Liquid CO2 is heated in a pressure vessel and brought into the supercritical state.

CO2 becomes supercitical at 7.4 MPa and ~31°C.
In this experiment, liquid CO2 is enclosed in a pressure vessel. Pressure and temperature are increased by using a heating cartridge, so that the CO2 changes to the supercritical state when the critical point (31°C, 7.4 MPa) is reached.
Afterwards cooling of the pressure vessel is followed by an abrupt re-condensation.