Gas and vapour density specific volume

For general engineering purposes it is often sufficient to consider that real gases, and vapours, behave ideally, and to use the gas law  

These equations will be sufficiently accurate up to moderate pressures, in circumstances where the value is not critical. If greater accuracy is needed, the simplest method is to modify equation 8.3 by including the compressibility factor z  

For mixtures, the pseudocritical properties of the mixture should be used to obtain the compressibility factor. 

Viscosity values will be needed for any design calculations involving the transport of fluids or heat. Values for pure substances can usually be found in the literature see Yaws (1993-1994). Liquid viscosities are given in Appendix C. Methods for the estimation of viscosity are given below. 

A rough estimate of the viscosity of a pure liquid at its boiling point can be obtained from the modified Arrhenius equation  

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