Experimental investigation of transcritical CO2 mixture power cycle with dual heat sources

Abstract

The CO₂ transcritical power cycle is a prominent technology for utilizing low- and medium-temperature heat sources. To enhance CO₂ cycle performance, CO₂ mixture working fluids are employed to address harsh operating conditions and high pressures. However, comparative experiments on the performance of different additives under various operating conditions have not been conducted. The mechanisms behind performance improvements in real-world environments remain validated. Therefore, this work conducted an experimental investigation on three additives at two mass fractions and pure CO₂. The test bench utilized two heat sources, hot water and hot air, and the selected working fluids were tested under varying maximum temperatures and pressures. The results demonstrate that the CO₂ mixture working fluids are less suitable for hot water with high specific heat and low temperature, leading to reduced heat absorption and mass flow rate. Nevertheless, the CO₂ mixture working fluids can significantly reduce condensing pressure by up to 20 % under identical condensing conditions. Compared to pure CO₂, the mixture working fluids show relative improvements of 2.45 % in maximum net power output and 19.46 % in thermal efficiency. CO₂ mixture working fluids exhibit a greater performance advantage over pure CO₂ at lower maximum pressure. Recommendations for selecting working fluid to maximize net power output are provided. This work provides operational data for CO₂ mixture working fluids in real-world environments, demonstrates their effect on the matching of heat and cold sources, verifies the potential of CO₂ mixtures to replace pure CO₂, and offers motivation for future research and component development.