Transient heat transfer performance of a vertical double U-tube borehole heat exchanger under different operation conditions

Zhu, Li; Chen, Sarula; Yang, Yang; Sun, Yong

doi:10.1016/j.renene.2018.07.073

Cited by 36 publications

(10 citation statements)

References 43 publications

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“…They estimated an optimal length for the heat capacity of the heat pump to enhance the performance of the system. A transient thermal performance of a vertical double U-tube borehole heat exchanger was numerically studied by Zhu et al (2019). They examined a ground heat exchanger at water velocity range of 0.1 m/s and 0.5 m/s.…”

Section: Introductionmentioning

confidence: 99%

A Perspective Model for Borehole Thermal Resistance Prediction of a Vertical U-Tube in Geothermal Heat Source

Tarrad¹

2020

AJTE

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The present work describes a mathematical model to postulate a short cut method for the preliminary thermal design of a ground single U-tube heat exchanger. A one-dimensional steady state heat transfer mode was assumed to derive a correlation for the borehole thermal resistance to heat transfer process. The model has considered the transformation of the U-tube system into a concentric single equivalent straight tube. Its diameter was estimated from the mutual interaction between fixed volume and fixed surface area models for the treatment of U-tube and equivalent tube geometry configurations. Three Copper single U-tubes of outside diameters, 12.7 mm, 15.88 mm and 19.05 mm with tube spacing of 42 mm, 55.6 mm and 67 mm respectively were utilized to build the heat exchangers. These borehole geometry configurations were investigated as direct exchange condensers circulating R-410A at a grout thermal conductivity range of (0.73-1.9) W/m.K. The results showed that the filling thermal conductivity has a vital role in the borehole thermal performance and heat transfer rate to or from the ground source. The specific total thermal resistance of the investigated configurations was halved when the grout thermal conductivity was increased from 0.73 W/m.K to 1.9 W/m.K. The present correlation was compared with other published models in the open literature and showed an excellent agreement.

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Section: Introductionmentioning

confidence: 99%

A Perspective Model for Borehole Thermal Resistance Prediction of a Vertical U-Tube in Geothermal Heat Source

Tarrad¹

2020

AJTE

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“…Heat exchange tubes are typically composed of high-density polyethylene (HDPE) [14] and are usually arranged in a U-shape in the borehole. The length of BHEs [15,16] is generally between 50 and 200 m (100 m is more common), and the diameter of the borehole is generally between 90 and 250 mm (150 mm is more common). Compared with the traditional cooling or heating method, the ground source heat pump provides economic benefits.…”

Section: Introductionmentioning

confidence: 99%

Thermo-Hydraulic Performance of U-Tube Borehole Heat Exchanger with Different Cross-Sections

et al. 2021

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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.

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“…The BHE has different types including U-shaped, double U-shaped, W-shaped, spiral-shaped, and coaxial [9][10][11]. Focus on the coaxial deep borehole heat exchanger, numerous researches have been conducted recently.…”

Section: Introductionmentioning

confidence: 99%

Performance analysis of a residential heating system using borehole heat exchanger coupled with solar assisted PV/T heat pump

et al. 2020

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Borehole heat exchanger (BHE) is a promising method for extracting heat from the deep geothermal energy which has been widely used for residential heating in high latitude areas. The solar assisted photovoltaic/thermal (PV/T) heat pump could convert solar energy into useful heat efficiently, and could be further used to heat water from the BHE to a higher temperature level. In this paper, a residential heating system using BHE coupled with solar assisted PV/T heat pump is therefore proposed with further performance analysis. The simulation results show that a larger mass flow rate could increase the BHE's heat extract capacity but also increase the flow resistance and pump power under nominal conditions. The circulating water would not extract heat from rock-soil if the inlet temperature exceeds 48.5 ℃ when mass flow rate is 12 kg/s. Furthermore, the maximum water temperature from this hybrid system could reach 40.8 ℃ while the solar fraction is 67.5% when the area of PV/T module is 1000 m 2 , solar irradiation is 600 W/m 2 and depth of the BHE is 2500 m. In the meantime, the heating COP of this hybrid system could reach 7.4 and the system could operate independently without power input from electrical grid.

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Transient heat transfer performance of a vertical double U-tube borehole heat exchanger under different operation conditions

Cited by 36 publications

References 43 publications

A Perspective Model for Borehole Thermal Resistance Prediction of a Vertical U-Tube in Geothermal Heat Source

A Perspective Model for Borehole Thermal Resistance Prediction of a Vertical U-Tube in Geothermal Heat Source

Thermo-Hydraulic Performance of U-Tube Borehole Heat Exchanger with Different Cross-Sections

Performance analysis of a residential heating system using borehole heat exchanger coupled with solar assisted PV/T heat pump

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