A study on the performance of a geothermal heat exchanger under coupled heat conduction and groundwater advection

Fan, Rui; Jiang, Yiqiang; Yao, Yihao; Deng, Shiming; Ma, Zhiyong

doi:10.1016/j.energy.2007.05.001

Cited by 198 publications

(60 citation statements)

References 5 publications

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“…Water content of the soil around the pile can also impact heat exchanger pile operation as the thermal conductivity is strongly influenced by the degree of saturation. Fan et al (2007) showed that the degree of soil saturation and ground water flow influence the heat transfer between a heat exchanger pile and the surrounding soil.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Friction Induced Thermo-Mechanical Stresses on a Heat Exchanger Pile in Isothermal Soil

2014

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In most analytical and numerical models of heat exchanger piles, strain incompatibilities between the soil and the pile are neglected, and axial stresses imposed by temperature changes within the pile are attributed to the thermal elongation and shortening of the pile. These models incorporate thermo-hydro-mechanical couplings in the soil and within the pile foundation, but usually neglect thermomechanical couplings between the two media. Previous studies assume that the stress changes imposed by temperature variations in a heat exchanger pile are mainly due to the constrained thermal elongation and shortening of the pile. Also, several recent approaches utilize spring models that focus only on the soil-pile interface in modeling temperature-induced stresses in a heat exchanger pile and implicitly ignore the effect of the full displacement field on soil-pile interaction. By contrast, in this paper, interface elements are introduced in a numerical model of a heat exchanger pile, analyzed in axisymmetric and stationary conditions. The pile is subjected to a uniform temperature increase, with free top and fixed top conditions in elastic and elasto-plastic soil profiles. Simulation results show that the constrained vertical elongation is the most detrimental factor for pile foundation performance. However it is worth noticing that while mechanical constraints (e.g., fixed top and/or fixed bottom) impose maximum stress increases at the ends of the pile, interface effects result in maximum stresses around the mid-length of the pile. This preliminary study indicates that soil-pile friction does not increase pile internal stresses to the point where it would be necessary to over-dimension the foundation pile for heat exchanger use. Furthermore, one cannot expect a significant gain in foundation performance due to the improvement of soil-pile frictional resistance as a result of increased lateral stresses at soil-pile contact. Additional numerical analyses are ongoing, in order to investigate the role of the degree of fixity induced by the building on the heat exchanger pile, and to extend these preliminary analyses to transient operational modes and cyclic thermo-mechanical loading of the heat exchanger pile.

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Section: Introductionmentioning

confidence: 99%

Analysis of Friction Induced Thermo-Mechanical Stresses on a Heat Exchanger Pile in Isothermal Soil

2014

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“…Also, most of previous studies derived conclusions based on the simulation results for BTES systems without considering the effects of regional groundwater flow (Lee and Jeong, 2008;Lee, 2008). It has been well known that the groundwater flow would have a significant impact on the heat transfer (Nagano et al, 2002;Fan et al, 2007). The present work extends previously reported researches on ATES systems to open BTES systems under various ground properties and operation parameters which are key factors influencing long-time performance of BTES systems.…”

Section: Introductionmentioning

confidence: 69%

Simulation on the cyclic operation of an open borehole thermal energy storage system under regional groundwater flow

Lee

2010

Geosci J

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Coupled hydrogeological-thermal simulation is performed to analyze the effect of the configuration of boreholes and operation schedule on the performance of the borehole thermal energy storage (BTES) system. This paper presents numerical investigations and thermohydraulic evaluation on the cyclic flow regime operation of open borehole thermal energy storage system under the effects of regional groundwater flow. A three-dimensional numerical model for groundwater flow and heat transport in the ground is used to determine the annual variation of recovery temperature from the thermal energy storage. The model includes the effects of convective and conductive heat transfer, heat loss to the adjacent confining strata, and hydraulic anisotropy. The operation scenario consists of cyclic injection and recovery after holding interval and four periods per year to simulate the seasonal temperature conditions. For different parameters of the system, performances were compared in terms of the variation of extraction temperature. The calculated water temperature at the producing pipe remains relatively constant within a certain range throughout the simulation period. Heat loss, injection/production rate, aquifer thickness, and permeability ratio used in the model are shown to impact the predicted temperature profiles at each stage and the recovery water temperature. The influence of pressure gradient, which determines the direction and velocity of regional groundwater flow, is substantial for all cases considered.

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“…A simulation model, proposed by Zarrella et al, successfully takes the thermal short-circuit process of PGHE and the difference of thermal properties between pile and ground into consideration [16,17], but also fail to consider the influence of groundwater flow. However, many researchers point out that the groundwater flow do enhance the heat transfer performance of GHEs [18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Numerical and analytical analysis of groundwater influence on the pile geothermal heat exchanger with cast-in spiral coils

Wang

Zhang

et al. 2015

Applied Energy

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A study on the performance of a geothermal heat exchanger under coupled heat conduction and groundwater advection

Cited by 198 publications

References 5 publications

Analysis of Friction Induced Thermo-Mechanical Stresses on a Heat Exchanger Pile in Isothermal Soil

Analysis of Friction Induced Thermo-Mechanical Stresses on a Heat Exchanger Pile in Isothermal Soil

Simulation on the cyclic operation of an open borehole thermal energy storage system under regional groundwater flow

Numerical and analytical analysis of groundwater influence on the pile geothermal heat exchanger with cast-in spiral coils

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