An ultra-high-temperature heat pump with multiple liquid separation condensation and ejector-assisted multi-pressure evaporation for large temperature lifts

Developing ultra-high-temperature heat pumps (UHTHPs) is a crucial pathway to decarbonize industrial heat supply. However, conventional UHTHPs suffer from significant irreversibility under large temperature lift, primarily due to inadequate temperature matching during the heat exchange process. In this study, leveraging a zeotropic mixture and incorporating the multi-temperature heat exchange concept, an ultra-high-temperature heat pump with multiple liquid separation condensation and ejector-assisted multi-pressure evaporation (LEUHTHP) is proposed. A mathematical model is developed and validated, and the baseline UHTHP (BUHTHP) is compared with three LEUHTHP configurations (LEUHTHP-I, LEUHTHP-II and LEUHTHP-III). Parametric analysis and performance optimization are further conducted under varying operating conditions. The results show that LEUHTHP-III achieves the highest coefficient of performance of 3.14, which is 22.7% higher than BUHTHP. The exergy efficiency improves by 11.89% to 17.09%, demonstrating substantially reduced irreversible losses. Increasing the regulation stage effectively enhances temperature matching in the condensation and evaporation processes. However, the improvement gradually diminishes as regulation stage increases, indicating a clear marginal utility effect. LEUHTHP-III outperforms BUHTHP in economic and environmental performance as well, reducing life cycle cost by 8.03% to 20.25% and life cycle climate performance by 46.29% to 52.54%. Performance optimization results suggest that a lower regulation stage is preferable for small temperature variations of the heat source and heat sink, whereas a higher regulation stage becomes advantageous as the temperature variations increase.