Molecular Dynamics Studies on Liquid-Phase Dynamics and Structures of Four Different Fluoropropenes and Their Binary Mixtures with R-32 and CO₂

Abstract

Fluoropropenes such as R-1234yf or R-1234ze(E) have attracted attention as low GWP (global warming potential) refrigerants, both as pure compounds but also to an increasing extent as components in refrigerant blends. In our earlier work [Raabe, G.; Maginn, E. J. J. Phys. Chem. B 2010, 114, 10133-10142 and Raabe, G. J. Phys. Chem. B 2012, 116, 5744-5751], we have introduced a transferable force field for different fluoropropene compounds. This molecular model has already been applied for predictive molecular simulation studies on the vapor-liquid phase equilibria in binary mixtures of the tetrafluoropropenes R-1234yf or R-1234ze(E) with the difluoromethane R-32 and CO2. In this work we present molecular dynamics simulations on the liquid phase properties of the pure fluoropropenes R-1234yf, R-1234ze, R-1234ze(E), and R-1216 and their binary mixtures with CO2 and R-32. Our study covers temperatures from 273 to 313 K, pressures up to 3.5 MPa, and different mixture compositions. We provide predictions on the densities and transport properties of the pure compounds and the binary mixtures to complement experimental data. Additionally, we have analyzed radial and spatial distribution functions in the systems to gain insight into their microscopic structures and preferred interaction sites.

Evaluation of R-1234ze(Z) as drop-in replacement for R-245fa in Organic Rankine Cycles – From thermophysical properties to cycle performance

“…In our earlier work [19], we have published predictions for the vapor pressure, saturation densities and heats of vaporization for this compound from molecular simulation studies employing our transferable force field model for fluoropropenes introduced in Ref. [22].…”

“…Fig. 3 shows a comparison of the predicted viscosities by the ECS approach in comparison with predictions from our Molecular Dynamics simulations [19] at different temperatures and p ¼ 2 MPa. Although the ECS model estimates slightly higher viscosities than our MD studies, the predictions from both approaches are generally in good agreement.…”

“…Comparison of the Tes-diagrams of R-1234ze(Z) ( ) and R-245fa (d) from REFPROP calculations. [19]) and by the ECS approach ( , [24]). Also shown are the calculated liquid viscosities of R245fa for comparison ( , [23]).…”

“…Though, their studies were based on estimated thermophysical properties due to the lack of experimental data. Since then information on the thermophysical properties for R-1234ze(Z) from both experiment [14e17] and molecular simulation [18,19] have become available, and recently also a fundamental equation of state from Akasaka et al [6]. This now allows for a detailed assessment on the performance of R-1234ze(Z) in technical applications.…”

“…Our studies thereby comprise a comparison of the thermophysical properties of R-1234ze(Z) and R245fa and resulting differences in the performance of the ORC cycle when using R-1234ze(Z) as drop-in replacement for R-245fa. As experimental information on R-1234ze(Z) only comprise data for vapor pressure and saturation densities, we complement the information on the thermophysical properties by data from our molecular simulations studies [18,19].…”