Multi-physics coupling study on thermal energy storage characteristics in closed/abandoned mine shafts
ZHANG Guoqing
LIU Zhan
CHU Zhaoxiang
XI Furui
YANG Liya
HE Peng
Abstract：Repurposing closed/abandoned mine spaces for renewable energy development serves as an effective approach to achieving car-bon peaking and neutrality goals.To explore the technical feasibility of thermal energy storage in abandoned vertical shafts,this study pro-poses a cyclic water storage system based on coaxial borehole heat exchangers.A transient fluid-solid coupled heat transfer model was de-veloped to characterize thermal interactions between mine water and geotechnical materials.Numerical simulations of thermal storage characteristics were conducted on the approximately 200 m-deep auxiliary shaft of the Xuzhou Woniushan Coal Mine,with model valida-tion achieved through comparison with three experimental datasets from literature.Subsequently,parametric sensitivity analyses were per-formed to investigate the thermal insulation performance of mine water under natural cooling conditions and the operational characterist-ics under the thermal storage mode.The results indicate that during the natural cooling phase following rapid heat storage,the thermal loss of shaft mine water exhibits second-order exponential decay characteristics,with 29.73%of the cumulative 100-day heat loss concentrated within the initial 10-day period;higher geothermal gradients(≥0.03 k/m)suppress natural convection and reduce deep-layer heat loss,en-hancing thermal preservation;shaft slenderness ratio exhibits a positive correlation with short-term heat loss,yet facilitates higher average water temperatures after long-term storage,favoring geothermal recovery during heating seasons.After comprehensive consideration,a slenderness ratio of 30-50 is recommended for thermal energy storage in mine shafts.Under thermal storage mode,increasing the injec-tion flow rate can rapidly elevate mine water temperature to the desired level in the short term,but this disrupts thermal stratification,signi-ficantly reducing storage efficiency,Conversely,raising the upstream heat source temperature enhances the axial water temperature gradi-ent and storage efficiency while decreasing the ratio of heat loss,thus relatively improving thermal storage performance.Moreover,in sol-ar seasonal thermal storage systems without insulation measures on the shaft,a volume-to-collector area ratio(Rv)of 2.5 to 3.0 m3/m2 is advisable to ensure mine water temperatures meet long-term heating demands.
Keywords：abandoned minecoaxial borehole heat exchangerthermal energy storagegeothermal gradientslenderness ratio
Publication Date：2025-04-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：13( 149-161 )