Friday, 1 January 2016

physical chemistry - Why is so different the temperatures of a compressed gas compared to a liquid/gas mixture of the same fluid and they are both at the same pressure?


Why does $\ce{C3H6}$ gas when compressed (in a centrifugal compressor) comes out with a pressure of $\pu{16 bar}$ and $\pu{90 °C},$ and when it is a mixture of $\ce{C3H6}$ liquid/gas stored inside of a vessel reaches also the $\pu{16 bar},$ but at a lower temperature of around $\pu{38 °C}?$


I know that when it is a vessel with stored $\ce{C3H6}$ liquid, some part of the liquid will vaporize until it reaches the equilibrium with the ambient temperature (vapor pressure). I know that if the vessel is exposed to a ambient temperature of $\pu{38 °C}$ and if has enough $\ce{C3H6}$ liquid to vaporize the equilibrium will be reach at a pressure of $\pu{16 bar}.$


But what I cannot understand is why if it is only gas and if I compress the gas to $\pu{16 bar},$ why does it come out with a temperature of $\pu{90 °C}?$ Shouldn't it come out with the same temperature of $\pu{38 °C},$ like the vessel?


If anyone at least could give me the subject/effect/topic so I can study just to get an answer to this question, I would be very grateful.


Note: This isn't a homework question. I work on a LPG storage facility and the other day I started thinking about this, but I cannot understand why this happens.




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