Experiment of heat transfer performance of spiral pile foundation heat exchanger in ground-source heat pump system

Experimentally studies the influences of spiral forms and flow velocity on the heat transfer performance of the heat exchangers. The results show that different pitches lead to different thermal resistances, the smaller the pitch is, the greater the thermal resistance is. The thermal resistance of single-spiral type is 34.58% smaller than that of tri-spiral, and the thermal resistance of double-spiral type is 25.71%smaller than that of tri-spiral. The larger the flow velocity in pipe is, the smaller the thermal resistance is, for single-spiral type, the thermal resistance under the velocity of 0.8 m/s is 3% and 9% smaller than that under the velocity of 0.6 m/s and 0.4 m/s respectively. When the flow in pipe is turbulent, the velocity has less impact on the heat exchange per unit pipe length.