  The main objective of this article is to study the nature of the Andrews
critical point in the gas-liquid transition in a physical-vapor transport (PVT)
system. A dynamical model, consistent with the van der Waals equation near the
Andrews critical point, is derived. With this model, we deduce two physical
parameters, which interact exactly at the Andrews critical point, and which
dictate the dynamic transition behavior near the Andrews critical point. In
particular, it is shown that 1) the Andrews critical point is a switching point
where the phase transition changes from the first order to the third order, 2)
the gas-liquid co-existence curve can be extended beyond the Andrews critical
point, and 3) the liquid-gas phase transition going beyond Andrews point is of
the third order. This clearly explains why it is hard to observe the gas-liquid
phase transition beyond the Andrews critical point. Furthermore, the analysis
leads naturally the introduction of a general asymmetry principle of
fluctuations and the preferred transition mechanism for a thermodynamic system.
