## 5 Conclusions  
In this paper, a new ORC installation, for low grade waste heat conversion to produce low power, has been experimentally studied. The interest in this installation results from its high compactness (0.25 m\({}^{3}\)), the different low-GWP working fluids used, and the performances achieved during the experimental tests. The pure fluid designed for the ORC, NovecTM649, and the zeotropic mixture, composed of NovecTM649 and HFE7000 in respective mass proportions of 80% and 20%, are both environmentally friendly fluids with a null Ozone Depletion Potential and a low Global Warming Potential. These fluids are, therefore, expected to be potential candidates to substitute for fluids traditionally used in ORCs, such as R-134a and R-245 fa. Regarding the ORC system, its compactness leads to interesting possibilities to implement this machine in residential and transport areas.  
This study presents the results of comparative experimental tests in the mixture and the pure fluid for the investigated ORC and the analysis of these results replaced in the available literature.  
With respect to the expansion element, the results obtained in pure NovecTM649 highlight the proper functioning of the specific axial micro-turbine. Regarding those obtained with the zeotropic mixture, the turbine is not mechanically impacted and operates approximately with the same performance as pure fluid. The slight decrease in the component efficiency comes from the lower thermodynamic properties of the HFE7000, the second pure fluid in the mixture. For the same power production range and heat source temperature, in comparison to the classical scroll expander technology, this turbine is very effective.  
The overall performances of this installation, at its optimal operating point, classify this ORC using the pure fluid and even more the zeotropic mixture as a high-performance low-power installation, compared to the literature available for low-temperature heat recovery. Hence, these fluids are definitely interesting and may efficiently replace fluids that will soon be banned in current installations. In addition, the use of a zeotropic mixture as a working fluid within an ORC can be a very useful parameter for the system's adjustment. Indeed, it is possible to improve the overall efficiency of the installation, according to the desired electricity requirements, by optimizing the use of the heat source. The results obtained show that, for power production needs in the range of 0-0.6 kW, the use of the zeotropic mixture fulfills the electrical needs and allows for the heat source's better utilization, as demonstrated with the corresponding 10% higher thermal efficiency values than the pure fluid values.  
Tests are currently underway on the ORC facility to complete the experimental study of this zeotropic mixture for other fluid mass proportions. The agreement in evolution temperatures between the sink source and the condensing glide, and the assumption underlying the highest zeotropic performances, will be deeply screened in future experimental investigations for the corresponding highest operating points.  
Conceptualization, Q.B., N.T., N.C., and N.V.; methodology, Q.B. and N.T.; software, Q.B.; validation, Q.B.; formal analysis, Q.B.; investigation, Q.B.; resources, N.T.; data curation, N.T.; writing--original draft preparation, Q.B.; writing--review and editing, Q.B., N.T., N.C., and N.V.; visualization, Q.B.; supervision, N.T. and N.C.; project administration, N.T.; funding acquisition, N.T. and N.C.  
This research was funded by the French Alternative Energies and Atomic Energy Commission.  
The authors would like to express their gratitude to the French Alternative Energies and Atomic Energy Commission and the Carnot Energies of the Future Institute.  
The authors declare no conflict of interest.