Gas-phase PVT properties measurements for iso-pentane by a magnetic levitation densimeter.

Organic Rankine Cycle (ORC) is an important solution for effective use of wasted heat. Many working fluid candidates are proposed and tested for ORCs use. Most of HFCs, for example, R245fa, are nonflammable but their large GWP (global warming potential, GWP=950 for R245fa) is not environmentally acceptable. Since GWP values of hydrocarbons are negligible, they are considered to be a promising candidate of ORC working fluid. Although hydrocarbons are flammable, it seems to be possible to use them for ORC applications if appropriate safety measures are applied. Among numbers of hydrocarbons, n-pentane (C5H12, tb = 36.1 °C) is used to ORC working fluid for geothermal power plants. Iso-pentane (C5H12, tb = 27.7 °C) is also one of the possible candidate of ORC working fluid. Therefore, its thermodynamic properties were measured in the present study. Originally developed PVT measurement system using magnetic levitation densimeter (MLD) was used. The MLD is installed inside a cryostat which covers wide temperature range from 260 K to 420 K. Pressure is controlled by a variable volume vessel with metallic bellows and measured by a quartz pressure transducer having a relative uncertainty of 0.01% of its full-scale. Density can be precisely measured as a buoyancy force acting on a sinker. In the present study, a total of 13 gas-phase PVT properties were obtained at temperatures from (350 to 400) K, pressures up to 1.0 MPa.