Suppose that I take a pressure vessel that can withstand up to 2000 PSI. Now I fill it with water (not completely, but around 90%) and start to heat it with a direct flame. What I want to know is, what will happen?

Although I don't know anything about it, here are some guesses that I think might happen:

  1. The water will begin to convert into gas. But since the volume is limited, therefore the pressure would increase (and keep on increasing) and the vessel may burst after the internal pressure crosses 2000PSI.
  2. The water won't convert into gas and would just take all the heat energy into itself. In other words, nothing would happen.

Those are my guesses and it would be great if you can help me out.

  • $\begingroup$ Please refrain from cross-posting the same questions on different pages like physics.se. Since you have already gotten an answer here, it would be appropriate, that you remove the question on our parent site. $\endgroup$ – Martin - マーチン Jul 20 '15 at 9:51

Look at the phase diagram of water to see what happens. Josiah Willard Gibbs invented these diagrams o help understand what happens as a substance is heated under pressure, and transitions from solid to liquid to gas and supercritical fluid (neither quite gas nor liquid).

Given sufficient heat, the vessel will burst. Above ~650 K, the water can no longer be liquefied by pressure, and behaves more like an ideal gas, so pressure continues to increase.

  • $\begingroup$ What i understood is: The water is kept in the vessel and is being heated. And when it would be ~ 300C, then the pressure will keep on increasing and increasing. And unless I allow the pressure to be released, the vessel may/will burst. ...Am I correct? $\endgroup$ – Anoneemus Jul 20 '15 at 15:48
  • $\begingroup$ That's basically it, except that pressure continually increases with temperature (there is some vapor pressure even at 0 C), but pressure increases in a more linear fashion above 300 C. $\endgroup$ – DrMoishe Pippik Jul 20 '15 at 16:11
  • $\begingroup$ And if I'm not wrong then at ~ 300C, the pressure inside the vessel would be around 10Mpa = ~1450PSI ? $\endgroup$ – Anoneemus Jul 20 '15 at 17:01

Why don't you just run the calculation and see for yourself (rather than forever speculating)? Do you know how to use the steam tables? Suppose the water is in a 1 liter container initially at 20 C, and the liquid takes up 90% of the volume, while water vapor in equilibrium with the liquid water at 20 C occupies the remainder of the volume. Now you raise the temperature to 50 C, and you allow the system to equilibrate. What is the new volume of the liquid water and what is the new pressure. Try higher temperatures and see what you get.


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