Monika Thol

Equation of State for the Lennard-Jones Fluid

An empirical equation of state correlation is proposed for the Lennard-Jones model fluid. The equation in terms of the Helmholtz energy is based on a large molecular simulation data set and thermal virial coefficients. The underlying data set consists of directly simulated residual Helmholtz energy derivatives with respect to temperature and density in the canonical ensemble. Using these data introduces a new methodology for developing equations of state from molecular simulation. The correlation is valid for temperatures 0.5 < T/Tc < 7 and pressures up to p/pc = 500. Extensive comparisons to simulation data from the literature are made. The accuracy and extrapolation behavior are better than for existing equations of state.

Communication: Fundamental equation of state correlation with hybrid data sets

A strategy is proposed for empirical fundamental equation of state correlations for pure fluids on the basis of hybrid data sets, composed of experimental and molecular simulation data. Argon and hydrogen chloride are used as examples.

Comparative study of the Grüneisen parameter for 28 pure fluids

The Grüneisen parameter γG is widely used for studying thermal properties of solids at high pressure and also has received increasing interest in different applications of non-ideal fluid dynamics. Because there is a lack of systematic studies of the Grüneisen parameter in the entire fluid region, this study aims to fill this gap. Grüneisen parameter data from molecular modelling and simulation are reported for 28 pure fluids and are compared with results calculated from fundamental equations of state that are based on extensive experimental data sets. We show that the Grüneisen parameter follows a general density-temperature trend and characterize the fluid systems by specifying a span of minimum and maximum values of γG. Exceptions to this trend can be found for water.

How well does the Lennard-Jones potential represent the thermodynamic properties of noble gases?

ABSTRACT The Lennard-Jones potential as well as its truncated and shifted (rc = 2.5σ) variant are applied to the noble gases neon, argon, krypton, and xenon. These models are comprehensively compared with the currently available experimental knowledge in terms of vapour pressure, saturated liquid density, as well as thermodynamic properties from the single phase fluid regions including density, speed of sound, and isobaric heat capacity data. The expectation that these potentials exhibit a more modest performance for neon as compared to argon, krypton, and xenon due to increasing quantum effects does not seem to hold for the investigated properties. On the other hand, the assumption that the truncated and shifted (rc = 2.5σ) variant of the Lennard-Jones potential may have shortcomings because the long range interactions are entirely neglected beyond the cut-off radius rc, are supported by the present findings for the properties from the single phase fluid regions. For vapour pressure and saturated liquid density such a clear assessment cannot be made.

The Behavior of IAPWS-95 from 250 to 300 K and Pressures up to 400 MPa: Evaluation Based on Recently Derived Property Data

Over the past several years, considerable scientific and technical interest has been focused on accurate thermodynamic properties of fluid water covering part of the subcooled (metastable) region and the stable liquid from the melting line up to about 300 K and pressures up to several hundred MPa. Between 2000 and 2010, experimental density data were published whose accuracy was not completely clear. The scientific standard equation of state for fluid water, the IAPWS-95 formulation, was developed on the basis of experimental data for thermodynamic properties that were available by 1995. In this work, it is examined how IAPWS-95 behaves with respect to the experimental data published after 1995. This investigation is carried out for temperatures from 250 to 300 K and pressures up to 400 MPa. The starting point is the assessment of the current data situation. This was mainly performed on the basis of data for the density, expansivity, compressibility, and isobaric heat capacity, which were derived in 2015 ...

Equation of state for 1,2-dichloroethane based on a hybrid data set

ABSTRACT A fundamental equation of state in terms of the Helmholtz energy is presented for 1,2-dichloroethane. Due to a narrow experimental database, not only laboratory measurements but also molecular simulation data are applied to the fitting procedure. The present equation of state is valid from the triple point up to 560 K for pressures of up to 100 MPa. The accuracy of the equation is assessed in detail. Furthermore, a reasonable extrapolation behaviour is verified.