Thermo-elastic and thermodynamic properties of light and heavy crude oil

Three different experiments, viz., ultrasound interferometry, differential scanning calorimetry, and density measurements were carried out over a wide range of temperature varying from 20°C to 70°C in light, heavy, and a mixture of light and heavy crude oil samples which differ considerably in its American Petroleum Institute gravity. The properties of the mixture have been discussed in terms of its deviation from the ideal values of mixing. The directly measured quantities such as the compression wave velocity, the specific heat at constant pressure, and the density were used to evaluate the temperature dependence of adiabatic compressibility, coefficient of volume expansion and the acoustic impedance. A correlation between thermo-elastic and thermodynamic functions of crude oils has been investigated. In particular, the ratio of the specific heats has been determined by making use of the thermo-elastic functions, which was further used to estimate the specific heat at constant volume. The values of the isothermal compressibility and the coefficient of volume expansion are used to evaluate the pressure–temperature dependence of crude oil conforming to in-situ reservoir conditions.     

PVT properties of polyethylene copolymer melts

PVT properties of four polyethylene random copolymers (ethylene-propylene, ethylene-1-butene, ethylene-1-hexene, and ethylene-1-octene) and linear polyethylene were measured at temperatures from 313 to 493 K and pressures up to 200 MPa. Dependence of properties such as specific volume, thermal expansion coefficient, isothermal compressibility, and characteristic parameter of equations of state on the length of the polymer branched chains were examined. It was found that the length of the branched chain did not affect the thermal expansion coefficient and isothermal compressibility. The specific volume of copolymers having longer branched chains were slightly larger than those copolymers with short branched chains.     

Vapor pressures and PVT properties of 1,1,1,3,3-pentafluoropropane (HFC-245fa)

The vapor pressures and PVT properties of superheated vapor and compressed liquid of 1,1,1,3,3-pentafluoropropane (HFC-245fa) were measured at wide range of temperature and pressure. The simple correlation for vapor pressures, compressibility factors of superheated vapor and specific volumes of liquid were developed on the basis of the present measurements. The critical pressure was calculated by extrapolating the developed vapor pressure equation to the critical temperature. Isothermal compressibility of liquid was calculated from the developed Tait equation. Specific volume data obtained show the good linearity in the Hudleston plots. Overall uncertainty in the vapor pressure, compressibility factor and specific volume measurements is estimated less than ±5 kPa, ±1.2% and ±0.09%, respectively.     

Estimation of second-order derivative thermodynamic properties using the crossover cubic equation of state

In this research, we apply the crossover cubic equation of state (XCubic EOS) [1] to the calculations of thermodynamic second-order derivative properties (isochoric heat capacity, isobaric heat capacity, isothermal compressibility, thermal expansion coefficient, the Joule–Thomson coefficient, and speed of sound). This equation of state is used to calculate those properties of pure systems (carbon dioxide, normal alkanes from methane to propane). We show that, over a wide range of states, the equation of state yields each property with a much better accuracy than the original PT equation of state and near the critical region, represents the singular behaviour well.     

Bulk Properties of n-Heptane–Water–Sodium Dodecyl Sulfate–n-Pentanol Microemulsions

The density, isothermal compressibility, and thermal expansion coefficient of macroscopically single-phase n-heptane–water–sodium dodecyl sulfate–n-pentanol microemulsions are measured by a precision dilatometric method at 25°C. The internal pressure and molar volume of the investigated microemulsion systems are calculated. It was shown that the bulk properties of direct microemulsions with various contents of the dispersed phase markedly differ.     

Densities,sound velocities,and refractive indexes of (tetralin + n-decane) and thermodynamic modeling by Prigogine–Flory–Patterson model

Mixtures of tetralin (1,2,3,4-tetrahydronaphthalene), an aromatic cyclic molecule, and n-decane present asymmetries in chemical nature, shape, and chain length, and are frequently found, e.g., in naphtha or kerosene fractions. Aiming at understanding the impact of these asymmetries on some thermophysical properties, this work presents densities, sound velocities, and refractive indexes for this binary system along with the properties of the pure components at T = (293.15, 303.15, 313.15, 323.15, 333.15, and 343.15) K over whole composition range and atmospheric pressure. From these data, the following derived properties were obtained: isentropic compressibility, molar refractivity, excess volume, excess isentropic compressibility, molar refractivity deviations, and thermal expansion coefficient. Several sound velocity mixing rules were tested, and the best result was for Nomoto mixing rule. Pure component densities and sound velocities were correlated with Prigogine–Flory–Patterson (PFP) model. The binary interaction parameter for this model was obtained from correlation of excess volumes and isentropic compressibilities. This model correlated experimental densities very well and correlated reasonably well sound velocities and thermal expansion coefficient.     

Volumetric and Transport Properties of Water–n-Octane–Sodium Dodecyl Sulfate–n-Pentanol Microemulsions

The density, isothermal compressibility, and thermal expansion coefficient of monophase water–n-octane–sodium dodecyl sulfate–n-pentanol microemulsions were measured in a wide range of the water-to-oil ratios. The internal pressure and molar volume of the investigated microemulsion systems were calculated. The conductivity of microemulsions was determined and its percolation character was revealed.     

Prediction of gas condensate properties by Esmaeilzadeh–Roshanfekr equation of state

The Esmaeilzadeh–Roshanfekr (ER) equation of state (EOS) is used to predict the PVT properties of gas condensate reservoir fluids. Three gas condensate fluid samples taken from three wells in a real field in Iran, referred here as SA1, SA4 and SA8, as well as five samples from literature have been used to check the validity of the ER EOS in calculating the PVT properties of gas condensate mixtures. Some experiments such as constant composition expansion (CCE), constant volume depletion (CVD) and dew point pressures are carried out on these samples. In order to have an unbiased comparison between the ER and the Peng–Robinson (PR) equation of state, van der Waals mixing rules are used without using any adjustable parameters (k_ij = 0). Also, no pure component parameters are adjusted. The critical properties and acentric factor for plus-fraction are estimated by the Kesler–Lee, Pedersen et al. and Riazi–Daubert characterization methods. The results of dew point pressure calculations show that the ER EOS has smaller error than the PR EOS. For some mixtures, relative volume, gas compressibility factor and condensate drop-out in CVD and CCE test were also predicted. Comparison results between experimental and calculated data indicate that the ER EOS has smaller error than the PR EOS. The total average absolute deviation was found to be 0.82% and 2.97% for calculating gas compressibility factor and gas specific gravity in CVD test. Also, the total average absolute deviation was found to be 2.06% and 3.42% for calculating gas compressibility factor and relative volume in CCE test.     

Ab initio calculation of structural,lattice dynamical,and thermal properties of cubic silicon carbide

We present first-principles calculations of the structural, lattice dynamical, and thermal properties as well as Raman results for cubic silicon carbide (3C SiC). The plane-wave pseudopotential approach to density functional theory (DFT ) in the local density approximation has been used to calculate the equilibrium properties of 3C SiC, i.e., the ground-state energy, the band structure, the valence electron density, the lattice constant, the bulk modulus, its pressure derivative, and the ionicity factor of the chemical bonds. The linear-response theory within DFT has been used to obtain the phonon frequencies, the eigenvectors, and the mean-square atomic displacements. Furthermore, we calculated the mode Grueisen parameters, the internal-strain parameter, the elastic constants, the Born effective charge, and the high-frequency dielectric constant. The specific heat at constant volume and at constant pressure, the thermal expansion coefficient, the temperature dependence of the lattice constant, and that of the isothermal and adiabatic bulk modulus have been derived within the quasi-harmonic approximation. Finally, the second-order Raman spectrum of 3C SiC has been calculated using phenomenological polarizability coefficients and ab initio frequencies and eigenvectors. © 1995 John Wiley & Sons, Inc.     

The reduced equation of state and related properties of molten high polymers

The significant-structure theory of liquids has been applied to molten amorphous polymers. Expressions of reduced states for these systems are derived for the equation of state and thermodynamic properties such as expansion coefficient, compressibility, internal pressure, and cohesive energy density, and the surface tension. The calculated values are in good agreement with experimental results in comparison with those from other models. In particular, our model predicts the corresponding dependence of the internal pressure better than other models.     

PVT properties of linear and dendritic polymers

The aim of this article is to examine the limits of applicability of the Simha‐Somcynsky (S‐S) equation of state (EOS) by comparing the pressure‐volume‐temperature (PVT) data and the derivatives (compressibility, κ, and thermal expansion coefficient, α) of anionic linear polystyrene (PS) with poly(benzyl ether) dendrimers (PBED). Fitting the PVT of PBED data to the S‐S EOS was similarly satisfactory as that of PS and the computed Lennard‐Jones (L‐J) interaction parameters showed similar errors of ca. 1%. Next, the experimental derivatives, α and κ of PS and PBED were compared with these functions computed from the S‐S EOS—good agreement was obtained for α at ambient pressure, P, indicating validity of the S‐S theory at least up to the first derivative. While the predicted κ = κ(P) dependence for PS and a linear PBED homologue was correct, for dendrimers the compressibility was higher at low pressure and it was lower at high P than theory predicts. Also the extracted values of the L‐J repulsion volume, v*, between a segment pair was smaller than expected. The specific architecture of dendrimer molecules is responsible for this behavior, since their 3D configuration is significantly different from the S‐S model with uniform segmental density and oxygen bonds in the main and side chains add flexibility. © 2009 NRC Canada. J Polym Sci Part B: Polym Phys 48: 322–332, 2010     

Volume expansion coefficients of the water-acetone system at temperatures of 278–323.15 K and pressures up to 1000 bar

Densities ρ at atmospheric pressure and compressibility coefficients k = (v ₀-v)/v ₀ were studied for the water-acetone system over the whole range of compositions at 278.15 and 288.15 K and at pressures up to 1000 bar. The measurement data and results obtained earlier were used to calculate the volume expansion α and pressure β coefficients at 278–323.15 K over the pressure range specified.     

The phase change in potassium chloride

Equations for the interaction of ions in an ionic crystal, developed earlier¹, which allow for the variation of compressibility with pressure, have been applied to calculation of properties connected with the phase transition of potassium chloride under pressure. The data used were only for the high pressure form of the compound. It was found that the calculated transition pressure was much closer to the observed value, if these equations were used; but simpler equations which use a constant compressibility were somewhat better in their calculated values for the lattice energy, molar volume, and change of volume with pressure for the low pressure form of potassium chloride (NaCl structure). It is concluded that, while calculations on these equations form a sensitive test of these equations, the fitting of the equation to the structure needs to be more elaborate.     

A new two-parameter cubic equation of state for predicting phase behavior of pure compounds and mixtures

In this work, a new two-parameter cubic equation of state is presented based on perturbation theory for predicting phase behavior of pure compounds and of hydrocarbons and non-hydrocarbons. The parameters of the new cubic equation of state are obtained as functions of reduced temperature and acentric factor. The average deviations of the predicted vapor pressure, liquid density and vapor volume for 40 pure compounds are 1.116, 5.696 and 3.083%, respectively. Also the enthalpy and entropy of vaporization are calculated by using the new equation of state. The average deviations of the predicted enthalpy and entropy of vaporization are 2.393 and 2.358%, respectively. The capability of the proposed equation of state for predicting some other thermodynamic properties such as compressibility, second virial coefficient, sound velocity in gases and heat capacity of gases are given, too. The comparisons between the experimental data and the results of the new equation of state show the accuracy of the proposed equation with respect to commonly used equations of state, i.e. PR and SRK. The zeno line has been calculated using the new equation of state and the obtained result compared with quantities in the literatures. Bubble pressure and mole fraction of vapor for 16 binary mixtures are calculated. Averages deviations for bubble pressure and mole fraction of vapor are 9.380 and 2.735%, respectively.     

Pressure dependence of viscosity

We reanalyze the pressure dependence of viscosity of liquids of constant composition under isothermal conditions. Based exclusively on very general considerations concerning the relationship between viscosity and "free volume," we show that, at moderate values of pressure, viscosity increases, as a rule, with increasing pressure, provided the liquid is in stable or metastable (undercooled) equilibrium states. However, even if the behavior of the viscosity is governed by free volume effects, deviations from a positive pressure dependence are possible, when the liquid's thermal expansion coefficient is negative. We derive an equation that allows one to quantitatively determine the pressure dependence of viscosity, which requires, in the simplest case, only the knowledge of the temperature dependence of viscosity at constant pressure, the thermal expansion coefficient, and the isothermal compressibility of the liquid. As an example, the negative pressure dependence of water in the range of temperatures 0-4 degrees C and of several silicate liquids, such as albite, jadeite, dacite, basalts, etc., could be explained in such a way. Other glass-forming liquids initially (for moderate pressures) show a positive pressure dependence of viscosity that changes to a negative one when subjected to high (approximately GPa) isostatic pressure. A detailed analysis of water and already mentioned silicate melts at GPa pressures shows that, in addition to free volume effects, other pressure induced structural transformations may have to be accounted for in a variety of cases. By this reason, the theoretical analysis is extended (i) in order to describe the pressure dependence of viscosity for systems that are in frozen-in thermodynamic nonequilibrium states (glasses, i.e., undercooled liquids below the glass transition temperature Tg) and (ii) to systems which undergo, in addition to variations of the free volume, pressure induced changes of other structural parameters. In such cases a decrease of viscosity with increasing pressure may occur, in principle, even if the thermal expansion coefficient is positive. In this way, the present analysis grants a general tool to estimate the pressure dependence of viscosity and supposedly settles the controversy in the current literature.     

Pressure–volume–temperature data and surface tension of blends of poly(ethylene oxide) and poly(methyl acrylate) in the melt

The pressure–volume–temperature behavior of miscible blends of poly(ethylene oxide) (PEO) and poly(methyl acrylate) (PMA) was studied over extended ranges of temperature and pressure. From pressure–volume–temperature data, the reduction parameters for the Flory‐Orwoll‐Vrij equation‐of‐state were determined. It was found that reduction parameters as well as density, thermal expansion coefficient, and isothermal compressibility vary with composition in a nonlinear manner. The surface tension of the blends in the molten state was measured over the whole composition range using the sessile drop method. The surface tension was found to display negative deviation from additivity pointing toward a remarkable surface excess of PMA. Moreover, surface tension displays a minimum in the range of low PEO content at weight fraction of ～0.19. In addition, the temperature coefficient of surface tension shows negative deviation from linearity. It stays constant when PMA is in excess. Results are discussed in terms of equation‐of‐state thermodynamics. The minimum of surface tension can be well explained by weak self‐association of PEO in the bulk. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1893–1900, 2010     

纳米尺寸材料的结构和性质III：铁纳米粒子的结构和性质

Molecular dynamics computer simulation has been carded out to study the structure and physical properties of iron nanoparticles with 331 to 2133 Fe atoms or with diameter from 2.3 to 4.3 nm. The core of liquid nanodroplets has the similar structure of the bulk molten iron liquid that has an average coordination number around 10.5 and the packing density around 0.45, although the closest Fe-Fe distance is slightly longer in the bulk liquid. Most of the iron nanoparticles formed from the cooling of molten nanodroplets have the same body center cubic crystal structure as it was observed in the bulk under the normal temperature and pressure. Lattice contraction was observed for iron nanoparticles. An amorphous solid and an HCP like solid were obtained accidentally during the quenching runs on Fe331 nanoparticles. The physical properties of iron nanoparticles such as molar volume, density, thermal expansion coefficient, melting point, heat of fusion, heat capacity and diffusion coefficient were estimated based on the results obtained from this simulation. The dependence of physical properties on the nanoparticle sizes was addressed.     

Small-angle x-ray scattering study of density fluctuation in pressure-densified polystyrene glasses

Densified polystyrene glasses, prepared by cooling from the liquid state under elevated pressure, were studied by small-angle x-ray scattering at ambient pressure. The density fluctuation, determined from the x-ray data, showed a decrease with increasing pressure up to about 1.5 kbar, and then leveled off to a fairly constant value. The reduction in the density fluctuation produced by the pressure is much greater than the associated decrease in the specific volume. The observed change in density fluctuation is consistent with the view that the density fluctuation in glassy polymers consists of dynamic and quasistatic components and that the first of these can be correlated with the compressibility of the glass. The present data on the density fluctuation, in conjunction with the available data on volume and enthalpy, can be interpreted to mean that in pressure-densified glasses unfavorable chain configurations are trapped in local energy minima, and the strain energy thus stored can promote segmental motion leading to volume expansion at temperatures far below T_g. Some preliminary evidence indicating the formation of microcavities in these pressure-densified glasses is also presented.     

Characterization of short glass fiber filled polystyrene by fiber orientation and mechanical properties

A quasi-steady state, non-isothermal, compressible, inelastic, and creeping flow of polymer melt into a thin cavity is analyzed to predict fiber orientation states. Modified Cross model and Tait's state equation are adopted to consider shear-thinning behavior and compressibility of the polymer melt. Second order tensors are introduced to describe 3-dimensional fiber orientation. Flow-induced fiber orientation can be predicted by solving the equations of change for the orientation tensor with a suitable closure approximation. The orthotropic closure is applied except for the case of low interaction coefficient. Fiber orientation develops mainly due to shear flow in the skin layer and due to stretching effect in the core layer. It turns out that the compressibility, which induces additional velocity gradients during packing, reduces development of the fiber orientation. Results are dependent upon the magnitude of the interaction coefficient. The larger the interaction coefficient, the smaller the orientation development and the effect of compressibility. To predict orientation dependent mechanical properties, the orientation averaging for an arbitrary orientation is carried out from the properties of a transversely isotropic unit cell. The compressibility reduces the axial modulus and increases the transverse modulus. Opposite trends are observed for thermal expansion coefficients. It is also observed that the consideration of compressibility reduces the overall anisotropy of the molded product. Effects of compressibility on mechanical properties of the parts are reduced as the interaction coefficient becomes larger.