Gas Power Cycle In Engineering Thermodynamics by PK NAG (Chapter-13)

A: Governing principle: Net work in an ideal Brayton cycle scales with cp·(T3−T4−(T2−T1)). With r_p≈6, T3=1200 K, and air-standard relations, T4 drops to ~700 K and T2 rises to ~500 K, leaving a few hundred kJ/kg. That order survives first-pass losses. Option B traps engineers who remember that low pressure ratios cancel out, but import that intuition beyond its range here.

A: Governing principle: Thermal efficiency follows the balance between added turbine work and added compressor work. At fixed T3 there’s a clear optimum r_p; below it, gains dominate, above it, compression penalty wins. Option B snares people who extrapolate low‑r_p textbook plots without checking the fixed‑T3 constraint.

A: Governing principle: For a given pressure ratio, lower compressor efficiency increases temperature rise. Fouling fits the symptom and the time-in-service trend, and it feeds directly into higher thermal stress assumptions. Option C catches engineers who know inlet temperature matters but miss that the delta observed exceeds ambient variation.

A: Governing principle: Back work ratio is W_c/W_t, not net over gross. For air-standard Brayton cycles with moderate r_p, compressor work is a large fraction but not all of turbine work. Option C tempts those who confuse shaft power balance with thermodynamic work terms.