Eli5: How do refrigerators work?



Eli5: How do refrigerators work?

In: Technology

Usually heat only wants to flow from a higher-temperature area to a lower-temperature area.

But something neat happens to gases when they compress and expand. Compressing a gas makes its temperature rise. Letting a gas expand makes its temperature lower.

So if you compress a gas, it will get hot. But what if you then take that hot, compressed gas, and let it cool down? Well, then , you have some cool, compressed gas. Now, if you let the gas expand again, it will get cold! Much colder than it was when you started.

So the trick is, you compress the gas over here outside the to make it hot, and then let it radiate all that heat away through the grille on the back of the fridge. Then you bring that compressed gas back over there to the inside the fridge, and then let it expand, and it gets very cold, and the cold gas is warmed up when heat flows into it from, say, your vegetables.

The fridge achieves all this by pumping the gas, called a refrigerant, through a closed circuit of pipes. (It’s actually not always in the gas phase; usually it condenses into a liquid for part of the cycle, but that’s not really important to the basic principle here. Refrigerants are generally fluids which boil and condense at just the right temperatures and pressures to make this process most efficient.)

Sensible heat is the heat you can read on a thermometer, latent heat is the heat required for a phase change ie (solid, liquid, gas). When boiling occurs in water let’s say, it will boil at 212 degrees (at standard pressure and temp). But not immediately, as it takes a significant amount of energy to go from liquid to gas. Your refrigerator uses a compound that boils at less than 32 degrees Fahrenheit, you run the “hot air” from inside the fridge over coils which contain that liquid, the refrigerant inside the coils boil and with it it absorbs a significant amount of energy from the “hot” air inside the fridge cooling it down

A refrigerator is a kind of [heat pump](https://en.wikipedia.org/wiki/Heat_pump), extracting heat from the cold inside and dumping it in the warm outside.

Amusing: Einstein himself got a patent for a [refrigerator](https://en.wikipedia.org/wiki/Einstein_refrigerator).