Heat exchanger design and performance evaluation for a high-temperature heat pump system under different two-phase correlations: 4E analysis

Supplying district heat and assisting the integration of renewable electricity, high-temperature heat pump technology is foreseen to play an essential role in renewable energy-powered thermal energy storage systems. However, existing studies on high-temperature heat pump performance prediction are usually based on utilizing specific heat transfer correlations of heat exchangers. It is difficult to guide the selection and combination of the two-phase correlations in the heat exchanger design and system performance assessment of the high-temperature heat pump. In the present study, we aim to focus on the impact of different two-phase correlations, and a comparative study is conducted among 8 correlations (4 flow condensation ones and 4 flow boiling ones) adopted for component design and system performance prediction. The results show that for designed condensers or evaporators, the dimensions, costs, and carbon emissions are significantly affected by different two-phase correlations. Among 16 pairs of two-phase correlations, little fluctuation of the system performance is observed at the design heat source temperature 80 °C. While at off-design heat source temperatures of 85, 90 or 95 °C, the energetic and exergetic performance parameters are significantly affected with high relative differences (9.88% of heating capacity, 3.27% of coefficient of performance, and 6.76% of exergy efficiency). Also, the system's economic and environmental performance indexes are influenced to some extent, with visible relative uncertainties (1.91% of the heating cost, 4.44% of the payback time, and 6.38% of the carbon emission). This research will help to promote the selection and utilization of two-phase correlations for the plate heat exchanger design and system assessment in larger renewable energy-powered high-temperature heat pump applications.