Joule kelvin expansion, thermodynamics

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SUMMARY

The discussion centers on the Joule-Kelvin expansion, a throttling process where the internal energy change (dU) is zero, leading to no heat transfer (dQ) and no work done (dW) against the surroundings. Participants clarify that while dW is zero in the context of external work, the gas can still exhibit internal work against itself. The confusion arises from the distinction between Joule-Kelvin expansion and free expansion, with emphasis on the importance of mass flow energy in understanding temperature changes in ideal gases during this process.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically the first law of thermodynamics.
  • Familiarity with the concepts of internal energy (dU), heat transfer (dQ), and work (dW).
  • Knowledge of the Joule-Kelvin effect and throttling processes.
  • Basic principles of ideal gas behavior, including the relationships between pressure (P), volume (V), and temperature (T).
NEXT STEPS
  • Research the Joule-Kelvin effect and its applications in refrigeration cycles.
  • Study the concept of isenthalpic processes and their significance in thermodynamics.
  • Learn about the implications of mass flow energy in thermodynamic systems.
  • Explore the differences between Joule-Kelvin expansion and free expansion of gases.
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Students and professionals in thermodynamics, mechanical engineers, and anyone studying gas behavior under varying pressure and volume conditions.

Chronos000
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Homework Statement




for a jk expansion, I know dU=0. I think this is because dQ=0 as its isolated and dW = 0 as there is no work done against the surroundings.

but is dW 0? does the gas do work against itself?

I have also seen that the temperature change of an ideal gas = 0. how can this be?
 
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Yes, dU = dQ = dW = 0. However, there is mass flow energy that must be accounted for. The Joule Kelvin (also called Joule Thomson) is a throttling process which usually reduces to an isenthalpic process.
 
I think I may have confused a jk expansion with a free expansion of gas where the gas is confined in volume V then is allowed to expand into a vacuum.

could you please explain further about this "flow energy"?
and for an ideal gas, I don't see how change in T =0 if there is a change in P and V
 

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