In recent years, Borehole Heat Exchangers (BHE) are very widely utilized to extract geothermal energy for building heating. For coaxial type of BHEs, an inner pipe is installed inside of an outer pipe, allowing the downward and upward flow to be separated. In some projects, very long coaxial BHEs are installed down to a 2-km depth, in order to extract more energy from the deep subsurface (Kong et al., 2017). Based on the flow directions, there are two types of coaxial BHEs. When downward flow is located in the inner pipe, it is called Coaxial-Centred (CXC) type. On the contrary, if the inflow is introduced in the annular space, it is called a CXA type. Detailed schematization of the CXA-type BHE system is shown in Figure 1. In this benchmark, the numerical model in OGS-6 has been tested for the 2 coaxial types of BHEs. The simulation results are compared with previous OGS-5 results and also the analytical solution proposed by Beier et al. (2014).
This is a companion discussion topic for the original entry at https://www.opengeosys.org/stable/docs/benchmarks/heat-transport-bhe/3d_coaxial_deep_bhe/
