Determine the final temperature in piston – cylinder:
One Kg of steam at 1.5MPa and 400ºC in a piston - cylinder device is cooled at constant pressure. Determine the final temperature and change in volume. If cooling continues till the condensation of 2/3 of the mass.
Sol.: Given that
Mass of steam m = 1kg
Pressure of steam P1 = 1.5MPa = 15bar
Temperature of steam T1 = 400ºC From superheated steam table
At P1 = 15bar, T1 = 400ºC Å1 = 0.1324m3/kg
Å2 = (2 x 0.1324)/3 = 0.0882m3/kg
Change in volume "Å = Å1 - Å2 = 0.1324 - 0.0882 = 0.0441m3/kg
The steam is wet at 15bar; thus, the temperature will be 198.32ºC.