How does a propane powered cool box cool down? Isn’t the act of burning gas creating heat?!
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The “propane” part is almost irrelevant. It is just a source of energy. You can achieve the same with a battery and and electric motor. Or a donkey. Or your own muscles.
The essential part is:
Take a closed elastic vessel full of any gas (a soda bottle full of plain air will do). Go to your living room and use force to compress it a bit. It warms up above room temperature. Go to your kitchen and let it cool, while still maintaining pressure on it. Go back to the living room, and release pressure. It cools below room temperature. Let it warm up. Then repeat. In each cycle you are warming a cool bottle in the living room, and cooling a warm bottle in the kitchen. You are transporting heat from the living room to the kitchen. After a while, the kitchen will be warmer, and the living room – colder.
As described, the effect is too small to notice. But if you ever used a manual pump to inflate a car tyre, you must have noticed that it does warm up.
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