How do you find Z when the temperature line ends on the compressibility chart?

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Discussion Overview

The discussion revolves around the challenges of determining the compressibility factor (Z) using a compressibility chart, particularly when the temperature line ends before reaching the desired pressure. Participants explore the implications of reduced pressure (P_r) and reduced temperature (T_r) values, and the behavior of the chart under these conditions.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions how to find a value for Z when the temperature line for T_r ends before the pressure of P_r = 0.75.
  • Another participant asks about the number of phases involved when both P_r and T_r are less than 1.0.
  • There is a repeated inquiry regarding why the T_r lines stop increasing in P_r after a certain point.
  • A participant speculates on the meaning of a dashed line in the compressibility chart, suggesting it represents the pseudo reduced specific volume.
  • There is a discussion about the implications of being below the saturated vapor line, with a participant assuming that the equation Pv = ZRT cannot be used in that region.
  • A participant poses a hypothetical question regarding the value of T_r at P_r = 0.4 and Z = 0.6, indicating that this is not a homework question but rather a curiosity.
  • Another participant provides a response of 0.86 for the hypothetical question posed.

Areas of Agreement / Disagreement

The discussion contains multiple competing views and remains unresolved regarding the best approach to find Z when the temperature line ends on the compressibility chart. There is also uncertainty about the implications of being below the saturated vapor line.

Contextual Notes

Participants express varying assumptions about the behavior of the compressibility chart and the conditions under which different equations can be applied. There are unresolved questions regarding the number of phases and the interpretation of specific lines on the chart.

zachdr1
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How do you find a value for Z using the compressibility chart when the temperature line you're trying to use ends?

For example, if you look at the compressibility chart and try to find a value for z with P_r = .75 and T_r = .96, you will notice that the line for T_r = .95 ends well before the pressure of .75. How do you find a value for Z in this situation?
 
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How many phases do you have to deal with when Pr, Tr are less than 1.0?
 
Bystander said:
How many phases do you have to deal with when Pr, Tr are less than 1.0?
1
 
Z.PNG
 
zachdr1 said:
Why do the Tr lines stop increasing in Pr after a while?
What do you think the dashed line in the figure represents?
 
Chestermiller said:
What do you think the dashed line in the figure represents?
the psuedo reduced specific volume

edit: i just realized you meant the saturated vapor line, anything below that line isn't a saturated vapor so I am assuming you can't use Pv=ZRT?

So if I asked you what the value for Tr is at Pr= .4 and Z=.6, what would your response be? This isn't a homework question by the way I just want to know what your response would be.
 
zachdr1 said:
the psuedo reduced specific volume

edit: i just realized you meant the saturated vapor line, anything below that line isn't a saturated vapor so I am assuming you can't use Pv=ZRT?

So if I asked you what the value for Tr is at Pr= .4 and Z=.6, what would your response be? This isn't a homework question by the way I just want to know what your response would be.
0.86
 

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