Chef: Wonderopolis kitchen! This is Chef Boyoboy speaking. How can I help you?
Caller: Yes, sir, I was WONDERing…is your refrigerator running?
Chef: The refrigerator? Of course, it's running!
Caller: Well, you'd better go catch it! Ah ha ha ha ha ha ha!
OK, so that's an old, old joke, but we still like it! It did make us WONDER, though…exactly how does a refrigerator work?
Before jumping into the science and mechanics of refrigerators, let's first take a moment to be thankful for their very existence. Long ago, people had to rely upon iceboxes and large chunks of ice to keep things cold. Even then, it was often only the very wealthy who could afford such a convenience.
Today, refrigerators are in every home, and we're sure glad they are. Aside from keeping drinks at a cool, enjoyable temperature, they also make our food safe to eat. Without refrigeration, most foods would spoil in a matter of days, if not hours. Refrigeration slows the growth of bacteria to the point where foods can last for weeks and even months if frozen.
So how do refrigerators keep all that food cool? Do they blow cold air over the food? Nope! They work much like your home's air conditioning system: they remove the warm air inside the refrigerator continually, releasing it outside the refrigerator until the air inside is nice and cool. To accomplish that task, they rely upon the science of gases.
The five major parts of a refrigerator's cooling system are fluid coolant (known as refrigerant), a compressor, condenser coils (outside), evaporator coils (inside), and an expansion valve. The compressor takes the vaporized refrigerant (more on this in a bit) and compresses it, raising its pressure as it pushes it through the condenser coils on the outside of the refrigerator.
In the condenser coils, the hot gas releases its heat to the outside air. As this happens, it cools and turns back into a liquid. It continues to cool down as it flows into the interior of the refrigerator. When it reaches the expansion valve, the liquid expands as it converts to a gas.
As it travels through the evaporator coils, the vaporized refrigerant absorbs heat from inside the refrigerator, cooling the air inside the refrigerator in the process. As it exits the evaporator coils, it reenters the compressor and the cycle begins again.
This cycle continues until a device called a thermocouple (basically a fancy thermometer) detects that the air inside the refrigerator has reached the desired temperature. At this point, it will shut off power to the compressor. After you open the refrigerator door and let more heat inside, the thermocouple will detect a rise in temperature and start the compressor again.
While all of this may sound a bit complicated, it's fairly simple, and you've probably experienced the same science of gases in your own day-to-day life. For example, have you ever gotten out of a swimming pool and felt a little cool despite standing in the bright sunshine? That happens because the water on your skin is evaporating, taking heat away from your skin in the process.