The behavior of supercritical (SC) fluid during a blowdown is under investigation. A model based on a steady state Homogeneous Equilibrium Model (HEM) and conditions with and without friction is presented. Calculations indicating three different possible regimes in a blowdown scenario are calculated with this model. The single-phase flow in the supercritical region and the transition either into sub-cooled water, a two-phase fluid or a superheated gas near the critical point results in an interesting flow with a wide range of behavior. Depending on the initial conditions and the geometry either vaporization or condensation can occur either in the pipe or at the exit. In addition, these results are to be extended to other fluids like CO2, R22 or R134a by comparing thermodynamic properties and their dynamic evolution to dimensionless SC water results. Finally the design of an experiment with initial data on the depressurization of a supercritical water system is presented.