Temperature pseudoreduced

Physical properties of gas mixtures are correlated with pseudoreduced temperature and pseudoreduced pressure in the same manner that properties of pure gases are correlated with reduced temperature and reduced pressure. 

First, calculate the pseudoreduced temperature, pseudoreduced pressure, and determine z. 

Second, calculate pseudoreduced temperature and psuedoreduced pressure. 

Notice that the minimum points of the z-factor isotherms of Figure 3-7 are rather sharp at values of pseudoreduced temperature below about 1.4. The slopes of the lines change from negative to positive rather abruptly. Equation B-20 does not predict accurately these slopes near these minima. Thus Equations B-19 and B-20 should not be used at Tpr less than 1.4 at ppr between 0.4 and 3,0 This difficulty was recognized in the preparation of Figure 6-4. At the minima, (dz/3pp,.)Tpr are zero, thus Equation 6-6 applies. The isotherms of Figure 6-4 were adjusted to pass through these points. 

The pseudoreduced temperature and pseudoreduced pressure, which replace Tr and P, are determined by... 

Examination of Figure 3-7 shows that at moderate pressure, say values of pseudoreduced pressure less than about 6.0, z-factor increases as temperature increases at constant pressure. That is, at pseudoreduced pressures less than about 6.0, the derivative of z-factor with respect to T is positive. 

At high pressure (for instance, at pseudoreduced pressures greater than about 11.0 on Figure 3-7 or Figure 3-8) z-factor decreases as temperature increases. Under these conditions, the derivative of z-factor with respect to T is negative. Thus, Equation 6-23 indicates that temperature increases as pressure decreases. 

As with single-component gases, if you know V and either T or P you can estimate the ideal pseudoreduced volume = VPj RT and use the other known reduced property to determine the unknown temperature or pressure from the compressibility chart. 

In instances where the temperature or pressure of a gas mixture is unknown, it is convenient, to avoid a trial-and-error solution using the generalized compressibility charts, to compute a pseudocritical ideal volume and a pseudoreduced ideal volume as illustrated below. Suppose we have given that the molal volume of the gas mixture in the preceding problem was 326 cm at 90.0 atm. What was the temperature ... 

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