| Citation: | LI Peng，LI Hangzhe，YANG Chao，et al. Numerical simulation on heat transfer performance of coaxical borehole heat exchanger[J]. Bulletin of Geological Science and Technology，2025，44（6）：1-11 doi: 10.19509/j.cnki.dzkq.tb20240032
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Shallow geothermal energy is a clean and stable renewable energy source. Ground-coupled heat pumps represents are a commonly used technology for developing and utilizing shallow geothermal energy in building heating and cooling systems. This technology extracts heat from the subsurface without pumping groundwater; thus causing minimal disturbance to the underground environment. The borehole heat exchanger serves as the primary component of heat exchange in ground-coupled heat pump systems, with the U-shaped configuration being the most prevalent. However, research and application of coaxial borehole heat exchangers in shallow geothermal energy remain relatively limited.
his study focuses on the shallow coaxial borehole heat exchanger and conducts numerical simulations to investigate their heat transfer performance, analyze sensitivity factors, and compare their efficiency with that of a U-shaped borehole heat exchanger.
The findings demonstrate that when traditional PE pipes are employed for both the inner and outer pipes of a coaxial borehole heat exchanger, thermal short-circuiting occurs between the annular fluid and the inner pipe fluid, resulting in a 23% reduction in heat transfer efficiency. The sensitivity factors influencing coaxial borehole heat exchangers performance are ranked as follows: Inlet temperature, initial soil temperature, circulating flow rate, thermal conductivity of casing and inner pipe materials, and thermal conductivity, backfill material. Under identical conditions, the U-shaped borehole heat exchanger exhibits an 8.57% higher heat transfer efficiency compared to coaxial borehole heat exchanges. However, when a coaxial borehole heat exchanger’s casing is constructed from steel and its inner pipe is insulated, its heat transfer efficiency exceeds that of the U-shaped borehole heat exchanger by 21.64%.
The research results can provide a reference for the research and application of shallow-buried pipe technology.
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