How does your Refrigerator really work? Simplified!
Hey friends, Happy Wednesday!
Let’s look at how refrigerators work this week. I aim to write my newsletter issues in a way one can follow them while traveling on a bus, having a coffee, waiting for food, etc. Let's jump in!
There are countless variations of the refrigerator models. Let’s discuss the standard ones.
How it works: 15-second answer
A very cold refrigerant liquid flowing through coils absorbs heat from the fridge's compartments, turning the items cold through heat transfer. This makes the liquid turn into a hot gas. The heat is then released to the outside environment, converting it back into a cold liquid after additional steps. This cycle maintains a cool environment, preserving food by transferring heat from inside to outside.
Shoutout!
Thanks to my friend Caitlin Olson for suggesting this week’s gadget. You can do so too here, and I’ll write about it in the coming weeks.
Basic Heat Transfer
Two objects with different temperatures will exchange heat with each other if they are in contact, in an ideal situation.
Notice how one object got hotter and the other got colder with time.
Figure 1: Temperatures of objects in contact changing with time (An example)
How does your Refrigerator work?
At the back of the fridge, a cold liquid (also called refrigerant) at approximately -30 degrees Celsius flows through the coils of tubes as shown in the figure. The special property of this liquid is that it can absorb heat extremely well.
For example, R-134a is a widely used refrigerant liquid with the chemical formula CH2FCF3.
Figure 2: Back of the fridge with coils for the refrigerant liquid to flow through
The coils (marked in blue on Figure 2. Right) are in direct contact with the air inside the fridge.
The refrigerant liquid in the coils takes the warmth from the air, making the air cooler because of the heat transfer we talked about. Most refrigerator models are designed with a fan inside to distribute the cool air evenly.
Because the air is now cooler, your peanut butter and other items inside also turn cold due to the heat transfer between the air and the items.
The cycle repeats. The cold refrigerant is passed again through the coils to keep the inside of the fridge cool.
But wait!
While making the compartments cooler, the liquid (refrigerant) became hotter and turned into a warm gas (similar to how water evaporates on heating). This is because the boiling point of the refrigerant is very low. So how do we turn it back into a cold liquid?
Additional Info - Cycling the refrigerant
Figure 3: Refrigeration cycle of a refrigerant liquid. The Evaporator is the stage we discussed in the last section.
Now we have the warm gas after cooling the refrigerator compartments. Here is what happens next to convert the gas to a low-temperature liquid again.
Compressor: The gas is further pressurized and made to reach a higher temperature.
Condenser: The hot gas passes through a different set of coils at the back of the fridge. These coils let the heat escape by providing a large surface area for effective heat exchange between the outside air and the hot gas. This is why the back of your fridge is always hot!
Now the gas turns into liquid after the heat transfer (because the heat escaped from the liquid).
Expansion valve: The pressure and temperature are then further reduced using an expansion valve. Now, we are ready to cycle the cold liquid back again to start making the compartments cooler.
All these are powered electrically. This is how your refrigerators work!
Question of the week
Why are the compartments of a refrigerator cold even when there are no items inside?
Reply to this email with your thoughts, and we’ll discuss. I’ll answer this in the next newsletter issue.
Tweet of the week
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Thank you for reading!
Have an amazing rest of the week, and take care!
Until next to next Wednesday,
Chendur