Experimental Comparative Study of an ORC Using Pure Fluid and Zeotropic Mixture for Waste Heat Recovery

orc2019 Tracking Number 46

The energy sector is facing major challenges in the upcoming century as energy demand is rising and its major impact on the global warming issue needs to be addressed. Among the solutions to overcome these challenges, renewable energies and process energy efficiency could be partially fulfilled by the use of the Organic Rankine Cycle (ORC) technology [1]. A previous study [2] with a compact ORC (0.25m3) has shown good performances of the system and the pure fluid used. This working fluid (NovecTM649) is confirmed as an interesting replacement fluid. In this study, the ORC performances with a zeotropic mixture (NovecTM649/HFE-7000) are investigated. The heat source of the system simulates a low grade waste heat recovery at 110°C. The experimental results are compared with the precedent pure fluid results for the same ORC. Thermodynamic analysis issued from the experimental data are carried out with EES software [3] coupled with REFPROP software [4] for the pure fluid and mixture thermophysical properties. As a preliminary investigation of this zeotropic mixture, the global performances of the system and the expansion component are screened and compared. The aim is to understand how the ORC operation is impacted by this “non-design fluid”. Indeed, the installation and all the components were originally designed to work with the pure fluid (NovecTM649). Such as the expander, a high speed micro turbine, which was specifically designed with this pure fluid. During experiments, the expander behaviours and performances from a qualitative point of view are similar for the mixture or the pure fluid as working fluids. At equivalent power production, the use of this zeotropic mixture leads to a significant increasing of the energetic and exergetic efficiencies. These results show that a zeotropic mixture could be an interesting adaptation parameter for an existing ORC to make an optimal utilisation of the available heat source.