Temperature distribution of long-length high temperature superconducting (HTS) cable cooled by slush-nitrogen

Abstract

A numerical model is established to calculate the temperature and pressure distribution of 3 km long high temperature superconducting (HTS) power cable. The circulating nitrogen enters the inner channel of the HTS power cable for cooling at the one end, flows to the other terminal, returns to the outlet of the outer channel, and exits from the HTS power cable. This paper considers the mass, the momentum, and the energy balance of liquid nitrogen, and the heat diffusion inside the HTS layer to obtain the realistic temperature and pressure distributions of the cable. The result shows that the inlet enthalpy of the subcooled liquid nitrogen is not sufficiently low to keep the maximum temperature of the compact HTS layer below 80 K. In addition, we found that the heat transfer between both channels are predominantly governed by the thermal conduction in the composite HTS layer not by the convective heat transfer in both channels. In order to supply nitrogen with lower enthalpy for ensuring sufficient subcooling through the whole cable region, using slush nitrogen is suggested and analyzed in the detailed numerical model. Thermo-hydraulic equations for slush nitrogen are incorporated in the numerical model. The results show that the maximum temperature of the HTS layer decreases by 6.2 K when slush nitrogen with solid volume fraction of 30% is supplied to the HTS cable. The analysis also revealed that the maximum temperature of HTS layer can be further decreased by suppressing the heat transfer between both channels. Further discussion on the effect of the inlet enthalpy of nitrogen and the heat transfer characteristics to the temperature distribution is elucidated in this paper.