Table 1 Parameters in the numerical model

Borehole length

L

2600

m

Borehole diameter

2\(r_{\text{b}}\)

216

mm

Diameter of inner pipe

2\(r_{\text{i}}\)

110

mm

Wall thickness of inner pipe

\(t_{\text{i}}\)

7.34

mm

Diameter of outer pipe

2\(r_{\text{o}}\)

178

mm

Wall thickness of outer pipe

\(t_{\text{o}}\)

5.87

mm

Thermal conductivity of inner pipe wall

\(\lambda _{\text{i}}\)

0.21

W m⁻¹ K⁻¹

Thermal conductivity of outer pipe wall

\(\lambda _{\text{o}}\)

1.3

W m⁻¹ K⁻¹

Soil and rock thermal conductivity

\(\lambda _{{\text{s}}}\)

2.5

W m⁻¹ K⁻¹

Heat capacity of soil/rock

\(\rho _{\text{s}}\) \(c_{{{\text{s}}}}\)

\(2.24\times 10^{6}\)

J m⁻³ K⁻¹

Thermal conductivity of grout

\(\lambda _{\text{g}}\)

1.3

W m⁻¹ K⁻¹

Heat capacity of grout

\(\rho _{\text{g}}\) \(c_{\text{g}}\)

\(3.8\times 10^{6}\)

J m⁻³ K⁻¹

Thermal conductivity of circulating fluid

\(\lambda _{\text{r}}\)

0.59

W m⁻¹ K⁻¹

Heat capacity of circulating fluid

\(\rho _{\text{r}}c_{\text{r}}\)

\(4.19\times 10^{6}\)

J m⁻³ K⁻¹

Viscosity of circulating fluid

\(\mu _{\text{r}}\)

\(1.14\times 10^{-3}\)

kg m⁻¹ s⁻¹

Flow rate of circulating fluid

\(Q_{\text{r}}\)

\(8.33\times 10^{-3}\)

m³ s⁻¹