Refrigerator Working Principle: How Does A Refrigerator (Fridge) Work?

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To put it simply there are 3 steps by which a refrigerator or a fridge works:

Cool refrigerant is passed around food items kept inside the fridge.
Refrigerant absorbs heat from the food items.
Refrigerant transfers the absorbed heat to the relatively cooler surroundings outside.

Most people wouldn’t know what to do without a refrigerators, as there are few things that can soothe your parched throat the same way a glass of chilled water does.

Although there were techniques that people used in ancient times to get their fill of cold water, they were certainly not as easy as opening a door at home and taking out a bottle of ice-cold water. Even if they could get cold water to drink, they certainly didn’t have anything that could make their food stay fresh for days or even weeks on end.

Fortunately, we have a little something that does all of these things for us – a refrigerator!

In this article, we will take a look at the science of a refrigerator, specifically the different parts of a refrigerator and how they actually work together to preserve our food for extended periods.

Refrigerator working principle

The working principle of a refrigerator (and refrigeration, in general) is very simple: it involves the removal of heat from one region and its deposition to another. When you pass a low-temperature liquid close to objects that you want to cool, heat from those objects is transferred to the liquid, which evaporates and takes away the heat in the process.

You may already know that gases heat up when you compress them and cool down when they are allowed to expand. That’s why a bicycle pump feels warm when you use it to pump air inside a tire, while sprayed perfume feels cold.

An aerosol air freshener feels cold to the touch because the gas is allowed to expand suddenly, which brings down its temperature. (Photo Credit : Pixabay)

The tendency of gases to become hot when compressed and cold when expanded, along with the help of a few nifty devices, helps a refrigerator cool the stuff being kept inside it.

Parts of a refrigerator

A refrigerator consists of a few key components that play a vital role in the refrigeration process:

Expansion valve

Also referred to as the flow control device, an expansion valve controls the flow of the liquid refrigerant (also known as ‘coolant’) into the evaporator. It’s actually a very small device that is sensitive to temperature changes of the refrigerant.

Compressor

The compressor consists of a motor that ‘sucks in’ the refrigerant from the evaporator and compresses it in a cylinder to make a hot, high-pressure gas.

This is what the compressor of a standard refrigerator looks like. (Photo Credit : Wikipedia Commons)

Evaporator

This is the part that actually cools the stuff kept inside a refrigerator. It consists of finned tubes (made of metals with high thermal conductivity to maximize heat transfer) that absorb heat blown through a coil by a fan. The evaporator absorbs heat from the stuff kept inside, and as a result of this heat, the liquid refrigerant turns into vapor.

Condenser

The condenser consists of a coiled set of tubes with external fins and is located at the rear of the refrigerator. It helps in the liquefaction of the gaseous refrigerant by absorbing its heat and subsequently expelling it to the surroundings.

Condenser coils

As the heat of the refrigerant is removed, its temperature drops to condensation temperature, and it changes its state from vapor to liquid.

Refrigerant

Also commonly referred to as the coolant, it’s the liquid that keeps the refrigeration cycle going. It’s actually a specially designed chemical that is capable of alternating between being a hot gas and a cool liquid.

In the 20th century, fluorocarbons, especially CFCs, were a common choice as a refrigerant. However, they’re being replaced by more environment-friendly refrigerants, such as ammonia, R-290, R-600A etc.

Refrigerator function: How does a refrigerator work?

The refrigerant, which is now in a liquid state, passes through the expansion valve and turns into a cool gas due to the sudden drop in pressure.

As the cool refrigerant gas flows through the chiller cabinet, it absorbs the heat from the food items inside the fridge. The refrigerant, which is now a gas, flows into the compressor, which sucks it inside and compresses the molecules together to make it into a hot, high-pressure gas.

Now, this gas transports to the condenser coils (thin radiator pipes) located at the back of the fridge, where the coils help dissipate its heat so that it becomes cool enough to condense and convert back into its liquid phase. Because the heat collected from the food items is given off to the surroundings via the condenser, it feels hot to the touch.

After the condenser, the liquid refrigerant travels back to the expansion valve, where it experiences a pressure drop and once again becomes a cool gas. It then absorbs heat from the contents of the fridge and the whole cycle repeats itself.