Experimental research on the performance of geothermal heat exchangers for different backfill materials

Makes an experiment on the heat transfer performance of double U-shaped geothermal heat exchangers(GHE) under the backfill materials of fine sand and medium-coarse sand, and obtains the variation curve of the underground heat transfer rate with the average in-tube fluid temperature. Experimental results show that there is a linear relationship between the underground heat transfer rate and the average fluid temperature. Within the normal operation temperature range of GHE, the underground heat transfer rate for fine sand is 10% for heat injection mode  and 6% for heat extraction mode  higher than that of medium-coarse sand. Suggests that selection of the backfill materials should base on both its influences on the heat transfer performance of GHE and its economic efficiency.