Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Karel Aim is active.

Publication


Featured researches published by Karel Aim.


Fluid Phase Equilibria | 1984

Perturbed hard-sphere equations of state of real fluids. II. Effective hard-sphere diameters and residual properties

Ivo Nezbeda; Karel Aim

Abstract Effective hard-sphere diameters for argon, krypton and xenon have been calculated from the currently most accurate perturbation theories using accurate pair-potential models. Based on the theoretical diameters and on pressure—volumes—temperature data for the real fluids, the van der Waals parameter ap is examined and two conjectures generalizing the behavior of ap are formulated. These conjectures make it possible to evaluate the effective hard-sphere diameters of simple liquids at the triple-point temperature from data for a few low-temperature pressure—volume isotherms. This fact, together with a corresponding-states principle that emerges from results for the theoretical diameters, forms the basis of a simple method which we propose for evaluating temperature-dependent effective hard-sphere diameters of a perturbed hard-sphere equation of state, independently of any pair-potential model and any perturbation theory. The applicability of the method is demonstrated for methane and its extension to nonsimple liquids is discussed. It is also shown that the use of an approximate theory and/or approximate pair-potential model may often result in a qualitatively misleading picture of ap behavior.


Fluid Phase Equilibria | 1978

Measurement of vapor-liquid equilibrium in systems with components of very different volatility by the total pressure static method

Karel Aim

Abstract To make feasible the experimental study of vapor-liquid equilibrium (VLE) in the systems mentioned in the title, a static apparatus for accurate measurement of total vapor pressures of solutions was constructed. Mixtures of known composition are prepared synthetically in a thermostated equilibrium cell by weight from pure degassed components and the total pressure is measured by a quartz Bourdon gage. A procedure was developed for degassing pure liquids to a degree corresponding to the high precision of pressure determination required. The static assembly was tested by comparing obtained isothermal vapor pressures and calculated excess Gibbs free energies with literature data for the benzene - cyclohexane system at 14 and 20°C, respectively. Additional experimental vapor-pressure data are presented for pure cyclohexane, benzene, and N-methylpyrrolidone (abbreviated throughout this paper as NMP) at 6–24°C and for the binary systems of benzene-cyclohexane at 8°C and cyclohexane - NMP and benzene - NMP at 8, 14, and 20°C over the entire composition range. The binary data were reduced by a modified Barkers method to evaluate excess Gibbs free energies and vapor phase compositions.


Fluid Phase Equilibria | 1983

Perturbed hard sphere equations of state of real liquids. I. Examination of a simple equation of the second order

Karel Aim; Ivo Nezbeda

Abstract Utility of a perturbed hard sphere equation of state based on a simplified Barker-Henderson theory for a square well fluid inclusive of the three-body contributions is examined for orthobaric densities and both sub- and supercritical isotherms of simple fluids. An attempt is made to interpret parameters of the equation and their temperature dependence in terms of independent molecular properties. Finally, some general conclusions on the family of perturbed hard sphere equations of state are drawn.


Molecular Simulation | 1993

The Lennard-Jones Fluid Revisited: Computer Simulation Results

Jiří Kolafa; Horst L. Vörtler; Karel Aim; Ivo Nezbeda

Abstract Pseudoexperimental data of high accuracy on the pressure and the internal energy of the Lennard-Jones fluid have been generated both by the Monte Carlo and molecular dynamics methods for five subcritical and three supercritical isotherms. Values of the chemical potential of the Lennard-Jones fluid computed by a new version of the gradual insertion particle method for two isotherms up to very high densities are also reported and discussed, and compared with existing data.


Fluid Phase Equilibria | 1987

Perturbed hard sphere equations of state of real fluids—II. Residual parameter ap of non-polar liquids

Ivo Nezbeda; Karel Aim

Using the accurate Baker-Fisher-Watts potential, the dipole-dipole-dipole three-body potential, and the EXP approximation, the residual term ap of a perturbed hard sphere equation of state for argon has been calculated and compared with experimental data. Individual contributions to ap, as well as to the pressure, have been assessed and compared with simple analytical expressions currently available. It is shown that (1) the frequently used high temperature approximation alone yields, necessarily, a very poor equation of state and (2) that an accurate perturbed hard sphere equation of state must contain additional terms having their origin in non-additive three-body interactions and certain higher-order perturbation contributions.


Fluid Phase Equilibria | 1989

On the way from theoretical calculations to practical equations of state for real fluids

Ivo Nezbeda; Karel Aim

Abstract Results obtained as a part of the work on the project aiming at utilizing the rigorous statistical mechanical results for practical equation of state calculations are reported. It is shown that the first-order term of the expansion of the Helmholtz free energy, the high-temperature approximation, can be factorized into simple temperature- and density-dependent terms. Over the entire range of the liquid state conditions investigated, the accuracy of the resulting equation of state defined by the hard sphere and high temperature approximation terms is found comparable with that of complex, many-parameter empirical equations.


Molecular Simulation | 2000

VAPOUR - LIQUID EQUILIBRIA OF DIPOLAR TWO-CENTRE LENNARD-JONES FLUIDS FROM A PHYSICALLY BASED EQUATION OF STATE AND COMPUTER SIMULATIONS

Martin Lísal; Karel Aim; Johann Fischer

Abstract The paper is concerned with the model fluid consisting of two-centre Lennard-Jones molecules with embedded axial dipole moment (2CLJD), particularly with its vapour–liquid phase equilibrium behaviour as calculated from different molecular simulation methods and from an analytical equation of state. The focus of the present study is the parameter region of large elongations (L in the range from 0.505 to 1.0) and large dipole moments (μ*2 in the range from 9 to 12) of the 2CLJD fluid. In order to assess the performance of independent molecular simulation methods and to examine the validity of a physically based equation of state of the augmented van der Waals type within this parametric region, we have calculated the 2CLJD model fluid properties along the vapour–liquid coexistence locus by the Gibbs ensemble Monte Carlo method, Gibbs-Duhem integration technique looking at the effect of different starting state points, the NpT plus test particle method, and from the equation of state. Within the entire region examined, fairly good mutual agreement of the independent simulation methods is observed. The equation of state represents a good compromise between the results of different simulation methods at intermediate elongations but fails at large elongations. The extended base of pseudoexperimental data is prerequisite for further equation of state development.


Fluid Phase Equilibria | 1989

Thermodynamic properties of the Lennard-Jones fluid. I. Simulation data, rigorous theories and parameterized equations of state

Karel Aim; Ivo Nezbeda

Abstract The pressures and internal energies of the Lennard-Jones (LJ) fluid were calculated by using the Weeks-Chandler-Andersen theory, EXP approximation, and the optimized reference HNC equation (RHNC). Comparison of the results with computer simulation data on eight isochores and seven isotherms shows that at reduced temperatures higher than 0.8 the RHNC theory predicts accurately the thermodynamic properties of the LJ fluid at all densities and that the EXP approximation performs also very well with the exception of a narrow range of conditions.


Fluid Phase Equilibria | 1993

The Lennard-Jones fluid revisited: new thermodynamic data and new equation of state

Karel Aim; Jiří Kolafa; Ivo Nezbeda; Horst L. Vörtler

Abstract The Lennard-Jones fluid appeared as a natural benchmark during the work on the project aimed at utilizing the rigorous statistical mechanical results for practical equation of state calculations for real fluids. As already reported, however, the so far available molecular simulation data and analytical equations of state were found unsatisfactory for the purpose. Hence a new highly accurate set of data on pressure (-volume-temperature) and internal energy by the Monte-Carlo and molecular dynamics methods and on the chemical potential by Monte Carlo with the new version of the insertion particle method was generated. The data has been used to develop and test a new accurate perturbed hard body equation of state for the Lennard-Jones fluid. The performance of the equation of state on pseudoexperimental data is documented and possible applications of the equation of state for calculating the thermodynamic properties of real fluids are discussed.


Fluid Phase Equilibria | 1996

Applicability of the second-order perturbation theory of anisotropic molecule fluids to real systems of constituents differing in molecular size and/or polarity

Karel Aim; Jan Pavlíček; Tomáš Boublík

Abstract An overview of the recent results obtained from the full second-order perturbation theory of the anisotropic molecule fluid for real systems is given. The performance of the theory has so far been examined upon (i) a series of n-alkanes with the carbon number up to 16, modeled as fluids of the Kihara rod-like molecules, (ii) their binary mixtures, (iii) a series of low-molecular linear chlorinated hydrocarbons with the carbon number up to 4, modeled as fluids of Kihara rods with assigned dipole moments, and (iv) mixtures of the linear chloroalkanes with n-alkanes. Parameters of the interaction potential for the pure compounds were evaluated from the data on the vapor-liquid coexistence region (namely the vapor pressure and saturated liquid density) of the real substances. Each of the parameters of the pair-potential for the pure n-alkanes is accurately represented as a function of the number of carbon atoms by a simple analytical expression. Using the conventional combining rules with only marginal corrections in the cross-terms, the excess Gibbs energies, excess enthalpies, and excess volumes as a function of both the composition and temperature are simultaneously represented succesfully for the n-alkane binaries and also for the chloroalkane + n-alkane mixtures.

Collaboration


Dive into the Karel Aim's collaboration.

Top Co-Authors

Avatar

Ivo Nezbeda

Academy of Sciences of the Czech Republic

View shared research outputs
Top Co-Authors

Avatar

Tomáš Boublík

Czechoslovak Academy of Sciences

View shared research outputs
Top Co-Authors

Avatar

Jan Pavlíček

Czechoslovak Academy of Sciences

View shared research outputs
Top Co-Authors

Avatar

Martin Lísal

Academy of Sciences of the Czech Republic

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar

William R. Smith

University of Ontario Institute of Technology

View shared research outputs
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge