1. Chapter 8. Production of Power from Heat 고려대학교 화공생명 공학과

2. Introduction Production of Power –Energy from the sun : Photovoltaric cells –Kinetic Energy from atmospheric wind : windmills – Fossil fuels, atomic fuels Chemical Energy  Heat  Power (Electrical Work) Efficiencies are low (35 – 50 %) –Fuel cell Chemical Energy  Power (Electrical Work) Greater efficiency (85 %)

3. Use of Fossil fuels Steam Power Plant : Fossil fuel and nuclear Internal combustion engines –Otto engines –Diesel engines –Gas turbine –Jet engines

4. 8.1 Steam Power Plant

5. Diagram of a real power plant

7. Steam Plant…

9. Carnot cycle Efficiency increases as T H increases T C decreases T S 12 3 4 THTH TCTC Vaporization process in the boiler Reversible, adiabatic expansion of saturated vapor into two-phase Condensation Isentropic compression

10. Rankine Cycle Several steps are almost impossible for practical reasons –2  3 : Steams with liquid content causes erosion problems in turbine blades –4  1 : Pumping of gas-liquid mixture is difficult

12. Rankine Cycle : alternative standard for power plant Two modification from Carnot cycle –1  2 : Heating beyond vaporization –3  4 : Complete Condensation T S 2 1 34 Heating of subcooled liquid (const P) Vaporization at const T and P Superheating Expansion (reduced moisture contents) Condensation Pumping of sat. liquid to boiler temperature Real path due to irreversibility

13. The Regenerative Cycles Higher efficiencies –Increased Boiler Temperature  Increased Boiler Pressure  Increased cost for construction –Lower condenser temperature  Lower condenser presure Stagewise preheating the feed water can improve efficiencies

14. Schematic Diagram of Regenerative Steam Plant

15. 8.2 Internal – Combustion Engines Characterisitcs of Steam Power Plant –Large heat transfer surfaces –Thick walls to to withstand high T,P impose a limit on heat absorption. –Complicated structure Characteristics of Internal-Combustion Engines –Combustion are carried out within engine –Complex thermodynamic analysis –No working fluid undergoes a cyclic process

16. The Otto Engine No working fluid undergoes cyclic process –An imaginary cyclic engine with air as working fluid – Equivalent in performance to actual engine

17. Otto Engine Cycle Pressure Volume Air / fuel mixture fed into the engine Air / fuel mixture are compressed by the piston Combustion of fuel : So rapid so that the volume remains const. Adiabatic expansion Valve opened and exhaust gas vented Piston pushes remaining exhasut gases 0 1 2 3 4

18. Thermodynamic Analysis of Otto Engine Increasing the compression ration is to increase the efficiency of engine. (Proof ?) Using idealized Otto engine A B C D P V

19. Otto Engine- Analysis R increases : efficiency increases

20. Diesel Engine Difference from Otto Engine –Compression is high, combustion is initiated spontaneously –High compression ratio, high efficiency A B C D V P

21. The Gas Turbine Engine Gas Turbine Engine –Advantage of high T and P for internal combustion engine –Advantage of using turbine rather than reciprocating engine

22. Gas-Turbine Engine Adiabatic compression Combustion Expansion Cooling (Back to original state)

23. 8.3 Jet Engines, Rocket Engines Turbojet Engine / Power Plant

24. Aircraft jet engines Liquid-Fuel Rocket Engine