Key Concepts

• • η = 1 − Tc / Th — theoretical maximum for any heat engine between these reservoirs
• • No real engine can exceed Carnot efficiency (2nd Law of Thermodynamics)
• • Increasing Th or decreasing Tc both improve efficiency
• • Efficiency → 100% only as Th → ∞ or Tc → 0 K (absolute zero)
• • Real engines: coal ≈ 38%, combined-cycle gas ≈ 60%, nuclear ≈ 33%
• • The area above the curve is thermodynamically impossible