Argon fluids

FIG. 1 The calculated surface tension of an argon fluid represented as a Lennard-Jones fluid is shown as a function of temperature. The GvdW(HS-B2)-functional is used in all cases. The filled squares correspond to step function profile and local entropy, the filled circles to tanh profile with local entropy, and the open circles to tanh profile with nonlocal entropy. The latter data are in good agreement with experiment. 

Almost all of the early MD studies used either model potential functions or effective potential functions constructed to reproduce structural data on condensed phase systems. Examples include the choice of Lennard-Jones parameters to reproduce argon fluids and the water potentials discussed earlier. A much more systematic approach is to combine... 

Borgelt, R, Hoheisel, C. Stell, G. (1990). Exact molecular dynamics and kinetic theory results for thermal transport coefficients of the Lennard-Jones argon fluid in a wide range of states. Phys. Rev., A42, 789-794. 

Figure A2.3.7 The radial distribution function g r) of a Lemiard-Jones fluid representing argon at T = 0.72 and p = 0.844 detennined by computer simulations using the Lemiard-Jones potential.

However, the discovery in 1962 by Voronel and coworkers [H] that the constant-volume heat capacity of argon showed a weak divergence at the critical point, had a major impact on uniting fluid criticality widi that of other systems. They thought the divergence was logaritlnnic, but it is not quite that weak, satisfying equation (A2.5.21) with an exponent a now known to be about 0.11. The equation applies both above and... 

In the theory of the liquid state, the hard-sphere model plays an important role. For hard spheres, the pair interaction potential V r) = qo for r < J, where d is the particle diameter, whereas V(r) = 0 for r s d. The stmcture of a simple fluid, such as argon, is very similar to that of a hard-sphere fluid. Hard-sphere atoms do, of course, not exist. Certain model colloids, however, come very close to hard-sphere behaviour. These systems have been studied in much detail and some results will be quoted below. 

At equilibrium, in order to achieve equality of chemical potentials, not only tire colloid but also tire polymer concentrations in tire different phases are different. We focus here on a theory tliat allows for tliis polymer partitioning [99]. Predictions for two polymer/colloid size ratios are shown in figure C2.6.10. A liquid phase is predicted to occur only when tire range of attractions is not too small compared to tire particle size, 5/a > 0.3. Under tliese conditions a phase behaviour is obtained tliat is similar to tliat of simple liquids, such as argon. Because of tire polymer partitioning, however, tliere is a tliree-phase triangle (ratlier tlian a triple point). For smaller polymer (narrower attractions), tire gas-liquid transition becomes metastable witli respect to tire fluid-crystal transition. These predictions were confinned experimentally [100]. The phase boundaries were predicted semi-quantitatively. 

Argon, helium, and their mixtures with other gases are used as the working fluids in plasma arc devices for producing plasma jets with temperatures in excess of 50,000 K. These devices are used for cutting metals and for spray coating of refractory alloys and ceramics (qv) (see Plasma technology). 

S. C. Lin, E. L. Reslei, and A. R. Kantiowitz,/. Appl Phjs. 26(1), 83—95 (fan. 1955) H. E. VetscReR, Approach to Equilibrium behind Strong Shock Waves in Argon, Pli.D. dissertation, Cornell University, Ithaca, N.Y., 1955 R. M. Patrick, Magnetohjdrodynamics of a Compressible Fluid, Pli.D. dissertation, Cornell University, Ithaca, N.Y., 1956 R. J. Rosa, EngineeringMagnetohjdrodynamics, Ph.D. dissertation, Cornell University, Ithaca, N.Y., 1956 J. Jukes, Ionic Heat Transfer to the Walls of a Shock Tube, Ph.D. dissertation, Cornell University, Ithaca, N.Y., (1956). 

Simple Fluids. Spherical compounds having Httle molecular interaction, eg, argon, krypton, xenon, and methane, are known as simple fluids and obey the theory of corresponding states. 

Ulizar, I. and Pilidis, P. (1996), A. semi-closed cycle gas turbine with carbon dioxide-argon as working fluid, ASME paper 96-GT-.345,... 

Adsorption of hard sphere fluid mixtures in disordered hard sphere matrices has not been studied profoundly and the accuracy of the ROZ-type theory in the description of the structure and thermodynamics of simple mixtures is difficult to discuss. Adsorption of mixtures consisting of argon with ethane and methane in a matrix mimicking silica xerogel has been simulated by Kaminsky and Monson [42,43] in the framework of the Lennard-Jones model. A comparison with experimentally measured properties has also been performed. However, we are not aware of similar studies for simpler hard sphere mixtures, but the work from our laboratory has focused on a two-dimensional partly quenched model of hard discs [44]. That makes it impossible to judge the accuracy of theoretical approaches even for simple binary mixtures in disordered microporous media. 

In the case of fluids which consist of simple non-polar particles, such as liquid argon, it is widely believed that Ui is nearly pairwise additive. In other words, the functions for n > 2 are small. Water fails to conform to this simplification, and if we truncate the series after the term, then we have to understand that the potential involved is an effective pair potential which takes into account the higher order-terms. 

Diffusivities. Our results for the dlffuslvltles of both systems are summarized In Table I. The pore average transverse dlffuslvlty for the bulk fluid at equilibrium agrees very well with experimental and simulation values for the dlffuslvlty of Argon at the same density and temperature (18.12.5). 

The extracts were then atomised and fed into the ROTARC reactor for high temperature treatment. In the first case the atomised extract was mixed with the torch gas (Argon) only. It was a pure pyrolysis, which was effective in the sooting of the reactor walls and it was making the scrubber fluid dirty. The disadvantage of the pure pyrolysis process confirmed our theoretical considerations on thermal destruction of PCB s presented in [9]. To avoid sooting, we fed steam into the reaction chamber in the amount of 10% above the stoichiometry. In this case, which we call the wet pyrolysis , we obtained the destruction efficiency of oil- PCB s at least 99.99%. The offgas analysis on the concentration of oil-PCB s were below the detection limit 0.2 ppm. 

Let us assume that a sphere with radius a is immersed in a liquid of finite volume, e.g., a mineral in a hydrothermal fluid. Diffusion in liquids is normally fast compared to diffusion in solids, so that the liquid can be thought of as homogeneous. Similar conditions would apply to a sphere degassing into a finite enclosure, e.g., for radiogenic argon loss in a closed pore space. Given the diffusion equation with radial flux and constant diffusion coefficient... 

---