Study on the thermal-mechanical properties and heat transfer characteristics of low leakage heat storage functional backfill body

The utilization of a heat storage functional backfill body to extract geothermal energy can organically combine backfill mining with geothermal resource exploitation technology, and promote the long-term sustainable development of the mining area. Based on the characteristics of heat storage backfill materials in the mine, low leakage rate stereotyped phase change material (FSPCM) was developed, and FSPCM was reused for partial backfill aggregate to prepare a low leakage rate heat storage functional backfill body (HSFBB). The mechanical and thermal properties of HSFBB mixed with different FSPCM contents were studied experimentally, and the heat-transfer characteristics of HSFBB were examined by building a phase change heat storage/release experimental platform. The results show that FSPCM has excellent heat storage performance, and the 24-h leakage rate is less than 1 %. When the FSPCM content was increased from 0 % to 25 %, the cracks of HSFBB increased gradually, and HSFBB's compressive strength dropped to 0.62 MPa from 3.92 MPa, which is a decrease of 84.2 %. The phase change cycle has little effect on the compressive strength of HSFBB with 5 %, 10 % and 15 % FSPCM content respectively. The content of FSPCM per unit volume of HSFBB is inversely proportional to thermal conductivity but proportional to specific heat capacity. The heat storage coefficient decreases with the increase of FSPCM content, but it is still in the usable range. The latent heat of HSFBB with different FSPCM content is similar. All of which are about 128 J/g. Experiments on heat storage/release reveal that latent heat and FSPCM content have a major impact on the heating of HSFBB at various sites.