Thermodynamic, Economic Analysis, and Multiobjective Optimization of a Novel Transcritical CO2 Rankine Cycle with a Vortex Tube

Abstract

The transcritical CO2 (TCO2) Rankine cycle has been receiving more and more attention for the lower irreversible losses and the excellent thermophysical characters of CO2. However, it is hard to condense CO2 to liquid due to its low critical temperature (about 31°C) under ambient conditions. In this paper, a novel transcritical CO2 Rankine cycle called TCO2 is proposed, in which a vortex tube is added to condense CO2 under ambient conditions. A mathematical model is established to analyze the parametric effects on thermodynamic and economic performance based on specific equipment investment cost; the model is verified with experimental data. Nondominated sorting genetic algorithm II is used to achieve multiobjective system optimization for obtaining optimum cycle performance. Parametric analysis results show that an increase turbine inlet temperature and vortex tube outlet pressure can increase exergy efficiency. A decrease in turbine inlet pressure and turbine inlet temperature can reduce the TCO2 cycle equipment investment cost. In addition, multiobjective optimization results indicate that a conflict exists between TCO2 cycle thermodynamic and economic performance based on specific equipment investment cost.