Off-design analysis and multi-mode operation strategy for a transcritical CO2 power cycle applied to deep-sea applications

Given its efficient performance and compact design, the transcritical CO2 power cycle system demonstrates broad application prospects in powering deep-sea equipment. However, fluctuations in seawater temperature under deep-sea conditions can readily lead to operational instability and impair the system's output performance. This research constructs an off-design model of the transcritical CO2 regenerative cycle under variable cold source conditions and proposes a novel mission-demand-driven optimal operational strategy for deep-sea environments. Quantitative analysis of system performance under varying cold-source parameters reveals that the influence of seawater temperature is substantially greater than that of seawater flow rate. As cold-source conditions deteriorate, a concomitant decrease in power generation efficiency of 2.91% is observed, and the net power output drops by 0.724 MW. Furthermore, the study pinpoints the optimum working fluid flow rate for net power output maximization, which can enhance net power generation by 0.36–0.52 MW. Simultaneously, the optimal flow rate for achieving the highest power generation efficiency is determined, resulting in an efficiency improvement of 0.01%–0.15%. Based on these findings and considering the environmental characteristics of typical sea areas, an intelligent operation strategy centered on controlling pump speed to regulate working fluid flow regulation is introduced, enabling dynamic mode switching according to different task requirements. This work provides a theoretical foundation and methodological support for the optimal scheduling and stable operation of deep-sea energy systems.