Numerical Kinetic Model Research Articles

Thermogravimetric analysis and kinetic modelling studies of selected agro-residues and biodiesel industry wastes for pyrolytic conversion to bio-oil

IEA's recognition of international trading prospect of pyrolysis oil as a biomass intermediate to bridge the demand and supply gap of biomass resources across the globe is likely to accelerate large-scale development of pyrolysis technology in coming years. The complex nature of pyrolysis reactions however have led to the development of numerous kinetic models which show a wide variation in activation energy and other kinetic parameters for the same biomass feedstock. This also leads to complexity in reactor designing and process upscaling. In the present study, eight biomass, including agro-residues and non-edible oil seed residues from Indian biodiesel industries, have been subjected to TGA analysis and the activation energies are calculated and compared using different models.

The local dissociation phenomenon in a nitrogen afterglow

We used the optical emission spectroscopy diagnostic to study the nitrogen afterglow of a pure N2 flowing dc discharge operating under particular experimental conditions to facilitate the simultaneous occurrence of the pink afterglow (PA) and the Lewis–Rayleigh afterglow. The PA is a special kind of nitrogen plasma occurring outside the direct influence of an external electric field. The phenomenon results from the flux of energy, introduced in the nitrogen molecules by the electrons in the discharge region, from the lower to the higher vibrational levels due to vibrational–vibrational (V–V) and vibrational–translational (V–T) exchange reactions. We studied the following set of experimental conditions: discharge electric current (I = 15–50 mA), gas pressure (p = 200–1070 Pa) and gas flow rate (Q = 400–1000 sccm). The emissions of the first positive system of the nitrogen molecules were monitored from the end of the discharge down to the end of the post-discharge tube. A kinetic numerical model developed to investigate the nitrogen afterglow generated a calibrating factor for the 580.4 nm band in such a way that the relative density of the N(4S) atoms could be measured along the afterglow. The experimental results indicated that N(4S) atoms are created locally in the afterglow producing atomic density profiles that follow the behaviour of the other species studied experimentally in the PA, such as , N2(B 3Πg), N2(C 3Πu), , , N+, , , N(2D) and N(2P). The numerical model was also used to fit the N2(B 3Πg), and the N(4S) experimental density profiles and to evaluate the participation of several kinetic pathways capable of producing local dissociation in the N2 afterglow. It was found that the dominant dissociation channel in the PA is the reaction . Its rate constant was estimated, being approximately 5 × 10−12 cm3 s−1.

Formation of recurring slope lineae by liquid brines on present‐day Mars

Recurring Slope Lineae (RSL) are small scale seasonal flow features identified by Mars Reconnaissance Orbiter that present several interesting characteristics such as an albedo contrast, seasonal dependence, and a strong preference for equator‐facing slopes. All of these characteristics strongly suggest a thermally driven mechanism such as a liquid triggered or dominated flow. Here we investigate the possibility that these features are formed by melting of brines of various compositions via a combination of thermodynamic and kinetic numerical models. Results suggest that a solution with a freezing temperature of ∼223 K can best reproduce the observed seasonality. Relatively high surface evaporation rates at the RSL locations make the flows quickly disappear over a single season. Our model reproduces well the seasonality of RSL and can explain the preference for equator‐facing slopes suggesting that brine flows, and therefore liquids, are possible on a small time and space scale today on Mars. However, if the RSL are indeed formed by brines, it may indicate that a recharge mechanism is active in order to maintain a source of brine over even short geological timescales, which would have important implications for the Martian water cycle.

The Chemical Kinetic Numerical Computation and Kinetic Model Parameters Estimating of Parallel Reactions with Different Reaction Orders

Abstract. Parallel reaction is a common reaction of chemical kinetics, and there are two types of parallel reactions according to the reaction orders equivalence: parallel reactions with same reaction orders and parallel reactions with different reaction orders. For the reason that the reaction orders are different, the chemical kinetic numerical computation and kinetic model parameters estimating of parallel reactions with different reaction orders is more complicated than parallel reactions with same reaction orders. In this paper, the 4th order Runge-Kutta method was employed to solve the numerical computation problems of complex ordinary differential equations, which was the chemical kinetic governing equations of parallel reactions with different reaction orders, and also, the Richardson extrapolation and Least Square Estimate were employed to estimate the kinetic model parameters of parallel reactions with different reaction orders. A C++ program has been processed to solve the problem and has been tested by an example of parallel reactions with different reaction orders.

Kinetic Assessment and Numerical Modeling of Photocatalytic Water Splitting toward Efficient Solar Hydrogen Production

Abstract Photocatalytic water splitting has been studied extensively as a promising technology for scalable and cost-efficient hydrogen production using solar energy. Although overall water splitting has been achieved under visible light irradiation, significant progress in reaction efficiencies at longer wavelengths is needed to enable practical solar energy conversion. This article reports recent advancements in kinetic investigation and numerical modeling of photocatalytic water splitting to understand problems with existing photocatalysts and develop strategies to boost the reaction efficiency. Kinetic investigation based on cocatalyst loading, light intensity, hydrogen/deuterium isotopes, and reaction temperature suggests that the majority of photoexcited carriers recombine before contributing to the water splitting reaction on the surface in most cases, and that improvement in semiconducting properties of photocatalysts by decreasing defect and donor concentrations is beneficial to boost photocatalytic performance. It is demonstrated that an appropriate material design to suppress generation of donor species actually improves photocatalytic activity. Numerical modeling of steady state carrier concentrations suggests that an asymmetric built-in potential in photocatalyst particles enhances charge separation and thus extends the lifetimes of photoexcited carriers. On the basis of the recent findings, we suggest strategies to improve the reaction efficiency of photocatalytic water splitting.

Application of a CHA-type zeolite membrane to the esterification of adipic acid with isopropyl alcohol using sulfuric acid catalyst

Abstract CHA-type zeolite membranes show extremely high dehydration performance and high acid stability. This study applied the membrane to the esterification of adipic acid with isopropyl alcohol using sulfuric acid as the catalyst. The membrane was placed in the vapor phase to avoid direct contact with sulfuric acid, and water vapor was removed by vapor permeation. A numerical kinetic model was constructed to understand the effect of dehydration by the membrane, and the experimental results were compared with the model predictions. The yield of diisopropyl adipate increased from 56% to 98% by membrane assistance. Moreover, the ester was produced in the high efficiency (yield>90%) despite the small membrane (35–80 cm 2 per kg of reactant), since the permeation flux of the membrane was significantly high. These results suggest that assistance by a CHA-type zeolite membrane is effective for the ester condensation reaction of adipic acid with isopropyl alcohol. This paper also discussed the stability of the membrane under the reaction conditions.

Simple kinetic numerical model based on rheometer data for ethylene–propylene–diene monomer accelerated sulfur crosslinking

AbstractA simple numerical model for the interpretation of the reaction kinetics in ethylene–propylene–diene monomer (EPDM) vulcanized with accelerated sulfur is presented. The model is based on the assumption that during vulcanization, a number of partial reactions occurs, both in series and in parallel, which determine the formation of intermediate compounds, including activated and matured polymers. Once written a standard first‐order differential equation (DIFF‐EQ) for each partial reaction, an ordinary DIFF‐EQ system (ODEs), was obtained and solved through Runge–Kutta algorithms. Alternatively and more efficiently, a single second‐order nonhomogenous DIFF‐EQ with constant coefficients was deduced, for which a closed‐form solution was derived, provided that the nonhomogenous term was approximated with an exponential function. Kinetic constants were evaluated through experimental data fitting on standard rheometer tests. To assess model predictions, an experimental campaign at different temperatures on two EPDM compounds was performed. They exhibited moderate reversion at intermediate and high curing temperatures. A nonlinear least‐squares fitting was performed to evaluate unknown constants entering into the DIFF‐EQ model proposed. Scaled rheometer curves fit rather well, also in the presence of reversion. In addition, partial reaction kinetic constants were provided: this gave an interesting insight into the different reticulation processes occurring during vulcanization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Self-consistent kinetic numerical simulation model for ring current particles in the Earth's inner magnetosphere

[1] A new self-consistent and kinetic model for ring current particles in the inner magnetosphere is presented. A closed set of nonlinear time evolution equations is derived that incorporates kinetic particle dynamics and self-consistent development of the electromagnetic field. The particle transport is described by a five-dimensional collisionless drift kinetic equation, in which particle trajectories are approximated by their guiding centers under the influence of a time-dependent electromagnetic field. The time evolution of the electromagnetic field follows the Maxwell equations with the feedback from particles through electric currents. A numerical simulation code solving the system of equations in a global inner magnetosphere in three spatial dimensions (or five dimensions in phase space) is developed. It is demonstrated that the propagation of magnetohydrodynamic waves can successfully be described by the present model. It is also found that the self-consistent coupling could affect the transport of energetic particles especially at low energies as well as the intensity and spatial distribution of field-aligned currents. These preliminary results suggest the importance of the self-consistent coupling in the global development of geomagnetic storms.

Numerical Kinetic Model of Axial Confinement in a Mirror Trap

Numerical kinetic model of axial confinement is developed. Simulations show that in semi-collisional regime axial losses are determined by narrow “beam” of cold ions. Analytical treatment is proposed for the case of square-well magnetic field. Simulation of the ambipolar trapping of axial losses in the intermediate collision frequency range shows that essential suppression of axial losses is possible even when ambipolar barrier is of the order of ion temperature.

Restriction point control of the mammalian cell cycle via the cyclin E/Cdk2:p27 complex

Numerous top-down kinetic models have been constructed to describe the cell cycle. These models have typically been constructed, validated and analyzed using model species (molecular intermediates and proteins) and phenotypic observations, and therefore do not focus on the individual model processes (reaction steps). We have developed a method to: (a) quantify the importance of each of the reaction steps in a kinetic model for the positioning of a switch point [i.e. the restriction point (RP)]; (b) relate this control of reaction steps to their effects on molecular species, using sensitivity and co-control analysis; and thereby (c) go beyond a correlation towards a causal relationship between molecular species and effects. The method is generic and can be applied to responses of any type, but is most useful for the analysis of dynamic and emergent responses such as switch points in the cell cycle. The strength of the analysis is illustrated for an existing mammalian cell cycle model focusing on the RP [Novak B, Tyson J (2004) J Theor Biol230, 563-579]. The reactions in the model with the highest RP control were those involved in: (a) the interplay between retinoblastoma protein and E2F transcription factor; (b) those synthesizing the delayed response genes and cyclin D/Cdk4 in response to growth signals; (c) the E2F-dependent cyclin E/Cdk2 synthesis reaction; as well as (d) p27 formation reactions. Nine of the 23 intermediates were shown to have a good correlation between their concentration control and RP control. Sensitivity and co-control analysis indicated that the strongest control of the RP is mediated via the cyclin E/Cdk2:p27 complex concentration. Any perturbation of the RP could be related to a change in the concentration of this complex; apparent effects of other molecular species were indirect and always worked through cyclin E/Cdk2:p27, indicating a causal relationship between this complex and the positioning of the RP.

Efficient generation of quasimonoenergetic ions by Coulomb explosions of optimized nanostructured clusters

Coulomb explosion of spherical ion clusters is studied, which are composed of homogeneous two-species (light and heavy) ions. A simple analytical model is developed to describe the explosion performance in terms of two dimensionless parameters, the charge-over-mass ratio, and the charge density ratio. One-dimensional kinetic numerical model is performed to compare with the analytical model and to evaluate the energy coupling efficiency of quasimonoenergetic ion generation. It is crucial to preform an iso-Coulomb-potential profile of the light ions in the cluster for efficient generation of quasimonoenergetic ions. By controlling the radial density profiles of the light and heavy ions, the overall coupling efficiency (equal to the summed kinetic energy of the light ions in the highest 1% energy band divided by total kinetic energy of both ions) is optimized to be >30%–40% when about 90% of the total number of light ions is contained in the thin 1% energy band.

A kinetic model to study film deposition during dusty plasma chemical vapor deposition process

A simplistic numerical kinetic model to predict the deposited film morphology in dusty plasma chemical vapor deposition reactors is developed. The morphological accretion of a circular object is studied in a two-dimensional geometry and the most important deposition phenomena are taken into account, i.e., surface diffusion and surface ion bombardment. Both isotropic and anisotropic plasmas are considered. It is shown that when the particle is located in an isotropic plasma, the deposited film maintains the original particle sphericity. Whereas, if the particle is assumed to levitate in the (pre) sheath forming around the bottom electrode of the reactor and ions contribute considerably to the deposition, the film develops in a nonuniform manner similar to experimental observations.

Ionization chemistry in H2O-dominated atmospheres of icy moons

The processes of the formation and dynamics of tenuous gaseous envelopes of icy moons in giant-planet systems are considered. Tenuous exospheres with relatively dense surface layers are likely to form around more massive icy satellites, such as, for example, the Galilean satellites Europa and Ganymede in the Jovian system. Escaping exospheres are formed in the case of low-mass icy moons, as happens for the icy satellite Enceladus in the Saturnian system. The main parent component of such gaseous envelopes is water vapor, which enters into the atmosphere as a result of thermal degassing processes, nonthermal radiolysis, and other active processes and phenomena on the icy surface of a satellite. A numerical kinetic model has been developed to study on a molecular level the processes of the formation, chemical evolution, and dynamics of tenuous gaseous envelopes dominated mainly by H2O. The ionization processes in such tenuous gaseous envelopes are caused by solar ultraviolet (UV) radiation and solar-wind and/or magnetospheric plasma. The primary processes when ultraviolet solar photons and plasma electrons affect the tenuous gas of the H2O-dominated atmosphere are responsible for the chemical diversity of the gaseous envelopes of icy moons. Ionization chemistry, including ion-molecular reactions, dissociative recombination of molecular ions, and the reactions of the charge exchange with magnetospheric ions, is important for the formation of chemical diversity in gaseous envelopes of icy satellites. The model considered in the study was used to numerically simulate the formation and development of chemical diversity in the tenuous gaseous envelope of Enceladus. The numerical results were compared to the direct Cassini measurements during its close flyby near Enceladus.

Dayglow on Mars: Kinetic modelling with SPICAM UV limb data

The UV spectrometer experiment SPICAM onboard ESA Mars Express has been orbiting Mars since December 2003. We present here some comparisons between airglow data that have been newly interpreted with the advanced kinetic model Trans-Mars. A series of numerical one-dimensional kinetic models, in the Trans-* family [Lilensten, J., Blelly. P.L., 2002. The TEC and F2 parameters as tracers of the ionosphere and thermosphere. J. Atmos. Solar-Terrestrial Phys. 64, 775–793] has been developed over the last years to take into account of airglow processes and yield altitude line profiles in planetary upper atmospheres (Earth, Venus, Titan and Mars). Trans-Mars is the last evolution of these simulations, applied to Mars. Electron and photon cross sections have been recently updated. The computed model line profiles are comparable to those of Fox and Dalgarno [1979b. Ionization, luminosity, and heating of the upper atmosphere of Mars. J. Geophys. Res. 84, 7315–7333] and Shematovich et al. [2008. Monte Carlo model of electron transport for the calculation of Mars dayglow emissions. J. Geophys. Res. (Planets) 113(E12), 2011]. Nearly 70000 limb UV spectra recorded by SPICAM between October 2004 and May 2006 are analysed in order to obtain altitude emission profiles on the main dayglow emissions. A variable point spread function (PSF) determined statistically throughout the wavelength range is used to estimate precisely the intensity of the airglow. This includes the Cameron bands ( a 3 Π - X 1 Σ ) of CO, the CO 2 + ultraviolet doublet ( B 2 Σ u + - X 2 Π g ) at 289.0 nm and the oxygen emission at 297.2 nm. Instrumental uncertainties of the emissions remain under 15%. Five groups of comparable orbits are selected to prepare for the data interpretation. The seasonal and solar activity effects on the dayside CO ‘Cameron Bands’, CO 2 + and OI(2972 Å) emissions are discussed in light of previous studies. These emissions exhibit for equatorial latitudes two maxima of intensity for L S = 140 ∘ and 290 ∘ (around Mars’ perihelion) and one local minimum at L S ∼ 40 ∘ . The peak at L S = 140 ∘ is corroborated by the neutral density profiles shown by Forget et al. [2008. The density and temperatures of the upper martian atmosphere measured by stellar occultations with Mars Express SPICAM. J. Geophys. Res., 1–25, submitted for publication] using SPICAM stellar occultation mode; these authors linked this sudden increase to a dust storm covering a large part of the planet, a quite unexpected event at this time of the year. A first comparison of altitude profiles of emission lines between data and the kinetic transport model shows a very similar shape and altitude peak when Viking CO 2 densities are divided by a factor 3 and uncertainties in the cross sections are taken into account. Overall intensities are, however, overestimated by our model by 25% on average for Cameron and CO 2 + emissions. The limits of the model and further improvements both on the data analysis and on the model are presented.

A comparative analysis of kinetic models of erythrocyte glycolysis

Since the 1970s, with Heinrich as a pioneer in the field, numerous kinetic models of erythrocyte glycolysis have been constructed. A functional comparison of eight of these models indicates that the production of ATP and GSH in the red blood cell is largely controlled by the demand reactions. The rate characteristics for the supply and demand blocks indicate a good homeostatic control of ATP and GSH concentrations at different work loads for the pathway, while the production rates of ATP and GSH can be adjusted as needed by the demand reactions.

Vibrational Relaxation of Methane by Oxygen Collisions: Measurements of the Near-Resonant Energy Transfer between CH4 and O2 at Low Temperature

Vibrational relaxation in methane-oxygen mixtures has been investigated by means of a time-resolved pump-probe technique. Methane molecules are excited into selected rotational levels by tuning the pump laser to 2nu3 lines. The time evolution in population of various vibrational levels after the pumping pulse is monitored by probing, near 3000 cm-1, stretching transitions between various polyads like 2nu3(F2) - nu3, (nu3+2nu4) - 2nu4, and (nu3+nu4) - nu4 transitions. Measurements were performed from room temperature down to 190 K. A numerical kinetic model, taking into account the main collisional processes connecting energy levels up to 6000 cm(-1), has been developed to describe the vibrational relaxation. The model allows us to reproduce the observed signals and to determine rate coefficients of relaxation processes occurring upon CH4-O2 collisions. For the vibrational energy exchange, the rate coefficient of transfer from O2 (v = 1) to CH4 is found equal to (1.32 +/- 0.09) x 10(-12) cm3 molecule-1 s(-1) at 296 K and to (1.50 +/- 0.08) x 10(-12) cm3 molecule(-1) s(-1) at 193 K.

Fluid-Fluid Interactions in Geothermal Systems

The main goal of geothermal geochemistry research is to identify the origin of geothermal fluids and to quantify the processes that govern their compositions and the associated chemical and mineralogical transformations of the rocks with which the fluids interact. The subject has a strong applied component: Geothermal chemistry constitutes an important tool for the exploration of geothermal resources and in assessing the production characteristics of drilled geothermal reservoirs and their response to production. Geothermal fluids are also of interest as analogues to ore-forming fluids. Understanding of chemical processes within active geothermal systems has been advanced by thermodynamic and kinetic experiments and numerical modeling of fluid flow. Deep drillings for geothermal energy have provided important information on the sources and composition of geothermal fluids, their reaction with rock-forming minerals, migration of the fluids, and fluid phase separation and fluid mixing processes. Based on findings to date, geothermal fluids may be classified as primary or secondary. Primary fluids are those found in the roots of geothermal systems. They may constitute a mixture of two or more fluids, such as water of meteoric origin, seawater and magmatic volatiles. Several processes can lead to the formation of secondary fluids, such as the boiling of a primary fluid that separates it into liquid and vapor and the un-mixing of a very hot brine by its depressurization and cooling. Further, secondary geothermal fluids form by the mixing of deep fluids with shallow ground water or surface water. In this chapter we summarize the geo-hydrological and geochemical features of geothermal systems and delineate the processes that produce the observed chemical composition of the various types of geothermal fluids found in these systems. The main emphasis is, however, on gas chemistry and the assessment of fluid phase separation below hot springs and around discharging wells drilled into liquid-dominated …

Simulation of horizontal slug-flow pneumatic conveying with kinetic theory

Wavelike slug-flow is a representative flow type in horizontal pneumatic conveying. Kinetic theory was introduced to establish a 3D kinetic numerical model for wavelike slug gas-solid flow in this paper. Wavelike motion of particulate slugs in horizontal pipes was numerically investigated. The formation and motion process of slugs and settled layer were simulated. The characteristics of the flow, such as pressure drop, air velocity distribution, slug length and settled layer thickness, and the detailed changing characteristics of slug length and settled layer thickness with air velocity were obtained. The results indicate that kinetic theory can represent the physical characteristics of the non-suspension dense phase flow of wavelike slug pneumatic conveying. The experiment in this paper introduced a new idea for the numerical calculation of slug-flow pneumatic conveying.

Complete thermodynamically consistent kinetic model of particle nucleation and growth: Numerical study of the applicability of the classical theory of homogeneous nucleation

A complete thermodynamically consistent elementary reaction kinetic model of particle nucleation and growth from supersaturated vapor was developed and numerically evaluated to determine the conditions for the steady-state regime. The model treats all processes recognized in the aerosol science (such as nucleation, condensation, evaporation, agglomerationcoagulation, etc.) as reversible elementary reactions. It includes all possible forward reactions (i.e., of monomers, dimers, trimers, etc.) together with the thermodynamically consistent reverse processes. The model is built based on the Kelvin approximation, and has two dimensionless parameters: S0-the initial supersaturation and Theta-the dimensionless surface tension. The time evolution of the size distribution function was obtained over the ranges of parameters S0 and Theta. At low initial supersaturations, S0, the steady state is established after a delay, and the steady-state distribution function corresponds to the predictions of the classical nucleation theory. At high initial supersaturations, the depletion of monomers due to condensation on large clusters starts before the establishing of the steady state. The steady state is never reached, and the classical nucleation theory is not applicable. The boundary that separates these two regimes in the two dimensionless parameter space, S0 and Theta, was determined. The model was applied to several experiments on water nucleation in an expansion chamber [J. Wolk and R. Strey, J. Phys. Chem. B 105, 11683 (2001)] and in Laval nozzle [Y. J. Kim et al., J. Phys. Chem. A 108, 4365 (2004)]. The conditions of the experiments performed using Laval nozzle (S0=40-120) were found to be close to the boundary of the non-steady-state regime. Additional calculations have shown that in the non-steady-state regime the nucleation rate is sensitive to the rate constants of the initial steps of the nucleation process, such as the monomer-monomer, monomer-dimer, etc., reactions. This conclusion is particularly important for nucleation from supersaturated water vapor, since these processes for water molecules at and below the atmospheric pressure are in the low pressure limit, and the rate constants can be several orders of magnitude lower than the gas kinetic. In addition, the impact of the thermodynamic inconsistency of the previously developed partially reversible kinetic numerical models was assessed. At typical experimental conditions for water nucleation, S0=10 and Theta=10 (T=250 K), the error in the particle nucleation rate introduced by the thermodynamic inconsistency exceeds one order of magnitude.

Kinetics of enzymatic hydrolysis of polysaccharide-rich particulates

Both pH and volatile fatty acid (VFA) inhibit the hydrolysis of particulate organic waste. It is not clear yet whether VFA or pH is the dominant factor in hydrolysis inhibition. The effects of pH and acetate on the enzymatic hydrolysis of potato samples containing mainly carbohydrate were studied at fixed pH values (5–9) and with/without 20 g L −1 acetate. The leaching liquors were refreshed at prescribed intervals. Experimental results showed that both pH and acetate influenced the hydrolysis of carbohydrate, but that pH was more influential than acetate. Numerous kinetic models could fit the hydrolysis data during the first 40 h of hydrolysis when inhibitive effects were not significant. The simplified Chen–Hashimoto model, −d S/d t = K H S/( K S( S 0 − S) + S), closely fit all of the experimental data. Also, the fitting achieved by applying the non-competitive inhibition model ( K H = K H 0 /(1 + I/ K I)) on three inhibitors (H +, OH −, total/undissociated/dissociated acetate) was excellent for carbohydrate hydrolysis.