Simple question that can be reworded as such: if I use a fire piston continuously, without anything in the piston. Will the continuous pushing and opening of the piston create net heat or will the decompression part, cool the gas inside the piston chamber exactly by the same amount as the compression heated it up.

I ask because I am looking for a way to turn kinetic energy into heat energy. I want to simply run a fire piston so it generates heat, without any fuel in it. Is this possible?

Thank you for your answer.

  • $\begingroup$ "I ask because I am looking for a way to turn kinetic energy into heat energy" kinetic friction creates heat from kinetic energy. $\endgroup$
    – Bob D
    Sep 10 at 12:48
  • $\begingroup$ What is a fire piston? $\endgroup$ Sep 10 at 12:53
  • $\begingroup$ Fire piston is a piston chamber and a piston. They are a little longer than the palm of a man. They are airtight.Pressing on the piston generates heat and a highly compressed air. Its primary purpose is to place something flammable in between the piston and the piston chamber, then set it on fire by a simple press on the piston. The temperatures in the piston can exceed 260 Celsius. Again, just want to know if performing this compression, without any flammable material, then releasing the piston, and letting the air decompress is it equivalent to ~260 Celsius cooling or not. Thank you $\endgroup$
    – Barny
    Sep 10 at 13:27
  • $\begingroup$ yes, kinetic friction creates heat, but the most obvious solutions grind at the materials that produce friction, which is not suitable. I don't want to regularly replace the material that acts as the medium for friction. $\endgroup$
    – Barny
    Sep 10 at 13:29
  • $\begingroup$ en.wikipedia.org/wiki/Fire_piston $\endgroup$
    – Bob D
    Sep 10 at 14:48

The laws of thermodynamics guarantee that you will be generating net heat, even without any friction.

Heat conduction is guaranteed to not be 100 % reversible. In this case heat conduction from the gas to the cylinder.

So I would recommend maximizing the amount of heat that gets conducted to the cylinder, for example by moving the piston fast down and fast up, but keeping it still for some time at the position where the gas is the hottest. I mean if you want to reach a low reversibility like 30 %. Without any optimization at all the reversibility might be for example 70 %.

The gas may be very cool after the decompression, but that's not important, I guess.

  • $\begingroup$ "The gas may be very cool after the decompression, but that's not important, I guess." That is the part that I am interested in. For example if a perpetual fire piston is left in the water, will the water heat up? Ignoring the fact that the piston is moving in and out and only focusing on the heat and cold generated by the compression decompression cycle. Is that a net benefit or a zero sum situation for the heating of the water? $\endgroup$
    – Barny
    Sep 11 at 13:48
  • $\begingroup$ @Barny The water heats up. Heating power is 70W if the guy pumping the piston does work at 70 W power. Another example: A 70 W fridge sucks heat from the room with its cool walls by power 100W. The warm backside of said fridge warms the room by power 170W. 170W-100W=70W $\endgroup$
    – stuffu
    Sep 12 at 4:55
  • $\begingroup$ Excellent. Thank you. As I cant select your message as the correct answer, will accept stuffu's response as the correct answer. Thank you. $\endgroup$
    – Barny
    Sep 12 at 6:03

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