• Basics

  • Can reverse the energy transfers in an ideal heat engine.
  • Work is done on the system to transfer energy from the cold to the hot reservoir.

• Two Devices

  • Refrigerator: Moves energy from the cold reservoir using work. Real World Example: Just like your kitchen fridge! When you leave leftover pizza in there, it stays cool because the refrigerator is removing heat from inside.
  • Heat Pump: Moves energy to the hot reservoir using work. Real World Example: Imagine it's a cold winter day. A heat pump can grab some of the outside chilliness and replace it with warmth inside your house. It's like a superhero version of a heater!

• The Refrigeration Cycle

  • Refrigerant (special fluid) gets pressurized and heated up by a compressor.
  • Hot gas refrigerant goes through coils outside the fridge.
  • Gas cools down (because your kitchen isn’t as hot) and turns into a liquid.
  • Liquid goes through an expansion valve and poof! Turns back into a gas.
  • This gas grabs heat from inside the fridge (making it cool inside) and heads back to the compressor.

• Characteristics of a Good Refrigerant:

  • Low boiling point (like the opposite of water on a stove).
  • High latent heat of vaporization (can store lots of energy when it evaporates).
  • Low specific heat of the liquid.
  • Low vapor density (it's a lightweight champ in the vapor world).
  • Easily turns into a liquid under moderate conditions.

• Types: Diesel engine, four-stroke petrol (Otto cycle) engine.
• Otto Cycle: Designed by Nicolaus Otto in the 19th century.
• A-B: Adiabatic compression (no heat exchange).
• B-C: Energy added under constant volume.
• C-D: Adiabatic expansion (also no heat exchange).
• D-A: Energy removed under constant volume.

Real World Example: Your car's engine probably follows a cycle similar to the Otto cycle, especially if it runs on petrol!

• Background: Introduced in the 1930s.
• Essence: If Object A is in thermal equilibrium with Object B, and Object B is in equilibrium with Object C, then A and C are in equilibrium.
• Real World Interpretation: Every time you use a thermometer to check your temperature, you're trusting the zeroth law!