Thermal characteristics in a spiral-tube buried in sand/bentonite/ graphite under cooling and heating modes

摘要

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.