Initial pressure of air, p1 = 8 bar
Initial temperature of air, T1 = 180 + 273 = 453 K
Final pressure of air, p2 = 1.4 bar
Final temperature, T2 = T0 = 20 + 273 = 293 K
Surroundings’ pressure, p0 = 1 bar
Mass of air = 1 kg
Initial velocity of air, C1 = 80 m/s
Final velocity of air, C2 = 40 m/s.
(i) Reversible work and actual work :
Availability of air at the inlet
Availability of air at the inlet
= 1.005 (453 – 293) – 293 (– 0.159) + \(\cfrac{80^2}{2\times10^3}\)
= 160.8 + 46.58 + 3.2 = 210.58 kJ
Availability at the exit
∴ Availability at the exit
= – 293 (– 0.09656) + \(\cfrac{40^2}{2\times10^3}\) = 29.09 kJ/kg
Reversible/theoretical work which must be available,
Wrev = 210.58 – 29.09 = 181.49 kJ.
Actual work developed can be calculated by using the energy equation for adiabatic steady flow process as follows :
(ii) Irreversibility and effectiveness :
Irreversibility, I = Wrev – Wactual
= 181.49 – 163.2 = 18.29 kJ/kg.
Effectiveness,