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

Abstract

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.

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