Refrigeration Machines #
A refrigeration machine transfers heat from cold to hot by supplying external work. Refrigerators, air conditioners and heat pumps all use the same principle.
The Refrigeration Cycle (4 phases) #
- Compression: compressor raises gas temperature and pressure
- Condensation: hot gas releases heat to the outside and becomes liquid
- Expansion: liquid passes through expansion valve, pressure and temperature drop
- Evaporation: cold liquid absorbs heat from inside and becomes gas
COP (Coefficient of Performance) #
$$COP_{fridge} = \frac{Q_{cold}}{W} \qquad COP_{heat\ pump} = \frac{Q_{hot}}{W} = COP_{fridge} + 1$$COP is always > 1. A COP of 3 means 3 kWh of heat transferred per 1 kWh of electricity.
Fridge vs Heat Pump #
Same device, different purpose: fridge cools the inside (useful = \(Q_{cold}\)); heat pump heats the inside (useful = \(Q_{hot}\)).
Refrigerants #
CFC (banned, ozone damage) → HCFC → HFC (greenhouse gas) → modern: HFO, CO₂, propane (low impact).
Conclusion #
Refrigeration machines are among the most ingenious devices: they move heat against nature using a simple phase-change cycle. With heat pumps, they’re also key to the energy transition.
Reply by Email