(156e) Thermophysical, Interfacial and Transport Properties of Low Global Warming Potential Refrigerants from Molecular Theory and Simulations

The Kigali´s amendment to the Montreal’s Protocol limits the use of hydrofluorocarbons (HFCs) as refrigerants, starting by 2019. This has promoted an active area of research towards the development of low Global Warming Potential (GWP) new refrigerants as well as their implementation in the corresponding applications. Hydrofluoroolefins (HFOs) have been proposed as an environmentally friendlier alternative to third generation HFC refrigerants, but further work on fully characterizing them, and their blends with other compounds, is still required to fully assess their performance to replace the ones in current use. In this work we have used the Statistical Associating Fluid Theory (SAFT) coupled with the Density Gradient Theory (DGT) and Rosenfeld's excess entropy scaling approach to predict the phase behavior, thermophysical, interfacial [1,2] and transport properties of refrigerant blends [3]. Molecular dynamics simulations have also been carried out for a further understanding of the molecular phenomena leading to the macroscopic behavior at selected conditions. We will present and discuss new results concerning third and fourth generation blends containing difluoromethane (R-32) for low to medium temperature refrigeration as well as other alternative attractive blends. Results show that binary mixtures of R-32 with propane (R-290), n-butane (R-600), isobutane (R-600a), trifluoroethane (R-143a) and pentafluoroethane (R-125) exhibit azeotropic phase behaviors at the bulk. The latter prevents any temperature glide across the refrigeration cycle, making it more efficient. In addition, mixtures with n-alkanes also exhibit an aneotropic behavior at the interface where the surface tension demonstrates a strong non-linear dependence on concentration. Molecular dynamic simulations allowed gaining molecular insight of the effect of the interactions at the aneotrope and validating density profiles predicted by the molecular theory. Regarding the transport properties calculations, parameters needed for the excess entropy scaling approach were fitted to saturated viscosity and thermal conductivity data for each of the pure refrigerants and used to predict properties up to high temperatures and pressures in excellent agreement with experimental data. The parameters were then utilized to fully predict transport properties of mixtures under consideration without the need of any extra binary interaction parameter. Mixtures predicted in this work include R-452B and R-454B as low GWP alternative HFO blends for R-32. The obtained results reinforce the validity of using molecular modeling and computational tools for addressing industrial needs, designing and optimizing the corresponding products and processes.

[1] WA Fouad, LF Vega, PCCP 19 (13), 8977-8988 (2017)

[2] WA Fouad, LF Vega, AIChE Journal 64 (1), 250-262 (2018)

[3] WA Fouad, LF Vega, J. Supercritical Fluids 131, 106-116 (2018)