Thermodynamics question - which process is this?

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Discussion Overview

The discussion revolves around identifying the thermodynamic process involved in an experiment where gas is rapidly released from a vessel after being pressurized. Participants explore the nature of the processes occurring during this gas release, considering concepts from thermodynamics.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant describes an experiment involving the rapid release of gas and questions whether the process is isochoric or adiabatic, noting the change in temperature and pressure.
  • Another participant suggests that the gas remaining in the vessel expands nearly adiabatically and reversibly while the gas being pushed out experiences a flow process with no enthalpy change, referencing the Joule-Thompson effect.
  • A follow-up question asks if work is done by the gas remaining in the cylinder, to which the response confirms that it is.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the thermodynamic processes involved, with no consensus reached on whether the process is isochoric or adiabatic. Multiple competing interpretations of the processes are presented.

Contextual Notes

The discussion includes assumptions about the definitions of isochoric and adiabatic processes, as well as the conditions under which the Joule-Thompson effect applies. The exact nature of the work done by the gas and the implications of the flow process remain unresolved.

GBA13
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Homework Statement


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.

Homework 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!

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!
 
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The gas that remained in the vessel expanded nearly adiabatically and reversibly when it pushed the gas out ahead of it. The gas that got pushed out through the valve experienced a flow process involving no enthalpy change (per unit mass), a so-called Joule-Thompson effect. So there were two basic things going on simultaneously.

Chet
 
Chestermiller said:
The gas that remained in the vessel expanded nearly adiabatically and reversibly when it pushed the gas out ahead of it. The gas that got pushed out through the valve experienced a flow process involving no enthalpy change (per unit mass), a so-called Joule-Thompson effect. So there were two basic things going on simultaneously.

Chet

Ok thanks, Chet! That will mean that some work will be done BY the gas remaining the cylinder doesn't it?
 
GBA13 said:
Ok thanks, Chet! That will mean that some work will be done BY the gas remaining the cylinder doesn't it?
Yes.
 
Great, thanks very much!
 

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