How a Refrigerator Works

A refrigerator works by using the refrigeration cycle to remove heat from the interior of the appliance and transfer it to the surrounding environment. By effectively moving heat energy to the outside, the transfer cools the space inside. This process relies on the principles of thermodynamics and the properties of refrigerants to efficiently transfer heat in the system.

To help you make the step from the theoretical diagrams you will see to the refrigerator in your home, here are three diagrams of common refrigerator layouts. Click on each diagram to see an enlarged view.

The old standby the top-freezer refrigerator

The next iteration, The Side-by-Side refrigerator

The French-door refrigerator, very common for higher-end units; frequently with two evaporators

The refrigeration cycle involves four main components: the compressor, the condenser, the expansion valve or capillary, and the evaporator, all of which manipulate the pressure and phase (liquid or gas) of the refrigerant to absorb heat inside the compartment and release it outside the compartment. You can see these components in the diagrams above as they are located in three different refrigerators. They all use the same principles of operation explained below.

• The cycle begins with the compressor, which is essentially a pump driven by an electric motor.
• The compressor's primary function is to compress the refrigerant gas, increasing its temperature and pressure.

• The hot, high-pressure refrigerant gas exits the compressor and enters the condenser, a series of coils or tubes located at the back or underneath the refrigerator.
• The gas releases heat to the surrounding environment (air), as the condenser fan blows air over the condenser tubes.
• As the refrigerant gas cools in the condenser, it condenses, releasing more heat, and becoming a warm liquid, still under high pressure.

• The high-pressure warm liquid refrigerant flows through a small diameter tube called a capillary tube that restricts the flow of liquid refrigerant.
• This capillary causes the refrigerant liquid to lose pressure as it flows through it.
• At the end of the capillary where it joins the evaporator, the now lower pressure in the evaporator allows the liquid refrigerant to expand and a small amount turns back into a vapor.
• In order to become a vapor this small portion of the liquid absorbs heat from the warm refrigerant liquid, cooling the remaining liquid and becoming a low-temperature mixture of cold low-pressure liquid with a bit of gas.
• Our diagram shows an expansion valve, the capillary does the same basic thing.

• The cold, low-pressure refrigerant liquid and gas mixture flows through the evaporator, a set of coils or tubes located inside the refrigerator compartment.
• The refrigerant liquid in the mixture vaporizes and to do so it absorbs heat from the air in the interior of the refrigerator, causing that air to cool.
• The evaporator fan circulates the air inside the fridge, to allow it to pass by the cold evaporator, and cool the interior of the fridge.
• This process of cooling the air continues until the desired temperature is reached. When the compressor is shut off, the flow of refrigerant stops, and the cooling stops.

• The refrigerant, now warmed and transformed fully into a low-pressure, cool gas, returns to the compressor, where the cycle begins anew.

• The refrigerator's temperature is maintained through a feedback control system involving temperature sensors and thermostats.
• When the temperature inside the compartments rises above a set point, the thermostat signals the compressor to start the refrigeration cycle.
• Once the desired temperature is reached, the thermostat signals the compressor to stop. When the compressor stops the cooling stops.

You can think of the refrigerant as a sponge for heat. A tightly gripped (i.e. compressed) sponge is plunged into a water-filled basin (the inside of the refrigerator). Releasing the sponge (reducing the pressure/expansion) allows it to absorb water (heat) from the basin. The soaked sponge is removed from the basin and squeezed (compression), causing the water to pour out into the kitchen. Repeat this process many times and you can remove much of the water from the original basin.

Another comparison is the human body's cooling mechanism—sweat. Your body uses a phase change (evaporating water) to cool you off. Your body supplies the heat to make that happen which cools you off. When the air is dry evaporation takes place rapidly. and the cooling effect is high. When the air is humid, the sweat doesn't evaporate as well and you feel hot and sweaty.

Good refrigerants have a low boiling point to be able to absorb heat even in chilly conditions like the inside of a fridge or freezer. They also have a high critical point, which determines the highest temperature they can exist as a liquid and a gas, and a high latent heat, which means they can absorb more heat during phase changes (like from a liquid to a gas). Finally, they rely on low viscosity to be able to flow throughout the system with minimal flow loss (except in the capillary tube), so the pressure can be manipulated to facilitate heat transfer and high density (to maximize the amount of energy stored in the compound, to increase its effectiveness further). Refrigerants are chosen for their chemical structures that possess these properties, and others like low toxicity and cost effectiveness.

A refrigerator works based on the principles of thermodynamics, pumping a refrigerant through a cycle of tubes, which absorbs heat inside the fridge and dissipates it outside.