Thermal Conductivity Test of Backfilled Material in Dual-Cycle Geothermal Power Generation System

Theoretical calculations and experimental studies have shown that in dual-cycle geothermal power generation system, the thermal conductivity ¿ of backfilled material is the main factors to determine the efficiency of underground heat exchanger coil. At room temperature, it is the density p and water content ¿ of backfilled material that determine the thermal conductivity once the composition of backfilled material given. In this paper, super-absorbent polymer is mixed with the backfilled material to increase soil-water storage, thermal storage and thermal conductivity performance and better improve the efficiency of dual-cycle geothermal power generation system. The thermal conductivity of super water-absorbent polymer is measured by the transient plane source (TPS) method with the Hotdisk thermal constant analyzer. The water ratio of super water-absorbent polymer is 1:200 and the temperature in experiment is based on the actual project from 0°C to 40°C. Thermal conductivity increases with temperature increase. It is 0.6 W / m.°C at about 30°C. Then, based on calculation, the thermal conductivity of super-absorbent polymer samples mixed with original soil (quality ration 1:1000) is tested with the Hotdisk thermal constant analyzer. At 30°C , the thermal conductivity is between 0.96 W / m.°C ~ 1.45 W / m.°C. These data provide a very important theoretical basis for the application of novle backfilled materials to dual-cycle geothermal power generation system.