Equations of State (EOS) are semi-empirical models used to calculate the physical and transport properties of fluids, required in the design of the components in a practical system. In order to have a reliable EOS, accurate experimental fluid data is required. However, in the near-critical region, especially for newer fluids, only limited experimental data is available. In recent years, operation in this region is gaining in interest for low-temperature heat recovery applications (which can convert geothermal, solar and waste heat into electricity or useful heat). Therefore, in previous years, an experimental setup, called a flow calorimeter, has been built (see figure) in order to extend the experimental database of isobaric specific heat capacities of newer refrigerants with a low Global Warming Potential (GWP), specifically in the near-critical region. This setup has been calibrated and initial data has been collected, however, a much more vast database is required, on several refrigerants, to develop sound EOS.
The objective of this thesis is to develop reliable Equations of State for several newer low-GWP refrigerants. For this purpose, an extensive measurement campaign has to be performed on the refrigerants of interest in a large temperature and pressure range.
This project fits into the Sustainable Development Goals (SDGs) adopted by the UN. The generated data and equations will be used as property input to design correlations for heat transfer to refrigerants in the near/supercritical region. This way, heat exchangers can be designed for trans- or supercritical ORC systems which have higher efficiencies than subcritical ones, making ORCs more interesting for their application in converting heat from low-grade heat sources such as solar, geothermal and waste heat.