You don’t need a physics degree to understand why refrigerators keep food cold. You have to understand that cooling is actually just transferring heat. In particular, it makes things feel colder by removing energy. Let’s look at the basic mechanism of refrigerants.
Take an ovenproof glass bowl and fill it with water. You’ll also need a thermometer that can measure up to 450°F. Place the thermometer in the water and place the bowl in the oven to reach 400°F.
Let’s see what happens. The water is heated to 212°F. Then it starts boiling. Although the oven air temperature is 400°F, the water temperature remains at 212°F. It won’t heat up until the last drop has evaporated. Only then will the temperature of the empty bowl rise until it is comparable to the temperature of the oven.
Think of it this way. Imagine an alien named Max living comfortably in a 400 degree Fahrenheit oven. For Max, the oven temperature is room temperature. Now imagine that there is a bowl of boiling water next to him at a temperature of 212°F. Boiling water feels very cold to Max. 188 degrees cooler than his normal surroundings.
This is exactly how we experience extreme cold. We are comfortable at 70°F. Liquid nitrogen boils at -320°F. If you put a jug of liquid nitrogen on your kitchen table, it will feel like a block of ice. This is not magic. It’s just a big difference in temperature from our comfort zone.
Explanation of the cooling cycle
Modern refrigerators use closed loops. Use the same refrigerant over and over again. You can mimic this cycle with Max and his water bowl. Here is the step-by-step process:
1.** Heat the water to boiling. ** Water in the oven boils at 212°F and turns to steam at 400°F. Max collects this vapor in a bag.
2.
** Compressed steam. ** Steam at maximum pressure into the steel container. The pressure rises. When the pressure rises, so does the temperature. The steam inside the tank reaches 800°F. The tank felt very hot to Max, who is used to temperatures of 400 degrees Fahrenheit.
3.
** Release the heat. **Place steel container in 400°F oven. Dissipates excess heat into the oven air. Temperatures return to 400 degrees. The high-pressure steam condenses back into pressurized liquid water.
4.
** Expands liquid. ** Max releases water from the pressure vessel into the boiler. The pressure drops. The water immediately begins to boil again and the temperature returns to 212°F.
Repeat these four steps and you will have a working refrigerator. The so-called “coldness” is actually heat drawn from inside the refrigerator and poured into the kitchen.
Why height matters
If you live at sea level, the boiling point of water is 212°F. In mountainous areas, however, the air pressure is lower. The boiling point drops to about 190-200°F.
This is why the cooking instructions on boxes of pasta often say “cook longer at higher altitudes”. Because the water is cold, it takes longer to transfer enough heat to the food. The same pressure principle applies to cooling. The lower the pressure, the lower the boiling point. That is the core trick. When you lower the pressure, the liquid gets colder.
