Experimental investigation of heat migration in biochar-biopolymer-based thermal backfill material

Abstract

Thermal backfill is required to maintain the appropriate temperature around underground thermally activated structures (TAS) to increase their thermal insulation performance. Biochar is a porous carbon-rich material with exceptional thermal insulation properties and a high degree of carbon stability in soil, making it appropriate to use as a thermal backfill. Therefore, this research work investigates heat transfer in soil-biochar composite (SBC) and soil-biochar-biopolymer composite (SBPC) as thermal backfill material. The thermal insulation potential of SBC and SBPC was examined by fabricating a soil column with highly plastic silty soil, sugarcane bagasse biochar, and hardwood biochar. To prepare samples, the soil is amended with 5 % and 15 % biochar (w/w) and (0.5 %, w/w) biopolymer. For heat transfer investigation, a heater rod was inserted into the center of the soil column, with temperature sensors installed at various radial distances of 25, 50, 75, 100, and 125 mm from the heater rod. Further, the spatio-temporal variations were recorded for two cycles of heating and ambient cooling. The results revealed that both SBC and SBPC exhibit lower temperatures than virgin soil throughout all radial distances and time during the 1st and 2nd heating and ambient cooling cycles. The maximum temperature difference between virgin soil and SBC varies from 4 °C (at 125 mm) to 20 °C (at 25 mm), depending upon the distance from the heater rod. The finding of this study established the SBC and SBPC can be efficiently used as thermal backfill to mitigate heat transfer from TAS.