Superheated water vapour at 180 psia and 500 degrees Farenheit is allowed to cool at a constant volume until the temperature drops to 250 degrees Farenheit. At the final state, determine:
(a) the pressure
(b) the quality
(c) the enthalpy.
Also, show the process on a T-v diagram with respect to saturation lines.
a) I prefer to work in the (p-v) diagram, which is more suggestive for watching steam processes.
I also prefer to work in SI units, but finally I will convert in british units as well.
Let's denote 1 = initial state where p1 = 180 psia = 12.41 bar
T1 = 500 deg.F = 260 deg.C = 533 K
Using the tables of Thermodynamic States of the Steam (you can find such a tables on Internet too), we determine the specific volume of superheated steam:
v1 = 0.190 m3/kg = 3.0436 feet3/lb
In order to know what is the state of steam at the end, we need first to determine the state (1s) on saturation line. Using the Tables for Saturated Steam and taking v1 = vG ...
This solution includes five steps of calculations with explanation.