Thermodynamic Behavior Of Fluids Research Articles

Calculation of density, vapor pressure and heat capacity near the critical point by incorporating cubic SRK EoS and crossover translation

With the emerging application of near-critical fluid, the subject of equation of state (EoS) covering the critical point is of great significance as the thermodynamic behavior of fluids near the critical point is different. Although many different EoSs are available for fluids at the moment, the ones which can give good quantitative results are still rare. Therefore, it is essential to have a suitable model for proper prediction of fluids behavior and their thermodynamic properties near the critical region. In this study, the crossover translation, which applies the asymptotic behavior of fluids and scaling laws near and far from the critical point, was used. Thermodynamic properties including density, vapor pressure and isochoric heat capacity of fifteen pure components in the saturated state and single-phase region on different isotherms were investigated near the critical point by Soave-Redlich-Kwong (SRK) equation of state and crossover SRK EoS and the results were compared with experimental data. According to the results, crossover SRK EoS predicted all of the mentioned properties with quantitative accuracy. The average absolute percent deviation (AAPD) of the saturated liquid density, saturated vapor density, density on isotherms, vapor pressure and isochoric heat capacity based on crossover SRK EoS were 0.0060,0.1287, 0.0171, 0.057 and 2.53, respectively.

Predicting the Thermodynamic Properties of the Modified Lennard-Jones Fluid from the Lennard-Jones Equation of State

The Lennard-Jones (LJ) potential has been widely used, even beyond fluid science, as a standard form to express interparticle interaction. However, numerical computation and simulation requires some convention for dealing with the potential's infinite tail. This delicate problem can be circumvented by adopting a truncated potential. The functional form of the latter should mimic that of the original potential as closely as possible, while simultaneously minimizing artificial effects caused by the resultant discontinuities. The advantage of choosing such a truncated LJ potential, called the modified Lennard-Jones (mLJ) potential, is that the thermodynamic behavior of fluids can be predicted from the extensive knowledge base regarding the LJ fluid. In this study, the properties of the mLJ fluid were treated as perturbations of the LJ fluid case, and the discrepancies were expressed as density series expansions. The second virial coefficient of the mLJ fluid was well reproduced by this method. Reproduction of the liquid–vapor coexisting envelope was also satisfactory, except in the vicinity of the critical point.

Partial derivatives of thermodynamic state properties for dynamic simulation

The thermodynamic behaviour of fluids can be accurately described by equations of state (EoS) in terms of the Helmholtz energy, with temperature and density as independent variables. The known properties in dynamic simulations of power or refrigeration cycles are usually different from temperature and density. Partial derivatives of state properties with respect to the known properties of the simulation have to be transformed into partial derivatives with respect to the independent variables of the EoS. This transformation is demonstrated step by step for the single-phase region, along the saturation line and within the two-phase region.

The Use of Combined Static- and Dynamic-Material-Balance Methods With Real-Time Surveillance Data in Volumetric Gas Reservoirs

Summary Estimating in-place volume associated with each well, leading to estimation of total reservoir in-place volume, is the cornerstone to any reservoir-management practice. Yet, conventional methods do not always lend themselves to routine applications, particularly when used in singular fashion. However, combining these methods on the same plot has considerable merit in that they converge to the same solution when material-balance (MB) -derived averagereservoir pressure is used in a volumetric system. This study presents a systematic procedure for estimating the gas-initially-in-place (GIIP) volume when real-time surveillance data of pressure, rate, and temperature are available at the wellhead. Specifically, we show that log-log diagnosis, followed by combined static- and dynamic-MB analysis and transient-productivity-index (PI) analysis, leads to consistent solutions. Thermodynamic behavior of fluids is also explored to ensure that converted pressures at the bottomhole and measured rates have consistency and accuracy for reservoir-engineering calculations. Layered systems were selected for this study because they represent most situations. Two synthetic cases probed issues pertaining to average-reservoir-pressure computation with the pseudosteady-state (PSS) approach, and two field examples validated the approach presented here.

Fluids in porous media: a morphometric approach

Predicting the relationship between the morphology of porous media and their physicalproperties, e.g, the conductivity, elasticity and permeability, is a long-standing problem andimportant to a range of applications from geophysics to materials science. Here, a set offour morphological measures, so-called Minkowski functionals, is defined which allows oneto quantitatively characterize the shape of spatial structures, to optimally reconstructporous media, and to accurately predict material properties. The method is based onintegral geometry and Kac’s theorem which relates the spectrum of the Laplaceoperator to the four Minkowski functionals. Analytic expressions for mean values ofMinkowski functionals in Boolean models allow the definition of an effective shape of agrain in a system made up of a distribution of arbitrarily shaped constituents.Reconstructing the microstructure using this effective grain shape leads to anexcellent match to the percolation thresholds and to the mechanical and transportproperties across all phase fractions. Additionally, the use of the effective shape ineffective medium formulations leads to good explicit predictions of bulk moduli.The method is verified for several model systems and sedimentary rock samples,demonstrating that a single tomographic image is sufficient to estimate the morphologyand physical properties such as permeabilities and elastic moduli for a range ofporosities.Also the thermodynamic behaviour of fluids in porous media, i.e., the shape dependence ofthe grand canonical potential and of surface energies of a fluid bounded by an arbitrarilyshaped convex pore, can be calculated in the thermodynamic limit fully from theknowledge of the Minkowski functionals, i.e., of only four morphometric measures. Thisremarkable result is based on Hadwiger’s theorem on the completeness of the additiveMinkowski functionals and the assumption that a thermodynamic potential is an‘additive’ functional which can be understood as a more precise definition for theconventional term ‘extensive’. As a consequence, the surface energy and otherthermodynamic quantities contain in the thermodynamic limit, beside a constant term,only contributions linear in the mean and Gaussian curvature of the pore and not aninfinite number of curvature terms. Finally, starting from a microscopic densityfunctional for an inhomogeneous fluid in a porous medium the phase coexistence(capillary condensation) and the critical point of the fluid is determined in terms ofstructure functions and morphological measures of the pore space and calculatedexplicitly for specific random porous structures using results from integral geometry.

Thermodynamic behavior of fluids in the supercritical region

A procedure for constructing a thermodynamic free energy of fluids is discussed which incorporates a crossover from singular thermodynamic behavior at the critical point to regular thermodynamic behavior far away from the critical point. The, procedure is based on an approximate solution of the renormalization-group theory of critical phenomena and yields an accurate representation of the thermodynamic properties of fluids in a large range of temperatures and densities around the critical point.

Thermodynamic Behavior of Fluids Near the Critical Point

Thermodynamic Behavior of Fluids Near the Critical Point