REVERSE TURBO BRAYTON CYCLE CRYOCOOLER DEVELOPMENT FOR LIQUID HYDROGEN SYSTEMS ( (Department of Mechanical, Materials and Aerospace Engineering) Dr. Louis Chow – Project Director Dr. Jayanta Kapat – Project Co-director Drs. Q. Chen (MMAE); L. An (AMPAC); C. Ham (FSI); K. B. Sundaram (ECE), T. Wu (ECE). Partners: Dr. Neelkanth Dhere (FSEC); Dr. Nagaraj Arakere (UF); Dr. Dan Rini (Rini Technologies, Inc.); Mr. Jay Vaidya (Electrodynamics Associates, Inc.); Mr. Bill Notardonato (NASA KSC) and Mr. George Haddad (NASA KSC). 1.Project Goals 2.Importance and Benefits to NASA 3.Key Issues to be Resolved for Project Success 4.Past, Current and Future Work 5.Time Line

PROJECT GOAL TO DESIGN AND BUILD A REVERSE TURBO BRAYTON CYCLE CRYOCOOLER Affordability & Reliability High-EfficiencyCompactness Light in weight20-30 W Cooling Power at 18 K 70% 85% 90% 75% 95% GPa 55%

IMPORTANCE & BENEFITS TO NASA Motor/Compressor unit Heat regenerator, Flexible lines, Cold head Cryomech G-M Cryocooler AL330 20K) UCF Miniature RTBC Cryocooler 18K) The rest of the cryocooler Motor/Compressor unit Ceramic micro-channel heat recuperator, Cold head, Expander/Alternator kg 24 kg 10 kg 12 kgThe rest of the cryocooler kg 22 kg Total weight COP0.005COP 0.01 All of the previous attempts of flight cryocoolers have cooling capacities less than 2 W at liquid hydrogen temperature. There are commercially available cryocoolers that have higher cooling powers but their weight restricts their possible usage for in-space applications. Long term propellant storage Propellant losses Propellant management and stocking Zero Boil-Off (ZBO) Key Issue Prevention Solution The proposed design can significantly contribute to NASA efforts on densification and ZBO storage of cryogenic propellants for missions to Mars.

KEY ISSUES Miniature High-speed Centrifugal Compressor Development, High-speed, High-efficiency Motor Development, and Integration and Testing of Compressor and Motor The integrated compressor/motor is key to RTBC, and is useful for many NASA and non-NASA applications. Examples include, Durable, light-weight cryogenic (liquid hydrogen) propellant storage and feed systems for the development of Unmanned Air Vehicles (UAV) and transport aircraft and, Future aircraft propulsion systems driven by electric power, where cryogenic and non-cryogenic high power density electric motors are useful. March 2004 NASA Panel Advice: To reduce the scope and develop a much improved compressor/motor over the current state-of-the-art Development Of Gas Foil Bearing And Heat Recuperator De-scoped from the project

CURRENT WORKFUTURE WORK Design and Fabrication of Miniature Centrifugal Compressor Design, Fabrication and Testing of High-Speed, High-Efficiency PMSM PAST WORK Miniature Centrifugal Compressor Design Verification by Numerical Simulation and Testing 5. Integration and Preliminary Testing of Motor/Compressor Test Assembly kW PMSM Design 7. Two-stage Centrifugal Compressor Design Fabrication and Integration of the 5.4 kW Motor/Two-stage Compressor Assembly Overall System Optimization Design: Rotordynamic study based on the two-impeller mounted shaft structure using FEA Design: Completed test rig design with features like single rotor, spring loaded bearing, closed gas passage structure and precision impeller tip clearance control mechanism Some Parts Fabricated: Bearing Loader, Gas Passage, Inlet Guide Vane and Top Plate Design: Slotless stator and high energy density permanent magnet lead to low electrical losses and high efficiency. Cylindrical structure with a large thickness hollow shaft design optimized to provide minimal rotor imbalance and high overall structural stiffness, thereby, preventing the shaft super-critical operation.

Overall Project Schedule/Tasks List Task 1. Design and Fabrication of Miniature Centrifugal Compressor Task 2. Design of a High-speed, High-efficiency PMSM Task 3. Fabrication and Testing of PMSM Task 4. Miniature Centrifugal Compressor Design Verification by Numerical Simulation and Testing (with appropriate scaling) Task 5. Integration and Preliminary Testing of the Motor/Compressor Assembly (by December 2005) Task kW Permanent Magnet Synchronous Motor (PMSM) – Design (by August 2005) Task 7. Two-stage Centrifugal Compressor – Design (by August 2005) Task 8. Fabrication and Integration of the 5.4 kW PMSM/Two-stage Compressor Assembly Task 9. Overall System Optimization – Systematic Testing of the Motor/Compressor Assembly, Evaluation, Possible Design Changes TIME LINE Overall Project Milestones: Phase III M1 – 12/31/04: Design verification of miniature centrifugal compressor by numerical simulation and testing (with appropriate scaling) (completed) M2 – 02/28/05: Design of the motor/compressor assembly test rig (completed) M3 – 07/30/05: Fabrication and integration of the motor/compressor assembly test rig (under progress) M4 – 08/31/05: Design of the 5.4 kW PMSM (under progress) M5 – 08/31/05: Design of the two-stage 313,000-rpm centrifugal helium compressor (under progress) M6 – 12/31/05: Preliminary testing of the 2 kW motor/one-stage compressor assembly