The Miller function, a sensitivity test for equations of state and theoretical vapor pressure data

For non-quantum fluids, the Miller function, h(T)=Tln(p/pc)/(T-Tc)h(T)=Tln(p/pc)/(T-Tc), with TcTc and pcpc the temperature and pressure at the critical point, presents a minimum in the liquid-vapor coexistence curve. By analyzing values from a NIST program for 105 fluids, we find that the temperature, TMTM, of this minimum is closely correlated with the normal boiling temperature, TbTb, and with the critical temperature of the fluid. We also demonstrate that the value of the minimum, hM=h(TM)hM=h(TM), is well correlated with the acentric factor. We show that the Miller function can be used as a powerful tool for checking vapor pressure values obtained from equations of state or from vapor pressure equations, especially near the critical point.

► The Miller function h   is a powerful tool for checking vapor pressure data.
► The Miller temperature TMTM has close correlations with Tc and Tb.
► The minimum value of the Miller function is well correlated with the acentric factor.
► h has the same critical behavior than the second derivative of vapor pressure.