Thermal equilibrium in open systems

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Discussion Overview

The discussion centers on whether an open system can reach thermal equilibrium, exploring theoretical implications and examples related to thermodynamics. Participants examine conditions under which thermal equilibrium might be achieved or challenged, particularly in systems with mass flow and work interactions.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question the possibility of thermal equilibrium in open systems, seeking clarification on the conditions that would allow or prevent it.
  • One participant proposes a specific example of an open system where a flow at T=400K enters and exits, suggesting that it can remain in thermal equilibrium while work is done, highlighting the role of isothermal compression.
  • Another participant elaborates on the scenario of an open system at steady state, discussing how shaft work and heat removal can affect the enthalpy and temperature of the gas, but expresses uncertainty about whether this constitutes thermal equilibrium.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether an open system can achieve thermal equilibrium, with multiple competing views and uncertainties remaining in the discussion.

Contextual Notes

Limitations include the dependence on specific definitions of thermal equilibrium and the conditions under which work and heat transfer occur in open systems. Unresolved mathematical steps related to enthalpy changes and temperature variations are also present.

PT12
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Is it possible for an open system to reach thermal equilibrium? why/why not?
 
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PT12 said:
Is it possible for an open system to reach thermal equilibrium? why/why not?
Can you provide an example of what you are alluding to?
 
You could define an system in which a flow at T=400K goes in, a flow at T=400K goes out, while inside it is compressed isothermally, couldn't you? It remains in thermal equilibrium while work is done, and it's an open system since there is mass flow in and out.
 
oobgular said:
You could define an system in which a flow at T=400K goes in, a flow at T=400K goes out, while inside it is compressed isothermally, couldn't you? It remains in thermal equilibrium while work is done, and it's an open system since there is mass flow in and out.
If you have an open system (fixed control volume) operating at steady state, and shaft work is being done to compress the gas, if the system is adiabatic (insulated), then the enthalpy per unit mass of the gas at the exit is higher than at the entrance. So the temperature of the gas increases. If heat is being removed from the control volume as the gas passes through, such that the heat removed is equal to the shaft work, then the inlet and outlet enthalpies per unit mass are the same, and the temperatures are the same. But, I'm not sure you would call this thermal equilibrium.
 

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