Investigation of the Influence of a Single Fissure on the Heat Storage/Release Characteristics of Backfill Coupled Heat Exchangers in Underground Stopes

Abstract

Abstract With the progressive depletion of shallow mineral resources and the increasing mining depth, the challenges posed by high well temperatures have become more prominent. To address this issue, both domestic and foreign research institutions have proposed a synergistic mining model that combines mineral deposits and geothermal resources. However, in deep mines, where high temperature, high stress, and high permeability pressures prevail, the long-term cyclic heat storage/release operations inevitably lead to fracture damage in the buried pipe filling body. Consequently, this damage alters the heat transfer performance of the system. This paper aims to establish a comprehensive three-dimensional mathematical model of a fissured buried tube-filler system by employing a combination of experimental tests and numerical simulations. The research focuses on the effects of fracture location, fracture width, and fracture cracking degree on various aspects, including temperature distribution, heat storage/release, outlet water temperature of the buried pipe, and the efficiency of the actual-sized buried pipe filler. Importantly, the study is conducted under the condition of no seepage flow. The results reveal several key findings. Firstly, in the case of bilateral heating, the proximity of the fissure to the heating side greatly influences the temperature distribution within the filling body, while the fissure located away from the heating side has a lesser impact. Secondly, the presence of fissures significantly hampers the heat transfer performance of the filling body. As the fissure width increases from 1mm to 10mm, the temperature drop during heat storage reaches 8.28%, and during heat release, it reaches 14.81%. Lastly, the average body temperature of the specimens decreases as the degree of cracking increases. After completing the heat release process, the average body temperature of fissure-free specimens and fully cracked specimens is recorded as 39.01°C and 35.82°C, respectively, representing a decrease of 8.17% in average body temperature.