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Simulation of heat transfer performance using middle-deep coaxial borehole heat exchangers by FEFLOW
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Abstract: Due to its large heat transfer area and stable thermal performance,the middle-deep coaxial borehole heat exchanger (CBHE) has become one of the emerging technologies to extract geothermal energy. In this paper,a numerical modeling on a three-dimensional unsteady heat transfer model of a CBHE was conducted by using software FEFLOW,in which the model simulation was compared with the other studies and was validated with experimental data. On this basis,a further simulation was done in respect of assessing the influencing factors of thermal extraction performance and thermal influence radius of the CBHE. The results show that the outlet temperature of the heat exchanger decreases rapidly at the initial stage,and then tended to be stable; and the thermal influence radius increases with the increase of borehole depth. The heat extraction rate of the borehole increases linearly with the geothermal gradient. Rock heat capacity has limited impact on the heat extraction rate,but has a great influence on the thermal influence radius of the CBHE. When there is groundwater flow in the reservoir,the increase of groundwater velocity will result in the rise of both outlet temperature and heat extraction rate. The heat affected zone extends along with the groundwater flow direction; and its influence radius is increasing along with flow velocity. In addition,the material of the inner pipe has a significant effect on the heat loss in the pipe,so it is recommended that the material with low thermal conductivity should be used if possible.
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Figure 1. Schematic diagram of a typical CBHE system (left) and the internal structure of CBHE (right)
Figure 4. Outlet temperature and heat extraction rate varying with operation time under different geothermal gradients
Figure 6. Temperature distributions of water inside the pipe under different geothermal gradients
Figure 7. Outlet temperatures and heat extraction rate varying with operation time under different rock heat capacities
Figure 9. Temperature distributions of water inside the pipe under different rock heat capacities
Figure 10. Outlet temperature and heat extraction rate varying with operation time under different groundwater velocities
Figure 11. Temperature distributions of water inside the pipe under groundwater velocities
Figure 12. Temperature distributions of water inside the pipe under thermal conductivity of inner pipe
Figure 14. Heat affected zone of the heat exchanger at 100 m, 500 m, 1 500 m and 2 000 m (groundwater velocity is 1.16×10-6 m/s)
Table 1. Parameters of the borehole and CBHE
Parameter Unit Value Borehole diameter m 0.25 Borehole depth m 2 000 Inlet pipe diameter m 0.177 8 Inlet pipe wall thickness m 0.008 05 Inlet pipe thermal conductivity W/(m·K) 45 Outlet pipe diameter m 0.1 Outlet pipe wall thickness m 0.01 Outlet pipe thermal conductivity W/(m·K) 0.42 Grout thermal conductivity W/(m·K) 3 
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Table 2. Major parameters used for model validation
Parameter Unit Value Borehole diameter m 0.311 Borehole depth m 2 000 Inlet pipe diameter m 0.177 8 Inlet pipe wall thickness m 0.009 19 Inlet pipe thermal conductivity W/(m·K) 45 Outlet pipe diameter m 0.11 Outlet pipe wall thickness m 0.01 Outlet pipe thermal conductivity W/(m·K) 0.45 Grout thermal conductivity W/(m·K) 4
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Table 3. Parameters used in the sensitivity analysis
Parameter Unit Lower limit Base value Upper limit Inlet temperature ℃ - 4 - Discharge rate of fluid m3/h - 15 - Porosity - - 0.3 - Thermal conductivity of rock W/(m·K) - 3 - Geothermal gradient ℃/m 0.02 0.03 0.05 Rock heat capacity 106 J/(m3·K) 1.5 2.0 3.5 Groundwater velocity m/s 1.16×10-7 0 1.16×10-5
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CAI Wan-long, WANG Feng-hao, LIU Jun, et al. 2019. Experimental and numerical investigation of heat transfer performance and sustainability of deep borehole heat exchangers coupled with ground source heat pump systems. Applied Thermal Engineering, 149: 975-986. doi: 10.1016/j.applthermaleng.2018.12.094 CHEN Chao-fan, SHAO Hai-bing, Dmitri N, et al. 2019. Numerical investigation on the performance, sustainability, and efficiency of the deep borehole heat exchanger system for building heating. Geothermal Energy, 7(1): 18. doi: 10.1186/s40517-019-0133-8 CHEN Ji-liang, JIANG Fang-ming. 2015. Desi-gning multi-well layout for enhanced geo-thermal system to better exploit hot dry rock geothermal energy. Renewable Energy, 74: 37-48. doi: 10.1016/j.renene.2014.07.056 DAI Chuan-shan, LI Jia-shu, SHI Yu, et al. 2019. An experiment on heat extraction from a deep geothermal well using a downhole coaxial open loop design. Applied Energy, 252: 113447. doi: 10.1016/j.apenergy.2019.113447 DENG Jie-wen, WEI Qing-fan, ZHANG Hui, et al. 2017. On-site measurement and analysis on energy consumption and energy efficiency ratio of medium-depth geothermal heat pump systems for space heating. HVAC, 47(08): 150-154. http://en.cnki.com.cn/Article_en/CJFDTOTAL-NTKT201708029.htm Diersch HJG, Bauer D, Heidemann W, et al. 2011. Finite element modeling of borehole heat exchanger systems. Computers and Geosciences, 37(8): 1122-1135. doi: 10.1016/j.cageo.2010.08.003 Gordon D, Bolisetti T, Ting DSK, et al. 2018. Experimental and analytical investigation on pipe sizes for a coaxial borehole heat exchanger. Renewable Energy, 115: 946-953. doi: 10.1016/j.renene.2017.08.088 Huchtemann K, Müller D. 2014. Combined si-mulation of a deep ground source heat ex-changer and an office building. Building and Environment, 73: 97-105. doi: 10.1016/j.buildenv.2013.12.003 KONG Yan-long, PANG Zhong-he, SHAO Hai-bing, et al. 2014. Recent studies on hydrothermal systems in China: A review. Geothermal Energy, 2(1): 19. doi: 10.1186/s40517-014-0019-8 Kwanggeun O, Seokjae L, Sangwoo P, et al. 2019. Field experiment on heat exchange perfor-mance of various coaxial-type ground heat exchangers considering construction con-ditions. Renewable Energy, 144: 84-96. doi: 10.1016/j.renene.2018.10.078 Le LM, Larroque F, Dupuy A, et al. 2015. Ther-mal performance of a deep borehole heat exchanger: Insights from a synthetic coupled heat and flow model. Geothermics, 57: 157-172. Doi:10.1016/j.geothermics.2015.06.014 (2015). LI Peng-cheng. 2018. Research on heat transfer characteristics of casing ground heat ex-changer with medium and deep ground source heat pump. Ph.D thesis. Harbin: Harbin Institute of Technology. LIU Jun, WANG Feng-hao, CAI Wan-long, et al. 2020. Numerical investigation on the effects of geological parameters and layered subsur-face on the thermal per-formance of middle-deep borehole heat exchanger. Renewable Energy, 149: 384-399. Doi:10.1016/j.renene. 2019.11.158 (2020). LIU Qi, JIANG Si-min, PU Ye-feng, et al. 2016. Hydro-geochemical simulation of the mixing balance of exploitation and reinjection of geothermal fluid. Journal of Groundwater Science and Engineering, 4(2): 81-87. http://gwse.iheg.org.cn/en/article/id/221 Morchio S, Fossa M. 2019. Thermal modeling of deep borehole heat exchangers for geothermal applications in densely populated urban areas. Thermal Science and Engineering Progress, 13: 100363. Doi:10.1016/j.tsep.2019.100363 (2019). PANG Ai-qiang, LU Lin, CUI Ping, et al. 2019. A new analytical heat transfer model for deep borehole heat exchangers with coaxial tubes. International Journal of Heat and Mass Transfer, 141: 1056-1065. Doi:10.1016/j.ijheatmasstransfer.2019.07.041 (2019). Renaud T, Verdin P, Falcone G. 2019. Numerical simulation of a deep borehole heat exchanger in the krafla geothermal system. International Journal of Heat and Mass Transfer, 143: 118496. Doi:10.1016/j.ijheatmasstransfer.2019.118496 (2019). Sapinska-Sliwa A, Rosen MA, Gonet A, et al. 2016. Deep borehole heat exchangers-A con-ceptual and comparative review. Interna-tional Journal of Air-Conditioning and Refri-geration, 24(01): 1-15. doi: 10.1142/S2010132516300019 WANG Shu-fang, LIU Jiu-rong, SUN Ying, et al. 2018. Study on the geothermal production and reinjection mode in Xiong County. Journal of Groundwater Science and Engineering, 6(3): 178-186. doi: 10.19637/j.cnki.2305-7068.2018.03.003 WANG Zhi-hua, WANG Feng-hao, LIU Jun, et al. 2017. Field test and numerical investigation on the heat transfer characteristics and op-timal design of the heat exchangers of a deep borehole ground source heat pump system. Energy Conversion and Management, 153: 603-615. doi: 10.1016/j.enconman.2017.10.038 Zanchini E, Lazzari S, Priarone A. 2010. Improving the thermal performance of coaxial borehole heat exchangers. Energy, 35(2): 657-666. doi: 10.1016/j.energy.2009.10.038 ZHAO Fang-hua. 2018. Research on single hole heat transfer power of ground source heat pu-mp system. Journal of Groundwater Science and Engineering, 6(1): 65-70. doi: 10.19637/j.cnki.2305-7068.2018.01.008 -
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