Eli5: Why cant we use boyle’s law to extract energy from hot air

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Things i know:
1. boyle’s law vaguely as; as pressure rises so does temperature.

2.Peltier devices can extract electricity given a large enough temperature differential, are there devices that do this better?

3. Heat pumps can pull heat from cold air on one side and make hot air on the other side.

I know i am missing some major steps here and ifs something ive always wondered about…

In: Physics

6 Answers

Anonymous 0 Comments

Boyle’s Law isn’t directly related to temperature; instead, Boyle’s Law simply states that changes in volume are inversely proportional to changes in pressure. In most applications, though, compressing a gas isn’t an isothermal process; pressure changes are typically accompanied with temperature changes.

As far as what you’re talking about; the primary limitation is the 2nd law of thermodynamics. ***All*** heat engines are limited by Carnot’s Law, which essentially states that your maximum efficiency is directly tied to the difference in temperatures across your reaction. In essence, the lower your temperature differential between the heat source and the ambient, the less efficient the process will become. As a direct result, most low-temperature heat engines have absolutely garbage thermal efficiency, and thus past a certain point there really isn’t much reason to use a heat engine.

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