ln(Hvap/Hvapo) = a1 + åai ×Tri-1×ln(1-Tr) , where the summation is from i = 2 to nTerms -1
Tr = T/Tc, Tc is the critical temperature, and Hvapo = 1 kJ/mol
Hvap = A×{1 - ( T / Tc )}n
Hvap/R = a1×t1/3 + a2×t2/3 + a3×t + a4×t2 + a5×t6
where t = 1 - T/Tc, Tc is the critical temperature, and R is the gas constant.