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

In summary, when using the compressibility chart to find a value for Z, if the temperature line you are trying to use ends before reaching the desired pressure, you cannot use Pv=ZRT. Additionally, when dealing with Pr and Tr values less than 1, there is only one phase to consider. The dashed line in the figure represents the pseudo reduced specific volume. If asked for the value of Tr at Pr=.4 and Z=.6, the response would be 0.86.
  • #1
zachdr1
91
0
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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  • #2
How many phases do you have to deal with when Pr, Tr are less than 1.0?
 
  • #3
Bystander said:
How many phases do you have to deal with when Pr, Tr are less than 1.0?
1
 
  • #4
Z.PNG
 
  • #5
  • #6
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?
 
  • #7
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.
 
  • #8
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
 

1. How does a compressibility chart work?

A compressibility chart is a graphical representation of the relationship between the pressure and volume of a gas at a constant temperature. It shows the compressibility factor, which is the ratio of the actual volume of a gas to its ideal volume. The chart is based on the ideal gas law and can be used to determine the behavior of a gas under different pressure and temperature conditions.

2. What is the purpose of using a compressibility chart?

The main purpose of using a compressibility chart is to predict the behavior of a gas at different pressure and temperature conditions. It is a useful tool for engineers and scientists in various industries, including chemical, oil and gas, and aerospace, as it helps in designing and optimizing processes and systems involving gases.

3. How do you read a compressibility chart?

To read a compressibility chart, you first need to determine the pressure and temperature of the gas you are interested in. Then, locate the corresponding point on the chart and read the compressibility factor. The closer the value is to 1, the more ideal the gas behaves. You can also use the chart to calculate other properties, such as density and specific volume, using the given relationships.

4. Can a compressibility chart be used for all gases?

No, a compressibility chart is only applicable for ideal gases, which follow the ideal gas law. Real gases, on the other hand, deviate from this law at high pressures and low temperatures. However, there are modified versions of the chart that can be used for non-ideal gases, such as the Lee-Kesler chart for hydrocarbons.

5. How accurate is a compressibility chart?

The accuracy of a compressibility chart depends on the accuracy of the data used to create it. Most charts are based on experimental data and have a high level of accuracy for ideal gases. However, for non-ideal gases, the accuracy may vary. It is always recommended to use multiple sources and charts to ensure the most accurate results.

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