Study of HTS Machine System Cooling With a Closed-Loop Thermosyphon: Stability of Unsteady Heat Load and Transient Conduction

Thermosyphoning (TS) is a heat exchange mechanism that uses a circulating refrigerant based on natural convection with no need for a mechanical pump. This cooling technique has been employed to circulate liquid coolant and gaseous coolant for high-temperature superconductor (HTS) rotating machine systems. These machines operate with an HTS field pole in the temperature range from 25 to 40 K, which are suitable temperatures for the survivability of HTS wires. The cryomechanical components are simple; there are a condenser, an evaporator, and adiabatic tubes located between the condenser and the evaporator. For applications to ship propulsion motors or generators of the radial gap type, the liquid/gas coolant flow along the adiabatic tube inside the rotating shaft may be considerably affected by the ship's rolling and/or pitching motion. In this work, we studied the temperature stability and heat load survivability of cryogenic TS, by constructing a 100 W @ 30 K-grade model. We investigated the temperature, thermal resistance, and heat flux, with a maximum load up to 60 W, of ground and onboard tests. The observed TS behavior indicates that there is sufficient survivability to assemble megawatt-class ship propulsion systems.