PhD student Peter Xiao with Advisor K. Haran
Superconducting machines have great advantages in specific power in high power applications. A major challenge lies in thermal management of the rotational cryogenic region, as traditional liquid-cryogen is limited by the transfer-coupler. The Stirling-cycle cryocooler is an ideal cooling device for lightweight superconducting rotors due to its compact design. Although most components of the cryocooler are symmetrical for a balanced rotation, it is not designed for a rotational environment because of the various moving and asymmetrical internal components, including its regenerator and the passive balancer.
One of my research efforts focused on validating the cryocooler performance at high-speed rotation. A test that spun the cryocooler to 2000 rpm has been performed and has proved the functionality of the apparatus. The results from the test showed that the cooling performance did not deteriorate with the rotational motion. In contrast, the rotation slightly improved the cooling capability as the rotation enhances the air-cooling effectiveness on the heat rejector.
Another direction of my research is to improve the superconducting machine design to accommodate the cryocooler’s low cooling power. Unlike liquid cryogen which has high cooling power, a cryocooler has 16 W cooling power at 77 K. This cooling power places stringent requirements on thermal flux in the cryogenic region. A spoke suspension is proposed to replace a traditional torque tube made of solid metal. A 1:2 subscale model has been constructed and is shown in the picture.