How a refrigerator works · OakCrest Academy

🧊 How a refrigerator works

A refrigerator does not make cold. It moves heat out of the box and releases it into the kitchen, which is why the coils at the back feel warm.
The compressor squeezes a gas called isobutane until its pressure is about nine times higher. Squeezing a gas heats it, to about 65 °C.
In the black coils at the back, the hot gas gives its heat to the kitchen air and condenses (turns from a gas into a liquid).
The liquid is forced through a very thin capillary tube. On the far side the pressure is so low that the liquid boils at −25 °C.
Boiling needs heat, so in the evaporator around the freezer box the refrigerant takes heat from the food. The gas returns to the compressor and the loop begins again.
In this model, a thermostat (a switch worked by temperature) starts the compressor when the fridge reaches 5 °C and stops it at 3 °C; the freezer box stays near −18 °C.

New words

refrigerant: the substance that travels round the loop, boiling inside the fridge and condensing outside it
compressor: a pump that squeezes a gas into a smaller space, raising its pressure and temperature
condense: to change from a gas into a liquid, giving out heat
evaporate: to change from a liquid into a gas, taking in heat
pressure: how hard a gas or liquid pushes on each square centimeter of its container, measured here in bar
insulation: material that slows the flow of heat, such as the foam in the walls

🏠 Try it for real

With a grown-up, carefully place your hand near (not on) the coils at the back of your fridge while it is running: they are warm. Then put a thermometer on a middle shelf, wait an hour, and read it. Is it between 3 and 5 °C? Explain it: in three or four sentences, tell a grown-up where the heat from the food goes, and why the back of the fridge is warm.

💭 Talk about it

A friend claims that on a hot day you could cool the kitchen by leaving the fridge door open. Is that true? Consider where the heat from the open box is released, and what the motor adds. What evidence could you collect with two thermometers to test the claim?

Now explain it back: point at each part and say what it does.