ABSTRACT Thermal characteristics in a vertical spiral-tube ground heat exchanger were addressed. The influences of backfill materials (sand/bentonite/graphite blend) and operation modes were examined. In the heating and cooling modes with Reynolds number of 2500, the integrated evaluation factors of tube in blend rose all by about 20% compared with in sand. The longer recovery time was helpful to improve the heat transfer of ground tube. In cooling mode, the surface heat transfer coefficients, ranged from 225 to 610 W m−2 K−1. The average surface heat transfer coefficient under heating mode was 11 percent higher than that in cooling mode.

中文翻译：

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埋在沙子/膨润土/石墨中的螺旋管在冷却和加热模式下的热特性

摘要 解决了立式螺旋管地埋式换热器的热特性。检查了回填材料（砂/膨润土/石墨混合物）和操作模式的影响。在雷诺数为2500的加热和冷却模式下，混合管的综合评价系数比砂管提高了20%左右。较长的恢复时间有利于改善地管的传热。在冷却模式下，表面传热系数范围为 225 至 610 W m-2 K-1。加热模式下的平均表面传热系数比冷却模式高11%。