met11
Chemical
- Nov 13, 2012
- 47
Hey everyone,
I was wondering if anyone could help me with something that I think I've figured out, but I just want to make sure is right. I'll walk through the logic, can you let me know if it sounds right? Say you had 5 lb of water in a vessel that is 1 cubic foot. This water is heated up to 338 degrees Fahrenheit and 100 psig. To find out the quality of the steam-water system, you look up the density in the steam tables that gives you 5 lb/ft3 at 100 psig, in this case it's a quality of 4.7%. Using that quality, you can calculate the total specific enthalpy using 0.047*hsteam + 0.953*hwater.
Now say that the vessel instantaneously expanded to 10 cubic feet. You would still have the 5 lb of water in 10 cubic feet. I wanted to see if the way I was getting the final system pressure was correct. Since this would be an isenthalpic expansion, the calculation above should still be satisfied at the new conditions (htotal = X*hsteam + (1-X)*hwater). The density of the new system is 0.5 lb/ft3. To find out the final pressure, do you just iterate through the steam tables until you find a pressure (at 0.5 lb/ft3 steam density for the second degree of freedom) with corresponding quality and enthalpies that make the total enthalpy equal to the original enthalpy?
I started second guessing myself as to whether this is the correct approach. Any guidance would be greatly appreciated
I was wondering if anyone could help me with something that I think I've figured out, but I just want to make sure is right. I'll walk through the logic, can you let me know if it sounds right? Say you had 5 lb of water in a vessel that is 1 cubic foot. This water is heated up to 338 degrees Fahrenheit and 100 psig. To find out the quality of the steam-water system, you look up the density in the steam tables that gives you 5 lb/ft3 at 100 psig, in this case it's a quality of 4.7%. Using that quality, you can calculate the total specific enthalpy using 0.047*hsteam + 0.953*hwater.
Now say that the vessel instantaneously expanded to 10 cubic feet. You would still have the 5 lb of water in 10 cubic feet. I wanted to see if the way I was getting the final system pressure was correct. Since this would be an isenthalpic expansion, the calculation above should still be satisfied at the new conditions (htotal = X*hsteam + (1-X)*hwater). The density of the new system is 0.5 lb/ft3. To find out the final pressure, do you just iterate through the steam tables until you find a pressure (at 0.5 lb/ft3 steam density for the second degree of freedom) with corresponding quality and enthalpies that make the total enthalpy equal to the original enthalpy?
I started second guessing myself as to whether this is the correct approach. Any guidance would be greatly appreciated
![[rofl]](/data/assets/smilies/rofl.gif "[rofl] [rofl]")
