Heat Exchange Effectiveness and Influence Mechanism of Coaxial Downhole in the Alpine Region of Xining City, Qinghai Province

Zhen Zhao, Xinkai Zhan, Baizhong Yan (), Guangxiong Qin and Yanbo Yu
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Zhen Zhao: Key Laboratory of Environmental Geology of Qinghai Province, Bureau of Environmental Geology Exploration of Qinghai Province, Xining 810007, China
Xinkai Zhan: School of Water Resources and Environment, Hebei GEO University, Shijiazhuang 050031, China
Baizhong Yan: Key Laboratory of Environmental Geology of Qinghai Province, Bureau of Environmental Geology Exploration of Qinghai Province, Xining 810007, China
Guangxiong Qin: Key Laboratory of Environmental Geology of Qinghai Province, Bureau of Environmental Geology Exploration of Qinghai Province, Xining 810007, China
Yanbo Yu: School of Water Resources and Environment, Hebei GEO University, Shijiazhuang 050031, China

Energies, 2025, vol. 18, issue 16, 1-25

Abstract: To enhance the development efficiency of medium–deep geothermal resources in cold regions, this study focuses on a coaxial borehole heat exchanger (CBHE) located in Dapuzi Town, Xining City, Qinghai Province. Based on field-scale heat exchange experiments, a three-dimensional numerical model of the CBHE was developed using COMSOL Multiphysics 6.2, incorporating both conductive heat transfer in the surrounding geological formation and convective heat transfer within the wellbore. The model was calibrated and validated against measured data. On this basis, the effects of wellhead injection flow rate, injection temperature, and the thermal conductivity of the inner pipe on heat exchange performance were systematically analyzed. The results show that in cold regions with high altitudes (2000–3000 m) and medium–deep low-temperature geothermal reservoirs (68.8 °C), using a coaxial heat exchange system for space heating delivers good heat extraction performance, with a maximum average power output of 282.37 kW. Among the parameters, the injection flow rate has the most significant impact on heat extraction. When the flow rate increases from 10 m 3 /h to 30 m 3 /h, the heat extraction power increases by 57.58%. An increase in injection temperature helps suppress thermal short-circuiting and improves the effluent temperature, but excessively high temperatures lead to a decline in heat extraction. Additionally, increasing the thermal conductivity of the inner pipe significantly intensifies thermal short-circuiting and reduces overall heat exchange capacity. Under constant reservoir conditions, the thermal influence radius expands with both depth and operating time, reaching a maximum of 10.04 m by the end of the heating period. For the CBHE system in Dapuzi, maintaining an injection flow rate of 20–25 m 3 /h and an injection temperature of approximately 20 °C can achieve an optimal balance between effluent temperature and heat extraction.

Keywords: geothermal energy; coaxial borehole heat exchange; heat extraction performance; thermal short-circuiting effect (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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