Use the generalized compressibility chart to estimate z for Problem 5.85 Compres

Question

Use the generalized compressibility chart to estimate z for

Problem 5.85 Compressibility Factors Use the generalized compressibility chart to estimate z for a. nitrogen at -125°C and 7 MPa z= b. helium at -257°C and 9 atm Reference Materials Physical Property Tables Generalized compressibility factors (Reprinted with permission from Chemical Process Principles Charts, 2nd Edition,by O.A. Hougen, K. M Watson, and R. A. Ragatz, John Wiley & Sons, New York, 1960.) (Based on L. C.Nelson and E. F. Obert, Trans. ASME, 76, 1057(1954).) Gen sur (Based on L. C.Nelson and E. F. Obert, Trans. ASME, 76, 1057(1954).) Generalized compressibility chart, high pressures (Based on L. C. Nelson and E. F. Obert, Trans. ASME, 76, 1057(1954).)

Explanation / Answer

Calculate the reduced properties

Part a

Nitrogen

Reduced pressure Pr = P/Pc

Pc = critical pressure = 33.54 atm

P = 7 MPa x 9.86 atm/MPa = 69.08 atm

Pr = 69.08/33.54 = 2.059

Reduced temperature Tr = T/Tc

= (-125+273.15)K/126.2K

= 1.174

From the charts

Z = 0.5

Part b

Helium

Pr = P/Pc = 9/2.26 = 3.98

Tr = T/Tc = (-257+273.15)/5.19 = 3.11

Z = 1.05

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