A 1-m3 insulated, rigid tank contains air at 800 kPa, 25°C. A valve on the tank is opened, and the pressure inside quickly drops to 150 kPa, at which point the valve is closed. Assuming that the air remaining inside has undergone a reversible adiabatic expansion, calculate the mass withdrawn during the process.
C.V.: Air remaining inside tank, m2.
Cont.Eq.: m2 = m ;
Energy Eq. m(u2 − u1) = 1Q2 − 1W2
Entropy Eq m(s2 − s1) = ∫ dQ/T + 1S2 gen
Process: adiabatic 1Q2 = 0 and reversible 1S2 gen = 0
Entropy eq. then gives s2 = s1 and ideal gas gives the relation
