Refrigeration systems use a refrigerant, a fluid that absorbs heat as it changes state from liquid to gas. Here's how it works:

1. Evaporation: The refrigerant is pumped through a system where it evaporates, absorbing heat from the surrounding environment (like the inside of your fridge).

2. Compression: The refrigerant vapor is then compressed, increasing its temperature.

3. Condensation: The hot refrigerant vapor is then passed through a condenser, where it releases heat to the outside environment.

4. Expansion: Finally, the refrigerant is expanded, lowering its temperature and turning it back into a liquid.

This cycle repeats, constantly absorbing heat from the inside of the fridge and releasing it to the outside.

There are many different types of refrigeration systems, but they all use the basic principle of absorbing heat using a liquid that undergoes a phase change.