MQL), enhanced oil recovery (EOR), drilling, brake oil, engine oil, water-miscible cutting fluids, cryogenic cutting fluids, controlled friction between tools and chips and tools and work, and conventional flood cooling during machining processes. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to examine the effects of velocity slip on the magneto hydrodynamics (MHD) axi‐symmetric viscous fluid flow between two disks having different stretching ratio. The flow takes place in the presence of temperature and concentration jumps. In the presence of joule heating and viscous dissipation, the investigation is carried out. The MHD flows are of utmost importance in industrial and engineering sectors because such flows can control the fluid flows with the help of Lorentz force. MHD flows are also helpful in biological fields such as wound treatments, surgeries, cancer therapy and in diagnosing diseases. The resulting system of PDE's is converted into ODE's by suitable similarity transformation. The HAM is used to solve the resulting non‐linear governing equations. The behavior of velocity, temperature and concentration profiles are observed graphically. When the stretching rate of lower disk is greater than the upper disk then the velocity rises due to increase in stretching ratio. The radial and axial components of velocity increase when the value of magnetic field increases. The temperature profile enhances for Eckert number while converse behavior is seen for stretching ratio parameters. The concentration profile increases when the value of Schmidt number is enhanced. [ABSTRACT FROM AUTHOR]

We introduce algorithmic advancements designed to expedite simulations in OpenFOAM using GPUs. These developments include the following. (a) The amgx4Foam library, which connects the open-source AmgX library from NVIDIA to OpenFOAM. Matrix generation, involving tasks such numerical integration and assembly, is performed on CPUs. Subsequently, the assembled matrix is processed on the CPU. This approach accelerates the computationally intensive linear solver phase of simulations on GPUs. (b) Enhancements to code performance in reactive flow simulations, by relocating the solution of finite-rate chemistry to GPUs, which serve as co-processors. We present code verification and validation along with performance metrics targeting two distinct application sets, namely, aerodynamics calculations and supersonic combustion with finite-rate chemistry. [ABSTRACT FROM AUTHOR]

Abstract The flow‐induced dissolution of porous rocks governs many important subsurface processes and applications. Solute mixing, which determines pore‐scale concentration fields, is a key process that affects dissolution. Despite its importance, the effects of pore‐scale mixing on large‐scale dissolution patterns have not been investigated. Here, we use a pore network model to elucidate the mixing effects on macroscopic dissolution patterns and solute transport. We consider two mixing rules at pore intersections that represent two end members in terms of the mixing intensity. We observe that the mixing effect on dissolution is the strongest at moderate Damköhler number, when the reactive and advective time scales are comparable. This is the regime where wormholes spontaneously appear. Incomplete mixing is shown to enhance flow focusing at the tips of the dissolution channels, which results in thinner wormholes and shorter breakthrough times. These effects on passive solute transport are evident independent of initial network heterogeneity.

This present study communicates entropy generation analysis in an unsteady flow of a reactive hydromagnetic micropolar fluid passing an exponentially stretchable sheet with multiple slip properties. The developed model scrutinizes the impacts of varying viscosity alongside with non-uniform heat source coupled with nonlinear thermal radiation. The formulated nonlinear equations describing the problem are carefully transformed into ordinary differential equations via similar transformations approach, while the solutions to the modified equations are sought using the Galerkin weighted residual method. A strong relationship exists between the results obtained in this study with the related published ones in literature in some limiting conditions. The current investigation reveals that the dimensionless velocity, temperature and concentration profiles depreciate with the unsteadiness parameter, whereas the micropolar material term accelerates the velocity profiles. Besides, the analysis shows that the hydrodynamic slip parameter improves heat and mass transfer irreversibilities while growth in the material micropolar term, Eckert and Prandtl numbers cause a rise in the entropy generation in the system. [ABSTRACT FROM AUTHOR]

Potential CO2 leakage from deep geologic reservoirs requires evaluation on a site-specific basis to assess risk and arrange mitigation strategies. In this study, a heterogeneous and realistic numerical model was developed to investigate CO2 migration pathways and uprising time in a shaly overburden, located in the Malaysian off-shore. Fluid flow and reactive transport simulations were performed by TOUGHREACT to evaluate the: (1) seepage through the caprock; (2) CO2-rich brine leakage through a fault connecting the reservoir with seabed. The effect of several factors, which may contribute to CO2 migration, including different rock types and permeability, Fickian and Knudsen diffusion and CO2 adsorption in the shales were investigated. Obtained results show that permeability mainly ruled CO2 uprising velocity and pathways. CO2 migrates upward by buoyancy without any important lateral leakages due to poor-connection of permeable layers and comparable values of vertical and horizontal permeability. Diffusive flux and the Knudsen flow are negligible with respect to the Darcy regime, despite the presence of shales. Main geochemical reactions deal with carbonate and pyrite weathering which easily reach saturation due to low permeability and allowing for re-precipitation as secondary phases. CO2 adsorption on shales together with dissolved CO2 constituted the main trapping mechanisms, although the former represents likely an overestimation due to estimated thermodynamic parameters. Developed models for both scenarios are validated by the good agreement with the pressure profiles recorded in the exploration wells and the seismic data along a fault (the F05 fault), suggesting that they can accurately reproduce the main processes occurring in the system. [ABSTRACT FROM AUTHOR]

[Display omitted] Aqueous foams are expected to constitute exquisite particularly suitable reactive medium for the oxidation of metals, since the reactant H+ can be supplied through the continuous liquid phase, while the reactant O 2 can be transported through the gas bubbles. To test this hypothesis, we investigated the oxidation of a metallic copper cylinder immersed in an aqueous foam. To study the relation between the transport of these reactants and the kinetics of the chemical reaction we use a forced drainage setup which enables us to control both the advection velocity of the H+ ions through the foam and the foam liquid fraction. We find experimentally that the mass of dissolved copper presents a maximum with the drainage flow rate, and thus with the foam liquid fraction. Modeling analytically the transfer of H+ and O 2 through the foams enables us to show that this non-monotonic behavior results from a competition between the advective flux of H+ ions and the unsteady diffusion of O 2 through the thin liquid films which tends to be slower as the area of the thin liquid films decreases with the drainage flow rate and the liquid fraction. This study shows for the first time how to optimize the foam structure and drainage flow in reactive foams in which the reactants are present both in the liquid and gaseous phases. [ABSTRACT FROM AUTHOR]

Constitutive laws relating fluid potentials and fluxes in a nonlinear manner are common in several porous media applications, including biological and reactive flows, poromechanics, and fracture deformation. Compared to the standard, linear Darcy's law, such enhanced flux relations increase both the degree of nonlinearity, and, in the case of multiphysics simulations, coupling strength between processes. While incorporating the nonlinearities into simulation models is thus paramount for computational efficiency, correct linearization, as is needed for incorporation in Newton's method, is challenging from a practical perspective. The standard approach is therefore to ignore nonlinearities in the permeability during linearization. For finite volume methods, which are popular in porous media applications, complete linearization is feasible only for the simplest flux discretization, namely the two‐point flux approximation. We introduce an approximated linearization scheme for finite volume methods that is exact for the two‐point scheme and can be applied to more advanced and accurate discretizations, exemplified herein by a multi‐point flux stencil. We test the new method for both nonlinear porous media flow and several multiphysics simulations. Our results show that the new linearization consistently outperforms the standard approach. Moreover our scheme achieves asymptotic second order convergence of the Newton iterations, in contrast to the linear convergence obtained with the standard approach. Key Points: State‐dependent permeability produces strong nonlinearity in multiphysics problemsIgnoring state dependency in solution scheme severely impacts convergenceA novel approach differentiating the finite volume flux stencil greatly improves nonlinear convergence [ABSTRACT FROM AUTHOR]

Fluid flow in fracture porosity in the Earth's crust is in general accompanied by crystallization or dissolution depending on the state of saturation. The evolution of the microstructure in turn affects the transport and mechanical properties of the rock, but the understanding of this coupled system is incomplete. Here, we aim to simulate spatio‐temporal observations of laboratory experiments at the grain scale (using potash alumn), where crystals grow in a fracture during reactive flow, and show a varying growth rate along the fracture due to saturation differences. We use a multiphase‐field modeling approach, where reactive fluid flow and crystal growth is computed and couple the chemical driving force for grain growth to the local saturation state of the fluid. The supersaturation of the fluid is characterized by a concentration field which is advected by fluid flow and in turn affects the crystal growth with anisotropic growth kinetics. The simulations exhibit good agreement with the experimental results, providing the basis for upscaling our results to larger scale computations of combined multi‐physical processes in fractured porous media for applications as groundwater protection, geothermal, and hydrocarbon reservoir prediction, water recovery, or storing H2 or CO2 in the subsurface. Plain Language Summary: In the Earth's crust fluid flow can occur in fractured rock and depending on the composition of the fluid and physical conditions minerals can precipitate or dissolve. This affects the properties of the rock system and is for example, of interest to subsurface engineering applications. In this work we simulate observations of laboratory experiments at the grain scale, where crystals grow in an open fracture during fluid flow. In these experiments, the growth rate of the crystals varies along the fracture since the supersaturation of the fluid decreases due to the crystallization. We use a multiphase‐field model for the numerical simulation of crystal growth in the open fracture and combine it with reactive fluid flow. With the presented model the driving force for grain growth is coupled to the local supersaturation, which enables the incorporation of reactive mass transport in open fractures. Our phase‐field simulations agree with the laboratory experiments. The presented simulative approach can be used for upscaling the results on microscale to larger length and time scales and can help to better predict the subsurface behavior for example, of groundwater, fractured geothermal, and hydrocarbon reservoirs. Key Points: Reactive fluid flow with advective mass transfer causes locally variable precipitation rate in open fractureA higher flow velocity or a higher supersaturation results in faster precipitation along the flow channelPhase‐field modeling allows reproduction of laboratory crystal growth experiments from an advecting fluid using transmitted light microscopy [ABSTRACT FROM AUTHOR]

Due to the synergetic effects of several types of nanomaterials, the primary goal of the hybrid nanofluid is to enhance the energy transport capabilities over a base fluid. Hybrid nanofluids have a wide range of applications in the industrial, technical, and medical industries, including solar heating systems, food processing, microchannel heat sinks (MCHS), and medicines. In this article, the researchers have investigated the water‐based hybrid nanofluid flow comprising silver and alumina nanoparticles past a spinning disk. The effect of Brownian motion, activation energy, magnetic field, and thermophoresis are taken into account. The PDEs are transformed into ODEs by means of suitable correspondence transformations. The modeled equations are solved by using a semi‐analytical method known as HAM. Graphical representations of the nanofluid and hybrid nanofluid profiles are used. The current findings are contrasted with those that have already been published and are confirmed to be remarkably comparable. The outcomes showed that the radial and tangential velocities of the nanofluids and hybrid nanofluid reduced as the magnetic factor augmented. Nanofluids and hybrid nanofluid surface drag is increased by magnetic factor. Hybrid nanofluid exhibits higher growth due to the magnetic factor than nanofluids do. The heat transmission rates of nanofluids and hybrid nanoliquid have grown as a result of the thermophoresis factor and nanoparticle volume fractions. In comparison to nanofluids, the hybrid nanofluid also possesses a better thermal conductivity. [ABSTRACT FROM AUTHOR]

In this study, we establish new homogenization results for chemical reactive fluxes in porous media using a nonlinear stochastic model with nonlinear random forces. This model is mathematically represented by a linear stochastic response equation, a nonlinear boundary condition, a nonlinear stochastic diffusion equation, and external nonlinear random forces that affect the solute concentration and diffusion in the fluid phase. A homogenized model made up of a nonlinear stochastic diffusion equation with extra terms reflecting the impact of the adsorption and chemical reactions occurring on the boundaries of the perforations and a stochastic differential equation with extra nonlinear term representing the limit for the surface problem is derived using the periodic unfolding operator method and probabilistic compactness results. To guarantee that the entire sequence converges, we also show the uniqueness result for the limit problem. Finally, we go over some applications for the interaction of chemical fluxes. [ABSTRACT FROM AUTHOR]

5G/Beyond 5G (B5G) networks provide connectivity to many heterogeneous devices, raising significant security and operational issues and making traditional infrastructure management increasingly complex. In this regard, new frameworks such as Anastacia-H2020 or INSPIRE-5GPlus automate the management of next-generation infrastructures, especially regarding policy-based security, abstraction, flexibility, and extensibility. This paper presents the design, workflow, and implementation of a security solution based on Unmanned Aerial Vehicles (UAVs), able to extend 5G/B5G security framework capabilities with UAV features like dynamic service provisioning in specific geographic areas. The proposed solution allows enforcing UAV security policies in proactive and reactive ways to automate UAV dynamic deployments and provisioning security Virtual Network Functions (VNFs) in the onboard Multi-access Edge Computing (MEC) node. A UAV has been ensembled from scratch to validate the proposal, and a raspberry-pi has been onboarded as compute node. The implementation provides a VNF for dynamic UAV management, capable of dynamically loading waypoints into the flight controller to address reactive autonomous flights, and anMLbased VNF capable of detecting image patterns. According to the security policies, the onboard VNFs can be dynamically configured to generate alerts to the framework and apply local reactions depending on the detection made. In our experiments, we measured the time it takes for the solution to be ready after receiving a security policy for detecting patterns in a specific geographical area. The time it takes for the solution to react automatically was also measured. The results show that the proactive flow configuration considering ten waypoints can be enforced in less than 3 s, and a local reactive flow can be enforced in around 1 s. We consider that the results are promising and aligned with other security enabler solutions as part of existing 5G/6G security frameworks. [ABSTRACT FROM AUTHOR]