Question

Use the generalized compressibility chart to estimate z for

a. nitrogen at 0°C and 100 MPa

b. helium at -255°C and 250 atm

Answer 1

Determining the Z, we need Tr and Pr (reduced properties) which we look for the critical temperature and pressure. These values are tabulated for each compound.

We use the Nelson Obert Chart for high pressures. See here http://entropy.sdsu.edu/testhome/Test/solve/basics/tables-SB/tablesRG/zNO.html

a) For nitrogen:

Tc=126.19K, Pc=33.96bar, T=273K, P=1000bar

We calculate the reduced properties:

Setting theses points on the chart we read the compressibility factor on the vertical axis

Z= 2.1

b) For Helium:

Tc=5.2K, Pc=2.275bar, T=18.15K, P=253.31bar

For helium, hydrogen and neon reduced properties ared calculated using the next equation.

Setting theses points on the chart we read the compressibility factor on the vertical axis

Z= 2.2