Experimental investigation on performances of capillary mat heat exchangers in a thermal energy tunnel

Capillary mat heat exchangers are increasingly used in transportation energy tunnels due to their large heat transfer area, uniform temperature, etc. Thermal energy tunnel, as a new type of energy tunnel, is different from transportation energy tunnels due to its internal heat source. To examine the feasibility of applying capillary mat heat exchangers in thermal energy tunnels, heat transfer performances of them are experimentally investigated in a thermal energy tunnel using 1:1 intermittent operating mode. The results show that the higher the initial air temperature (T0) in the tunnel is, the greater is the heat transfer rate per mat area (q). As the T0 increases by 10°C, the q increases by 45.9%. The q increases with the increase of circulating water velocity (u), presenting an exponential change. When u increases up to 0.1m/s, the q tends to be stable. The lower the inlet temperature of circulating water (tin) is, the greater is the q. During the heat transfer process, the q reaches 143.09W/m2~187.22W/m2, which is much higher than that of transportation energy tunnels. The results can provide a basis for the design and application of capillary mat heat exchangers in energy tunnels with internal heat sources.