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Numerical and experimental study of transient conjugate heat transfer in helical closed‐loop geothermal heat exchangers for application of thermal energy storage in backfilled mine stopes
Author(s) -
Templeton Jeffrey D.,
GhoreishiMadiseh Seyed Ali,
Hassani Ferri P.,
Sasmito Agus P.,
Kurnia Jundika C.
Publication year - 2020
Publication title -
international journal of energy research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.808
H-Index - 95
eISSN - 1099-114X
pISSN - 0363-907X
DOI - 10.1002/er.5457
Subject(s) - heat exchanger , geothermal gradient , borehole , geothermal energy , heat transfer , thermal , geothermal heating , computer simulation , volumetric flow rate , mechanics , thermal energy storage , thermodynamics , engineering , mechanical engineering , geology , geotechnical engineering , physics , geophysics
Summary The geothermal potential available from deep underground mines has yet to be utilized. However, stope‐coupled heat exchangers (SCHE) are aiming to take advantage of the unused low‐grade geothermal energy. Backfilled stopes provide a unique opportunity to install nonlinear heat exchangers, as the geometry is not limited to the shape of a borehole. Helical pipes deliver superior fluid mixing and heat exchange compared to straight pipes, due to the effect of the secondary flow within the helical pipe. The helical closed‐loop geothermal heat exchanger enables the backfilled stopes of the mine to be repurposed as thermal energy storage units. This article delves into the experimental results from a unique state‐of‐the‐art laboratory scale helical closed‐loop heat exchanger with varying thermophysical parameters. Additionally, a novel conjugate numerical model is developed and its results are validated against the base case of the experimental studies. Additionally, the numerical model is validated in a spatial‐temporal sense with thermocouple data from the experimental rig. The numerical model is also applied to a helical SCHE situated within a backfilled stope for the first time. The results of the numerical model suggest that the pumping rate through the SCHE has a significant effect on the heat exchange rate and the overall energy transfer between the SCHE and the backfill. Additionally, the temperature contours from the numerical model suggest that a decreased pitch/helical diameter will increase the storage capacity of the helical SCHE. Overall, an average of 2.5 MW can be stored over the first 4 days of geothermal charging with the investigated full‐scale SCHE, boasting a pseudo‐steady‐state storage rate of 1.7 MW.