Pressure Drop and Heat Transfer Analysis of Long Length Internally Cooled HTS Cables

High temperature superconducting (HTS) cables, internally cooled by liquid nitrogen (LN2), are being explored for efficient power transmission. The cooling requirements of a HTS cable depend on the geometry, length, and operating current. The HTS cable at the operating temperature receives heat flux from different sources such as the leads at the ends, ac losses through superconductor and the heat-in-leak through insulation. These losses need to be accommodated by a refrigeration system at one or more locations along the length of the HTS cable. In this context, it is important to estimate the pressure drop in long length HTS cables and associated pumping power required to pump the cryogenic fluid (LN2) internally through the central channel between two terminations. In the present work, long length HTS cables based on BSSCO and YBCO tapes are considered for analysis, where the thermophysical properties of LN2 are considered to be temperature dependent. Pressure drop and heat transfer analyses are carried out for different flow rates of LN2 to obtain the friction factor, pumping power and heat transfer rate. This analysis is useful in characterizing the operating flow regime and safe operating temperature range in HTS cables.