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1. Two engineers are discussing if typical 100 psig compressed air used in a pne

ID: 1778785 • Letter: 1

Question

1. Two engineers are discussing if typical 100 psig compressed air used in a pneumatic driven and controlled manufacturing operation can be considered an ideal gas and, therefore, allows them to use the ideal gas law. You can assist them by referencing the compressibility factor “Z”. Use the compressibility factor Z and the information from Figure A-1 (of our course textbook) to quantitatively and computationally justify if the 100 psig shop air can, or cannot, be considered an ideal gas. (Recall that for many applications values of “Z” within the range of 0.97 to 1.03 could easily allow the use of the ideal gas law with few problems and little error.)

T5.00 3.00 1.00 1.40 1.30 120 1.15 0.90 0.80 0.85Y 0.90 90 0.70 0.95 10L 0.60 a. 0.50 0.40 0.30 0.0 0.1 0.3 0.5 Reduced pressure, pA 0.2 0.4 0.6 0.7 0.8 0.9 1.0 Figure A-1 Generalized compressibility chart, pR S 1.o. Source: E. F. Obert, Concepts of Thermodynamics, McGraw-Hill, New York, 1960.

Explanation / Answer

Pressure, P=100 psig= 114.69 psia= 790759.714 Pa = 7.804 atm

taking T=25 C= 298K

Pc=37.25 atm; Tc= 132.41 K

Pr = 7.804/37.25=0.209

Tr= 298/132.41=2.25

from graph value of Z is approx 0.98 or 0.99 which is well within range

hence air can be considered ideal gas