Abstract
For reducing the initial GSHP investment, the heat transfer efficiency of the borehole heat exchange (BHE) system can be enhanced to reduce the number or depth of drilling. This paper proposes a novel and simple BHE design by changing the cross-sectional shape of the U-tube to increase the heat transfer efficiency of BHEs. Specifically, in this study, we (1) verified the reliability of the three-dimensional numerical model based on the thermal response test (TRT) and (2) compared the inlet and outlet temperatures of the different U-tubes at 48 h under the premise of constant leg distance and fluid area. Referent to the circular tube, the increases in the heat exchange efficiencies of the curved oval tube, flat oval tube, semicircle tube, and sector tube were 13.0%, 19.1%, 9.4%, and 14.8%, respectively. (3) The heat flux heterogeneity of the tubes on the inlet and outlet sides of the BHE, in decreasing order, is flat oval, semicircle, curved oval, sector, and circle shapes. (4) The temperature heterogeneity of the borehole wall in the BHE in decreasing order is circle, sector, curved oval, flat oval, and semicircle shapes. (5) Under the premise of maximum leg distance, referent to the heat resistance of the tube with a circle shape at 48 h, the heat exchange efficiency of the curved oval, flat oval, semicircle, and sector tubes increased 12.6%, 17.7%, 10.3%, and 7.8%, respectively. (6) We found that the adjustments of the leg distance and the tube shape affect the heat resistance by about 25% and 12%, respectively. (7) The flat-oval-shaped tube at the maximum leg distance was found to be the best tube design for BHEs.
Highlights
With increasing awareness of environmental protection and the continued development of science and technology, the world energy structure is developing toward multipolarization, from traditional fossil fuels to cleaner wind energy, water energy, tidal energy, geothermal energy, etc. [1,2,3,4,5,6]
If the soil temperature is high, geothermal energy can be converted into other forms of transportable energy, such as electricity [8]; otherwise, it can be directly used or stored, as achieved using ground source heat pump system (GSHP) [9,10]
borehole heat exchanger (BHE), the fluid temperature at the tube inlet/outlet continues increasing and gradually in reaches an equilibrium state over time, which means the heat of fluid absorbed from in out the heater and the heat released by the BHEs reaches a dynamic balance
Summary
With increasing awareness of environmental protection and the continued development of science and technology, the world energy structure is developing toward multipolarization, from traditional fossil fuels to cleaner wind energy, water energy, tidal energy, geothermal energy, etc. [1,2,3,4,5,6]. In comparison with the traditional circular buried pipe, this new type of oval buried pipe can reduce the internal heat resistance of the borehole by 0.125 m·K/W, and can increase the heat transfer efficiency of the borehole by 18.47%, which is suitable for use in high-density areas such as cities. Based on the above analysis, we employed COMSOL multi-physics to study the heat transfer characteristics of BHEs with different cross-sectional pipes (circle, curved oval, flat oval, semicircle, and sector) through three-dimensional numerical analysis. Based on the thermal response test (TRT), the rationality of the material parameters, boundary conditions, and geometric dimensions of the analysis model were verified; subsequently, under the premise of the same cross-sectional area and leg distance between pipes, the temperature at inlet and outlet, heat resistance of BHEs, heat flux distribution at inlet and outlet, and temperature distribution at borehole wall were studied. The findings in this paper are expected to support the design and improvement of GSHPs
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
