Experimental Data For Argon Research Articles

Scaling Migdal model and a nonparametric equation of state for argon

In this work, the nonparametric equation of state (NEOS) for matter is studied. We consider a methodical approach that is connected with some correlation between NEOS and Migdal’s scaling equation of state. We have analyzed the NEOS structure and have used additional functions depending on physical arguments (the density ρ, the temperature T). Additionally, we have used a methodical approach connected with correlation between NEOS and Benedek’s hypothesis. A variant of NEOS, based on experimental data for argon has been developed. This input array includes CV values, densities on the saturation line and data (p, ρ,T). We have defined NEOS field of use: by density 0.67 ⩽ ρ/ρc ⩽ 1.22; by temperature 0.99 ⩽ T/Tc ⩽ 1.08 at ρ < ρc and 0.997 ⩽ T/Tc ⩽ 1.08 at ρ > ρc. Here ρc, Tc are critical parameters. NEOS is compared with experimental data on properties mentioned. These results are analyzed.

Nonlinear nonequilibrium kinetic model of the Boltzmann equation for a gas with power-law interaction

A model kinetic equation approximating the Boltzmann equation on a wide range of the intensities of nonequilibrium states of gases is derived to describe rarefied gas flows. The kinetic model is based on a distribution function dependent on the absolute velocity of gas particles. Themodel kinetic equation possesses a high computational efficiency and the problem of shock wave structure is solved on its basis. The calculated and experimental data for argon are compared.

Nonlinear nonequilibrium kinetic model of the boltzmann equation for monatomic gases

A model kinetic equation approximating the Boltzmann equation in a wide range of nonequilibrium gas states was constructed to describe rarefied gas flows. The kinetic model was based on a distribution function depending on the absolute velocity of the gas particles. Highly efficient in numerical computations, the model kinetic equation was used to compute a shock wave structure. The numerical results were compared with experimental data for argon.

Comparison of the new nucleation theory with experimental data

For the case of particles interacting in accordance with the Lennard-Jones potential, we carry out a comparison of our nucleation theory with experimental data for argon.

Isotherm and heat of adsorption in porous solids with defective pores—adsorption of argon and nitrogen at 77 K in Saran activated carbon

The isotherm and isosteric heat of a porous solid are studied in terms of the local isotherms and isosteric heats of individual pores with defective walls, rather than graphitic walls as commonly assumed in the literature. We point out the incorrect formulas that have been used in the literature, and present a correct formula to calculate the isosteric heat for a porous solid. The correct formula is illustrated with a direct Monte Carlo (MC) simulation of systems of two pores of different sizes, and finally we apply our theory to experimental data of argon and nitrogen adsorption at 77 K on S600H and S84 Saran charcoals to derive their pore size distributions (PSD). We show that the PSD derived from the fitting either the isotherm only or the heat curve only may not be reliable. It is necessary to utilize both the isotherm and heat curves in the derivation of a more reliable PSD. We also show that it is essential to use defected walls of carbon pores to model adsorption in pores as the model using graphitic walls can not describe isotherm and heat of adsorption adequately.

Characterization of Cabot non-graphitized carbon blacks with a defective surface model: Adsorption of argon and nitrogen

A grand canonical Monte Carlo simulation (GCMC) is used to study the adsorption of argon and nitrogen on non-graphitized carbon black. The surface is assumed to be finite in length and composed of three graphene layers, the top layer of which contains defects. The isotherm obtained for the non-graphitized carbon shows a smooth S-shaped type while that obtained for the perfect graphene layer shows a wavy type. The isosteric heat is also affected by the defect; its behaviour versus loading exhibits a decrease at the beginning and then slightly increases once the first layer has been formed. The decreasing behaviour of isosteric heat at low loadings is not observed in the case of graphitized carbon black. The simulated results are compared against the experimental data of argon and nitrogen at 77 and 87.3 K on the Cabot carbon black BP 280, 460 and 2000. It is found that the defected finite surface describes well the data of these blacks. For the case of BP 2000 we have found that besides the defects of the surface, this sample contains a small population of small micropores having a width of 8.2 Å and its specific pore volume of 0.08 cm 3/g.

Effects of quadrupole moments of graphite surface on adsorption of simple gases on graphitized thermal carbon black

The quadrupole moment of carbon atoms in the graphite layer has a surface mediation effect on the adsorption of simple gases on graphitized thermal carbon black. Basically, the graphite surface exerts an electric field in the volume space above the surface, inducing a dipole moment on every particle above the surface. The dipole moment in each particle is modelled with the Drude oscillator model. Because of polarization, the dipole–dipole interaction gives lower intermolecular potential energy between adsorbed particles. As a result the adsorption isotherm in the region where monolayer is being completed is lower than that if this effect of induced dipole is neglected. This phenomenon of reduction in the intermolecular interaction has been tested against the experimental data of argon on graphitized thermal carbon black, and the agreement between our model and the data is excellent. We also tested the surface defect (geometrical factor) as a possible reason for surface mediation, but the results fail to agree with experimental data, lending support to the possibility of surface electric effect as the principal reason for the surface mediation.

An analytic expression for the first shell of the radial distribution function

A simple analytical expression for the first shell of the radial distribution function (RDF) is proposed. This expression, which has only three adjustable parameters, satisfies all the limiting cases of the hard-sphere RDF at high temperatures, the ideal gas RDF at zero density, the dilute-gas RDF at low densities, and the location of the peak in the first shell. The only requirement is the introduction of a potential function into the model. This theory has been applied to the Lennard Jones, Kihara, and square-well pair intermolecular potential energy functions. The first-shell RDF results are in good agreement with the available computer simulation data for the RDF of the Lennard Jones fluid and the experimental data for argon. By introducing the radius of truncation for the RDF, it is shown that information on the first shell of the RDF is sufficient to predict macroscopic properties of fluids. Calculations of radii of truncation of RDF for various properties indicate that they are always in the range of the first shell of RDF.

Accurate analytical expressions of thermodynamic properties of supercritical Lennard-Jones fluids

Extensive computer simulations have been carried out in order to obtain analytical expressions for such thermodynamic properties as the Helmholtz free energy, internal energy, entropy, equation of state, isothermal compressibility, thermal expansion coefficient, heat capacities at constant volume and constant pressure, etc., of a Lennard-Jones fluid. The proposed expressions combine accuracy with simplicity and they are valid over the entire supercritical region. The number of simulated states was 265, covering a range of temperatures T = (1.3−2.6) and densities from ρ = (0.1−0.844) (both in reduced units). The given number of states permits us to fit the computer simulation data by the corresponding analytical expressions with a total guarantee of confidence. Because the heat capacity at constant pressure is related to the other quantities, such as the internal energy (through the heat capacity at constant volume) and to the equation of state (through the isothermal compressibility and the thermal expansion coefficient), in testing the goodness of our analytical relations we compared our C p values with other theoretical values taken from the literature, and found excellent agreement. We also compared our C p results with experimental data for argon, using our own recently proposed Lennard-Jones intermolecular parameters. Good agreement was again found.

Vapour pressure curves obtained from different equations of state—A quantitative analysis

Vapour pressure curves for simple fluids have been obtained using different equations of state, and predictions are compared with experimental data of argon. For this, a previous quantitative test of these equations should be made in order to determine their theoretical foundations, mathematical simplicity and accuracy in predicting the thermodynamic behaviour of these systems. The results show that, despite the simplicity of our models, the thermodynamics obtained from these models is in accordance with experimental data of argon on a wide range of temperatures and pressures. An extra advantage of our models is their theoretical background. It will permit a straightforward extrapolation to study other non-simple systems as polar fluids.

The isochoric-, isobaric- and saturation-heat capacities of the Lennard-Jones fluid from equations of state and Monte Carlo simulations

Isochoric-, isobaric- and saturation-heat capacities are calculated from the modified Benedict-Webb-Rubin type equation of state (EOS) of Johnson et al. (1993) and from the van der Waals theory based EOS given by Mecke et al. (1995) for the Lennard-Jones fluid. The isochoric- and isobaric-heat capacities are also determined from NVT and NpT ensemble Monte Carlo simulations. A method is proposed for the determination of the saturation heat capacity using the appropriate fluctuation formulae in both ensembles. The EOS-based theoretical results show reasonable agreement with the simulation data. Comparing with real liquids the theoretical heat capacities based on EOSs, calculated along the vapour-liquid saturation curve, agree well with experimental data for argon and methane.

An effective triplet potential for argon

Abstract Miyano Y., 1994. An effective triplet potential for argon. Fluid Phase Equilibria , 95: 31-41. An effective triplet potential is proposed. This triplet potential expresses the effects of Axilrod-Teller three-body interactions on a pair of molecules, and is given as a simple function of density and the distance between the pair of molecules. The computer time for Monte Carlo simulations of fluids with both a pair potential and the effective triplet potential is almost equivalent to that of fluids with only the pair potential. By using an accurate pair potential together with this effective triplet potential, Monte Carlo simulations are performed to estimate the thermodynamic properties of argon, and the results are compared with the experimental properties, the saturated vapor and liquid densities, the heats of varporization and the second virial coefficients. The comparisons show that the simulation results for fluids with only the pair potential give poor agreement with the experimental data, especially for the heats of vaporization where the simulation results give very large deviations. However, the simulation results for fluids with both pair potential and triplet potential give very good agreements with the experimental data of argon.

Prediction of gas adsorption in 5a zeolites using Monte Carlo simulation

AbstractAdsorption of air in 5A zeolites was studied using Monte Carlo simulations in the grand canonical ensemble (μ, V, T constant). Site‐site potentials were used to model the adsorbate‐zeolite and adsorbate‐adsorbate interactions. The potential model contains one adjustable parameter that was fit to a single experimental isotherm data point. Adsorption isotherms and heats of adsorption were determined for pure argon, oxygen, and nitrogen at 203.15 K, 233.15 K, and 297.15 K from 0.1 bar to 4.0 bar. Multicomponent adsorption isotherms were determined for binary mixtures of oxygen and nitrogen at 203.15 K. The results for the pure‐component isotherms are in excellent agreement with experimental data. The results for the heat of adsorption are in good agreement with experimental data for argon and oxygen, but not for nitrogen. The results for multicomponent adsorption isotherms are qualitatively correct; however, the simulation was not able to quantitatively predict mixture data.

Hypersonic rarefied flow around a circular disk.

Rarefied flows around a circular disk in a hypersonic stream are analyzed by the direct simulation Monte Carlo method. The domain of calculation is fully three-dimensional. The rarefaction effect upon such quantities as the flow field, the drag and heat transfer coefficients, and the recovery temperature is shown for Kn=0.1 - 20 at the wall to a stagnation temperature ratio of 0.5 and 1. The drag coefficient is in good agreement with the experimental data of argon by Legge. The cell network proposed here can easily be applied to lifting flows.

Apparatus for the measurement of compressibility isotherms of gases up to 10 kbar: Experimental data for argon at 298.15 K

An apparatus for the measurement of compressibility isotherms of gases up to pressures of 10 kbar and at temperatures between 273 and 350 K is described. It is based on a gas expansion method in which the pressure distortion of the experimental volume is evaluated by calibration with the measuring gas at lower pressures. The apparatus can easily be adapted for isochoric measurements over a wide temperature range. Measurements on argon at 298.15 K show that the method is capable of giving a precision of 0.02%–0.06% for the density, 0.1% for the pressure, and 2 mK for the temperature.

Thermal conductivity of the Lennard-Jones liquid by molecular dynamics calculations

Precise results for the thermal conductivity of the Lennard-Jones liquid obtained by equilibrium molecular dynamics (MD) are presented. These are compared in detail with previous nonequilibrium MD results. Effects due to the truncation of the potential and the particle number dependence are considered. The contributions of the partial correlation functions to the total one were separately calculated. Main results are: (i) in contrast to the viscosity, the thermal conductivity is rather insensitive to the MD conditions, even for the state corresponding virtually to the triple point of argon. The reason for this originates from the simple short ranged time decay of the correlation function. (ii) For the states considered, the partial correlation function involving the ‘‘potential–potential’’ term governs the transport coefficient. (iii) Nonequilibrium MD and MD give consistent values, except for the nonequilibrium method devised by Heyes which generates data far off the range permitted by the error bars. (iv) The computed thermal conductivities fall well in line with experimental data for argon.

A simple isotherm equation for describing gas adsorption on heterogeneous microporous solids

A simple isotherm equation for describing gas adsorption on solids showing heterogeneity of microporous structure is proposed. It is shown that this equation gives a good representation of the experimental data of argon, nitrogen and benzene adsorption on different types of activated carbons. Its parameters may be used to characterize heterogeneity of microporous structure of the solids.

Apparatus for sound velocity measurements in gases up to 10 kbar: Experimental data for argon

An apparatus for the measurement of sound velocity in gases up to pressures of 10 kbar and down to temperatures of 77 K is described. Important features of the experimental setup include a specially designed ultrasonic cell with double reflectors, based on the phase comparison pulse-echo technique, and a vacuum type of cryostat using a cold finger system for temperature control. Detailed measurements on argon down to the melting line show that the method is capable of giving a precision of 0.02% for the sound velocity.

Calculation of the current-voltage-pressure characteristics of dc diode sputtering discharges

The relationship between current density, applied voltage, and pressure in dc diode discharges used for sputter deposition has been calculated using a model which considers the electron and ion currents within the cathode dark space. Electrons emitted from the target cause ionization primarily at the interface between the dark space and negative glow and ions crossing the dark space suffer symmetric charge exchange collisions with neutrals. The resulting expression for the characteristic is of the form J = B−2/3 (Va−V0)3/2, where V0 is the minimum voltage at which the discharge can be maintained. The values of B and V0 have been obtained by comparison with experimental data for argon and oxygen discharges with a Ta sputtering target. They vary approximately as (pressure)−4/3 and (pressure)−1, respectively. Values of B calculated from the experimental data for J and Va in argon and oxygen discharges agree with the values obtained from the model and measured values for the dark space distance. Comparison of the model with experimental data gives an estimate of the average value of Townsend’s ionization coefficient.

A complete iterative inversion procedure for second virial coefficient data

A new iterative procedure which enables potential energy functions to be obtained from second virial coefficient data has recently been devised and shown to work with essentially exact data. To examine the applicability of the method to real and imperfect data, we have tested it on pseudoexperimental data which, though calculated from a known potential energy function, incorporates random errors. The results show that the method works well on data containing random errors comparable with those believed to exist in the experimental measurements on argon. The procedure was also shown to be satisfactory when applied to the experimental data for argon.