Constant Volume Question

[blackvioet]

So here is my problem. I have a vessel with a constant volume and super heated vapor inside it starts at 150C at atmospheric pressure and then I seal the vessel. I then cool it to room temperature 20C, so I think in this case that when I cool down the vessel it will be a saturated liquid, part water and part vapor. I am trying to determine what the pressure and the quality inside the vessel will be, am I correct in my thinking that the pressure should just be the saturation pressure at room temperature?

I know that there will be condensation, and heat loss as it cools, but I think that the specific volume should remain the same, so I can calculate the quality at room temperature from the specific volume when it was a super heated vapor.

 

[racookpe1978]

The actual total volume will be the same for this (homework?) problem, but the specific volume (of each unit mass of gas will change: You are going from a 100% gas mixture to a saturated gas on top of liquid mixture. The difference in enthalpy is the heat lost to the environment during the cooldown.

 

[blackvioet]

Ok that makes sense I can calculate the heat loss, but then the internal pressure will be just the saturation pressure at room temperature correct?

 

[racookpe1978]

let me play the "professor" and ask back: "How could it be anything different?" After all the energy in the superheated gas is lost (irretrievably) to the "infinite room" the only thing left in the closed PV is the original gas vapor and the condensed vapors as liquid on the bottom and sides.