Design and development of an apparatus for evaluating multi-layer insulation effectiveness

Abstract

The development of the cryogen-free ultra-high field superconducting (CRUISE) motor presents a significant advancement in electric propulsion technology. This is especially true for high power density applications such as aircraft propulsion. The CRUISE motor aims to achieve a rated power of 10 MW with a specific energy density of 40 kW/kg and an efficiency of 99.4 %, outperforming existing motor technologies. A key component of the CRUISE motor is the cryogenic low-loss rotor, cooled by a rotor-mounted cryocooler which can maintain the superconducting coils at 50  K. Given the limited cooling power capacity of cryocoolers, the total rotor loss must remain below 10 W, necessitating the use of a highly efficient radiation shield. In this study, a carefully designed and accurate experimental setup that directly measures small heat inputs was developed to characterize the thermal performance of multi-layer insulation (MLI) thermal shields under controlled cryogenic conditions of 50 K and above. Interleaved MLI samples with different layer numbers were tested and evaluated. By reducing parasitic heat losses, this apparatus enabled highly accurate assessment of MLI performance, underscoring the importance of layer density, compression, and fabrication quality in minimizing thermal conductance. The findings reveal that while uncompressed MLI systems meet the stringent thermal management requirements of the CRUISE motor, operational compression significantly impacts their thermal conductance. The study further validates the developed models and identifies opportunities for optimizing MLI layer alignment, spacer design, and resilience to compression, paving the way for more efficient thermal management in a variety of applications.