A. Introduction

It is increasingly the case that engineers have to design and operate plants involving pure fluid substances and mixtures for which the required thermophysical properties are essentially unknown. The direct experimental investigation of such properties would involve undue expense and delay. Accordingly one must have recourse to estimated data. It is the purpose of this series of sections to present critically assessed methods for the estimation of thermophysical properties and to recommend appropriate procedures for their reliable use. The series start with the estimation of the critical properties.

Critical properties of fluids are of greatest importance and are often required in corresponding states correlations to estimate other properties such as heat capacity, enthalpy, density, viscosity and thermal conductivity. For engineering applications and in the absence of experimental data reliable estimates of physical properties are required. We present below estimation techniques for the calculation of the critical constants and the acentric factor of fluids. The acentric factor is an important property which is often used as a third parameter in corresponding states methods. Estimation methods are usually developed in particular units, not always in the recommended SI units. Care is therefore taken to specify the units of interest associated with each estimation technique. The accuracy of each technique is also quoted wherever possible.

B. Critical Temperature

(a) Fedors method