3 kg of steam in a piston -cylinder device at 400 kPa and 175 degree Celsius undergoes a mechanically reversible , isothermal compression to a final pressure such that the steam becomes just saturated. What is the work required for the process.
3 kg of steam in a piston -cylinder device at 400 kPa and 175 degree Celsius undergoes a mechanically reversible , isothermal compression to a final pressure such that the steam becomes just saturated. What is the work required for the process.
T=175^{\circ}C \\v=0.503\;m^{3}/kg \\S=7.055\;kJ/kgK \\P=400\;kPa \\u=2606\;kJ/kg
For saturated vapour
v=0.216\;m^{3}/kg \\u=2579\;kJ/kg \\S=6.622\;kJ/kgK
We have
q=T\left ( s_{2} -s_{1}\right )
\\=\left ( 175+273 \right )\left ( 6.622-7.055 \right ) \\=-193.983 \\W=q-\left ( u_{2}-u_{1} \right ) \\=\left ( -193.984-\left ( 2579-2606 \right ) \right )\times 2 \\= -500.94\;kJ
Therefore work required for the process is approximately -501 kJ.
