Experimental Investigations and Numerical Simulation of Thermal Performance of a Horizontal Slinky-Coil Ground Heat Exchanger

Abstract

Abstract:A model test system of horizontal slinky coil ground heat exchanger (HSCGHE) was established according to the similarity theory. A 2-D mathematical model of HSCGHE was built and experimentally validated. Experimental and numerical investigations of effects of different parameters on the thermal behavior of HSCGHE were undertaken. The results show that the heat release rate of the slinky coil and soil temperature around it increase as the inlet fluid temperature of coil increases. The soil temperature operated in intermittent mode can get a recovery, and thus the heat release rate of the coil can be improved effectively. For a given condition, reducing the coil central interval distance can increase the heat release rate of the HSCGHE, but also results in the decrease of the heat release rate per unit length of the coil. Therefore, the coil central interval distance cannot be decreased without limit. At the same time, the thermal performance of HSCGHE is related to the ground surface wind velocity. The heat release rate in the sandstone is the largest, followed by sand, the lowest for clay. Additionally, with the increase of buried depth of coil, the heat release rate increases, but the increase degree gradually becomes small. Thus, the buried depth cannot be too deep and should be determined by thermal performance, excavation cost and safety requirements.

Development of a Phase Change Backfill Material with High Heat Capacity and High Thermal Conductivity Used for Ground Source Heat Pumps

“…The intermittent operation mode is regarded as an effective approach to mitigate thermal imbalance risk. Zhang et al [22] conducted experimental and numerical study of thermal performance of a horizontal slinky-coil ground heat exchanger and concluded that the soil temperature operated in intermittent mode can get a recovery, and thus, the heat release rate of the coil can be improved. Wang et al [23] simulated and studied the heat exchange performance of PCM-backfilled buried pipes under intermittent operation in summer, and the results showed that the PCM with low phase change temperature could significantly improve the heat exchange rate of the buried pipes at the early stage of intermittent operation.…”

Effect of intermittent operation on the thermal efficiency of energy tunnels under varying tunnel air temperature

“…condensing temperature and evaporating temperature) can be optimised from the knowledge of the ideal IR which in turn increases the efficiency of the GSHP system [26]. The mean heat exchange rate of a GHE is higher in intermittent operation compared to continuous operation which makes it more efficient with regards to energy performance and soil temperature variation [27][28][29][30][31][32][33]. For soil with high thermal conductivity the rate of soil thermal recovery increases during intermittent operation, which improves the performance of the GHE [34].…”