1% Smarter #19 – How Does a Refrigerator Work?

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Have you ever wondered how a refrigerator works?

Okay maybe it’s just me…😋

But if I’ve piqued your interest now, here is a simplified version so read on. 📗

What did people do without refrigerators?

Firstly let’s take a step back and see how people used to preserve food before the invention of the refrigerator and its subsequent mass adoption for home use in the 1920s.

It seems our ancestors were pretty enterprising and came up with a variety of ways of preserving food including:

1. Curing
2. Pickling
3. Boiling
4. Heating
5. Sugaring
6. Canning
7. Burial
8. Fermentation

So it is not like the art of food preservation only began with the advent of the refrigerator.

The principle of nature that refrigeration exploits

Here is a really good video explanation.

It’s best to start at the fundamental principle of nature before diving into the specifics of how a refrigerator works.

So the key point is that this is an application of the following scientific principles of nature:

1. When liquid evaporates it absorbs heat (e.g. when your hand is wet it feels cold due to the water evaporating and cooling your hand)
2. When liquid condenses it releases heat (e.g. on a very humid hot day your frosty beer will have water condensing on the outside of the bottle which warms the beer)

It turns out humans are pretty clever, just with those two findings and a few other tricks we exploited those properties and created the refrigerator.

Key components that make up a refrigerator

There are five major components that enable refrigeration.

1. Expansion valve/device
2. Evaporator coil
3. Condenser coil
4. Compressor
5. Refrigerant (also known as a coolant)

The cooling process

Remember we said that evaporation cools and condensation warms?

That is what the evaporator and condenser coils do. As their name suggests one is for cooling and the other is for warming.

So here is a nice diagram showing the process.

You will notice that there are coils running inside the refrigerator and they loop around the outside as well.

What is running inside the coils is the refrigerant.

The refrigerant is a liquid chemical that circulates inside the coils continuously in a loop alternating between the condenser coils outside and the evaporator coils inside. Here is a list of commonly used refrigerants for any chemistry nerds out there. 🧪

Here is a overview of the cooling process summarized from this awesome video (see below). Note: because of a difference in temperature and pressures, the refrigerant is continuously transitioning between a liquid and a gas state and back again. These pressures are managed by the compressor and expansion valve.

1. Starting at the evaporator, the heat from the inside of the fridge evaporates the coolant running through the coils thus producing a cooling effect.
2. The heated gas then travels down to the compressor, which pressurizes the gas, which pushes it through the condenser coils behind the fridge. During this process, the refrigerant radiates its heat away to the ambient air. Here it compresses under pressure, turning most of the refrigerant back into a liquid. This also explains why warm air rises from the back of your fridge and why fridges have air vents.
3. When the refrigerant has run its course through the condenser, it re-enters the inside of the fridge via the expansion valve, which is a tiny hole constricting the tubing between the high pressure condenser and low pressure evaporator.
4. As the refrigerant re-enters the evaporator coils, the sudden decrease in pressure causes about half the liquid to explosively evaporate. It again picks up heat from inside the fridge and flows down to the compressor again.
5. And this cycle keeps repeating in an infinite loop.

In short, this process effectively transfers heat from the inside of the refrigerator to the outside environment via the refrigerant, thus creating a cooling effect inside the insulated cabinet of the refrigerator.

A few extra parts

Other than the five main components described earlier, additionally there are some other components that are important for the smooth operation of your refrigerator.

1. Fan that aids in the cooling and defrost process.
2. Heating element to defrost the internal evaporator coils from time to time, without which you will find your fridge might frost up and no longer operate properly. See for example here.
3. Thermometer that measures the temperature inside the fridge and turns on the compressor when the temperature gets too high. That is the sound you hear when the fridge “turns on”.

The thermometer measures the temperature inside the fridge and turns on the compressor when the temperature gets too high. That is the sound you hear when the fridge “turns on”.

Additional resources

1. How does a Refrigerator work? – by Learn Engineering (YouTube video)
2. Refrigerator working – The Basics by Learn Engineering (YouTube video)
3. First How Things Work Encyclopedia – (there is a page explaining a fridge) – I enjoy reading children’s books at times as they are often great introductions to a subject even for adults. See below tweet.

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