Equation of State of Octafluorocyclobutane in the Range of Operation Parameters of Power Plants operating on the Organic Rankine Cycle

The objective of the work is to construct the equation of state of octafluorocyclobutane to allow high metrological level of calculation of cycles and processes of ORC based power plants. This objective was achieved by developing an equation of state in the form of a polynomial dependence of the compressibility coefficient of the virial type on the reduced density and temperature. To construct the equation of state, experimental measurements in the superheated steam area and in the supercritical steam area were used. New experimental measurements on the density of octafluorocyclobutane are used to obtain the equation of state in the pressure range from 1 MPa up to 10 MPa and from 100°C to 450°C. The measurement uncertainty over the entire range was within 0.1–0.25%. Eleven equivalent equations of state were obtained with a mean square deviation of 0.255% in density with 25 coefficients. The most significant result is the extension of the existing database of the basic thermodynamic properties of octafluorocyclobutane what allow the use of this substance in the entire range of operation parameters of power plants. The significance of the obtained results is in the equation of state what confirmed the possibility of using the REFPROP 10.0 database outside the previously guaranteed temperature range (350°C) for calculating properties, except for heat capacities for the calculation of which a new equation of state is proposed. The experimentally justified equation of state allows to perform a design of cycles and processes of power plants based on octafluorocyclobutane