Compressibility factor for the

Notice that the shapes of the isotherms of compressibility factors for the three gases given in Figures 3-2, 3-3, and 3-4 are very similar. The realization that this is true for nearly all real gases led to the development of the Law of Corresponding States and the definition of the terms reduced temperature and reduced pressure. Reduced temperature and reduced pressure are defined as... 

Obtain the compressibility factor for the mixture. Employ Kay s method, as described in step 2 of Example 1.5. Thus Z is found to be 0.933. 

This equation can be solved straightforwardly or by trial and error. The largest real root is the compressibility factor for the vapor in this case, Z = 0.73431. 

Calculate the compressibility factor for the mixture. In a manner similar to that used in the previous problem, an expression for the fugacity coefficient in vapor mixtures can be derived from any equation of state applicable to such mixtures. If the Redlich-Kwong equation of state is used, the expression is... 

Values of the compressibility factor for the saturated vapor appear in the table. 

The qnantity of gas or vapor in a container is a function of (in descending order of importance) the container volnme, inclnding the connected piping and other nonisolated equipment, the pressure, the molecular weight of the gas or vapor, the temperature, and the compressibility factor for the gas or vapor. The following eqnation can be used with sufficient accuracy for hazards evaluations ... 

Here, Z is the compressibility factor for the mixture R, T, and P are the universal gas constant, reactor temperature, and pressure, respectively. Substituting Equations 9.5 and 9.7 into Equation 9.6 and simplifying gives... 

This permeation relationship can be used in the separation calculations for liquid mixtures by assuming that P, = Dj/zRT in the gas-phase format and all units are consistent, with the permeability incorporating the averaged or mean compressibility factor for the reject and permeate. Using the mean compressibility factor partially offsets the effect of pressure difference on the flux relationship for component /. In other words, the permeability coefficient itself can be perceived as dependent on the initial pressure P and final pressure Py and changes with the particular operating conditions. 

This procedure would define a pseudo-critical volume and temperature. However, it is more convenient to change the pseudo-critical volume variable to a pseudo-critical pressure by defining an empirical pseudo-critical compressibility factor for the mixture ... 

We plot next in Figure 8.5 the compressibility factors for the same gases, but this time versus the reduced pressure = P/Pg, and at the same value of the reduced temperature = T/T, say equal to 1.05. We notice that in this case, the points for both gases fall on the same practically curve, i.e. they have the same value of z at the same values of P and (this is why only the curve for methane is shown). We refer to fluids that are at the same P and values, i.e. at the same distance from the critical point, as being in Corresponding States. 

Pressures of the order of 1000-2000 bars are required to bring the volume of the nonelectrolyte to that of the salt at the same temperature. Figure 1 shows the compressibility factors for the salt and nonelectrolyte for the asymmetric system. The compressibility factor for the salt is about eight less than that of the nonelectrolyte for all systems and at all temperatures and volumes. This difference should now be simply related to the Coulomb field in the salt. 

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