Table 4 Influences of fracture water flow on heat transfer rate of single borehole in FN I and FN II in the case study

Sum of apertures, m

2.520

1.477

Water velocity, u, (m/s)

3 × 10^–4

7 × 10^–4

1.1 × 10^–3

3 × 10^–4

7 × 10^–4

1.1 × 10^–3

Coefficient of heat convection, h, W/(m² k)

32.77

49.54

61.92

32.77

49.54

61.92

Total heat transfer rate by convection Q_w, W

388.93

588.05

734.95

227.95

344.67

430.76

Heat transfer rate by convection per length of borehole, q_w, W/m

154.34

233.35

291.65

154.34

233.35

291.65

Heat conduction Q_b, W

5899.2

5940.92

Total heat transfer rate of a single borehole, W

6329.85

6528.97

6675.87

6127.15

6243.87

6329.96

Share of convection by fracture water in total heat transfer of single borehole

6.14%

9.01%

11.01%

3.72%

5.52%

6.81%