Thermal Conductivity of Pure Fluids and Multicomponent Mixtures Using Residual Entropy Scaling with PC-SAFT—Application to Refrigerant Blends

Abstract

The statistical associating fluid theory (SAFT) was used to predict the thermal conductivity of multicomponent mixtures, through the concept of residual entropy scaling. The concept suggests that the transport properties of fluid, when reduced using an appropriate reference, can solely be described through a monovariant dependence on residual entropy. The thermal conductivity of an ideal gas mixture based on the Chapman and Cowling approximation with a Mason and Saxena mixing rule, was used as a reference for entropy scaling. The proposed model was applied to fully predict the thermal conductivity of refrigerant blends containing hydrocarbons, hydrofluorocarbons, hydrofluoroolefins, and carbon dioxide. The model showed good agreement with experimental data, as well as with predictions made by the extended corresponding state approach. In general, the absolute average deviation scored by the model was below 10% for all considered mixtures. However, a crossover term within the SAFT framework will be required to properly capture the enhancement in thermal conductivity near the critical point. Article pubs.acs.org/jced

Entropy Scaling of Thermal Conductivity: Application to Refrigerants and Their Mixtures

“…The relative deviations of the experimental values from both models are illustrated in Figure . We could potentially compare with the other RES approaches such as those proposed by Fouad or Liu et al. ; however, these models use either the PC-SAFT EoS or CPA EoS to calculate residual entropy, the implementations of which are not available to us.…”

“…1,32 The enhancement is significant and even relatively far from the critical point. 33 None of the previously published RES approaches [13][14][15][16]31 for thermal conductivity take the critical enhancement into account, while this research will be the first one to do so.…”

“…A reliable model able to accurately predict the thermal conductivity of fluids, especially the newly commercialized pure refrigerants and their mixtures, would significantly push forward the application of new refrigerants in the industry. Many thermal conductivity models have been proposed, including empirical thermal conductivity correlations for refrigerants, , hard-sphere schemes, − the extended corresponding states (ECS) model, , other corresponding state methods, , and residual entropy scaling (RES) approaches. − Among these methods, the RES approach has attracted increasing attention in recent years because, according to the RES approach, the dependence of thermal conductivity on the thermodynamic state (typically dependent on temperature and density for pure fluids) is reduced to a univariate function of residual entropy in a wide temperature and pressure range. Since only one variable is required, compared to other models, far fewer experimental data points are needed to obtain the parameter(s) of the RES model for a pure fluid, and ideally, no additional fitted parameters (apart from those required in the equation of state, EoS) are needed for mixtures.…”

“…The RES approach was originally developed by Rosenfeld in the 1970s. It is a hypothesis based on the analysis of hard spheres and inverse-power-law potentials in the liquid phase and was investigated by isomorph theory in recent years. − This approach has been verified for the viscosity of the Lennard-Jones fluid and hundreds of real fluids (hydrocarbons, − refrigerants, − and other commonly used fluids , ) but only verified for thermal conductivity of a few real fluids. − , Compared to viscosity, the major challenge in modeling thermal conductivity is that the critical enhancement, which arises from the long-range density fluctuations that occur in a fluid near its critical point, is significant in a much wider window in temperature and density. , The enhancement is significant and even relatively far from the critical point . None of the previously published RES approaches − , for thermal conductivity take the critical enhancement into account, while this research will be the first one to do so.…”

“…18−22 This approach has been verified for the viscosity of the Lennard-Jones fluid 12 and hundreds of real fluids (hydrocarbons, 23−25 refrigerants, 26−28 and other commonly used fluids 29,30 ) but only verified for thermal conductivity of a few real fluids. [13][14][15][16]31 Compared to viscosity, the major challenge in modeling thermal conductivity is that the critical enhancement, which arises from the long-range density fluctuations that occur in a fluid near its critical point, is significant in a much wider window in temperature and density. 1,32 The enhancement is significant and even relatively far from the critical point.…”