Evidence for instantaneous resonant modes in dense fluids with repulsive Lennard-Jones force

1999 ◽  
Vol 110 (1) ◽  
pp. 447-450 ◽  
Author(s):  
Ten-Ming Wu ◽  
Wen-Jong Ma
Keyword(s):  
Dense Fluids ◽  
Lennard Jones ◽  
Resonant Modes

Investigation of the density dependence of the shear relaxation time of dense fluids

2005 ◽  
Vol 83 (3) ◽  
pp. 236-243 ◽  
Author(s):  
Mehrdad Bamdad ◽  
Saman Alavi ◽  
Bijan Najafi ◽  
Ezat Keshavarzi
Keyword(s):  
Relaxation Time ◽  
Shear Modulus ◽  
Density Dependence ◽  
Radial Distribution ◽  
Shear Viscosity ◽  
Viscosity Coefficient ◽  
Dense Fluids ◽  
Lennard Jones ◽  
Shear Relaxation ◽  
Shear Relaxation Time

The shear relaxation time, a key quantity in the theory of viscosity, is calculated for the Lennard–Jones fluid and fluid krypton. The shear relaxation time is initially calculated by the Zwanzig–Mountain method, which defines this quantity as the ratio of the shear viscosity coefficient to the infinite shear modulus. The shear modulus is calculated from highly accurate radial distribution functions obtained from molecular dynamics simulations of the Lennard–Jones potential and a realistic potential for krypton. This calculation shows that the density dependence of the shear relaxation time isotherms of the Lennard–Jones fluid and Kr pass through a minimum. The minimum in the shear relaxation times is also obtained from calculations using the different approach originally proposed by van der Gulik. In this approach, the relaxation time is determined as the ratio of shear viscosity coefficient to the thermal pressure. The density of the minimum of the shear relaxation time is about twice the critical density and is equal to the common density, which was previously reported for supercritical gases where the viscosity of the gas becomes independent of temperature. It is shown that this common point occurs in both gas and liquid phases. At densities lower than this common density, even in the liquid state, the viscosity increases with increasing temperature.Key words: dense fluids, radial distribution function, shear modulus, shear relaxation time, shear viscosity.

The behaviour of fluids of Quasi-Spherical molecules. II. High density gases and liquids

1954 ◽  
Vol 7 (1) ◽  
pp. 18 ◽  
Author(s):  
SD Hamann ◽  
JA Lambert
Keyword(s):  
High Density ◽  
Corresponding States ◽  
Inert Gases ◽  
Dense Fluids ◽  
Cell Method ◽  
Lennard Jones ◽  
Law Of Corresponding States

Lennard-Jones and Devonshire's (1937) cell method has been used to compute some properties of dense fluids composed of effectively spherical molecules interacting according to the potential U( R ) = A/R28 - B/R7 The results are quite different from those for the more usual (12,6) potential and they explain the failure of such substances as CI4, SF6, . . . , to obey the same law of corresponding states as the inert gases. In particular the different entropies of evaporation (Trouton constants) of the two classes of materials are given correctly by the theory.

scholarly journals Determination of Molecular Diameter by PVT

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
Vahid Moeini ◽  
Mehri Deilam
Keyword(s):  
Experimental Data ◽  
Potential Energy ◽  
Internal Pressure ◽  
Potential Function ◽  
Supercritical Fluids ◽  
Accurate Calculation ◽  
Dense Fluids ◽  
Lennard Jones ◽  
The Relationship

We derive an equation for calculation of molecular diameter of dense fluids, with using simultaneous Lennard-Jones (12-6) potential function and the internal pressure results. Considering the internal pressure by modeling the average configurational potential energy and then taking its derivative with respect to volume to a minimum point of potential energy has been shown that molecular diameter is function of the resultant of the forces of attraction and the forces of repulsion between the molecules in a fluid. The regularity is tested with experimental data for 10 fluids including Ar, N2, CO, CO2, CH4, C2H6, C3H8, C4H10, C6H6, and C6H5CH3. These problems have led us to try to establish a function for the accurate calculation of the molecular diameter based on the internal pressure theory for different fluids. The relationship appears to hold both compressed liquids and dense supercritical fluids.

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