Nelson and Obert charts

For reduced pressures over 0.15, the Nelson and Obert chart for 0 < < 1 still appears to be quite accurate, except... 

Calculate the reduced temperature, reduced pressure, and reduced volume, and to use any two of these parameters to obtain the compressibility factor, z, from the Nelson and Obert charts. 

Calculate the ideal critical volume and ideal reduced volume, and be able to use V - as a parameter in the Nelson and Obert charts. 

Viswanath and Su compared the z factors from the Nelson and Obert charts, the Lydersen-Greenkorn-Hougen charts, and the two-parameter Tr and p ... 

However, this problem cannot be worked exactly the same way as the preceding problem because we do not know the pressure of the O2 in the tank. Thus we need to use the other parameter, Fr, that is available on the Nelson and Obert charts. We first calculate... 

Vcj = RTJPc- It can be used to calculate which is a parameter on the Nelson and Obert charts. 

Possibly the most widely employed charts are those of Nelson and Obert [7,2]. These contain graphs of Z as a function of reduced pressure, Py, and reduced temperature, Ty, for 0 < Py < 0.1 and 0.6 < T,- < 2.0 as a small-scale (1x1 in.) inset for 0 < P,. < 1, 0.6 < Ty < 5.0 and for larger ranges. No saturation-boundary curves are given, and the small-scale in.set is difficult to use. In general applications, the author has found the need for a low-pressure/low-temperature chart of "readable accuracy" with an indicated saturation boundary.. Also, some of (he Nelson/Oberl data may not be accurate. 

The gas-phase density is the reciprocal of the molar volume, pv = 1/K, and hence can be estimated from any equation of state, for example, the Redlich-Kwong equation (1949), Kunte and Doraiswamy s (1958) plots of reduced density as a function of P, and provide a quick and reasonably accurate method of estimating vapor density. From our point of view, the most useful are the charts developed by Nelson and Obert (1954) in which the compressibility factor Z defined as Z = PV/R T is plotted as a function of P for various values of based on experimental data for a number of compounds. Then the density may be calculated from... 

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