M.I. Parra

Improving the prediction of liquid saturation densities from models based on the corresponding states principle

The liquid saturation density of pure fluids is commonly predicted using models based on the corresponding states principle. Nevertheless, it is well-known that these models are not always accurate near the triple point. In this work we use simple modifications of several of those models in order obtain good accuracy at any temperature. In particular, for each model we change a fixed coefficient to a variable coefficient, which permits the model to reproduce exactly the value of the density at the triple point. The accuracy of a model based on a scale-variable-reduced-coordinate framework, and of a new simple predictive model recently proposed by us is also checked. This latter model does not contain adjustable coefficients but only two variable coefficients that depend on the temperature and density at both the critical and the triple point. We find that a simple modification of the well-known and straightforward Rackett model gives excellent accuracy (mean average absolute deviation 0.9%) in the whole temperature range for 107 fluids of different kinds.

Prediction of the enthalpy of vapourisation for anhydrides, formates, acetates, propionates, butyrates, esters, and ethers

Four analytical correlations based on the use of the corresponding states principle were used to calculate the enthalpy of vapourisation of fluids. Three of these correlations require as inputs the critical temperature and the acentric factor. The fourth requires a molecular Lennard–Jones parameter and the acentric factor. Results for 184 polar and non-polar fluids grouped into 9 families are compared with the values accepted by the Design Institute for Physical Property (DIPPR) project. Recommendations are given for the use of each model and for the choice of the adequate model for each family of fluids.

Evaluación de Modelos de Predicción de Densidades Líquidas de Saturación de Aldehídos, Cetonas y Alcoholes

Se ha disenado un programa de ordenador que permite estudiar la validez de expresiones empiricas para predecir la densidad de liquidos saturados puros. El programa incluye una base de datos con valores aceptados de literatura a fin de comparar los calculados con los modelos. Para cada dato, el programa indica la desviacion absoluta y porcentual. Para cada fluido y para cada familia de fluidos se lista el intervalo de temperaturas y se obtienen desviaciones absolutas y porcentuales, indicando a que temperatura se produce la maxima desviacion. Ademas se generan graficas que permiten visualizar los datos junto a las predicciones de los modelos. Se ha estudiado la validez y exactitud de ocho expresiones analiticas, basadas en el principio de estados correspondientes, para predecir la densidad liquida de saturacion de aldehidos, cetonas y cuatro familias de alcoholes.