Generalized approach to thermodynamic cycle analysis

Engineering studies of Rankine cycle energy systems using working fluids other than water-steam are often hindered by lack of good experimental data for the thermodynamic functions (enthalpy, entropy, internal energy, specific heat) and physical properties. The use of thermodynamic functions based on generalized equations of state, along with physical properties estimation methods, is proposed and demonstrated. It is shown that they can be used to predict, with acceptable accuracy, the thermodynamic properties in a system power cycle analysis. Such an analysis requires a minimal knowledge of a fluid's physical properties. The performance of a binary power system with a Rankine bottoming cycle using various fluids is examined. The generalized approach is compared with analyses based on actual thermodynamic data. Three secondary fluids (isobutane, propane, ammonia) are compared in the High Temperature Gas-cooled Reactor Gas Turbine (HTGR--GT) binary cycle in which helium is the primary fluid. Isobutane is examined as a working fluid in several high-pressure closed-cycle geothermal power systems in which water is the primary fluid. For the HTGR--GT bottoming cycle, the calculated power outputs using the generalized approach agree to within 9 percent of those calculated using real input data; for the geothermal systems the agreement is within 15 percent