Question

Air enters a compressor in steady flow at 140 kPa, 17°C and 70 m/s and leaves it at 350 kPa, 127°C and 110 m/s. The environment is at 100 kPa, 7°C. Calculate per kg of air

(a) The actual amount of work required

(b) The minimum work required

(c) The irreversibility of the process

Answer 1

Minimum work required

T₂ = 127ºC = 400 K

T₁ = 290 K

T₀ = 280 K

= 110.55 – 16.86 + 3.6 = 97.29 kJ/kg

Actual work required

= h₂ - h₁ + \(\frac{V_2^2 - V_1^2}{2000}\)

= (110.55 + 3.6) kJ = 114.15 kJ

∴ Irreversibility of the process 

= T₀ (s₂ - s₁)

= T₀(ΔS)_univ = 16.86 kJ/kg