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.