Critical point
The critical point is where the distinction between liquid and vapor disappears. Above the critical temperature and pressure, the fluid becomes supercritical and there is no classic boiling/condensing phase change.
Two key numbers: Tc and Pc
Critical temperature (Tc)
Above Tc, you cannot liquefy the fluid by increasing pressure alone.
Critical pressure (Pc)
The pressure at the critical point. Near Pc and Tc, properties can change rapidly with small shifts in temperature or pressure.
Why the critical region matters
- Charts and property tables can show strong gradients near the critical point; numerical results may become more sensitive to inputs.
- For certain systems (e.g., transcritical CO2), the operating line crosses the critical region and “condensation” is replaced by gas cooling.
- For blends, the “critical point” can be less sharp in practice (often a critical curve/region), so published Tc/Pc should be treated as a helpful reference, not a universal boundary for all behaviors.
Try it in FluidTool
Use the calculator to explore a fluid across temperatures and pressures near Tc/Pc. The fluid landing pages also list Tc/Pc for quick reference.