Fluid characteristic of liquid nitrogen flowing in HTS cable

For long distance operation of High-temperature superconducting (HTS) cables, evaluations of heat transfer and fluid flow dynamics of liquid nitrogen (LN2) flowing in the HTS cable is important. However, the LN2 flow is complicated when the cable core is housed in a spiral corrugate cryostat-pipe and positioned at an eccentric position to the center of the cryostat-pipe. In this study, the effect of a configuration of a spiral corrugate cryostat-pipe on the pressure drop was evaluated using computer simulation. As a result, it was confirmed that the calculated pressure drop in the spiral corrugate pipe is 17 times larger than that in the straight pipe due to the shrinking and expanding of the LN2 flow at the concave domain. This shrinking and expanding of LN2 flow was assumed to be the flow in a gradual contraction pipe and a gradual expansion pipe respectively, so that the pressure drop was calculated by a theoretical arithmetic analysis. For verification of this calculation, the calculated value was compared with the measured value of a HTS cable system, which was constructed in NEDO project. As a result, these values were agreed well each other and it indicated that the pressure drop in the spiral corrugate pipe could be evaluated by this calculation.