Nib asked
How does a refrigerator work step by step?
A refrigerator does not make cold. It moves heat out of the food and into your kitchen, using a sealed loop of refrigerant that is squeezed hot, cooled to liquid, then allowed to boil icy cold.
6 steps, drawn by Nib. Read it here, or watch him draw it. Updated .
1the myth
Most people picture a fridge as a machine that makes cold and pumps it into the box. Cold is just the absence of heat, so there is nothing to make. What the machine does is carry heat from the inside, where your food is, to the outside, where your kitchen is.
A fridge moves heat; it does not make cold.
a common mix-upA fridge does not manufacture cold. It carries heat from the food compartment out into the room.
2heat goes out
The heat you pull out of the food does not vanish. It leaves through the black coils on the back or bottom of the fridge, so those coils feel warm. The heat you feel is the heat taken from your food plus the energy the compressor used. That is why leaving the fridge door open warms a kitchen rather than cooling it.
The heat taken from the food, plus the motor's energy, ends up in the kitchen.
Would an open fridge door cool a closed room?
Show the answer
No. The room would end up warmer, because the heat removed plus the compressor's energy is released into it.
3the loop
Heat only flows from hot to cold by itself, so moving it from cold food to a warmer room needs a trick. The trick is a sealed loop of pipe filled with a refrigerant, a fluid that boils at a very low temperature. A common one, R-134a, boils at minus 26.3 degrees Celsius at normal air pressure. Around the loop sit four parts: a compressor, a condenser, an expansion valve and an evaporator.
A sealed loop of refrigerant, with four parts, carries the heat.
Why does the fridge need a special fluid that boils at a very low temperature?
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Boiling soaks up lots of heat, and a fluid that boils far below freezing can soak up heat from food that is already cold.
4squeeze and shed
Step one: the compressor squeezes the refrigerant vapor. Squeezed gas gets hot, hotter than the kitchen air. Step two: that hot vapor runs through the condenser, the coils on the back, where the room air is cooler, so the heat flows out to the room and the refrigerant condenses into a liquid.
Squeezed gas is hotter than the kitchen, so it sheds its heat there and turns liquid.
5release and soak
Step three: the liquid is forced through the expansion valve, a very narrow opening, into a low pressure zone. Some of it flashes into vapor, which chills the rest. Step four: in the evaporator coils inside the fridge, the cold refrigerant absorbs heat from the air around your food as it finishes boiling into vapor. The vapor returns to the compressor and the loop begins again.
Dropping the pressure makes the liquid boil icy cold, and boiling soaks up the food's heat.
What happens to the refrigerant as it boils in the evaporator?
Show the answer
It absorbs heat from inside the fridge and turns back into vapor.
6the whole idea
The whole fridge on one page: heat is soaked up from the food by boiling refrigerant, carried around the loop, and dumped into the kitchen where the compressed vapor condenses. Electricity runs the compressor that makes the carrying possible.
Soak up heat, squeeze, shed it to the room, release: electricity pays to carry heat uphill.
Next time you feel warmth behind your fridge, that is your dinner's heat, on its way out to the kitchen.