What is the purpose of a refrigerator?
Most people think that it makes food and other things cold. But that’s not quite correct. What it actually does is remove heat from food.
Rule No. 1:
Heat always flows from the higher-temperature to the lower-temperature object.
For example, let’s put a can of soda (at, say, 60 degrees) into a refrigerator with cold air in it (at, say, 40 degrees.) Heat will flow from the can, into the air. The temperature of the can will start to drop.
When will the soda can be cold?
Rule No. 2:
The heat flow will continue until their temperatures are equal.
If you keep the air inside the refrigerator at 40 degrees, Then heat will stop flowing when the soda can reaches 40 degrees.
But there’s a little problem with that.
Rule No. 3:
As the heat flows, the lower temperature rises, and the higher temperature drops.
As the soda can gives heat to the air, the temperature of the can goes down, but the temperature of the air inside the fridge around the can will go up.
We don’t want the temperature of the air inside the fridge to rise…we want to keep it at 40 degrees. How do we do that?