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Research Papers

New Correlations for Thermal Resistances of Vertical Single U-Tube Ground Heat Exchanger

[+] Author and Article Information
Quan Liao

Key Laboratory of Low-Grade Energy Utilization Technologies and Systems, Ministry of Education,  Chongqing University, Chongqing 400030, China;  College of Power Engineering,  Chongqing University, Chongqing 400030, China

Chao Zhou

 College of Power Engineering,  Chongqing University, Chongqing 400030, China

Wenzhi Cui

Key Laboratory of Low-Grade Energy Utilization Technologies and Systems, Ministry of Education,  Chongqing University, Chongqing 400030, China; College of Power Engineering,  Chongqing University, Chongqing 400030, China

T. C. Jen

Department of Mechanical Engineering,  University of Wisconsin-Milwaukee, Milwaukee, WI 53211

J. Thermal Sci. Eng. Appl 4(3), 031010 (Jul 17, 2012) (7 pages) doi:10.1115/1.4006516 History: Received December 22, 2011; Revised March 29, 2012; Published July 17, 2012; Online July 17, 2012

A new 2D numerical model of a single U-tube ground heat exchanger is proposed and a four-thermal-resistance model is adopted to evaluate the effective pipe-to-borehole, pipe-to-pipe, and borehole-to-borehole thermal resistances. The influence of temperature distributions on both borehole surface and outer diameter of two pipes to these thermal resistances has been thoroughly studied. The best-fit correlations of effective pipe-to-borehole, pipe-to-pipe, and borehole-to-borehole thermal resistances are proposed and compared with the available equations in the literature. It is found that the present correlations of thermal resistances for ground heat exchanger are more accurate than those of available formulas. Furthermore, based on these obtained thermal resistance correlations, an analytical model is proposed to evaluate the heat transfer performance of the ground heat changer.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of a typical single U-tube ground heat exchanger

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Figure 2

Computational domain and meshes in a new 2D model

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Figure 3

Diagram of four-thermal-resistance model within borehole

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Figure 4

Comparisons of dimensionless borehole thermal resistance between validation model and Bennet Eq. 7

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Figure 5

Nonuniform temperature distributions along the perimeter of borehole and outer diameter of pipes

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Figure 6

Comparisons of dimensionless borehole thermal resistance at θ1  = 0.375 and θ2  = 4 when σ is between −0.2 and 0.6

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Figure 7

Comparisons of dimensionless borehole thermal resistance at θ1  = 0.7 and θ2  = 4 when σ is between −0.2 and 0.6

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Figure 8

Comparisons of dimensionless borehole thermal resistance at σ = 0.1 and θ2  = 3.5 when θ1 is between 0.43 and 0.7

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Figure 9

Comparisons of dimensionless borehole thermal resistance at σ = 0.1 and θ2  = 7.0 when θ1 is between 0.25 and 0.85

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Figure 10

Comparisons of dimensionless borehole thermal resistance at σ = −0.2 and θ1  = 0.5 when θ2 is between 3.0 and 7.0

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Figure 11

Comparisons of dimensionless borehole thermal resistance at σ = 0.6 and θ1  = 0.5 when θ2 is between 3.0 and 7.0

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Figure 12

Thermal resistance network for a ground heat exchanger

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