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I What is the difference between types of expansions?

  1. Mar 2, 2016 #1
    Can someone differentiate between differet types of expansion,
    1. Joule's expansion (free expansion)
    2. Adiabatic expansion
    3. Joule - Thomson or Joule - Kelvin expansion
  2. jcsd
  3. Mar 2, 2016 #2


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    I think that 1 and 3 are both specific types of 2, as both are defined to be adiabatic - which just means thermally isolated.
    Type 1 is when a thermally-isolated container is divided into two parts separated by an openable divider, with one part containing gas and the other a vacuum, and the divider is then opened, to allow the gas to expand into the vacuum part.
    Type 3 is a more complicated process (explained here) where a gas is forced through a valve or porous plug, and the system where this happens is thermally isolated.
    Both 1 and 3 are irreversible processes.

    An example of an adiabatic expansion that is neither type 1 or 2 would be where the gas in a cylinder expands by pushing back a piston, while remaining thermally isolated. I think (but am not sure) that that would be a reversible process.
  4. Mar 3, 2016 #3
    An adiabatic expansion involving a piston and cylinder is not necessarily reversible.
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