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 would not know what to do without a refrigerator, as there are few things that can soothe their dried-out throat as much as a glass of chilled water.
Although there were techniques people used in ancient times to provide themselves with cold water, it was certainly not as easy as opening a door at home and taking a bottle of ice-cold water. Even if they could get cold water to drink, they certainly had nothing to keep their food fresh for days or even weeks.
Fortunately, we have a little thing that does all these things for us – a fridge!
In this article we will take a look at the science of a refrigerator, in particular the different parts of a refrigerator and how they actually work together to preserve our food for longer periods of time.
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Refrigerator working principle
The principle of refrigeration and cooling is very simple: it involves removing heat from one region and depositing it in 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 into 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 get hot when they are compressed and cold when they expand, along with the help of some refined devices, helps a refrigerator cool the stuff stored in it.
Parts of a fridge
A refrigerator consists of several key components that play a crucial role in the cooling 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 part cools the material stored in 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.
Refrigerants
Also referred to as coolant, it is the liquid that keeps the refrigeration cycle going. In fact, it is a specially developed 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 refrigerants. However, they are being replaced by more environment-friendly refrigerants such as ammonia, R-290, R-600A, etc.
Refrigerator function: How does a refrigerator work?
A refrigerator works in the following steps:
- The compressor compresses the refrigerant gas. The compressed gas heats up as it is pressurized.
- The coils on the back of the refrigerator let the hot refrigerant gas dissipate its heat. The refrigerant gas condenses into liquid at high pressure.
- The high-pressure liquid flows through the expansion valve.
- The liquid immediately boils and vaporizes, its temperature dropping to about -25°F, as the cold gas flows through the expansion coils (inside the refrigerator) it makes the inside cold by absorbing heat.
- The low pressure refrigerant gas is sucked up by the compressor, and the cycle repeats.
Do you remember how a refrigerator works?
Now, let’s discuss the working of a refrigerator in more detail. The compressor, which is a critical component of the refrigerator, compresses the refrigerant gas. As it undergoes high pressure, the gas heats up. 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. 
The high pressure liquid that we have now flows through the expansion valve. Think of the expansion valve as a small hole. On one side of the hole is high-pressure refrigerant liquid. On the other side of the hole is a low-pressure area (because the compressor is sucking gas out of that side). After passing through the expansion valve, the liquid experiences a drop in the pressure. As a result, it becomes a cool (to the tune of -25°F) gas. When this cool gas flows through the expansion coils (installed inside the fridge), it absorbs heat and therefore make the insides of the fridge cold. This low pressure refrigerant gas is once again sucked by the compressor, and the whole cycle repeats, keeping the contents of a refrigerator perpetually cold.
