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Thermal Test and Modeling Analysis of Buried Pipe Borehole With Barite Powder Backfill
In order to study the effect of backpacking containing barite powder on the heat transfer efficiency of buried pipe borehole in mountainous and plain areas of Beijing, comparative analysis of laboratory experiments and field thermal response experiments were carried out. The quaternary boreholes in plain area were backfilled with medium sand and the bedrock boreholes in mountainous area were backfilled with cement mortar. Laboratory experiments showed that the thermal conductivity of medium sand backfill increased gradually with the increase of barite powder content, and the thermal conductivity increased by 0.037 W/m•K for every 1% increase of barite powder content from 1% to 10%. When the specific gravity of barite powder was 5%, the thermal conductivity of medium sand backfill samples was increased by about 14%. When 5% barite powder was added into cement mortar, the thermal conductivity was increased from 1.76W /m•K to 1.89W /m•K with an improvement ratio of 7.3%. According to the field thermal response test results, under summer conditions in the same site, the heat transfer rate of backfilling borehole containing barite powder increased by 2.4W/m and 3.5% per meter compared with that of medium-sand backfilling borehole in plain area. The heat transfer rate of cement mortar backfill containing barite powder was increased by 2.7W/m and 3.9% per meter. The numerical simulation model of quaternary system and bedrock area was established. It was found that the content of barite powder was increased to 10% and the heat transfer rate of boreholes was increased by about 5.5%. In general, the heat transfer capacity of buried pipe is improved and its sustainability is better after adding barite powder.