Figure 4.
The image shows a scatter plot with temperature difference between inlet and undisturbed ground in degrees Celsius on the horizontal axis from 0 to 25, and heat transfer rate in watts per square metre on the vertical axis from 0 to 100. Data points are grouped by material or condition. For mudstone till, heat transfer rates increase from about 10 at 8 degrees to about 30 at 22 degrees. For sandstone, values rise from about 15 at 8 degrees to about 33 at 22 degrees. For groundwater flow, values increase from about 25 at 8 degrees to about 55 at 15 degrees. For high airflow, values increase from about 35 at 8 degrees to about 90 at 23 degrees. The image shows that higher temperature differences correspond to higher heat transfer rates, with high airflow giving the largest values.Tunnel energy per unit area for different conditions