Heat engines convert heat energy into mechanical work by transferring energy from a hot reservoir to a cold reservoir. Efficiency measures how much of the input heat is converted to useful work.

Key Concepts:

• Efficiency (η): Ratio of work output to heat input
• Carnot Efficiency: Maximum possible efficiency for a heat engine operating between two temperatures
• Work Output (W): Useful energy produced by the engine
• Heat Input (Q_in): Energy absorbed from the hot reservoir
• Heat Output (Q_out): Energy expelled to the cold reservoir

Key Formulas:

• η = W / Q_in - Efficiency from work and heat input
• η = 1 - Q_out / Q_in - Efficiency from heat input and output
• η_Carnot = 1 - T_c / T_h - Carnot efficiency (T in K)
• W = Q_in - Q_out - Work output

Engine Types:

• Carnot (ideal, reversible)
• Rankine (steam power plants)
• Otto (gasoline engines)
• Diesel (diesel engines)
• Brayton (jet engines, gas turbines)

Units:

• Heat/Work: J, kJ, cal, kcal
• Temperature: K, °C, °F (convert to K for Carnot efficiency)

Applications:

• Power plants and electricity generation
• Automotive and aircraft engines
• Refrigeration and heat pumps (reverse cycle)
• Thermodynamic cycle analysis