Forces free-volume distribution

Most MC studies of small clusters have used free-volume conditions. However, the choice of boundary conditions has a pronounced effect on the properties of small clusters. For a Leonard-Jones potential and a Boltzmann distribution function, the average potential energy given by Eq. (21) vanishes in the limit of an infinite number of configurations. Physically, this corresponds to the evaporation of particles from the surface and is not unexpected. If there is no constraining force on the cluster, there should be a net escape of... 

The experiments in the CSTF vessel showed that for most accident scenarios the assumption of a homogeneous distribution of the aerosols in the free volume is justified, in particular during periods when steam and/or other hot gases rise from the lower levels of the containment. Such a situation induces natural convection forces which are strong enough to keep the aerosol concentration reasonably uniform. In addition, the experiments demonstrated that the steam condensation... 

Significant improvement in the performance of these models is obtained by accounting explicitly for the nonrandom distribution of molecular species and free volume and for highly specific forces between neighboring molecules resulting in hydrogen bonding [5-8]. 

The predicted self-diffusion coefficients depend principally on the quality of the force fields used to model the interactions not only between the penetrant and polymer matrix, but also intramolecular interactions between polymer chains. These last ones, strongly affect the quality of the amorphous polymer cell and in particular the total free volume its distribution and dynamics which in their turn affect the predicted values of diffusion coefficients. The role of chain relaxation and matrix fluctuations in explaining the diffusion mechanism of small gas penetrants as N2 in rubber polymer membranes has been clearly... 

The main factors affecting small penetrants permeability in polymeric material include free volume and its distribution, " density, tanperature and pressure, crystallinity," polymer chain length, mobility and packing, solute size, and affinity for the material. In addition, computational parameters used in the simulations such as the type of force field employed and the size of the model also affect the permeability value computed. An increase in tanperature generally leads to a decrease in the solubility and conversely for the diffusion. For all three physical quantities P, S, and D, the tanperature dependence can be described by a Van t Hoff-Arrhenius equation. In particular, for the solubility... 

In a reservoir at initial conditions, an equilibrium exists between buoyancy forces and capillary forces. These forces determine the initial distribution of fluids, and hence the volumes of fluid in place. An understanding of the relationship between these forces is useful in calculating volumetries, and in explaining the difference between free water level (FWL) and oil-water contact (OWC) introduced in the last section. 

If the interval r is large compared with the time for a collision to be completed (but small compared with macroscopic times), then the arguments of the distribution functions are those appropriate to the positions and velocities before and after a binary collision. The integration over r2 may be replaced by one over the relative distance variable r2 — rx as noted in Section 1.7, collisions taking place during the time r occur in the volume g rbdbde, where g is the relative velocity, and (6,e) are the relative collision coordinates. Incomplete collisions, or motions involving periodic orbits take place in a volume independent of r when Avx(r) and Av2(r) refer to motion for which a collision does not take place (or to the force-field free portion of the... 

If the NMR response is capable of estimating the pore size distribution, then it also has the potential to estimate the fraction of the pore space that is capable of being occupied by the hydrocarbon and the remaining fraction that will only be occupied by water. The Free Fluid Index (FFI) is an estimate of the amount of potential hydrocarbons in the rock when saturated to a given capillary pressure. It is expressed as a fraction of the rock bulk volume. The Bulk Volume Irreducible (BVI) is the fraction of the rock bulk volume that will be occupied by water at the same capillary pressure. The fraction of the rock pore volume that will only be occupied by water is called the irreducible water saturation (Siwr = BVI/cj>). The amount of water that is irreducible is a function of the driving force to displace water, i.e., the capillary pressure. Usually the specified driving force is an air-water capillary pressure of 0.69 MPa (100 psi). 

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