Showing papers on "Binary system published in 1994"

Hydrodynamics of Binary Coalescence. II. Polytropes with Gamma=5/3

Abstract: We present a new numerical study of the equilibrium and stability properties of close binary systems using the smoothed-particle hydrodynamics (SPH) technique. We adopt a simple polytropic equation of state $p=K\rho^\gam$ with $\gam=5/3$ and $K=\,$constant within each star, applicable to low-mass degenerate dwarfs as well as low-mass main-sequence stars. Along a sequence of binary equilibrium configurations for two identical stars, we demonstrate the existence of both secular and dynamical instabilities, confirming directly the results of recent analytic work. We use the SPH method to calculate the nonlinear development of the dynamical instability and to determine the final fate of the system. We find that the two stars merge together into a single, rapidly rotating object in just a few orbital periods. Equilibrium sequences are also constructed for systems containing two nonidentical stars. These sequences terminate at a Roche limit, which we can determine very accurately using SPH. For two low-mass main-sequence stars with mass ratio $q\lo0.4$ we find that the (synchronized) Roche limit configuration is secularly unstable. Degenerate binary configurations remain hydrodynamically stable all the way to the Roche limit for all mass ratios $q e1$. Dynamically unstable mass transfer can also lead to the rapid coalescence of a binary system, but the details of the hydrodynamic evolution are quite different. We discuss the implications of our results for double white-dwarf and W Ursae Majoris systems.

Phase separation in binary hard-core mixtures

Abstract: We report the observation of a purely entropic demixing transition in a three-dimensional binary hard-core mixture by computer simulations. This transition is observed in a lattice model of a binary hard-core mixture of parallel cubes provided that the size asymmetry of the large and small particles is sufficiently large (≥3, in the present case). In addition, we have performed simulations of a single athermal polymer in a hard-core solvent. As we increase the chemical potential of the solvent, we observe a purely entropy-driven collapse of the polymer: the scaling of the radius of gyration Rg of the polymer with the number of segments N changes from that of a polymer in a good solvent to that of a collapsed polymer. Both for the study of the hard-core demixing and of the polymer collapse, it was essential to use novel collective Monte Carlo moves to speed up equilibration. We show that in the limit σ1/σ2→0, the pair distribution function for an off-lattice binary hard-core mixture of parallel cubes with side lengths σ1 and σ2 diverges at contact for the large particles. For the lattice system, we calculated the pair distribution functions g(r) up to the fourth virial coefficient. The difference in g(r) at contact for a binary system and a pure system at the same packing fraction gives a rough criterion, whether the mixture phase separates

The formation of close binary systems

Abstract: A viable solution to the origin of close binary systems, unaccounted for in recent theories, is presented. Fragmentation, occurring at the end of the secondary collapse phase (during which molecular hydrogen is dissociating), can form binary systems with separations less than 1 au. Two fragmentation modes are found to occur after the collapse is halted. The first consists of the fragmentation of a protostellar disc due to rotational instabilities in a protostellar core, involving both an $m=1$ and an $m=2$ mode. This fragmentation mechanism is found to be insensitive to the initial density distribution: it can occur in both centrally condensed and uniform initial conditions. The second fragmentation mode involves the formation of a rapidly rotating core at the end of the collapse phase which is unstable to the axisymmetric perturbations. This core bounces into a ring which quickly fragments into several components. The binary systems thus formed contain less than 1 per cent of a solar mass and therefore will need to accrete most of their final mass if they are to form a binary star system. Their orbital properties will thus be determined by the properties of the accreted matter.

Phase equilibria for carbon dioxide-ethanol-water system at elevated pressures

Abstract: For applications related to the use of supercritical C02 to concentrate ethanol solutions from a fermentation broth, vapor-liquid equilibria for the CO 2 C 2 H 5 OH and the CO 2 C 2 H 5 OHH 2 O system were measured at 313.2, 323.2, 333.2, and 343.2 K at pressures up to 18.5 MPa over a wide range of ethanol concentration. A circulation type of equilibrium apparatus in which both vapor and liquid phases were continuously recirculated was adopted for measurements. Using C02, aqueous ethanol can be concentrated above atmospheric azeotropic composition (89.4 mol %) when the pressure in the ternary system CO 2 C 2 H 5 OHH 2 O is below the critical pressure of the binary system CO 2 C 2 H 5 OH. The experimental measurements for the phase equilibria were compared with the results predicted by Patel-Teja equation of state using each one of the four types of mixing rules: conventional, Wilson, Yu et al., and Adachi and Sugie. Good estimation was obtained for the phase equilibria of the binary systems except for the conventional mixing rule. It was also found that the phase behavior of the ternary system can be better predicted by the Patel-Teja equation of state with the Adachi and Sugie mixing rule than with the three other mixing rules, though the concentration is not estimated satisfactorily.

Interacting binaries: topics in close binary evolution.

Abstract: The ideas of how binary systems evolve with mass exchange have been largely inspired by the surprising characteristics of Algol-type ecUpsing binary systems^. Such systems consist of an unevolved main-sequence star, in the case of Algol: a B 8 V star of 3.7 MQ, together with a less massive subgiant (i.e. more evolved) companion star, in the case of Algol: of spectral type G 8 III (0.8 M©). This situation, with the more evolved star having the smaller mass of the two, is just opposite to what one would expect on evolutionary grounds, as stars of larger mass are expected to live shorter and thus at any time to be in a more advanced stage of evolution than stars of smaller mass. This is what is called the "Algol-paradox". Crawford [50] was the first one to realize that this paradoxical situation can be explained if one asstmaes that largescale mass transfer can take place during the evolution of a binary system: he hypothesized that the subgiant components in Algol systems were originally the more massive components of these systems. As the more massive star evolved faster than its less massive companion it was the first to have evolved away from the main-sequence towards the giant branch. The presence of the close companion, however, prevented such an evolution: when the outer layers of the expanding (sub)giant came under the gravitational influence of the companion, they were captured by that star, causing the latter to increase its mass at the expense of the sub(giant) companion. The (sub)giant transferred so much of its mass that it was finally able to restabilize its interior structure. At that moment it had become the less massive of the two stars. The first -very courageousattempt to carry out a real calculation of this type of evolution with mass transfer was by Morton [174]. He demonstrated the correctness of Crawford's conjecture that mass tranfer, once it begins, becomes unstable and continues until the (sub)giant has become the less massive star of the two. In his calculations, however, he still assumed that the orbital period of the system does not change during the mass transfer. He just kept it fixed.

Viscosity, Density, and Surface Tension of Binary Mixtures of Water and N-Methyldiethanolamine and Water and Diethanolamine and Tertiary Mixtures of These Amines with Water over the Temperature Range 20-100.degree.C

Abstract: The density and viscosity of aqueous solutions of N-methyldiethanolamine were measured over the temperature range 60-100 o C. The density and viscosity of aqueous solutions of diethanolamine and diethanolamine+ N-methyldiethanolamine were measured over the temperature range 20-100 o C. The surface tension of aqueous solutions ofthe above mixtures was measured over the temperature range 20-80 o C. The concentration ranges were 10-50 mass % N-methyldiethanolamine, 10-30 mass % diethanolamine, and 50 mass % totalamine concentration with mass ratios of 0.0441-0.5883 (diethanolamine to N-methyldiethanolamine). The measured quantities were found to be in agreement with the literature where data were available

New Loading Technique for a Vibrating Tube Densimeter and Measurements of Liquid Densities up to 39.5 MPa for Binary and Ternary Mixtures of the Carbon Dioxide-Methanol-Propane System

Abstract: Special equipment has been designed and constructed to measure pressure-volume-temperature (PVT) data through the vibrating tube method. At constant temperature, pressure is increased by steps using a pressurizing cell. For each stabilized pressure value, the vibrating frequency of the tube is recorded and translated into density through calibration with known density samples. Experimental PVT measurements on several pure compounds and mixtures have been carried out. Data reliability has been verified by comparisons with literature data available for methane-, ethylene-, methanol-, propane-, 4-methyl-1-pentene-, and n-heptane-methylcyclopentane binary mixtures for temperatures between 298 and 398 K and pressures between 2.5 and 39.5 MPa. New data are given for binary and ternary liquid mixtures of the carbon dioxide-methanol-propane system at four temperatures, 323, 348, 373, and 398 K, between 2.5 and 39.5 MPa.

Equilibrium, stability, and orbital evolution of close binary systems

Abstract: We present a new analytic study of the equilibrium and stability properties of close binary systems containing polytropic components. Our method is based on the use of ellipsoidal trial functions in an energy variational principle. We consider both synchronized and nonsynchronized systems, constructing the compressible generalizations of the classical Darwin and Darwin-Riemann configurations. Our method can be applied to a wide variety of binary models where the stellar masses, radii, spins, entropies, and polytropic indices are all allowed to vary over wide ranges and independently for each component. We find that both secular and dynamical instabilities can develop before a Roche limit or contact is reached along a sequence of models with decreasing binary separation. High incompressibility always makes a given binary system more susceptible to these instabilities, but the dependence on the mass ratio is more complicated. As simple applications, we construct models of double degenerate systems and of low-mass main-sequence star binaries. We also discuss the orbital evoltuion of close binary systems under the combined influence of fluid viscosity and secular angular momentum losses from processes like gravitational radiation. We show that the existence of global fluid instabilities can have a profound effect on the terminal evolution of coalescing binaries. The validity of our analytic solutions is examined by means of detailed comparisons with the results of recent numerical fluid calculations in three dimensions.

Studies on the thermodynamics of the fullerene C60-C70 binary system

Abstract: Partial pressures of C[sub 60] and C[sub 70] were measured as a function of temperature at several compositions from pure C[sub 60] to pure C[sub 70] in the C[sub 60]-C[sub 70] binary system. The measurements were carried out in the temperature range 600-800 K by using Knudsen effusion mass spectrometry. The pressure-temperature-composition data suggest that the two fullerenes are soluble in each other in the solid state to the extent of about 30%, with a miscibility gap in between. A binary phase diagram is reported on the basis of these studies. The partial pressures of both C[sub 60] and C[sub 70] in equilibrium with fullerite were also measured as a function of temperature. The enthalpy and entropy of vaporization of each species are derived from the pressure-temperature data for every solid phase studied. The thermodynamic data suggest that C[sub 60] and C[sub 70] are more strongly bound in fullerite than in the solid solution or in the pure phases. This indicates the influence of higher fullerenes. 28 refs., 11 figs., 10 tabs.

Thermochemistry of binary alloys of transition metals : the systems Cu-Ce, Me-Pr, and Me-Nd (Me = Cu, Ag, Au)

Abstract: The standard enthalpies of formation of the congruently melting intermetallic compounds in the (Pr, Nd)-(Cu, Ag, Au) binary systems were determined by high-temperature direct synthesis calorimetry at 1473 ± 2 K. The liquid-liquid enthalpies of mixing for the same systems were measured by the same technique in the range of compositions available for experiments at 1473 ± 2 K. Additionally, the heats of mixing in the Cu-Ce system were remeasured. The results obtained for the solid alloys are compared with values calculated from Miedema’s semiempirical model.

Use of empirical polarity parameters to describe polymer/liquid interactions: Correlation of polymer swelling with solvent polarity in binary and ternary systems

Abstract: Dimroth and Reichardt polarity parameters ET(30) have been used, in a new approach, to quantitatively describe the swelling features due to polymer liquid interactions in binary and ternary systems. With the help of a polyurethaneimide (PUI) synthesized from polytetramethyleneglycol 650, sorption of pure liquids was first examined, and it was shown that a linear relationship between the molar swelling Gm and the ET(30) values well fits the experimental data of each of the two series studied, i. e., aliphatic alcohols and linear ethers: Gm = a+b ET(30). The slope value b, regarded as the sensitivity of the polymer to the liquid polarity, is 3 times higher for the aprotic series. The proposed correlation was further proved valid from the study of published results concerning nine binary systems polymer–liquid, whatever the polarity of the liquids in a given family (alcohols, esters, ketones, hydrocarbons) and the nature of the polymer. Finally, that method was tested on two types of PUI-alcohol-ether ternary systems, and it was found for each case that the partial molar swelling due to an homologous set of solvents can also be described by a similar law. © 1994 John Wiley & Sons, Inc.

The Lifshitz line in binary systems: Structures in water/C4E1 mixtures

Abstract: In a recent publication we compared phase behavior and scattering data obtained from SANS in water, n‐alkane, n‐alkyl polyglycol ether (CiEj) mixtures. By analyzing the scattering spectra using the Teubner–Strey formula, it is possible to determine a measure for the amphiphilic strength of each system called the amphiphilicity factor, fa. It was demonstrated that the amphiphilicity factor is constant on a variety of surfaces within the three‐dimensional space of composition and temperature. For instance, the Lifshitz surface, where fa=0, depends on composition and temperature and may be a precursor for the Lα phase. Here we show that the same sequence exists in the binary system water/C4E1, where the surfaces become lines in the two‐dimensional composition‐temperature planes. Variations in amphiphile concentration and solution temperature allow one to reach almost the entire accessible amphiphilicity scale (∞≳fa≳−1) within this simple binary mixture. The occurrence of the Lifshitz surface at high C4E1 con...

Temperature-transforming model for binary solid-liquid phase-change problems part ii: numerical simulation

Abstract: The model and numerical scheme developed in Part I were first verified with upward freezing experiments of an NH4Cl-H2O solution on a cold isothermal surface. Then, two-dimensional convection problems with different buoyancy terms in binary solid-liquid phase-change systems were studied. Finally, the model was used to simulate the solidification of an aqueous ammonium chloride solution in a rectangular cavity. The comparison of the results obtained from the present studies with the experimental and numerical results from the literature revealed a good agreement.

Non-isothermal Adsorption of Nitrogen-Carbon Dioxide Mixture in a Fixed Bed of Zeolite-X

Abstract: The binary adsorption of nitrogen and carbon dioxide on zeolite-X was investigated. The adsorption equilibria of pure and binary systems were measured by static methods. In the binary system the equilibrium Selectivity of CO2 over N2 was very high: about 525 at a CO2 mole fraction of 0.14 and a temperature of 15°C. Consequently, N2 can be considered as inert when its mole fraction is less than 0.8. The ideal adsorbed-solution theory (IAST) predicted quite well the binary equilibrium data, while the extended Langmuir isotherm showed a great deviation. The dynamics of fixed-bed adsorption of CO2-N2 gas mixture (CO2 14.86 mole percent) was analyzed by the cell model under non-isothermal conditions, incorporated with binary adsorption equilibria, mass and heat transfer resistances and variation of gas velocity in the bed. The concentration and temperature history curves were determined and compared with the theoretical results. This cell-model with IAST predicted well the dynamic behavior of the adsorption bed.

Vapor-Liquid Equilibria of n-Hexane + Cyclohexane + n-Heptane and the Three Constituent Binary Systems at 101.0 kPa

Abstract: Vapor-liquid equilibrium data for the title ternary system and the three constituent binary systems have been measured at 101.0 kPa by using a dynamic equilibrium still. The binary data were tested for thermodynamic consistency and were correlated by the Wilson, NRTL, and UNIQUAC equations. Predictions for the ternary system by these equations have been compared with the experimental data.

Mass spectrometric investigations of fullerenes. I. Vapour pressure over the C60/C70 binary system

Abstract: The absolute vapour pressures over pure C60, C70, fullerite and over the binary C60/C70 system are calculated from ion intensities vs. temperature up to 800 K using the Knudsen effusion mass spectrometric method. The vapour pressures (Pa) of C60 and C70 are given as a function of temperature (K) by the equations: Corresponding Second Law enthalpy and entropy changes for sublimation are: Results are discussed in terms of sample purity and pretreatment and correlated with data obtained by other authors. Fullerenes containing residual organic solvents (fullerite) partly decompose upon thermal treatment to amorphous carbon.

Binary alkaline earth oxide mixtures: Estimation of the excess thermodynamic properties and calculation of the phase diagrams

Abstract: A survey of available experimental excess thermodynamic properties for the binary alkaline earth oxide mixtures is given. The known excess thermodynamic properties of the oxide mixtures are evaluated and missing values are estimated by analogy with the binary common-ion alkali halide mixtures. The phase diagrams of the oxide mixtures corresponding to the evaluated / estimated excess properties are calculated and compared with the available experimental phase diagrams.

High-Pressure, Molecular Weight-Dependent Behavior of (Co)polymer-Solvent Mixtures: Experiments and Modeling

Abstract: Cloud-point data as a function of polymer molecular weight are presented for polyethylene (PE)-dimethyl ether (DME) and poly(ethylene-co-methyl acrylate) (35 mol % acrylate) (EMA)-butane mixtures to temperatures of 210°C and pressures of 2700 bar. The cloud-point curves for PE-DME, at temperatures below ∼125°C, and EMA-butane, at temperatures below ∼150°C, order with respect to the weight average molecular weight. The cloud-point behaviors for these two systems along with the poly(ethylene-co-acrylic acid) (4.1 mol % acid) (EAA)-butene system are modeled with the statistical associating fluid theory (SAFT). For each system, a constant value of the binary interaction parameter, k ij , is fit to the parent-solvent cloud-point curve and is used in subsequent calculations

Solubility of anthracene in binary alkane + 2-butanol solvent mixtures

Abstract: Article discussing the solubility of anthracene in binary alkane + 2-butanol solvent mixtures.