Throttling process (Joule Thomson coefficient)

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Discussion Overview

The discussion revolves around the Joule-Thomson coefficient and its implications during the throttling process, particularly focusing on isenthalpic curves for real and ideal gases. Participants explore the behavior of gases under varying pressures and temperatures during throttling, questioning the nature of the graphs produced and the significance of the inversion point.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the sudden change in temperature at the inversion point in the isenthalpic graph is due to the deviation of real gases from ideal gas behavior.
  • Others argue that the graph for an ideal gas would consist of horizontal lines parallel to the abscissa, indicating constant enthalpy.
  • A participant questions the possibility of isenthalpic curves touching the ordinate axis, suggesting that this could imply a positive temperature at zero pressure.
  • Another participant clarifies that a zero pressure value does not literally mean zero pressure, but rather indicates low pressures where deviations from ideal gas behavior are minimal.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of gases during the throttling process, particularly regarding the interpretation of isenthalpic curves and the implications of pressure and temperature changes. There is no consensus on the nature of the inversion point or the meaning of zero pressure in the context of the graphs discussed.

Contextual Notes

The discussion includes assumptions about ideal versus real gas behavior, the interpretation of graphical data, and the implications of pressure and temperature conditions that remain unresolved.

theo dsouza
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This is a graph obtained during throttling process by keeping pressure and temperature at the inlet of the valve fixed and varying them at the outlet to get different isenthalpic curves for different inlet pressures and temperatures.

Is it true that the sudden change in temperature of this isenthalpic graph at the inversion point is due to the deviated nature of a real gas from the ideal gas? Will the graph for an ideal gas be lines parallel to the abscissa?
 
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theo dsouza said:
View attachment 79412
This is a graph obtained during throttling process by keeping pressure and temperature at the inlet of the valve fixed and varying them at the outlet to get different isenthalpic curves for different inlet pressures and temperatures.

Is it true that the sudden change in temperature of this isenthalpic graph at the inversion point is due to the deviated nature of a real gas from the ideal gas?
I don't see any sudden changes at the inversion point.
Will the graph for an ideal gas be lines parallel to the abscissa?
Yes. The lines of constant enthalpy for an ideal gas undergoing a throttling process are horizontal on the graph. Note that, even in the low pressure region (where we usually expect ideal gas behavior), the isenthalpic lines are not horizontal. This is because the Joule Thompson coefficient is the result of deviation from ideal gas behavior.

Chet
 
In some graphs of the Isenthalpic curves (not the one above) I've seen that the isenthalpic curves touch the ordinate axis to give a positive temperature value and a zero pressure value on the exit side of the throttle valve. Is this possible?
 
theo dsouza said:
In some graphs of the Isenthalpic curves (not the one above) I've seen that the isenthalpic curves touch the ordinate axis to give a positive temperature value and a zero pressure value on the exit side of the throttle valve. Is this possible?
The zero pressure value doesn't really mean zero pressure; it just means "at low pressures," where deviations from ideal gas behavior are negligible. Obviously, if you go all the way to zero pressure, the gas is not longer present, and its temperature is meaningless.

Chet
 

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