A Robust, High-Efficiency Turboexpander for Long-Life Cryocoolers

Cryogenic cooling objectives for space applications require reduced size, weight, and input power; longer life and increased reliability; and increased net cooling load. The Reverse-Brayton expander cycle has the potential to meet all these objectives. Previous efforts to implement this cycle for long-life cryocoolers utilized "room temperature" tilting pad bearings. The warm bearings provided a negative impact to the turboexpander and the overall cryocooler efficiency. Follow-on efforts to implement tilting-pad bearings operating from room-temperature down to cryogenic temperatures have been unsuccessful. A novel design for a robust, high-efficiency cryocooler turboexpander which will operate in environments from room temperature to cryogenic temperatures is proposed. This turboexpander will incorporate actively-controlled, tilting-pad bearings which AFAB is developing outside of this program. This turboexpander has the potential to improve overall efficiency by 50 percent over existing warm bearing supported turboexpanders. Additionally, the all-cryogenic turboexpander eliminates the need for thermal isolation hardware between the bearing compartment and turbine. This also reduces turbine overhang for greatly improved rotordynamics, reduced vibration, and increased structural integrity of the housings. During Phase I, we will design the turboexpander components (less bearings); conduct detailed flow, thermal, and structural analysis; and generate an assembly layout drawing of the resulting turboexpander. Benefits: These turboexpanders will improve the efficiency and reliability of cryocoolers. These next generation cryocoolers can be utilized to improve refrigerators for medical MRI units and cryogenic liquifiers.|