Experimental investigation on heat transfer performance and thermal stress of segment lining in a heating power energy tunnel

Energy tunnel is a tunnel that uses the positioned absorber pipes to collect heat outside or inside the tunnel. Heating power energy tunnel collects the heat emitted by the heating pipelines installed in the heating power tunnel. During the heat extraction process, the variation of tunnel air temperature may affect the heat transfer performance and bring about thermal stress of the tunnel lining. In this paper, a heating power energy tunnel with the similarity ratio of 1:5 is constructed using the shield-driven method in Beijing, and experiments are performed under different initial air temperatures in the tunnel, fluid temperatures at the inlet and fluid velocities in an intermittent operation mode. The results show that the heat flux extracted (q) ascends with increasing the tunnel initial air temperature. when the initial air temperature changed from 40 to 60 °C, the heat flux q increases by 33.3 % after 120 min operation. The thermal stress of the segment lining (σ_t) exhibits logarithmic growth with the increment of tunnel initial air temperature. Both q and σ_t show a negatively linear relationship with the inlet fluid temperature of the absorber pipe. q and σ_t also increase logarithmically with fluid velocity in the absorber pipe. Sensitivity analysis indicates that, among the three operation parameters, the variation of tunnel initial air temperature has the highest impact on q and σ_t. The results also indicate that the segment lining of the heating power energy tunnel is in safety while achieving the maximum heat flux under present test conditions. These findings are of great significance in guiding the design of energy utilization systems and tunnel linings for internal heat source energy tunnels.