1. Closed Brayton Cycle Power Conversion Design James C. Conklin 18 February 2004 conklinjc@ornl.gov

2. The Advanced High Temperature Reactor 03-239R

3. Brayton Cycles  Brief History Open cycle –G. Brayton, 1872, piston –A. Elling, 1903, gas turbine –O. von Ohain & F. Whittle, 1930’s, aircraft Closed cycle –Ackeret & Keller, 1935 2 MWe demonstration, 1939 –~20 systems built

4. Brayton Cycle Demonstrator 3-kWe, 1962

5. Experimental Split-shaft Automotive Turbomachine

6. CBC Design Outline Cycle performance –Calculate flows and state points Heat exchanger design –Pressure drop –Size, footprint Turbomachine design –Flow path –Stage design

7. Simple CBC

8. Heat Flows  Simple Cycle

9. Three Reheat-Intercooling

10. Cycle Performance Parameters Determine Performance Compressor pressure ratio Allowable pressure drop Turbomachine polytropic efficiencies Turbine inlet/compressor inlet temp ratio Recuperator effectiveness Compressor intercooling Turbine reheat

11. Simple Cycle Performance

12. Derivation of Cycle Performance Simple Cycle-I

13. Derivation of Cycle Performance Simple Cycle-II

14. Derivation of Cycle Performance Simple Cycle-III

15. Derivation of Cycle Performance Simple Cycle-IIII

16. Compressor Intercooling

17. Sample Parameter Variations- Helium

18. “Spider Plot” Shows Parameter Sensitivity

19. Working Fluid Affects Cycle Performance

20. Heat Exchanger Design Method from Kays & London

21. Ntu-effectiveness method For sizing problem with balanced flow For rating problem with balanced flow

22. Recuperator Design Requires Finned Surface Detail

23. Working Fluid, Pressure and Pressure Drop Affects Size (and Costs)

24. Turbomachinery Characteristics Choice of flow geometry, determine mass and volume flow of working fluid from cycle efficiency and state point calculations –Radial (<1 MW) –Axial (>1 MW)

25. Euler Pump/Turbine Fundamental Relationship

26. Flow and Stage Loading Coefficient Determination

27. Turbomachine Map To Determine Velocity Triangle(s)

28. Blade Speed Must Be Chosen Tip speed/sonic <1 Blade stress Generator limit –Gearbox might be necessary –Frequency conversion –Bearings

29. For constant mass flow and shaft power, annulus area varies inversely with pressure, resulting in smaller and faster machine

30. Design Trade-offs Must Be Evaluated-I Working fluid choice –Nitrogen: well-developed turbomachine infrastructure(+), higher thermal efficiency(+), large heat exchangers(-), low sonic speed(-) –Helium: turbomachine infrastructure development needed(-), larger turbomachine (-), lower efficiency(-), small heat exchangers(+), high sonic speed(+) –HeXe mixtures: Sonic speed low(-), good compromise for other parameters, but development done only for small (~100 kWe), radial flow machines.

31. Design Trade-offs Must Be Evaluated-II Pressure: High pressure generally results in smaller, but heavier equipment. Possible increase in number of stages Pressure drop: efficiency & size  as  P/P  HX effectiveness: efficiency & size  as  Intercooling and reheat: efficiency & size  as number . Increased  P/P might negate possible efficiency gain

32. References Staundt, R.L., 1987, Design Study of an MGR Direct Brayton-Cycle Power Plant, MITNPI-TR-018, The Massachusetts Institute of Technology, Cambridge, Massachusetts. Kays, W.M., and London, A.L, 1984, Compact Heat Exchangers, 3 rd Edition, McGraw Hill Pierce, B.L., 1982, “The Influence of Recent Heat Transfer Data on Gas Mixtures (He-Ar, H 2 -CO 2 ) on Closed Cycle Gas Turbines, Journal of Engineering for Power, Vol. 103, pp. 114-117 Wilson, D.G., and Korakianitis, T. 1998, The Design of High Efficiency Turbomachinery and Gas Turbines, 2 nd Edition, Prentice Hall