Heat Engines and Refrigerators - Key Concepts for JEE and CBSE Board Exams

Heat Engines:

• Types:

  • External Combustion Engine: Heat source outside engine (e.g., steam engine).
  • Internal Combustion Engine: Heat source inside engine (e.g., petrol or diesel engine).

• Efficiency: Measure of engine’s ability to convert heat input into useful work. It must always be less than 1 (or 100%)

• Carnot Cycle: Idealized thermodynamic cycle that describes the most efficient heat engine possible.

Refrigerators:

• Types:

  • Vapor Compression Refrigeration: Commonly used method, uses compressor and evaporator.
  • Vapor Absorption Refrigeration: Uses heat instead of mechanical work to provide cooling.

• COP (Coefficient of Performance): Measures the efficiency of refrigeration. COP> 1.

• Carnot Refrigerator: Idealized thermodynamic cycle for refrigerators, describes most efficient refrigeration process possible.

Thermodynamic Cycles:

• Otto Cycle: Idealized cycle for gasoline (petrol) engines.

• Diesel Cycle: Idealized cycle for diesel engines.

• Dual Cycle: Combination of Otto and Diesel cycles, used in some engines for improved efficiency.

• Rankine Cycle: Idealized cycle for steam turbines used in power plants.

Heat Pumps:

• Types:

• Vapor Compression Heat Pump: Similar to vapor compression refrigeration, but used for heating.

• Vapor Absorption Heat Pump: Uses heat instead of mechanical work for heating.

• COP: It is the ratio of heat output to the work input.

Applications:

• Heat Engines: Used in vehicles (cars, trucks, etc.), power plants, ships, and other machines that require mechanical work.

• Refrigerators: Used in homes, restaurants, grocery stores, and other places to preserve food and other perishable items.

• Heat Pumps: Used for heating homes and commercial buildings.