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The contents of the Free expansion page were merged into Joule expansion on 21 July 2018 and it now redirects there. For the contribution history and old versions of the merged article please see its history. |
Adiabatic expansion isn't isothermal for an ideal gas. The given equation is only true for an isothermal expansion.
For an ideal gas (), adiabatic expansion / compression obeys . This gives a temperature drop during expansion. The thermal energy is used to accelerate the atoms / molecules during the expansion. If there is no wall (i.e. free expansion), the atoms are never stopped and expansion never finishes. See Adiabatic process, ideal gas, and isothermal process SMesser ( talk) 00:26, 11 February 2013 (UTC)
On second thought, I'm going to back off calling this "wrong", but... there's something odd here about defining "free" expansion. The equation works if there's a wall that bounces the escaping gas back - i.e. if there's some containment. That situation conserves energy by redirecting the escape velocity back into thermal energy. I'm just not sure I'd call it free. This is probably because I've been worried lately about what happens while the gas is expanding. That expansion is both isentropic and adiabatic, but its the atoms reflecting off the walls that raises the entropy again by mixing the fast-moving atoms with the slow-moving ones. Since temperature in an ideal monatomic gas is essentially the width of the velocity distribution function, this also raises the temperature....
So maybe "free expansion" should be split into two cases? One with, and one without a wall? Or perhaps there should be some other sort of disambiguation here. SMesser ( talk) 01:23, 11 February 2013 (UTC)
I would be willing to merge this (shorter) article into the more complete Joule expansion article. How does one initiate that process?-- guyvan52 ( talk) 16:51, 31 December 2013 (UTC)
This redirect does not require a rating on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | |||||||||||
|
The contents of the Free expansion page were merged into Joule expansion on 21 July 2018 and it now redirects there. For the contribution history and old versions of the merged article please see its history. |
Adiabatic expansion isn't isothermal for an ideal gas. The given equation is only true for an isothermal expansion.
For an ideal gas (), adiabatic expansion / compression obeys . This gives a temperature drop during expansion. The thermal energy is used to accelerate the atoms / molecules during the expansion. If there is no wall (i.e. free expansion), the atoms are never stopped and expansion never finishes. See Adiabatic process, ideal gas, and isothermal process SMesser ( talk) 00:26, 11 February 2013 (UTC)
On second thought, I'm going to back off calling this "wrong", but... there's something odd here about defining "free" expansion. The equation works if there's a wall that bounces the escaping gas back - i.e. if there's some containment. That situation conserves energy by redirecting the escape velocity back into thermal energy. I'm just not sure I'd call it free. This is probably because I've been worried lately about what happens while the gas is expanding. That expansion is both isentropic and adiabatic, but its the atoms reflecting off the walls that raises the entropy again by mixing the fast-moving atoms with the slow-moving ones. Since temperature in an ideal monatomic gas is essentially the width of the velocity distribution function, this also raises the temperature....
So maybe "free expansion" should be split into two cases? One with, and one without a wall? Or perhaps there should be some other sort of disambiguation here. SMesser ( talk) 01:23, 11 February 2013 (UTC)
I would be willing to merge this (shorter) article into the more complete Joule expansion article. How does one initiate that process?-- guyvan52 ( talk) 16:51, 31 December 2013 (UTC)