Chemical Reaction Model Research Articles

A novel combination of mathematical modelling approaches for simulating nearly hypersonic, viscous, reacting magnetogasdynamic flows

This work focuses on the mathematical combination of magnetogasdynamics (MGD) and the Dunn and Kang chemical kinetic model with a multi-component Harten–Lax–van Leer Contact (HLLC) local Riemann solver using high-order interpolation schemes. Due to the nature of nearly hypersonic, unsteady, viscous, reacting MGD flows, the gas dissociates which is taken into account with 11 species and 26 chemical reactions along with the temperature dependent transport properties through the Wilke model. In the present work, the electromagnetic effects are considered by solving a Poisson equation simultaneously with the chemical reaction equations. The non-linear convective terms are treated numerically with third-, fifth- and seventh-order Weighted Essentially Non-Oscillatory (WENO) interpolation schemes along with second-, fourth- and sixth-order central finite difference schemes for the viscous terms. The combination of these numerical and physical models are analysed for stability and validated for benchmark problems such as (a) Hartmann flow as MGD validation test case and (b) the shock-tube problem for testing the chemical reaction model in which case the reaction rate controlling temperature suggested by Park has also been taken into account. Furthermore, a complex physical problem of an external aerodynamic flow over the cube for the Mach number varying from 1.25 to 3 have also been investigated, because a limited number of studies is available for understanding the flow behaviour of sharp cornered blunt bodies such as cubes. The knowledge of shock structures of these objects has become imperative to predict the atmospheric re-entry trajectories of de-orbiting CubeSats, space debris or fragments of launch vehicles. The main physical finding is that the shock structures are observed to be much more resolved compared to previous works, especially in the wake region. The knowledge gap is bridged by detailing the shock structures and showing the dependence of the shock standoff distance on total enthalpy of the flow.

Artificial intelligence in interdisciplinary life science and drug discovery research.

Artificial intelligence in interdisciplinary life science and drug discovery research.

Leaching of Ti and V from the non‐magnetic fraction of ilmenite‐based ore: Kinetic and thermodynamic modelling

AbstractA source of Ti and V found in Brazil contains important content of both elements and has not been explored yet. Such resources would supply the demand for the battery market (Li‐ion and redox flow), robotics, unmanned aerial vehicles, and 3D printers. The hydrometallurgical route is essential to obtain different high purity products. The goal of the present work was to study the HCl leaching of Ti and V from the non‐magnetic fraction of ilmenite‐based ore. The effects of solid–liquid ratio, NaHF2, Fe0, and chloride ions were evaluated. The optimized conditions were the solid–liquid ratio of 1/6–1/12 and NaHF2 of 10 wt.% for 4 h under reducing leaching. Kinetic modelling fitted better for the chemical reaction model. The activation energy was 14.5, 15.4, and 15.5 J/mol for Ti, V, and Fe, respectively. No improvement was obtained as the concentration of chloride ions increased.

STUDY OF FLUID DYNAMICS AND SULFUR MASS TRANSFER BETWEEN STEEL AND SLAG IN A LADLE FURNACE CONSIDERING DRAG AND NON-DRAG FORCES

In this work fluid dynamics and a basic study of the sulfur transfer at the steel/slag interface in the ladle during argon gas agitation was developed. Mass transfer and chemical reaction models coupled with Computational Fluid Dynamics (CFD) were employed. The multiphasic simulation was solved using the Eulerian model considering drag and non-drag forces, and the flow pattern was validated through Particle Image Velocimetry (PIV) technique. The sulfur transfer rate was tracked by two approximations: (1) unidirectional constant rate Mass Transfer Model (MTM), and (2) unidirectional constant rate Mass Transfer Model coupled with Chemical Reaction Model (MTM+CRM) using Arrhenius equation. It was found that including the non-drag forces affects the fluid dynamics structure. Otherwise, the desulfurization rates increase as the argon gas flow rate increases, finding that the MTM model predicts ~15% less sulfur in the steel than the MTM+CRM, whose results were compared with plant measurements reports.

Thermokinetics synergistic effects on co-pyrolysis of coal and rice husk blends for bioenergy production

In-depth thermodynamic and kinetic synergistic effects of the coal and rice husk blends on co-pyrolysis have been investigated for bioenergy production. The thermokinetic rate parameters were determined for chemical, one-dimensional diffusional, and phase interfacial reaction models especially when fitted to the Coats-Redfern method. The fitted models exhibited thermokinetic rate parameters. The thermogravimetric analysis in view of the thermodynamic parameters including enthalpy, Gibbs free energy, and entropy imparted the prominent degradation temperature ranges (Stage A: 200 °C–400 °C, Stage B: 410 °C–560 °C) for co-pyrolysis reactions of blends. The proportional increase of rise husk into coal for Stage A caused an increase in the apparent values of activation energy, enthalpy specifically for one-dimensional diffusional, and phase interfacial reaction models. In case of Stage B, the increasing share of rice husk into coal proved to be beneficial in decreasing values of activation energy and enthalpy. Positive synergies for 80:20 and 60:40 coal-rice husk blends were calculated. In addition to characterisation analysis of all samples; co-pyrolysis and co-gasification experiments were completed in a tubular fixed bed reactor at Stage B and onwards temperatures for synergised blends. The resultant co-pyrolysis biochar samples revealed honeycomb structure useful in adsorption applications. The gas chromatography-mass spectrometry analysis of the bio-oil yields 23% phenols, 11% acids, and methoxy phenols for the 60:40 coal-rice husk blend. The product gas composition of 2% H2, 14% CH4, and 4% CO2 for the 80:20 coal-rice husk blend increased to 3% H2, 12% CH4, and 5% CO2 for the 60:40 blend. The co-gasification process substantially increased the production of H2 up to 14%-17% when compared to co-pyrolysis results. The approach used in this study can be utilized to capitalize on synergy to enhance co-pyrolysis of appropriate blends and their products can be used in further future applications upon upgradation.

Modelling of tribo-chemical reactions in HiPIMS W-C:H coatings during friction in different environments

The modelling of simultaneous chemical reactions in complex systems was successfully applied to mechano(tribo)chemical reactions during friction between steel ball and High Power Impulse Magnetron Sputtered (HiPIMS) W-C:H coatings in humid air, dry nitrogen, hydrogen and in vacuum. The main mechano(tribo)chemical reactions leading to transfer layer formation in humid air - oxidation of WC and Fe, water vapor decomposition and carbon hydrogenation - were confirmed. In nitrogen, the decomposition of WC producing carbon was predicted. The prediction in hydrogen was only the formation of methane. In vacuum, the decomposition of WC and FeOWO3 into W and Fe and CO formation were dominant. Thus, the friction is controlled via amount of hydrogenated carbon resulting from the dominant mechano(tribo)chemical reactions.

Mild sulphuric acid pre-treatment for metals removal from biosolids and the fate of metals in the treated biosolids derived biochar

Biosolids are contaminated with heavy metals (HMs) and alkali and alkaline earth metals (AAEMs). These metals limit the suitability of biosolids for land application as well as their pyrolytic conversion to high-quality products. In this work, a mild sulphuric acid pre-treatment of biosolids was carried out at different stirring speeds (300–900 rpm), temperatures (25–100 °C), extraction time (0–180 min), and acid concentration (1–5% v/v) to reduce the metals load in biosolids and their biochar derived from pyrolysis. The metal leaching process was very rapid and reached equilibrium in less than 30 min. The optimum conditions removed about 75–95% HMs and 80–95% AAEMs except Ca due to the formation of CaSO4 hydrates. Temperature was the driving parameter for Cd and Ni extraction, whereas temperature and acid concentration played the leading roles in Cu extraction. The shrinking core product layer diffusion and surface chemical reaction models described the extraction kinetics of Ni, Cu and Cd. A leaching activation energy of 10.02 kJ/mol and 7.37 kJ/mol was estimated for Ni and Cd, respectively. FTIR, SEM and XRD characterisation of the treated biosolids jointly indicated that the leaching mechanism was dominated by acid dissolution of metal-containing components followed by ion exchange of metal species with protons from H2SO4. Treatment at 25 °C and 3% H2SO4 lowered the biosolids ash content by 50% and preserved the physicochemical attributes, which enhanced the pyrolysis upcycling of the treated biosolids. Pre-treatment influenced the migration characteristics of the metals during pyrolysis and the produced biochar had several folds lower HMs and AAEMs contents than the raw biosolids-derived biochar.

Improvement of kinetic parameters and modeling of the N2O chemical reaction in combustion

N2O is a significant nitrogen oxide and an important precursor of NO formation. It plays a vital role in understanding the formation and control of nitrogen oxides. Research on the N2O reaction mechanism model is relatively scarce compared to that on NO. This work further supplements the N2O reaction mechanism model based on previous research on NOx. The rate constant and activation energy of the N2O elementary reaction were re-evaluated through comparative analysis of kinetic parameters and experimental parameters in a large number of studies, and the elementary reaction involving N2O was improved by a sufficient comparative analysis through several sets of experimental data. The kinetic parameters of N2O + M⇌N2 + O + M were updated, and the third-body enhancement factor of CO2, H2O and O2 for unimolecular reactions were determined to be 2.0, 6.0, and −4.0, respectively. The rate coefficients of N2O + O⇌NO + NO and N2O + O⇌N2+ O2 were revalued according to the triple relationship. The NH mechanism of N2O formation is in good agreement with the experimental results, which follows the previous parameter selection. The Pre-exponential factor of HCN + O⇌NCO + H was revalued to be 2.4E5 cm3mol−1s−1. These results provide a reference for follow-up related research on N2O and nitrogen oxides.

Research on Fire Prediction Method of High-Voltage Power Cable Tunnel Based on Abnormal Characteristic Quantity Monitoring

The proportion of cable lines in the urban distribution network is increasing. The fire hazard of important cable channels is prominent, which has a serious effect on the safety and stable operation of the power system. In recent years, intelligent mobile inspection and fire extinguishing devices have been applied in tunnels. The determination of firepower and location is conducive to the rapid and effective fire suppression of intelligent devices. Therefore, this study proposes a fire early warning method of a high-voltage power cable tunnel based on abnormal characteristic quantity monitoring. Based on the modified model of complex pyrolysis and combustion chemical reaction, the fire development of different fire source powers and fire locations is simulated. The temperature distribution and characteristic gas concentration under different simulation conditions are analyzed. The results show that the monitoring data of temperature, flue gas concentration, and CO and CO2 concentration need comprehensive analysis to effectively reflect different fire conditions. The characteristic data set is selected and processed to form a total sample. The fire prediction model is trained and tested. The accuracy of the proposed prediction model is 92%.

Thermal decomposition of precursor of SmBiO3 buffer layer for YBCO high-temperature superconducting tape

In order to explore the rapid preparation process of the buffer layer of the high-temperature superconducting tape, the thermal decomposition and the phase formation kinetics of buffer layer precursor were studied. The precursor solution was prepared by using lactic acid as solvent, and nitrates as solutes. The synthesis mechanism of SmBiO3 phase was determined by the combination of universal integral method, differential method and multi-rate scanning Kissinger method, and the related kinetic parameters were solved. The results show that the thermal decomposition processes of the precursor is divided into two stages from room temperature to 800 °C. The second stage of SmBiO3 phase synthesis reaction obeys the second order chemical reaction model. The average apparent activation energy and the pre-exponential factor of the synthesis reaction calculated by the integration and the differential methods are 73 kJ/mol and 3.24 × 104/min, respectively.

Hybrid approach to accurate modeling of coupled vibrational-chemical kinetics in carbon dioxide

In the present study, a new hybrid approach is proposed to modeling coupled vibrational and chemical kinetics in carbon dioxide (CO2) and products of its decomposition. The study develops and completes our previous work carried out for a single-component CO2 gas. The model is based on self-consistent implementation of state-to-state chemical and energy production rates into the equations of multi-temperature CO2 kinetics. It distinguishes vibrational temperatures of all CO2 modes and diatomic species and thus takes into account multiple relaxation mechanisms including intra-mode, inter-mode, and inter-molecular energy transitions as well as state-specific dissociation and exchange reactions. Other advantages of the proposed full multi-temperature approach are the possibility of capturing strong non-equilibrium effects in a flow, straightforward implementation of the chemical-vibrational coupling terms, easy update for new models of state-specific reaction rates. Comparisons with the results obtained in the frame of a detailed but numerically demanding state-to-state approach for the problem of spatially homogeneous relaxation showed good accuracy of the new model under the wide range of initial conditions; at the same time, traditional multi-temperature approaches failed to provide accurate predictions of non-equilibrium flow parameters under arbitrary deviations from equilibrium. Effects of chemical reaction models and selective mode excitation are assessed. The numerical efficiency of the developed model is found acceptable compared to that of the state-to-state approach.

Effects of gypsum-salt rock on mineral transformations in a saline lacustrine basin: Significance to reservoir development

Gypsum-salt rock is typically developed in carbonate reservoirs, and this rock has both constructive and destructive effects on the reservoir. The ways in which gypsum rock controls reservoir development are closely related to the diagenetic conditions. In this study, a typical saline lacustrine basin, the Qaidam Basin in China, was selected to examine the influence of gypsum-salt rock on the development of the carbonate reservoir under different diagenetic conditions. Four main geological factors were assessed: formation condition (temperature), typical salt mineral (anhydrite), and fluid properties (Ca2+ and Mg2+), along with multi-group fluid–rock chemical reaction models devised using multiphase-flow solute-transport simulation technology. Mineral dissolution, precipitation, and transformation in the reservoir under various temperature, pressure, fluid, and mineral conditions were analyzed, and the change of reservoir porosity was calculated. The results showed that the concentration of Ca2+ in fluid controls the dissolution and precipitation of carbonate minerals in the reservoir; moreover, continuous and sufficient Mg2+ is a necessary condition for dolomitization. Precipitation of anhydrite decreases with increase of temperature, verifying that anhydrite precipitates more easily at low temperature. Dissolution of calcium-containing minerals in overlying gypsum-salt rock can lead to mineral precipitation in the subjacent reservoir and reduce its quality.

Co-pyrolysis of municipal sewage sludge and microalgae Chlorella Vulgaris: Products’ optimization; thermo-kinetic study, and ANN modeling

Co-pyrolysis of microalgaeChlorella vulgaris(MCV) and municipal sewage sludge (MSS) was performed in a fixed-bed reactor to explore the influence of temperature (400–600 °C), mixing ratio (MCV/MSS = 0–1), and Argon flow rate of 0.20 to 0.80 L/min on pyrolysis products. The process was optimized using RSM to maximize bio-oil (BIO), minimize biochar (BIC), and biogas (BIG) yields. According to the ANOVA results, the mixing ratio has the most remarkable impact on BIO yield, and temperature has the highest influence on both BIC and BIG efficiency. By using numerical optimization, the optimum values of reaction parameters were T = 520 °C, mixing ratio (MCV/MSS) = 0.82, and Argon flow rate of 0.55 L/min. The third, second, and third-order of chemical reaction models can fit the pure MSS, MCV, and mix pyrolysis utilizing the Coats-Redfern technique, respectively. Also, master plots approaches were used to identify dominant reaction mechanisms. The values of the Eα calculated from non-model fitting methods for MSS, MCV, and co-pyrolysis are obtained in the domain of 79.19–125.59, 182.41–194.73, and 149.55–216.61 kJ/mol, in that order. The presence of the synergetic and inhibitive influences generated by the co-pyrolysis of MSS and MCV has been demonstrated by the improved and reduced weight loss rate, respectively. Furthermore, artificial neural network (ANN) models with the architectures (3*8*3) and (2*8*1) were built to simulate and predict pyrolysis yields and the thermal decomposition of individual and co-pyrolysis process, demonstrated a strong agreement between the actual data and predicted data (R2 ⩾ 0.999) are considerably closer to 1.

Influence of high temperature non-equilibrium effects on Mach 12 scramjet inlet

To better understand the high temperature non-equilibrium effects of a high Mach number (above Mach 8) scramjet inlet, the thermal and chemical non-equilibrium flow of Mach 12 two-dimensional inlet is numerically analyzed by using the thermochemical non-equilibrium gas model including a two-temperature model and air chemical reactions. The thermal equilibrium flow is simulated by using the models of thermally perfect gas and chemical non-equilibrium gas. It is found that the thermal non-equilibrium effects are relatively strong near the cowl shock and in the outer layer of the boundary layer, and gradually weaken in the downstream zone of the cowl shock. The chemical non-equilibrium effects and thermal equilibrium flows mainly exist in the high-temperature region of the boundary layer. Compared with the chemical non-equilibrium gas, the oxygen dissociation reaction near the lower wall for the thermochemical non-equilibrium gas is weaker in the external compression section; It is stronger due to fully excited vibration energy, in the internal compression section. Compared with the other models, the inlet compression ability for the thermochemical non-equilibrium gas is higher, the coefficient of mass flow and total pressure recovery for it are lower. Hence, the high temperature non-equilibrium effects can not be ignored in the design of the high Mach number scramjet inlet.

Critical condition and transient evolution of methane detonation extinction by fine water droplet curtains

Two-dimensional numerical simulations with Eulerian–Lagrangian method and reduced chemical reaction model are conducted to study the methane detonation propagation across a water curtain with finite thickness. The critical length of the water curtain with sprayed droplets is determined through parametric simulations with different water mass loadings and droplet sizes. The influence of water curtain length on the methane detonation is examined by the trajectories of peak pressure and time history of average heat release rate. The results indicate that the water curtain not only inhibit the incident detonation wave, but also prevent the detonation re-ignition after the incident wave is quenched. Moreover, unsteady response of gaseous methane detonation to water curtain are analyzed. The detonation re-initiation process behind the water curtain near the critical loading is also captured. In addition, mechanism of detonation inhibition with fine water droplets are discussed. It is found that energy and momentum exchanges start immediately when the detonation wave enters the water curtain area, but the mass transfer starts well behind the detonation wave due to the finitely long droplet heating duration. It is shown that the convective heat transfer by water droplets plays a significant role in quenching a detonation.

Development of a Charge-Implicit ReaxFF for C/H/O Systems.

Modeling chemical reactions in condensed phases is difficult. Interaction potentials (or force fields) like ReaxFF can perform this modeling with a high overall accuracy, but the disadvantage of ReaxFF is a low simulation speed arising from costly algorithms, in particular charge equilibration. Therefore, we reparametrized ReaxFF to incorporate Coulomb forces into other terms of the force field. Because of this change, our charge-implicit ReaxFF-CHO is >2 times faster than the original parametrization. Despite the lack of explicit electrostatic interactions, our potential can correctly model the reactions and densities of systems containing carbon, hydrogen, and oxygen atoms. We have used the new potential to simulate bombardment of trehalose by water clusters. It has been observed experimentally that these water projectiles can increase the sensitivity of secondary ion mass spectrometry by more than an order of magnitude, but no explanation for this phenomenon was given. Our simulations show that the increase in the intensity of the recorded signal coincides with the emission of trehalose–water complexes.

Suppressing Chaos for a Fractional‐Order Chaotic Chemical Reaction Model via PDζ Controller

In this work, based on the earlier publications, we build a new fractional‐order chemical reaction model. Computer simulations manifest that the fractional‐order chemical reaction model presents chaotic behavior under a certain parameter condition. To eliminate the chaotic dynamical property, a suitable fractional‐order PDζ controller with time delay is designed. Regarding the time delay as a bifurcation parameter, we set up a novel delay‐independent stability and bifurcation criterion guaranteeing the stability and the creation of Hopf bifurcation of the controlled fractional‐order chemical reaction model. The influence of time delay on the stability and Hopf bifurcation of the controlled fractional‐order chemical reaction model is revealed. At last, numerical simulations are performed to sustain the rationality of the designed PDζ controller. The obtained conclusions of this work are completely novel and have immense application prospects in the chaos control of chemical reaction systems. Furthermore, the research idea can also be utilized to suppress the chaos of a lot of fractional‐order chaotic models.

Heat and radiative fluxes in strongly nonequilibrium flows behind shock waves

State-to-state and two-temperature theoretical models for high-temperature strongly nonequilibrium reacting and radiating air flows are developed in the framework of the generalized Chapman - Enskog method. In the theoretical approach, the sets of governing equations for coupled fluid dynamics, chemical kinetics, internal energy transitions and radiation are derived; the algorithms for the calculation of state-resolved transport coefficients are developed and implemented. The proposed models are applied for 1-D simulations of shock waves in air under high-temperature conditions observed in flight experiments. Nonequilibrium mixture composition, temperatures and pressure profiles are obtained and compared for various models of chemical reaction rate coefficients. Flow variables strongly depend on both the kinetic-theory approach and chemical reaction model; species molar fractions and temperature show significantly different behaviour for the state-to-state and two-temperature simulations. Transport properties and radiative fluxes are calculated as functions of the distance from the shock front. It is found that diffusion provides a major contribution to the total energy flux whereas the role of heat conduction is weak due to the compensation effects. It is shown that under considered conditions, two-temperature models are not applicable for correct predictions of radiative heating.

Dynamics and Hopf Bifurcation of a Chaotic Chemical Reaction Model

Taking into account an ideal mixture and a well-stirred reactor, some dynamical aspects for a 3-dimensional chaotic system are carried out. Positivity and boundedness of solutions are discussed. Equilibria are investigated and method of linearization is implemented for asymptotic behavior of system about these equilibria. Lyapunov function is constructed to prove the global stability of positive equilibrium point. Moreover, it is proved that system undergoes Hopf bifurcation about its interior (positive) equilibrium. An explicit criterion of Hopf bifurcation without finding the eigenvalues is used for the existence of Hopf bifurcation. Numerical simulation is presented for the illustration of theoretical discussion. Lyapunov dimension is approximated and maximum Lyapunov characteristic exponents are plotted to ensure the chaotic behavior of the model.

Diffusion-driven instability of both the equilibrium solution and the periodic solutions for the diffusive Sporns-Seelig model

<abstract><p>In this paper, a reaction-diffusion Sporn-Seelig model subject to homogeneous Neumann boundary condition in the one dimensional spatial open bounded domain is considered. Of our particular interests, we are concerned with diffusion-driven instability of both the positive constant equilibrium solution and the Hopf bifurcating spatially homogeneous periodic solutions. To strengthen our analytical results, we also include some numerical simulations. These results allow for the clearer understanding the mechanisms of the spatiotemporal pattern formations of this chemical reaction model.</p></abstract>