How does the refrigerator work
In the summer, do you ever get out of the pool and get too cold while standing in the sun? This water is evaporating. Air carries water vapor, and with it some heat is drawn from your skin.
This is similar to what happens inside old refrigerators. Instead of water, the refrigerator uses chemicals to do the cooling.
There are two things to know about cooling.
1. A gas that cools when expanding.
2. When you have two things of different temperatures touching or coming close to each other, the hotter surface cools and the colder surface warms. This is a physical law, or in other words, a law of thermodynamics.
old refrigerators
If you look at the back or bottom of an old refrigerator, you'll see a long, thin tube that coils back and forth. This tube is connected to a pump powered by an electric motor.
Inside the tube is freon, which is a type of gas. Freon is the trade name for the gas. This gas is chemically called Chloro-Flouro-Carbon, or CFC. This gas has been found to be harmful to the environment if leaked from refrigerators. To date, other chemicals are used in a slightly different process (see next section below).
CFCs start out as liquids. The pump pushes the CFC through a lot of the coils in the freezer area. There the chemical turns into steam. When that happens, it absorbs some of the heat that may be in the freezer compartment. While doing this, the coils get colder and the freezer starts to get cold.
In the regular part of your refrigerator, there are fewer files and more space. Therefore, less heat is absorbed by the coils and CFC vapor.
The pump then absorbs the CFC in the form of vapor and pushes it through thinner tubes located on the outside of the refrigerator. By compressing it, the CFC turns into a liquid and heat is released and absorbed by the surrounding air. That's why it might be a little warmer behind or under the refrigerator.
Once the CFC has passed through the external coils, the liquid is ready to go back through the freezer and refrigerator over and over again.
Today's refrigerators
Modern refrigerators do not use CFCs. Instead they use ammonia gas. Ammonia gas turns into a liquid when cooled to -27 degrees Fahrenheit (-6.5 degrees Celsius).
Engine and compressor pressurize the ammonia gas. When it is compressed, the gas heats up when compressed. When you pass pressurized gas through the coils in the back or bottom of a modern refrigerator, the hot ammonia gas can lose its heat to the air in the room.
Remember the law of thermodynamics.
When it cools, the ammonia gas can turn into a liquid ammonia because it is under high pressure.
The ammonia fluid flows through what's called an expansion valve, which is a tiny tiny hole through which the fluid must squeeze. Between the valve and the compressor there is a low pressure zone because the compressor draws in ammonia from this side.
When liquid ammonia hits a low pressure area, it boils and turns into a gas. This is called evaporation.
The coils then pass through the freezer and the regular part of the refrigerator where the cooler ammonia in the coil draws heat from the compartments. This keeps the inside of the freezer and the entire refrigerator cool.
The compressor sucks in the cold ammonia gas, and the gas returns it through the same process over and over again.
How does the temperature stay the same indoors?
A device called a thermocouple (essentially a thermometer) can sense when the temperature in the refrigerator is as cold as you want it to be. When this temperature reaches, the device cuts off the electricity to the compressor.
But the refrigerator is not completely closed. There are places, like around doors and where pipes go through, that can leak a bit.
So when the cold from inside the fridge starts escaping and the heat seeps in, the thermocouple restarts the compressor to cool the fridge again.
This is why you will hear the refrigerator compressor motor running for a short time and then turning itself off.
However, today's refrigerators are highly energy efficient. What is sold today consumes about a tenth of the amount of electricity that was built 20 years ago. So, if you have an old refrigerator, it's best to buy a new one because you'll save money (and energy) over a long period of time.