Question

A rigid vessel of volume 0.86 m3 contains 1 kg of steam at a pressure of 2 bar. Evaluate the specific volume, temperature, dryness fraction, internal energy, enthalpy, and entropy of steam. The steam is heated to raise its temperature to 150°C. Show the process on a sketch of the p–v diagram, and evaluate the pressure, increase in enthalpy, increase in internal energy, increase in entropy of steam, and the heat transfer. Evaluate also the pressure at which the steam becomes dry saturated.

Answer 1

Special volume:

$\frac{V}{m}=\frac{0.86}{1}=0.86 \frac{m^3}{kg}$

Internal energy:

$U=\frac{3}{2}PV=\frac{3}{2}*200000*0.86=258$ kJ

(here $P=2$ bar $=200000$ Pascal)

Enthalpy:

$H=U+PV=258+172=430$ kJ

Entropy:

$S=\frac{Q}{T}=\frac{U}{T}=\frac{258}{423}=0.61$ $\frac{J}{K}$

(here $T=150$ C $=150+273=423$ K.