Thermodynamic property measurements for hydrofluorobutenes by a magnetic levitation densimeter.

Thermodynamic cycles involving a phase transition at high temperatures such as organic Rankine cycle (ORC) or high-temperature heat pump is a key technology to realize more effective use of wasted heats. In order to achieve these technologies, a new working fluids which fit an elevated temperature range are demanded. Among a number of candidate, some hydrofluoroolefins (HFOs) were chosen and studied in the present work. A newly developed PVT property measurement system was used to measure PVT properties and vapor pressures of the test fluids. A commercially available magnetic levitation densimeter by Rubotherm GmbH was employed as a density measurement device. Wide temperature and pressure range (up to 423 K and 20 MPa) was achieved by installing originally designed cryostat system. To keep good measurement performance even under high-temperatures or high-pressures, a silicon single crystal sinker was prepared. The density and the mass of the sinker was calibrated by a state-of-the-art calibration equipment. Density measurement uncertainty is not greater than (0.009 to 0.013)%, whereas temperature and pressure measurement uncertainties are 0.018 K and 2.6 kPa, respectively.