Class Exercise 3 – Properties of Substances
1. A 1 m3 rigid vessel contains steam at 6 bar and 600oC is cooled by transferring heat
from the system to the surroundings.
a. Determine the temperature and pressure at which the steam starts to
condense.
b. Calculate the mass of the liquid at the end of the cooling process when the
pressure reaches 0.6 bar.
c. Sketch a T-v diagram to show the processes.
[130oC, 270.3kPa; 24.5%, 1.1275kg]
2. Steam at a pressure of 100 kPa and a quality of 50% initially fills a rigid vessel
having a volume of 0.5 m3. The steam is then heated, causing the pressure in the
vessel to rise to 150 kPa.
a. Determine:
i. The mass of the steam in the vessel.
ii. The temperature and quality of the steam after the heating process.
iii. The mass of the vapour, mg and liquid, mf in the vessel after the
heating process.
b. If the steam in the vessel is now further heated, what would the pressure and
temperature in the vessel be when all steam has turned into saturated
vapour?
c. Sketch the processes in part (a) and part (b) on P-v and T-v diagrams,
indicating clearly the temperatures, pressures and the paths.
[0.59kg; 111.4oC, 73%; 0.4307kg, 0.1593kg; 2.11 bar, 121.84oC]
3. Refrigerant-134a in a rigid vessel at a pressure of 1 MPa and a temperature of 100oC
was cooled until the pressure drops to 500 kPa.
a. Determine the final state of the refrigerant.
b. Sketch the process on a P-v and T-v diagrams.
[66.3%; 15.71oC]
4. A rigid vessel having a volume of 0.5 m3 initially contains water vapour mixture at 400
kPa. The quality of the mixture is 40 percent. Heat is then transferred to the system,
causing the pressure in the vessel to rise to 700 kPa.
a. Calculate the initial mass of the mixture in the vessel.
b. Determine the mass of the vapour and liquid in the vessel after the heat
transfer process.
c. Sketch the process on a P-V and T-V diagrams.
[2.693kg; 67.9%, 1.831kg, 0.862kg]
