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With a growing number of PCMs and new, suitable PCM candidates, an overview is not only important, but also increasingly complex. Classification of PCM was thus changed significantly in the past decades. A review of classification of PCMs from recent years shows that not only different classification criteria are used, but more important that they are often mixed, used inconsistently, even without a clear goal. Focusing on the main goal of current classification schemes, to give an overview of the material options for the search for new, suitable PCM candidates, including already established PCMs, a consistent classification is developed in a desktop study. For this, first, the general options for classification criteria are reviewed, and then the appropriate ones selected. Then, based on them a new, revised PCM classification is suggested. It is specifically detailed with regard to mixtures; for binary mixtures it is based on a literature review performed within the study. The result also stresses the importance of specific R&D: for pure substances the sources and the chemical modification, and for mixtures their optimization by new compositions, additives, etc. [ABSTRACT FROM AUTHOR]

In this work, the dynamic viscosity of Newtonian fluids is modeled using Eyring's theory and the residual Helmholtz free energy. In order to estimate this energy, a modified Peng-Robinson cubic equation of state is applied. The pseudo-experimental data have been obtained from two databases (DIPPR and NIST databses) most commonly used in the development of thermodynamic models, where DIPPR data are used to obtain the parameters and generalization of the model and the NIST data are used to evaluate the predictive capabilities of the generalization procedure. The adjustable parameters of the model have been determined from data in the liquid and vapor coexistence for n-alkanes and n-alcohols. Later these parameters have been generalized using simple mathematical expressions that depend on the molecular weight of each substance. The predictive capabilities of the model are evaluated in the liquid and vapor single-phases. The absolute deviations during the correlation process are below 3.27%, while in the prediction process they are below 5.60%. The generalized model is extended to binary mixtures using a simple mixture rule with one interaction parameter. The experimental data of the mixtures are obtained from different literature works and the absolute deviations are around 8.19% (without binary interaction coefficients) and 3.45% (with binary interaction coefficients). Finally, the model is compared with others in the literature using an analysis of variance in order to establish if there is a statistically significant difference between the deviations of the models used in the comparison. The statistical results show that the model developed in this work provides acceptable results. [ABSTRACT FROM AUTHOR]

A viscosity model based on the Peng-Robinson cubic equation of state is applied. The model has been used to correlate and predict viscosities of pure substances and mixtures especially in the saturation zone. The parameters of the model are generalized in terms of the molar mass. The generalized expressions are estimated by fitting the experimental data for a group of alkanes and alcohols. Average deviations between calculated values and experimental data for alkanes and alcohols are 6.26% and 7.21%. Some predictive calculations are performed for alkanes and alcohols finding average absolute deviation of 3.99% and 13.76%. To extend the model to mixtures, some binary mixtures calculations are performed using three mixing rule approaches. The results obtained with the simple, one and two interaction parameters mixing rules are 18.66%, 10.31% and 3.85%. The results indicate that the new viscosity model provides results that can be considered adequate and consistent taking in account the simplicity of the generalized expressions. [ABSTRACT FROM AUTHOR]