Speaker
Description
Electrified aircraft are being developed to address climate change and pollution by reducing the fuel burn and emissions of aircraft. Achieving a substantial impact necessitates focusing on single- and twin-aisle aircraft, which currently dominate world-wide emissions and contain propulsion systems with about 20+ MW ratings. Multi-MW superconducting electric machines are being developed to electrify these aircraft due to their very high specific power and, often more importantly, their very high efficiency. Most of these electric machines employ superconductors on their rotor, thereby requiring cryogenic cooling of the rotating system. An attractive solution is to conductively cool the rotor using a cryocooler that rotates with the rotor. NASA has been developing a 50 K pulse tube cryocooler for its high efficiency megawatt motor (HEMM) that can operate while rotating at 6,800 rpm. The design of this cryocooler and testing of its linear motor have been discussed in prior work [1-3].
This paper will present the first measurements of the complete HEMM cryocooler. The design and results of a stationary (non-rotating) test of the cryocooler will be described. The data will include the heat lift and coefficient of performance as a function of temperature, displacement of the piston, temperature distribution and the performance of the thermal management system, and vibration. A discussion of lessons learned in the manufacture and assembly of the cryocooler will also be presented. The primary performance data will be compared to existing predictions for the cryocooler obtained from commercial cryocooler design software and computational fluid dynamics simulations of the cryocooler’s heat exchanger. These predictions account for the measured performance of the linear motor.
The status of this work is as follows. All the fabricated parts of the cryocooler have been received. Most of those parts have been assembled to verify that the manufacturing was completed successfully. The test rig hardware has been received and assembly is underway. The linear motor has been assembled and tested, including successful operation at resonance using open loop control of the piston’s measured displacement. The remaining instrumentation will be received by end of December. The remaining tasks include completing the in-house joining of some feedthroughs and the regenerator (by end of December), assembling the remainder of the cryocooler and pressure testing it (by end of January), instrumenting the cryocooler and integrating it into the test rig (by end of February), and completing the testing (by mid-April). This leaves adequate time to prepare the presentation and secure internal approval to release it.
- Dyson, R.W. et al., “High Efficiency Megawatt Machine Rotating Cryocooler Conceptual Design,” AIAA/IEEE Electric Aircraft Technologies Symposium, Indianapolis, IN, 2019.
- Duffy, K.P. et al., “Design, Analysis, and Testing of the HEMM Cryocooler Linear Motor,” AIAA/IEEE Electric Aircraft Technologies Symposium, New Orleans, LA, 2020.
- Duffy, K.P. and Szpak, G., “Dynamic Bellows for a Pulse Tube Cryocooler Application,” AIAA SCITECH 2022 Forum, AIAA 2022-0446, San Diego, CA, 2022.
