5 replies to this topic

[Rookie]

I know that a gas operating above its critical temperature cannot condense, no matter how much pressure you increase. Is the other way around true? Will a liquid boil if it's operating above its critical pressure and you increase the temperature?

Thanks in advance.

[Doggert]

If you are at the critical pressure and you increase the temperature above the critical temperature, you will be left with a supercritical fluid. This is basically a substance wherein the gas and liquid phases are indistinguishable (on a phase diagram, you'll note that the critical line separating gas and liquid ends at the critical point).

[Art Montemayor]

Rookie:

If a fluid is at a condition that is above its critical pressure and it is heated to higher temperatures (while holding the pressure constant), it cannot boil.

It cannot boil simply because of the fact that it was originally above its critical pressure. If you look at the corresponding Mollier Diagram (or a Temp - Entropy chart) you will quickly see that the critical point (where the critical pressure is found) is the point that defines where the liquid phase is to be found - down, below the critical pressure. That's why the "Phase envelope" is found below the Critical Point. Any fluid found above (higher) the critical pressure is ordinarily in the super critical phase zone - or superheated vapor. But by definition, the fluid is not in the liquid phase and, therefore, cannot be "boiled".

[JoeWong]

Rookie,
Let me share my 2-cent worth information...

Doggert & Mr. Montemayor have clearly defined supercritical fluid...

See HERE for boiling liquid (at critical pressure) transform to supercritical fluid when temperature is increased.

See this VIDEO CLIP for the transformation...


JoeWong

[Rookie]

Thank you for the quick responses. So, what is the phase of the fluid above its critical pressure but below its critical temperature?

Thanks in advance.

[Doggert]

Thank you for the quick responses. So, what is the phase of the fluid above its critical pressure but below its critical temperature?

Thanks in advance.

Depends on how far above the critical pressure you are.

Some fluids can go to a solid state at extremely high pressures, but for most fluids you would simply be at compressible liquid state.

Look at this link, and it should explain everything that's been talked about in this thread:

http://en.wikipedia......ermodynamics)