Question

In a rotary compressor, air enters at 1.1 bar, 21° C where it is compressed adiabatically to 6.6 bar, 250°C. Calculate the irreversibility and the entropy production for unit mass flow rate. The atmosphere is at 1.03 bar, 20°C. Neglect the K.E. changes.

Answer 1

Minimum work required

W_min = Availability increase

= h₂ – h₁ – T₀(s₂ – s₁)

= mc_p (T₂ – T₁) – T₀ Δs

= 1 × 1.005 (523 – 294) – 293 × 0.064647

= 211.2 kJ/kg

Actual work required (W_act) = 230.145 kJ/kg

∴ Irreversibility = T₀ Δs 

= 293 × 0.064647

= 18.942 kJ/kg