Correlation of latent heats of vaporization

Abstract

Generalized equations for vapor pressure and PVT behavior are used to develop a functional relationship between latent heat of vaporization and reduced temperature and pressure.This function leads to a graphical correlation which utilizes the slope M of the vapor-pressure curve at the critical point. The correlation gives the latent heat of vaporization at any temperature in the two-phase region for any substance for which the critical point and one vaporpressure point are known. The correlation i s particularly useful for prediction of latent heat of vaporization near the critical point by the use of information far removed from the critical. fncluded in the study are polar, nonpolar, organic, inorganic, and metallic substances. General predictions of latent heat as a function of temperature are within a few percent wherever comparisons can be made with experimental data.The prediction of latent heats of vaporization has been the objective of many investigations. Shenvood and Reid ( 1 ) and Fishtine (2, 3) present excellent summaries of previous work in this area. Only three correlations most closely related to the method developed in this paper will be mentioned. Meissner ( 4 ) presented a graphical representation of AHJT, as a function of the reduced temperature and pressure. Watson ( 5 ) developed an exponential expression to predict the latent heat of vaporization of any temperature if the latent heat at one temperature and the critical temperature of the substance are known. Su (6) proposed a correlation for latent heat of vaporization based on a reference state. He suggested the use of a generalized vapor-pressure plot of log P, vs. 1/T, to give the ratio of the latent heat at any temperature to that at the reference point.

Equations of State—applied Thermodynamics Symposium

“…Its parameter is the key to the PVT behavior along the critical isometric, it shows how the complete vapor pressure curve of any substance is determined from one vapor pressure point and the critical point, and it is the basis of one of the more precise generalized correlations of latent heat of vaporization (22).…”

Revisiting the Clausius/Clapeyron Equation and the Cause of Linearity

“…This is further emphasized by the Watson plot in Figures 6 and 7. In a Watson plot, we find that ln ∆H vap /R versus ln(1 − T r ) yields a straight line [15][16][17]. In Figure 6 we consider the case of ln ∆H vap /(R∆Z vap ) and ln ∆H vap /R (where ∆Z vap = 1) versus ln(1 − T r ).…”

“…Therefore, ∆Z vap decreases with increasing temperature. Likewise, ∆H vap is not constant as evident by the Watson equation typically introduced in the undergraduate curriculum [15][16][17]. Below the critical point ∆H vap > 0, and at the critical point ∆H vap → 0.…”

Revisiting the Clausius/Clapeyron Equation and the Cause of Linearity

“…6 and 7. In a Watson plot, we find that ln ∆H vap /R versus ln (1 − T r ) yields a straight line [15][16][17]. In fig.…”