Thermodynamic efficiency of subcritical and transcritical power cycles utilizing selected ACZ working fluids

Abstract

An improvement of the thermodynamic efficiency of machines and devices applied for energy conversion is nowadays one of the most important research topics. Increased thermodynamic efficiency brings elevated power production with relatively lower sources/consumption, positively affecting sustainability. This paper presents the research results aimed at comparing various subcritical and transcritical power cycles, and novel results related to their thermodynamic efficiencies. Simulations were proceeded using selected wet (or ACZ type) working fluids for given maximal and minimal cycle temperatures. Three novel markers, two of them are special points (ACZ-S and ACZ-T), and the third is an efficiency characteristics band on the inlet temperature-efficiency diagram, are introduced in this study. They can provide a novel perspective on the efficiency of subcritical and transcritical power cycles with predetermined temperature ranges. Engineers and scientists may obtain the greatest efficiency of the system based on a special configuration in the architecture or an enhancement in the present thermal power plant. In specific conditions (e.g., one can find certain combinations of vapour quality and operating cycle temperature ranges), the efficiency of superheated ORC (Sup-ORC) outperforms the maximal efficiency of ORC. The Sup-ORC may perform lower efficiency than subcritical ORC towards the critical point of working fluids.