A refrigerator is a common household appliance that keeps food cold and fresh. But how does it actually work? The key principle is that when a liquid evaporates, it absorbs heat from its surroundings. This is why sweat cools your skin on a hot day. A refrigerator uses a special liquid called a refrigerant that evaporates at a very low temperature. By making the refrigerant evaporate inside the fridge, heat is pulled from the interior, cooling the air and the food inside. The refrigerant then carries that heat away and releases it outside the fridge, usually through coils at the back or bottom.

This cycle repeats continuously, maintaining a cold environment inside. The main components of a refrigerator are the compressor, condenser, expansion valve, and evaporator. The compressor is a pump that pressurises the refrigerant gas, raising its temperature. The hot, high-pressure gas then flows through the condenser coils on the outside of the fridge, where it releases heat to the surrounding air and condenses into a liquid. The liquid refrigerant then passes through an expansion valve, which suddenly reduces its pressure, causing it to cool rapidly. This cold liquid then enters the evaporator coils inside the fridge, where it absorbs heat from the interior and evaporates into a gas.

The gas is then sucked back into the compressor, and the cycle starts again. The refrigerant is a crucial part of the system. Early refrigerators used toxic or flammable gases like ammonia, methyl chloride, or sulfur dioxide. In the 1920s, chlorofluorocarbons (CFCs) were developed as safer alternatives. However, scientists later discovered that CFCs damage the ozone layer when released into the atmosphere. International agreements like the Montreal Protocol led to a phase-out of CFCs. Today, most refrigerators use hydrofluorocarbons (HFCs) or hydrocarbons like isobutane. HFCs do not harm the ozone layer but are potent greenhouse gases.

The hot, high-pressure gas then flows through the condenser coils on the outside of the fridge, where it releases heat to the surrounding air and condenses into a liquid.

Newer refrigerants with lower global warming potential are being developed to reduce environmental impact. The location of the freezer compartment affects efficiency. In a top-freezer model, cold air naturally sinks, so the freezer on top helps keep the refrigerator section cool. In a bottom-freezer model, a fan is needed to circulate cold air upward. Side-by-side refrigerators have the freezer on one side and the fridge on the other, which can be convenient but often uses more energy. The insulation in the walls of the refrigerator also plays a vital role.

Modern refrigerators use polyurethane foam insulation, which is very effective at preventing heat from entering. The door seals, or gaskets, must be airtight to maintain the cold temperature inside. Refrigerators have become much more energy-efficient over the years. In the 1970s, a typical refrigerator used about 1,800 kilowatt-hours per year. Today, an energy-efficient model uses around 350 kilowatt-hours per year, thanks to better compressors, improved insulation, and more precise temperature controls. Many refrigerators now have an Energy Star rating, indicating they meet strict efficiency guidelines. Some advanced models use inverter compressors that run at variable speeds, adjusting cooling output to match demand, which saves energy and reduces noise.

Additionally, features like automatic defrost and temperature sensors help maintain consistent conditions without wasting power. Proper use and maintenance can extend the life of a refrigerator and improve its performance. It is important to keep the coils clean, as dust buildup makes the compressor work harder. The door seals should be checked regularly for leaks. Placing hot food directly into the fridge forces the appliance to work harder, so it is better to let food cool first. Overfilling the fridge can block air circulation, while leaving it too empty means the fridge has to cool more air volume. Setting the temperature between 3°C and 5°C for the fridge and -18°C for the freezer is recommended. By understanding how a refrigerator works, you can use it more efficiently and reduce your energy bills.