Technical equation of state models for heat transfer fluids made of biphenyl and diphenyl ether and their mixtures

• Technical equation of state models for heat transfer fluids were developed.
• The models are based on the iPRSV and the PC-SAFT equation of state.
• The performance of both models was assessed by comparison with experimental data.
• The accuracy of the model is satisfactory for engineering applications.

Complete thermodynamic models were developed for the estimation of thermodynamic properties of biphenyl (C12H10, CAS number 92-52-4), diphenyl ether (C12H10O, CAS number 101-84-8), and of their mixtures. These compounds are used as heat transfer fluids, both in the liquid and in the vapor phase, especially in the eutectic formulation (commercially known mainly as Therminol® VP-1 and Dowtherm® A). In particular, these fluids are adopted as thermal energy carriers in concentrated solar power plants using parabolic troughs linear concentrators. The developed models are based on the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) and on the improved PRSV (iPRSV) technical equations of state (EoS), complemented by the Wong–Sandler mixing rules. The models’ performance is discussed and their predictions compared with experimental data. It is proven that, from an engineering viewpoint, sufficiently accurate predictions can be obtained with both models. The model based on the PC-SAFT EoS is overall more accurate, but its mathematical complexity could play a significant role if computation time is an issue. On the other hand, the iPRSV-based model could be the solution of choice for applications requiring maximum computational efficiency such as, e.g., the process-level simulation of parabolic troughs solar collectors.