previous    next

Fluids

Critical point



The phase boundary for gas-liquid does not continue to the right for higher and higher temperatures. Above a certain temperature, the critical temperature, a gas cannot be liquefied, no matter how much pressure is applied.

Critical temperature Tc and pressure pc.


Demonstrations of this phenomenon are usually done by sealing a glas tube which, at room temperature, contains some substance in the liquid phase filling about one half of the glas tube. The other half of the glas tube is filled with the vapor (gas) of the same substance. One observes easily the surface of the liquid which separates liquid from gas. By heating the tube to a temperature above the critical temperature suddenly the surface of the liquid disappears. Consequently, only the gas phase exists.



water