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Figure 6.8
Extracting bulk properties from systems with a high number of molecules
(left) and a low number of molecules (right).
containing a large number of molecules allows a greater number of molecules to
be included in the influence zone of each node as the resolution of the system
moves up to meso scale resolutions, when compared to a system of molecular
scale dimensions of the same density (Figure 6.8).
6.3 MESO SCALE SIMULATIONS
The small scale tests performed up to now have tested the lower limits of this
method for extracting bulk ensemble properties from molecular simulations. The
results may be less accurate because the ensemble averages have low numbers of
molecules. Nevertheless, the method provides a framework that allows the charac-
terization of bulk effects from a molecular model. These bulk fluid properties have
a definitive meaning above the molecular scale over large numbers of molecules.
The bulk properties have a definite definition on a continuum scale, but there are
a wide range of governing equations that can predict bulk fluid behaviour at these
scales. The aim of this method is to capture the behaviour of these properties at
meso scales, where they have meaning but cannot be characterized by continuum
equations. It is particularly important to characterize the fluid in terms of mean-
ingful properties relevant to solving engineering problems occurring at the meso
scale. In this section simulations are performed at meso scale dimensions to ex-
amine the way in which the behaviour of this method, and the dynamics of the
molecular model, change when a large number of molecules is used.
The system used is similar in form to the slit channel used previously to aid
comparison with smaller systems; this is shown in Figure 6.9. The slit chan-
nel is approximated by two parallel sheets of graphite separated by 93 nm,
with modified boundary potentials to approximate an infinite solid comprised of
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