Entropy and entransy analyses and optimizations of the Rankine cycle

The Rankine cycle has been widely used in industry, and the optimization of the Rankine cycle is of great significance to energy utilization improvement. In this paper, both the concepts of entropy generation and entransy loss are applied to analyzing the thermodynamic processes of the Rankine cycle that receives heat from the exhaust-heat boiler with a hot stream and releases heat to a cold stream. In order to get the maximum output power, the mass flow rate of the working medium is optimized. Theoretical analysis and numerical results show that both the maximum entransy loss rate and the minimum entropy generation rate correspond to the maximum output power when the inlet temperatures and the heat capacity flow rates of the streams are prescribed. When the inlet temperatures or the heat capacity flow rates of the streams is not prescribed, smaller entropy generation rate does not lead to larger output power but larger entransy loss rate still leads to larger power output for this kind of cases.

► Entransy loss is applied to optimizing the Rankine cycle.
► Larger entransy loss leads to larger power output for the cycle.
► The concept of entransy dissipation cannot be used to optimize the cycle.
► Smaller entropy generation does not always leads to larger power output.