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Thermodynamic Cycles

Thermodynamic Cycles. Carlos Silva November 18 th 2009. Thermodynamic Processes. Different Processes. Isobaric. Isometric. Isothermal Δ T = 0 but Q ≠ 0. Adiabatic Δ T ≠ 0 but Q = 0. Cyclic If clockwise – heat engine If counterclockwise – heat pump. Thermodynamic Cycles.

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Thermodynamic Cycles

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  1. Thermodynamic Cycles Carlos Silva November 18th 2009

  2. Thermodynamic Processes

  3. Different Processes Isobaric Isometric Isothermal ΔT = 0 but Q ≠ 0 Adiabatic ΔT ≠ 0 but Q = 0 Cyclic If clockwise – heat engine If counterclockwise – heat pump

  4. Thermodynamic Cycles

  5. Ideal (Carnot) Cycle • Carnot Theorem • No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between those same reservoirs Pressure-Volume Temperature-Entropy

  6. Real Cycles • There are no ideal cycles • Irreversible systems, losses of heat

  7. Types of Cycles • Heat Engine • Rankine • Gas Power Systems • Brayton • Internal Combustion Engines • Otto, Diesel,Stirling, Atckison • Refrigeration • Heat Pump • Air Conditioning

  8. HEAT ENGINE

  9. Heat Engines • Converts thermal energy (heat) to mechanical output (work) • The working fluids are gases and liquids. • Phase change cycles • The engine converts the working fluid from a gas to a liquid. • Rankine • Regenerative • Gas cycles • The working fluid is always gas • Carnot • Stirling

  10. Rankine (Classical steam engine) • Generation power plants • practical Carnot Cycle • heat addition and ejection are isobaric (and not isothermal) • Working fluid is alternatively vaporized and condensed

  11. PV vs TS diagrams

  12. Alternative Rankine cycles Super Heat Reheat Regenerative

  13. Reheat and Regenerative

  14. Efficiencies

  15. GAS power systems

  16. Brayton Cycle (Joule Cycle) • Usually used in gas turbines • Basis of jet engines

  17. Examples 1968 Howmet TX 480 MW GE unit J85 GE unit Jet Engine diagram A-37 Dragonfly

  18. Combined Cycle • Combining Rankine and Brayton cycles

  19. INTERNAL COMBUSTION

  20. Special type of heat engines • Combustion of fuel used to produce work directly • in heat engines is used to heat the fluid • the expansion of the high temperature and pressure gases, produced by the combustion, directly applies force to a movable component of the engine, such as the pistons or turbine blades and by moving it over a distance, generate useful mechanical energy • combustion is usually intermittent

  21. Otto engine • Gasoline vehicles • External ignition • Octane rating- measure of the resistance of gasoline and other fuels to detonate at constant volume. • The higher the value, the slower the fuel burns

  22. Diesel engine • Diesel cars • no external ignition • highest efficiency due to compression ration • low speed engines can exceed 50% • Diesel Cetanes • combustion quality during compression ingnition

  23. Stirling Cycle • Similar to Otto cycle • replace adiabatic per isothermals • Used in Micro CHP

  24. Atkison Cycle • four-stroke cycle to occur in a single turn of the crankshaft • designed to bypass patents covering the existing Otto cycle engines

  25. REFRIGERATION AND HEAT PUMP

  26. Vapor compression cycle • Refrigerator vapor • Freon

  27. Heat Pump • Can pump heat in two directions • reversing valve

  28. Absorption Heat Pump • Heated by gas, solar thermal, etc..

  29. Air Conditioning • Refrigerator + resistance • Heat pump

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