If I were to fill a 700c 25mm road bike tire with some water and pump the tire to, say 100psi, and punch a tiny hole in the tire, the water will start to spray out.

My question is: does the water temperature rise, even of momentary, at the location of the hole where it is coming out or does the water temperature stay the same?

  • $\begingroup$ Since the pressure is released (atmospheric pressure being lower), temperature should increase. $\endgroup$ – Exocytosis May 11 at 18:37
  • $\begingroup$ @Exocytosis why would "releasing pressure" imply a higher temperature? $\endgroup$ – Eagle May 11 at 19:21
  • $\begingroup$ Because energy is released from the tire as well as water? $\endgroup$ – Exocytosis May 11 at 19:36
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    $\begingroup$ Need clarification. How many cc of water are you thinking in terms of. In other words, what percent is water and what percent is air. $\endgroup$ – Bob D May 11 at 22:03

The temperature will decrease. Water is slightly compressible, so it expands a bit as it exits the hole, doing work on its surroundings. The water loses internal energy in the process: its temperature decreases. It’s called adiabatic cooling. In going from 100 psi to atmospheric pressure, if the water is near room temperature, it will cool by about 0.01 degrees C.

  • $\begingroup$ The compressibility of water is i believe 46.4 parts per million per atmosphere or 316 parts per million at 100 psia. Do you believe that is “slightly “ compressible? To me that’s incompressible. $\endgroup$ – Bob D May 11 at 19:07

The compressibility of water is only 46.4 parts per million per atmosphere. At 100 psia that’s 316 parts per million. Any expansion of the water and cooling resulting from it should be negligible. The compressed air on the other hand will undergo adiabatic cooling. So the temperature of the water air spray combination should be lower, but due to the expansion of the air .

Hope this helps

  • $\begingroup$ Interestingly, this process is used in snowmaking guns, but the mixture needs to be mostly (compressible) air with just a little (incompressible) water to work. $\endgroup$ – Pere May 11 at 19:52
  • $\begingroup$ @Pere Makes sense since it’s the expansion of the air that does the cooling. Too much water will make it inefficient making slush $\endgroup$ – Bob D May 11 at 20:01
  • $\begingroup$ Expansion of the water itself will cause cooling of about a hundredth of a degree C. Up to interpretation whether that's negligible. $\endgroup$ – Ben51 May 11 at 20:13
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    $\begingroup$ It’s definitely negligible compared to the adiabatic cooling of the compressed air in the tire. That is what cools the water mixed with air in the spray $\endgroup$ – Bob D May 11 at 20:24
  • $\begingroup$ Agreed, but not clear from question whether there’s any air in the tire or not. $\endgroup$ – Ben51 May 11 at 21:19

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