Chemical Equilibrium Conditions Research Articles

Capability of the Kd model to predict radionuclides behaviour and transport in unsaturated columns under steady flow conditions

In the frame of the IRSN Chernobyl Pilot Site Project, a waste trench containing hot particles was instrumented to study the fate of radioactive pollutants. Results have shown the formation of a 90 Sr plume in the downstream aquifer, mainly present in the Aeolian layer after 15 years. Laboratories experiments were performed to analyse the transport of 90 Sr and 137 Cs in the Aeolian sand in both saturated and unsaturated conditions. Batch experiments were performed to study the chemical equilibrium state of the soil/solution system under static conditions. Stirred flow-through reactor experiments were performed to study the kinetics and reversibility of sorption reactions at the surface of solid particles under dynamic conditions. Column experiments in the structured porous media were also performed in saturated and unsaturated flow conditions. Experimental data pointed out a non-linear, instantaneous and reversible sorption process of 90 Sr. 137 Cs exhibits a non-linear behaviour with a partial irreversible sorption process. A suitable cation-exchange model was used to describe the solute/soil reactions. The former model was coupled with transport models to describe behaviour of 90 Sr and 137 Cs in both saturated and unsaturated steady flow conditions. Main transport parameters were identified and discussed. An effective simple Kd type approach to describe radionuclides transport properties under unsaturated conditions was evaluated.

SHARE: Statistical hadronization with resonances

SHARE: Statistical hadronization with resonances

Performance study of a magnetohydrodynamic accelerator using air-plasma as working gas

The fundamental performance of a linear Faraday type magnetohydrodynamic (MHD) accelerator under chemical and thermal equilibrium conditions is studied in this paper. Quasi-one dimensional numerical simulation is performed to characterize acceleration along the specified channel. In order to solve the set of differential equations of magnetohydrodynamics, the MacCormack scheme is employed. In this present calculation, a working gas of air-plasma, consisting of diatomic molecules of nitrogen, oxygen and hydrogen, is considered in order to actualize application of the MHD accelerator propulsion system. Numerical results show the characteristics of flow velocity, gas temperature and electrical conductivity of the MHD accelerator with the working gas of air-plasma. The computations are compared with numerical simulation results using the inert gas of argon evaluated in past studies.

Numerical study of the hadron-quark mixed phase

The Coulomb screening effect and the finite-size effect such as surface tension are figured out in the hadron-quark deconfinement phase transition. We study the mixed phase of the quark droplets immersed in hadron matter. We see that the droplet phase is mechanically unstable if the surface tension is strong enough. Once the Coulomb potential is properly taken into account, we could effectively satisfy the condition for charge chemical equilibrium in the Maxwell construction. As a result, we suggest the Maxwell construction revives the physical meaning effectively.

Flame stabilization with a tubular flame

A new technique to stabilize a flame in a high-velocity stream with use of a tubular flame has been proposed. To elucidate the validity of this technique, an experiment has been conducted by mounting a tubular flame burner on the nozzle. Flame stability limits and temperature distributions around the burner port have been determined, and experiments have been extended to the ducted combustion to measure pressure fluctuations and to analyze the burned gases. Results show that the tubular flame can successfully stabilize the main flame up to 130 m/s, which is the upper limit of the present supply facility. The main flame is well anchored at the exit of the nozzle, and the tubular flame efficiently supplies heat and radicals to the main flame. In the ducted combustion, the pressure fluctuations are reduced significantly. The exhaust gas analyses, however, indicate that an almost chemical equilibrium condition can be achieved at 50 m/s, but not at 90 and 130 m/s. Since the energy input relative to the main flame is just 6.1% at 130 m/s, the present tubular burner is not enough to burn all the unburned gas completely at high velocities, although the main flame can be anchored. The slit length and/or the slit width of the tubular flame burner should be larger to overcome this shortage. From the above results, it is concluded that the tubular flame has a potential for stabilizing a flame in a high-speed stream.

Numerical Simulation for the Performance of a Magnetohydrodynamic Accelerator

Recent results of our quasi-one-dimensional numerical simulation for the performance of an MHD accelerator under chemical and thermal equilibrium conditions are presented. For the present study, the working gas was changed to air-plasma from inert gas of argon plasma, which was studied previously to actualize the application of an MHD accelerator propulsion system. The numerical simulation confirmed the performance of MHD accelerators with segmented Faraday, Hall, and diagonal electrode connections. In order to solve the set of differential equations of magnetohydrodynamics, the MacCormack scheme is employed. The results show several parameters of MHD accelerator performance with air-plasma working gas. The calculation results are compared with previous results to clarify the effect of the difference in working gases.

Gibbs function continuation for the stable computation of chemical equilibrium

We consider the computation of the chemical equilibrium state of an ideal gas mixture of given elemental composition, with and without general linear constraints on the species present. While computer programs to solve these problems have been available for more than 30 years, it is found that they are not always successful in determining the chemical equilibrium state in the presence of constraints. We present here the new method of Gibbs function continuation, which is guaranteed to determine the chemical equilibrium state for all well-posed constrained and unconstrained problems.

Thermodynamic derivations of conditions for chemical equilibrium and of Onsager reciprocal relations for chemical reactors.

For an isolated chemical reactor, we derive the conditions for chemical equilibrium in terms of either energy, volume, and amounts of constituents or temperature, pressure, and composition, with special emphasis on what is meant by temperature and chemical potentials as the system proceeds through nonequilibrium states towards stable chemical equilibrium. For nonequilibrium states, we give both analytical expressions and pictorial representations of the assumptions and implications underlying chemical dynamics models. In the vicinity of the chemical equilibrium state, we express the affinities of the chemical reactions, the reaction rates, and the rate of entropy generation as functions of the reaction coordinates and derive Onsager reciprocal relations without recourse to statistical fluctuations, time reversal, and the principle of microscopic reversibility.

The dispersion of chemically reactive species in the atmospheric boundary layer

The role of turbulence in the dispersion of atmospheric pollutants that react with linear (decay) and nonlinear (second-order) chemical reactions is examined. The most relevant processes that drive the reactivity of species emitted in a surface area or released by a point source are studied by deriving the dimensionless scaling numbers from equations for the atmospheric turbulent reacting flow. The first number is the ratio of the time scale of turbulence to the time scale of the chemical reaction, namely the Damkohler number. The second number is the ratio of the concentrations of the species present in the chemical transformations. In this paper, model results and experimental studies of turbulent reacting flows in the atmospheric boundary layer are presented to show the modifications and control exerted by turbulence on the atmospheric chemistry as a function of these numbers and processes. We also discuss how the chemical transformation is affected when species are in a state of chemical equilibrium. By studying the plume dispersion of a reactant, that decays with a simple chemical reaction, one can analyse the dependence of concentration fluctuations on the Damkohler number. The study is extended to plumes that react nonlinearly. In such reacting systems, the large gradients and segregation of species result in a significant reduction in the reaction rates. Because of this modification, the chemistry of species related to NOx and HOx can be very different from the chemistry in conditions where the species are uniformly mixed. The lack of complete observational evidence is hampering our understanding of these processes and our evaluation of numerical modelling results. Finally, we discuss briefly how to represent, in the form of a parameterization, the effect that turbulence can have on the reactivity of species emitted by a point source or an area source.

L′ andM′ Photometry of Ultracool Dwarfs

We have compiled L' and M' photometry of 63 single and binary M, L,and T dwarfs obtained at UKIRT using the MKO filter set. This compilation includes new L' data for 8 L dwarfs and 13 T dwarfs and new M' data for 7 L dwarfs, 5 T dwarfs, and Gl 229A. We compute L_bol, BC_K, and T_eff for 42 dwarfs whose flux-calibrated JHK spectra, L' photometry, and trigonometric parallaxes are available, and we estimate these quantities for 9 other dwarfs whose parallaxes and flux-calibrated spectra have been obtained. BC_K is a well-behaved function of near-IR spectral type with a dispersion of ~0.1 mag for types M6-T5; it is significantly more scattered for types T5-T9. T_eff declines steeply and monotonically for types M6-L7 and T4-T9, but is nearly constant at ~1450 K for types L7-T4 with assumed ages of ~3 Gyr. This constant T_eff is evidenced by nearly unchanging values of L'-M' between types L6 and T3. We compare the observed K, L', and M' luminosities of L and T dwarfs in our sample with those predicted by model atmospheres with varying surface gravities and sedimentation efficiencies. The models indicate that the L3-T4.5 dwarfs generally have higher gravities (log g = 5.0-5.5) than the T6-T9 dwarfs (log g = 4.5-5.0). The predicted M' luminosities of T dwarfs are 1.5-2.5 times larger than those derived empirically for the T dwarfs in our sample. This discrepancy is attributed to absorption at 4.5-4.9 um by CO, which is not expected under the condition of chemical equilibrium assumed in the models. We determine that the L3 dwarf Kelu-1 and the T0 dwarf SDSS J0423-0414 are probable binary systems. We compute log(L_bol/L_sun) = -5.73 +/- 0.05 and T_eff = 600-750 K for the T9 dwarf 2MASS J0415-0935, which supplants Gl 570D as the least luminous and coolest brown dwarf presently known.

Model for Gas–Condensate Phase Equilibria for Estimating C7+Critical Properties Using Genetic Algorithm

A reliable prediction of the phase behavior is necessary in determining the compositions of the gas and liquid phases at various pressures. These calculations require stepwise computational procedure using a cubic equation of state (EOS). Since the heavy components in the petroleum mixtures have the strongest effect on the characteristics of the fluids, critical properties must be estimated for the petroleum fractions making up heptanes-plus. A phase equilibria calculation of a gas–condensate system with Peng–Robinson equation of state was done by satisfying the condition of chemical equilibrium. A genetic algorithm was used to determine the optimum critical properties of heptanes-plus (C7+) fraction. The predictions of the model are compared with the experimental results of the constant volume depletion (CVD) test.

Solution of Cubic Equations by Iteration Methods on a Pocket Calculator

Sometimes it is necessary to solve cubic or higher-order equations in the investigation of chemical equilibrium systems. Solving these kinds of equations may cause difficulties for chemistry students. Methods for solving cubic equations by inexpensive pocket-size programmable calculators are presented. Using these methods, students are able to solve cubic equations arising from analysis of the chemical equilibrium states without the need for a PC. In addition, by practicing such programs, students will learn to write more useful programs on their calculators.

Nucleon Instability in a Degenerate Magnetized Nucleon–Electron Gas

In the framework of the model of a degenerate relativistic ideal neutron–proton–electron gas (np+e− gas) in an external superstrong constant and homogeneous magnetic field, we study the effect of the magnetic field on the state of chemical equilibrium of the np+e− gas and on the processes of electronic (β−) and positronic (β+) nucleon decay taking the effects due to the interaction between the nucleon anomalous magnetic moments and the magnetic field into account. For sufficiently large values of the magnetic induction, the proton density in chemical equilibrium must exceed the neutron density. Including the interaction between the nucleon anomalous magnetic moments Mn,p and the magnetic field results in an insignificant reduction of the proton density, but, as in the case Mn,p = 0, the proton density in chemical equilibrium in the presence of the superstrong magnetic field exceeds the neutron density. We show that if the interaction between the nucleon anomalous magnetic moments and the superstrong magnetic field is taken into account, then the positronic decay of a free proton (i.e., a proton not entering the composition of an atomic nucleus) into a neutron, a positron, and a neutrino can become energetically allowed. We discuss the necessary conditions for realizing the phase transition from the nucleon phase to the quark phase of the substance in the central region of a strongly magnetized neutron star.

Radial mixing in protoplanetary accretion disks

The outer regions of protoplanetary accretion discs are formed by material from the parent molecular cloud of the freshly forming stars. The interstellar dust in this material is a mixture of species which does not correspond to any kind of chemical equilibrium state between the solid and gaseous phases. Mass accretion carries this material into the warm inner disc zones where chemical and physical processes are activated which convert the non-equilibrium solid-gas mixture into a chemical equilibrium mixture. Part of the equilibrated material is then mixed outwards by turbulent diffusion and large-scale circulation currents. This work specifically considers the evolution of the main dust components, viz. from the interstellar mixture of amorphous Mg-Fe-silicates, into a chemical equilibrium mixture of crystalline Mg-silicates, and iron. The basic set of equations for calculating the evolution of a mixture of silicates and iron is derived. Model calculations based on stationary, one-zone α-discs are combined with the advection-diffusion-reaction equations for the dust evolution to study the interstellar to equilibrium dust conversion and the radial mixing of equilibrated dust into the outer disc regions. This determines the mixture of the main dust components which form the mineral inventory of planetesimals. It is found that the results of the model calculation for the resulting mineral mixture are in rough agreement with the composition of matrix material of primitive meteorites and dust in cometary nuclei.

Tellurium nanowire arrays synthesized by electrochemical and electrophoretic deposition

This article describes both electrochemical deposition and electrophoretic deposition of high-density tellurium (Te) nanowire arrays with wire diameters of 60 nm and lengths of 15–20 μm in the nanochannels of anodic aluminum oxide (AAO) templates. The Te nanowires synthesized via electrochemical deposition (ECD) are generally single crystalline in nature with the wire longitudinal axis along the [001] direction, whereas those synthesized via electrophoretic deposition (EPD) show polycrystalline structures with numerous tiny Te crystallites packed randomly in the wires. The single-crystalline Te nanowires produced by the ECD route are believed to form under a near chemical equilibrium condition; however, the imposed transport and the rapid packing of Te nanocrystallites in the nanochannels of AAO template in external fields lead to polycrystalline Te nanowires in the EPD process. This comparative study of the Te nanowire formation in the nanochannels of AAO template will facilitate the tailoring of the growth of other inorganic nanowires of high quality.

Energy and Exergy Analyses of the Pulse Detonation Engine

Energy and exergy analyses have been performed on a pulse detonation engine. A pulse detonation engine is a promising new engine, which uses a detonation wave instead of a deflagration wave for the combustion process. The high-speed supersonic combustion wave reduces overall combustion duration resulting in an nearly constant volume energy release process compared to the constant pressure process of gas turbine engines. Gas mixture in a pulse detonation engine has been modeled to execute the Humphrey cycle. The cycle includes four processes: isentropic compression, constant volume combustion, isentropic expansion, and isobaric compression. Working fluid is a fuel-air mixture for unburned gases and products of combustion for burned gases. Different fuels such as methane and JP10 have been used. It is assumed that burned gases are in chemical equilibrium states. Both thermal efficiency and effectiveness (exergetic efficiency) have been calculated for the pulse detonation engine and simple gas turbine engine. Comparison shows that for the same pressure ratio pulse detonation engine has better efficiency and effectiveness than the gas turbine system.

Cluster composition of liquid water derived from laser-Raman spectra and molecular simulation data

Studying the behaviour of aqueous solutions of carbohydrates and other molecules commonly encountered in food science always leads to the fundamental question about the structure of bulk liquid water. The present study is an attempt towards the development of a mixture model of water structure based on information derived from experimental Raman spectra of water as well as molecular simulation data of isolated water clusters. The model assumes that liquid water is a thermodynamically ideal mixture of small water clusters in a state of chemical equilibrium. The equilibrium obeys the law of mass action and the van't Hoff temperature dependence of equilibrium constants. In order to validate the model and estimate its chemical equilibrium constants, Raman spectra of liquid water, predicted by the model, were compared with the isotropic components of carefully selected experimental spectra of pure liquid water, determined in the stretching vibration region at various temperatures. The theoretical Raman spectrum of bulk water was obtained by superposition of spectra of individual clusters, assuming their composition-based additivity. The spectra of small clusters were obtained from the Gaussian 98 programme using the 6-311+G(d,p) basis set together with the BLYP method. The model can reproduce the main features of the experimental Raman spectra of liquid water in the entire range of stretching vibration frequencies, at temperatures ranging from −30 to 300 °C. The resulting cluster composition of liquid water was found to be strongly temperature-dependent. At room temperature, water tetramer and pentamer are predominant, whereas the predicted concentrations of monomeric and dimeric water are very low. The latter gradually increase with increasing temperature at the expense of larger clusters. At its current stage of development, the model should be considered an alternative mathematical tool for more rational and rigorous analysis and interpretation of the Raman spectra of liquid water rather than a definite model of bulk water structure.

Effects of oxygen and water on the resonance electron capture reactions of low electron affinity compounds

The reactions of the molecular anions of several low electron affinity (EA) compounds, including anthracene, quinazoline, benzophenone, quinoxaline, and azulene, with oxygen and water have been studied by pulsed high pressure mass spectrometry (PHPMS). It is shown that in the simultaneous presence of oxygen and water, these molecular anions, M −, are rapidly destroyed and the ion, O 2 −(H 2O), is rapidly formed. It is shown that the high rate with which this transition occurs can not be explained by the simplest model envisioned that is based on well-known ion molecule reactions. These results can be explained, however, by inclusion into the model of a previously uncharacterized reaction between the molecular ion–oxygen complex, MO 2 −, and water. The results reported here explain why the molecular anions of compounds that have lower EA’s than that of azulene are not readily observed in electron capture ion sources of 1 atm buffer gas pressure. In addition, it is shown that the reactions characterized here lead to a state of chemical equilibrium between the M − and O 2 −(H 2O) ions within the PHPMS ion source from which the EA values of the low-EA compounds can be determined. By this method the electron affinities of anthracene, quinazoline, benzophenone, and quinoxaline are found to be 0.54, 0.56, 0.61, and 0.68 eV, respectively.

Chemical Equilibrium in Hydrothermal Systems: The Case of Los Azufres Geothermal Field, Mexico

This work presents a review of the geological, hydrogeochemical, and mineralogical information related to the Los Azufres geothermal field, along with new isotopic data from hydrothermal calcite and quartz. The equilibrium state between present-day geothermal fluids and hydrothermal mineral phases in this field was examined using mineralogical, thermochemical, as well as isotopic data. Hydrothermal minerals in Los Azufres are typical for neutral to alkaline, high-temperature thermal fluids, forming an incipient to complete propylitic alteration of the primary rocks. The comparison of activity diagrams of common hydrothermal phases to mineralogical observations at Los Azufres shows that the reservoir rocks tend to approach a state of chemical equilibrium with hydrothermal fluids percolating through them. This tendency to equilibrium has been corroborated by analysis of the oxygen isotopic composition of hydrothermal calcite, whose σ18O values are in equilibrium with present geothermal or meteoric waters. Although 18O/16O ratios from some hydrothermal quartz samples show equilibrium with present-day fluids, others indicate the presence of fluids with higher 18O/16O ratios than modern geothermal water. The oxygen isotopic composition of hydrothermal quartz can thus be used as an indicator of isotopic compositions of fluids at the time of quartz precipitation.

Demythicizing the Gibbs Potential for Determination of Chemical Equilibrium Conditions

Demythicizing the Gibbs Potential for Determination of Chemical Equilibrium Conditions