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Research Papers

An Improved Thermal-Resistance-Capacitance Model for Vertical Single U-Tube Ground Heat Exchanger

[+] Author and Article Information
Quan Liao

College of Power Engineering,
Chongqing University,
Chongqing 400044, China
e-mail: QuanLiao@cqu.edu.cn

Yongxiang Fan, Xiaobo Zhu, Jintang Li

College of Power Engineering,
Chongqing University,
Chongqing 400044, China

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received December 18, 2017; final manuscript received August 11, 2018; published online October 23, 2018. Assoc. Editor: Matthew R. Jones.

J. Thermal Sci. Eng. Appl 11(1), 011016 (Oct 23, 2018) (11 pages) Paper No: TSEA-17-1492; doi: 10.1115/1.4041437 History: Received December 18, 2017; Revised August 11, 2018

Based on four-thermal-resistance-capacitance network within a borehole, an improved thermal-resistance-capacitance model (TRCM), which takes into account the effect of nonuniform temperature distribution along the borehole perimeter, is proposed for vertical single U-tube ground heat exchanger. For a given geometric and physical parameters of ground heat exchanger, the numerical simulations of the conventional TRCM based on three-thermal-resistance-capacitance network within borehole, the improved TRCM based on four-thermal-resistance-capacitance network within borehole and three-dimensional (3D) finite volume computational fluid dynamics (CFD) model by using fluent software were conducted, respectively. Through the comprehensive comparisons of simulation results between these above-mentioned three models for vertical single U-tube ground heat exchanger, it could be concluded that the proposed improved TRCM could not only provide relatively high accurate results, but also remarkably decrease the solving time as compared to the benchmark 3D finite volume CFD model. Since the proposed TRCM has better performance than the one based on three-thermal-resistance-capacitance network within borehole and 3D finite volume CFD model, a new reliable and feasible TRCM for vertical single U-tube ground heat exchanger could be available for the design and optimization of ground heat exchanger, the data interpretation of thermal response test (TRT) and other applications of ground heat exchanger in real industrial engineering.

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References

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Figures

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Fig. 1

Temperature distribution along perimeter of borehole for a vertical single U-tube ground heat exchanger on a horizontal plane [18]

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Fig. 2

Schematic diagram of vertical single U-tube ground heat exchanger

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Fig. 3

Geometric parameters of borehole for vertical single U-tube ground heat exchanger

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Fig. 4

Schematic diagram of three-thermal-resistance-capacitance network within a borehole

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Fig. 5

Horizontal thermal-resistance-capacitance network for the soil region in a conventional TRCM of ground heat exchanger

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Fig. 6

Three-thermal-resistance-capacitance series network for unit depth of ground heat exchanger at horizontal plane

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Fig. 7

Schematic diagram of conventional TRCM for vertical single U-tube ground heat exchanger

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Fig. 8

Schematic diagram of four-thermal-resistance-capacitance network within a borehole

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Fig. 9

Horizontal thermal-resistance-capacitance network for the soil region in the improved TRCM of ground heat exchanger

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Fig. 10

Four-thermal-resistance-capacitance series network for unit depth of ground heat exchanger at horizontal plane

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Fig. 11

Schematic diagram of improved TRCM for vertical single U-tube ground heat exchanger

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Fig. 12

Geometric configuration and meshes for 3D finite volume CFD model of vertical single U-tube ground heat exchanger: (a) Borehole region and (b) Soil region

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Fig. 17

Relative error of carrier fluid outlet temperature versus operation time based on the benchmark results of 3D finite volume CFD model

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Fig. 16

Comparisons of carrier fluid outlet temperature between these three models within 80 min from the beginning time

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Fig. 15

Comparisons of outlet average temperature of carrier fluid versus operation time between the CFD model and the improved TRCM

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Fig. 14

Comparisons of outlet average temperature of carrier fluid versus operation time between the CFD model and the conventional TRCM

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Fig. 13

Inlet/Outlet average temperature of carrier fluid between the 3D finite volume CFD simulation and TRT field experimental test

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Fig. 19

Comparisons of temperature distribution of carrier fluid along the depth between the improved TRCM and CFD model

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Fig. 18

Comparisons of temperature distribution of carrier fluid along the depth between the conventional TRCM and CFD model

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