Study on the mechanism of the optimal discharge pressure for a transcritical CO₂ system

The optimal discharge pressure is the essential factor affecting the operating performance of the transcritical CO₂ system. This paper presents a detailed study on the mechanism of the optimal discharge pressure from the perspective of fixed gas cooler outlet temperature and the heat transfer pinch point. The fixed gas cooler outlet temperature mainly analyzes the mechanism of the optimal discharge pressure from the enthalpy difference of isotherm in the supercritical region. The heat transfer pinch point mainly analyses the optimal discharge pressure at low inlet water temperatures, in which the subcritical region close to the critical point is considered. The effect of different parameters on optimal discharge pressure and system performance is discussed. The results indicate that the unique CO₂ physical properties and the pinch point in the gas cooler cause the optimal discharge pressure of the transcritical CO₂ system. The physical properties mainly affect the optimal discharge pressure at the high inlet water temperature, while the pinch point mainly affects the optimal discharge pressure at the low inlet water temperature. The inlet and outlet water temperatures are the most significant factors affecting the system's performance.