College of Energy Engineering,Xi’an University of Science and Technology
College of Architecture and Civil Engineering,Xi’anUniversity of Science and Technology
College of Science,Xi’an University of Science and Technology

Abstract:The abundant underground space created during the mining process of the deposits provides the basic condi⁃tions for the large⁃scale storage of renewable energy such as solar energy. A novel method of realizing seasonal storageof renewable energy,such as solar energy,is the construction of backfill heat exchangers (BFHEs)with a heat storage/release function by inserting ground heat exchangers into backfill bodies in mines. However,thermal interference is⁃sues can affect their storage/ release performance and should not be overlooked. In this study,the COMSOL softwarewas used to create a validated three⁃dimensional unsteady heat transfer model for a typical serpentine tube BFHEs,and the effects of tube spacing,tube diameter,backfill body’s thermal conductivity and specific heat were quantitative⁃ly investigated on the thermal interference of tube⁃to⁃tube and layer⁃to⁃layer of BFHEs using the thermal interfer⁃ence coefficient of tube⁃to⁃tube (Itub)and the thermal coefficient of layer⁃to⁃layer (Ilay),respectively. Additionally,theItub and Ilay’s sensitivities to the investigated parameters were discussed by reference to the relative sensitivity parame⁃ters. The findings indicate that the Itubpresents a decreasing and then increasing trend over time,but the overall changeis small (0.92-1.00). This reflects that the thermal interference of tube⁃to⁃tube has a minor impact on single⁃layeredserpentine BFHEs. The Ilay falls monotonically and considerably,and is lower than 0.25 and 0.49 at the end of heatstorage/ release processes,respectively. This means that the thermal interference of layer⁃to⁃layer deteriorates seriouslywith the heat storage/ release for multi⁃layered serpentine BFHEs. The sensitivity analysis reveals that Ilay is noticea⁃bly more sensitive to the investigated parameters than Itub. The sensitivities of Ilay to specific heat,tube spacing,ther⁃mal conductivity and tube diameter decrease in descending order,with the first two parameters having positive effectsand the latter two having negative effects. During the most time of heat storage/ release,the Itub is most sensitive to tubespacing. The effects of key parameters on thermal interference in BFHEs were quantified in this study,and the relativefindings provide a basis for optimizing the serpentine tube arrangement and preparing backfill materials to reduce theeffect of thermal interference.thermal interference;backfill heat exchangers;heat storage/ release;seasonal energy storage;serpentineburied tube