How a refrigerator works:

Back to main heat and temperature page

Back to cool questions about heat

Background question 1: Why does it feel cold when rubbing alcohol evaporates from your skin?

Answer: Evaporation of a liquid takes away heat. As the rubbing alcohol evaporates it absorbs heat and creates the cool feeling.

In the fridge: Similarly, a refrigerator uses the evaporation of a liquid refrigerant to absorb heat from the food compartment.

Background question 2: Why do aerosol underarm deodorants feel cold when they are sprayed on?

Answer: Pressure is proportional to temperature. The contents of the aerosol can are under pressure at room temperature. When you spray the contents out, the contents are able to expand and there is a decrease in pressure. Because there is a decrease in pressure, there is a corresponding decrease in temperature.

In the fridge: A similar process happens inside a refrigerator. The liquid refrigerant flows through an expansion valve. (You can think of the expansion valve as a small hole like the one on an aerosol can.) As the refrigerant moves through the hole, it moves from a high-pressure zone to a low-pressure zone. The decrease in pressure corresponds with a decrease in temperature. Pressure is proportional to temperature! In the evaporator, the liquid also expands and evaporates, and as you know, evaporation of liquid takes away heat. The end result of this is that the gas is very, very cold!

The first goal is to get heat out of the food compartment!

Food compartment

Evaporator and heat exchanging tubes

Cold temperature

Colder temperature

Heat travels from warmer areas to cooler areas

Heat travels from warmer areas to cooler areas. This is the 2nd law of thermodynamics. Inside your refrigerator there are icy-cold heat-exchanging tubes that absorb heat from the warmer food compartment. The heat leaves the food compartment because the icy-cold heat-exchanging tubes are much colder.

The second goal is to get heat out of the refrigerator.

Increasing the temperature of the refrigerant will accomplish this!

The warm gaseous refrigerant is cycled to the compressor where it is pressurized and heated. Again, pressure is proportional to temperature. In short, the temperature of the refrigerant is increased because the pressure is increased.

Why increase the temperature of the refrigerant? Heat can only move from warmer temperatures to cooler temperatures.

The artificially heated refrigerant gas is cycled to the condenser. These are the heat-exchanging tubes at the back of your refrigerator. Because these tubes are much warmer than the surrounding kitchen air, heat can leave the refrigerator! The gas cools and condenses into liquid as the heat leaves.

The cycle repeats with the cool liquid refrigerant shooting through the expansion valve etc.

A review concerning refrigerators and how they work:

Part of the fridge:

What it does:

Why it happens:

What happens next:

1) Expansion valve and evaporator

2) The expansion valve allows the cool liquid to expand and evaporate as a gas. The evaporation results in a dramatic drop in temperature. It becomes icy-cold!

3) Pressure is proportional to temperature.

Evaporation of a liquid takes away heat.

4) The very cold gaseous refrigerant is cycled to the heat-exchanging tubes inside the refrigerator.

5) Heat exchanging tubes inside the refrigerator.

6) The heat-exchanging tubes absorb heat from the food compartment. The food gets cold as heat leaves!

7) Heat moves from warmer areas to colder areas. In other words, heat moves from the warmer food compartment to the icy-cold heat-exchanging tubes.

8) As heat leaves, the food compartment gets colder. Meanwhile, the gaseous refrigerant is being warmed. The warmed gas is then cycled to the compressor.

9) The compressor is a mechanical device that pressurizes the warm gaseous refrigerant.

10) The compressor pressurizes the warm gas and makes it hot.

11) Pressure is proportional to temperature.

12) The hot gas is cycled to the condenser.

13) The condenser is a collection of heat-exchanging tubes at the back of the refrigerator.

14) The hot condenser gives off heat to the warm kitchen. The gas turns to liquid as it loses its heat to the kitchen.

15) Heat moves from warm areas to cool areas. In other words, the heat jumps from the hot tubes at the back of the refrigerator to the warm kitchen air.

16) Heat leaves the refrigerator for good! The refrigerant cools, condenses and turns into a liquid. The process repeats again when the refrigerant is cycled to the expansion valve and evaporator.

Learn more about how refrigerators work

Back to main heat and temperature page