  A numerical model is built, simulating the principles of kinetic gas theory,
to predict pressures of molecules in a spherical pressure vessel; the model
tracks a single particle and multiplies the force on the spherical walls by a
mole of molecules to predict the net pressure. An intermolecular attractive
force is added for high-density simulations, to replicate a real fluid; the
force is chosen to ensure the fluid matches the Peng-Robinson equation of state
as it is compressed to a near supercritical density. The standard deviations of
the molecule position and velocity with respect to temperature and density is
studied to define the entropy. A parametric study of a Stirling cycle heat
engine utilizing near-supercritical densities is modeled, to study how the
temperature dependence of the attractive intermolecular Van der Waal forces can
affect the net total entropy change to the surrounding environment.
