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Doctoral Degree Defense

Doctoral Degree Defense. A MINIATURE REVERSE-BRAYTON CYCLE CRYOCOOLER AND ITS KEY COMPONENTS: HIGH EFFECTIVENESS HEAT RECUPERATOR AND MINIATURE CENTRIFUGAL COMPRESSOR. Defender: Lei Zhou Advisor: Dr. Louis C. Chow Dr. Jay Kapat

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Doctoral Degree Defense

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  1. Doctoral Degree Defense A MINIATURE REVERSE-BRAYTON CYCLE CRYOCOOLER AND ITS KEY COMPONENTS: HIGH EFFECTIVENESS HEAT RECUPERATOR AND MINIATURE CENTRIFUGAL COMPRESSOR Defender: Lei Zhou Advisor: Dr. Louis C. Chow Dr. Jay Kapat Committee members: Dr. Louis C. Chow; Dr. Jay Kapat; Dr. Q. Chen; Dr. R. Chen; Dr. Larry Andrew Department of MMAE University of Central Florida NOV 10th,2003

  2. Research Background • Applications • Oxygen/Nitrogen liquefaction • Infrared image sensor array • Electronic device cooling • Out space exploration • HTS (High temperature superconductor) cooling

  3. General refrigeration cycle

  4. General COP

  5. Technology Pros Cons S High efficiency, compact Vibration, unreliable P Compact, reliable, no moving parts Efficiency lower than Stirling G Simple, reliable Bulky, gas purity sensitivity, inefficient R Compact, no vibration, efficient Moving part Major Cryogenic Technologies • Stirling machine • Pulse tube • Gifford-McMahon • RTBC (reverse Turbo-Brayton Cycle)

  6. Cycle efficiency vs. compressor electrical power Proposed miniature RTBC Courtesy of Ray Radebaugh, NIST-Boulder

  7. Cycle efficiency vs. operating temperature Proposed miniature RTBC Courtesy of Ray Radebaugh, NIST-Boulder

  8. Cryocooler Applications and Operating Regions Proposed miniature RTBC

  9. Heat exchanger to Ambient 5 Heat regenerator turbine motor 3 6 4 generator compressor 1 2 Heat Load RTBC concept COP=Heat removed from heat load end / Power input to system

  10. RTBC Mollier Diagram Heat out Work in Heat exchange Work out Heat in

  11. Miniature RTBC cryocooler • Proposed cooling power: 20Watt at 77K • Proposed COP: 0.08~0.1 • Miniature size • Miniature single stage mixed flow centrifugal compressor • Micro channel heat recuperator • Integrated high efficiency motor/alternator • Advanced air-foil bearings

  12. Advantages of miniature RTBC cryocooler • Portability • Suitable for weight/size critical applications • Simplicity • Low maintenance • Low cost

  13. Miniature cryocooler concept m mm cm m Macro scale Micro scale Meso scale   0.1kW W  10mW  Poor COP  Good COP  Best COP

  14. Thermal efficiency analysis of miniature reverse-Brayton cycle(1)

  15. Thermal efficiency analysis of miniature reverse-Brayton cycle(2)

  16. Thermal efficiency analysis of miniature reverse-Brayton cycle(3)

  17. Heat exhausted=261W 5 Heat regenerator turbine motor 3 6 4 generator compressor 1 2 Cooling Load=20W Result of thermal efficiency analysis:system parameters COP=0.083 T5=300.2K Mass flow rate=2.81g/s Eff=0.993 T4=440K T3=299.5K Pmotor=262W T6=76.0K Pressure ratio=1.75 T1=64K T2=74.4K

  18. Insulated surface d L w s d Micro-channel heat recuperator Tcold,in Thot,in Cold end Hot end

  19. Stacked multi-layer construction

  20. Y X Z d Cold Neon w d Hot Neon Physical model

  21. Hot gas node Wall Cold gas node Interface Insulation material Hot fluid Hj+1 Hj Wj Wt Wj+1 Metal Material Cj Cj+1 Cold fluid Numerical Model (1-D)

  22. Fig.5 axial heat conduction in wall Numerical simulation for single material

  23. dt VS. Length (total temperature different =220K)

  24. 1-D Numerical for two material

  25. Comparison of heat conductivity

  26. Configuration 1+1 (1mm) 10+10 (10mm) 40+40 (40mm) T(K) 3 30 120 SiO2 0.377 0.848 0.853 Metal 0.4005 0.5333 0.6198 Alternative Insulator/Metal 0.4003 0.937 0.991 Comparison of single material and two materials

  27. Conclusion of micro-channel heat recuperator design • 1-D numerical simulation is suitable for the performance estimation of the micro-channel heat recuperator • With proper parameter selection, the micro-channel heat recuperator can achieve 0.99 effectiveness at an acceptable pressure loss • For the reason of manufacturing, this heat recuperator may be constructed as many thin layers stacked together. It provides the possibility of two materials (one have high heat conductivity and another have very low heat conductivity) stacked alternatively to provide 0.99 effectiveness. • This simulation provides the guidance to select the material to manufacture the heat recuperator. LTCC may be a good candidate due to its low heat conductivity and high solidity after cured.

  28. Centrifugal compressor design • Advantages of single stage centrifugal compressor • Simplicity: only 1 moving part • Reliability (better than reciprocating compressor) • Possible high efficiency • No vibration: high revolution speed (>>100 kRPM) • Compact • Disadvantages: • Difficult design: complicated flow field • Relatively expensive: manufacturing rows of blades in small size • Low compression ratio

  29. Testing Compressor specifications • Working fluid: Nair • Operating pressure: 1 bar • Operating temperature: 300K • Mass flow rate: 4.5 g/s • Compression ratio: 1.7 • Bearing: conventional ball bearing • Driver type: direct Motor

  30. Compressor Design flow chart Basic layout design Basic thermodynamics and sizing Geometry design 1-D flow calculation 3-D CFD verification Manufacturing and testing

  31. Radial IGV • Mixed flow impeller • Axial diffuser Basic Layout Flow direction

  32. R-Z plane X-Y plane

  33. 3-D geometry design ---- hub-shroud contour (R-Z plane) Impeller hub curve Impeller shroud curve IGV shroud curve IGV hub curve

  34.  0,0 3-D geometry design ---- X-Y plane blade angle X-Y projection line of blade at shroud/hub surface Trailing edge Leading edge

  35. Geometry implementation in Pro/Engineer(1)

  36. Geometry implementation in Pro/Engineer(2)

  37. Geometry implementation in Pro/Engineer(3)

  38. Introduction of 2-zone model of impeller

  39. 3-D view of IGV

  40. 3-D view of diffuser

  41. Compressor assembly (1)

  42. Compressor assembly (2)

  43. 3-D CFD geometry# #: 3-D simulation results is provided by Xiaoyi Li

  44. 3-D results

  45. 3-D results

  46. CFD results Flow Separation inertia force and centrifugal force Suggestion reduce the length of IGV add deswirl vane

  47. Conclusion of compressor design • 2-zone model is the most powerful 1-D design tool in centrifugal compressor design. With proper mathematics and interactive program codes, 3-D geometry can be designed and then implemented with pro/engineering software • 3-D CFD simulation show the improvements should be done in next design. Mixed flow impeller with axial diffuser may have severe flow separation problem at the bending section. A deswirl vane is needed before this section • Impeller may need to be refined with inducer to reduce entrance separation.

  48. Pressure and Temperature at Inlet Compressor Testing Run set up Mass Flow Controller Power Out of Motor Motor Case Temperature Motor Bearing Temperature Pressure and Temperature after Mixer Bearing Temperature Pressure and Temperature at Diffuser Exit Motor Bearing Temperature Power In Bearing Temperature

  49. Coupler design speed: ~30,000 RPM Coupler with steel sleeve in test run ~97,000 RPM Testing assembly (coupler improvement)

  50. Testing assembly To mass flow rate meter

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