This equation computes the acentric factor (`omega`)[1], a measure of the non-sphericity of molecules.
The acentric factor characterizes the phase of gases.
The acentric factor computed here is a function of the reduced pressure at the reduced temperature, `T_r` = 0.7.
The acentric factor, `omega`, is one of the set of state description parameters that includes: molecular weight, critical temperature, critical pressure, and critical volume.
The reduced properties of fluids are a set of state variables which are normalized by the fluid's state properties at the fluid's critical point. In this equation two reduced properties are used:
[1] Acentric factor
Source: Wikipedia
URL: https://en.wikipedia.org/wiki/Acentric_factor
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