Thermal and Hydraulic Behavior of Liquid Nitrogen Flow in Vertical Sections of HTS Cables

Abstract

An analytical study is conducted on the process of temperature rise and pressure drop in vertical flows of subcooled liquid nitrogen (LN). This thermal and hydraulic behavior should be carefully taken into account for the cryogenic cooling of HTS cables to be installed in underground utility tunnels including vertical sections. The gravitational effect is included in the momentum (modified Bernoulli) and energy equations to calculate the temperature and pressure distribution along ascending or descending flow of LN. In order to examine its influence on cryogenic design requirements for electrical and mechanical safety, the process is plotted on phase (pressure-temperature) diagram of LN and compared with the horizontal flow. The gravitational effect in vertical flows is significantly affected by the LN flow rate, the thermal load per unit length, and the surface roughness.