1. The problem statement, all variables and given/known data Hello everyone! I recently did an experiment, one of the parts was rapidly releasing some gas from a large vessel. We had previously increased the pressure, let it settle and then opened a value to let some out. I am wondering which thermodynamic process this approximates to. 2. Relevant equations From the data collected the temperature definitely changed by a couple of degrees and of course the pressure changed as we let some air out! 3. The attempt at a solution At the moment I am stuck between two answers, either isochoric or adiabatic. As far as I know the real difference between these two processes is Isochoric happens at a constant volume while adiabatic doesn't. This is what I am trying to figure out. If you think of the vessel as a control volume then the volume is constant but if you think of all the gas originally in the cylinder as the volume then it increases massively when some of it is left in the open. Thanks for any help you guys can offer!