An ejector-enhanced multi-heat exchanger heat pump cycle adopting R600a/R290 mixture refrigerants: 4E assessment

Recently, the vapor compression heat pump cycle technology has demonstrated numerous advantages in drying applications. However, conventional heat pump cycles that use expansion valve throttling suffer from large throttling losses. Meanwhile, the implementation of environmental regulations has accelerated the application of environmentally friendly refrigerants. In response, this paper proposes an ejector-enhanced multi-heat exchanger heat pump cycle (EMC) utilizing low-GWP natural mixture refrigerants R600a/R290 for drying applications. Thermodynamic models are established to assess energy, exergy, economic, and environmental (4 E) performance as a foundation for evaluating EMC relative to the conventional heat pump drying cycle (CHPC). Energy analysis results indicate that EMC demonstrates significant improvements compared to CHPC under the given conditions, with a heating coefficient of performance 39.67 %–89.41 % higher and a volumetric heating capacity 32.34 %–82.99 % greater. The results of both exergy analysis and economic analysis indicate that the two cycles exhibit relatively similar performance in these aspects. Additionally, to further evaluate potential improvements in exergy and economic aspects, advanced exergy and exergoeconomic analyses are incorporated for the proposed cycle, and analysis results emphasize the compressor as a critical component due to its vital role in improving the cycle's exergy and economic performance. Furthermore, environmental analysis results show that EMC reduces CO₂ emissions by 34.29 % based on Life Cycle Climate Performance (LCCP) and exhibits minimal carbon emissions during refrigerant leakage and manufacturing stages, owing to the use of natural refrigerants R290 and R600a. Ultimately, EMC shows more significant performance improvements at higher high-temperature condenser outlet temperatures or lower high-temperature evaporator inlet temperatures, which means a promising future for EMC in heat pump drying applications.