C.V. A + B, control mass of constant total volume.
Energy equation: mA(u2 – u1)A + mB(uB2 – uB1) = 1Q2 – 1W2
Process equation: V = C ⇒ 1W2 = 0
T = C ⇒ (u2 – u1)A = 0 (ideal gas)
The pressure on both sides of the piston must be the same at state 2. Since two-phase: