ME200 - Lecture 34

ME200 - Lecture 34 - 1 Ideal Rankine Cycle ME 200...

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Unformatted text preview: 11/16/2010 1 Ideal Rankine Cycle ME 200 Thermodynamics I Purdue University , Dr. Tim Pourpoint – [email protected] Lecture 33 November 17 th , 2010 • Last Lecture: – Heat transfer and work during a reversible, steady process Outline – Difference between Pdv (related to closed system) and vdP (related to open system) work – Strategies to minimize either work output in multi stage turbines (heating the working substance between successive stages) or work input in multi ‐ stage compressors (cooling the working substance between successive stages) • Today: ME 200 ME 200 2 – Ideal Rankine Cycle • Next week: – Exam #3 this evening from 8 to 9pm in WTHR 200 – Covers lectures 1 to 32, emphasis on 2 nd law – Solve SP32 BEFORE the exam , there will be an isentropic efficiency problem 11/16/2010 2 Vapor Power Cycle • Goal: To generate electricity from heat input ME 200 ME 200 3 • Heat Input Sources: – Fossil fuels (oil, coal, natural gas) – Nuclear fission – Geothermal Continue Vapor Power Cycle – Solar radiation – Garbage/Trash • Cycle Working Fluid: – Water/Steam ME 200 ME 200 4 • Environmental Issues: – Air pollution – Thermal pollution – Waste products – Safety 11/16/2010 3 • Question: What is the upper limit of vapor power cycle performance? • Answer: Continue Vapor Power Cycle 1 2: adiabatic, reversible compression 2 3: isothermal, reversible heat input 3 4: adiabatic, reversible expansion 4 1: isothermal, reversible heat rejection 2 3 T Q H = T S 23 W net net H L 3 H H 23 Note : W Q Q Q T d s T S T H ME 200 ME 200 5 1 4 s Q L = T S 14 H H 23 2 1 L L 4 1 4 Q T d s T S T L Continue Carnot Power Cycle • System Schematic: hot reservoir @ T H T H = constant H Q T L = constant L Q in W out W reversible, isothermal reversible, isothermal reversible, adiabatic ME 200 ME 200 6 net H L L L 4 1 L th,C H H H H 23 H Thermal Efficiency : W Q Q Q T S T 1 1 1 Q Q Q T S T cold reservoir @ T L 11/16/2010 4 • Example 36.1: • Given: T H = 450 o F and T L = 212 o F • Find: Thermal efficiency of Carnot Cycle • Solution: th,C = 0.26 Continue Vapor Power Cycle th,C Question: How to implement the Carnot Power Cycle with a real working fluid? ME 200 ME 200 7 T L /T H 1 • Answer: Put the cycle in the two ‐ phase dome Carnot power cycle T 2 3 T H s 1 4 s 1 =s 2 s 3 =s 4 H T L ME 200 ME 200 8 However, in real life we have to “deal” with deviations from Carnot: ‐ finite temperature difference across the heat exchanger ‐ difficult to compress 2 ‐ phase mixture ‐ non ‐ isentropic compression and expansion Introduce Rankine power cycle 11/16/2010 5 Ideal Rankine Power Cycle • System Schematic and T ‐ s diagram: ME 200 ME 200 9 • Define ideal Rankine power cycle: – Neglect the finite temperature difference of heat exchanger...
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This note was uploaded on 12/11/2011 for the course ME 200 taught by Professor Gal during the Fall '08 term at Purdue.

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ME200 - Lecture 34 - 1 Ideal Rankine Cycle ME 200...

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