Question

A piston cylinder device contains 0.2 kg of water initially at 800 kPa and 0.06 m3. Now 200 kJ of heat is transferred to the water while its pressure is held constant. Determine the final temperature of the water. Also, show the process on a T-V diagram with respect to saturation lines.
[ 721.1oC]

Answer 1

$E_{in}-E{out}=\Delta E{system}$

$Q_{in}-W_{b, out}=\Delta U=m(u_2-u_1)$

$Q_{in}=m(h_2-h_1)$

$v_1=V_1/m=0.06/0.2=0.3(m^3/kg)$

For $p_1=800(kPa)$ and $v_1=0.3(m^3/kg)$ we have that $h_1=2950.4(kJ/kg)$

$200=0.2\cdot(h_2-2950.4)\to h_2=3950.4(kJ/kg)$

For $p_2=800(kPa)$ and $h_2=3950.4(kJ/kg)$ we have that $T_2\approx720°C$