Abstract
We report on recent efforts to develop a systematic method, based on the technique of rational approximation, for creating mathematical models of real-fluid equations of state and related properties. Equation-of-state models for real fluids are usually created by selecting a function p ∗ (T,n) that contains a set of parameters &{;γ i &}; chosen such that p ∗ (T,n) provides a good fit to the experimental data. (Here p is the pressure, T is the temperature, and n is the density.) In most cases a nonlinear least-squares numerical method is used to determine {γ i }. There are several drawbacks to this approach: (1) one has essentially to guess what p ∗ (T,n) should be; (2) the critical region is seldom fit very well; and (3) nonlinear numerical methods are time consuming and sometimes not very stable. The rational approximation approach we describe may eliminate all of these drawbacks. In particular the function p ∗ (T,n) is dictated by the data, and its numerical implementation involves only linear algorithms.
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