I came across this paper:
Baker, B. (1999). An easy to perform but often counterintuitive demonstration of gas expansion. American Journal of Physics, 67(8), 712-713. http://scitation.aip.org/content/aapt/journal/ajp/67/8/10.1119/1.19357
And I didn't fully understand the explanation. I can't see how this is any different from the Joule free expansion experiment with no temperature change.
Essentially the author of the article says that the atmosphere does work on the gas and increases its internal energy. This is the reason for the temperature increase. However wouldn't that logic also lead to a temperature increase in the joule free expansion?
Any insight would be much appreciated.