Impact of volumetric system design on compressor inlet conditions in supercritical CO2 cycles

The paper aims to improve the understanding of the dependency of compressor inlet conditions close to the critical point in supercritical CO2 (sCO2 ) cycles on different volumetric cycle designs. The compressor inlet conditions are fixed by the specific static outlet enthalpy of the main cooler and the static pressure determined by the mass of CO2 in the closed cycle. While in a previous study the authors analyzed effects on the compressor inlet conditions with respect to the specific static enthalpy in the pseudocritical region for constant inlet pressure, this paper focuses on the influence of the volume of the heater and cooler. The analysis is based on experimental observations from two different experimental sCO2 cycles, the SUSEN loop and the HeRo loop. The change of compressor inlet pressure upon change of the cooling power is substantially different and caused by the different volumetric design of the cycles. A simple model based on the volumes of the hot and cold sections in the cycle is developed to understand the dependency of compressor inlet conditions on the volumetric design. In terms of the volumetric design of the cycle, the paper will improve the knowledge of the challenges in stable compressor operation close to the critical point.