3 kg of water vapor contained in a pistoncylinder assembly e

3 kg of water vapor contained in a piston-cylinder assembly expands adiabatically. Below is the data for state 1 and state 2 Determine: The work developed in the process, kJ The amount of entropy produced Is this process possible? why? Determine the final temperature, T_2s, if the process is isentropic with p_2s = 1 bar Determine the final temperature, T_2s, if the process is isentropic with p_2s = 1 bar (include the energy balance equation and entropy balance equation for the problem)

Solution

at 3 bar 500 C

h1 = 3490 kJ/kg

s1 = 8.33 kJ/kg-K

at 1 bar 360 C

h2 = 3200 kJ/kg

s2 = 8.42 kJ/kg-K

a) Q - W = m ( h2 - h1)             ( Q = 0 Adiabatic)

     W   = 3 * (3200 - 3490) = -870 kJ

b) Entropy change = m * (s2 - s1) = 3 * (8.42 - 8.33)   = 0.27 kJ/K

c) Yes the process is possible because entopy is increasing in the process.

d) From steam tables at p2s = 1 bar and s2 = s1 = 8.33 kJ/kg-K

     we get T2   = 333 C