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# 110124_new - 2nd Law of TD Carnot engine entropy...

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1 CHM3400 - Lecture 8 Jan 24 2 nd Law of TD: Carnot engine, entropy change (Chapter 4 p. 87-95) Carnot engine (heat and work) Entropy change (mixing of gases, phase transitions, heating)

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2 Carnot engine The concept of entropy came out of studies of the steam engine in the 19 th century. It was found that not all heat could be converted into mechanical energy . Efficiency of the engine : efficiency = net work done by heat engine heat absorbed by engine 2 1 2 T T T efficiency = Carnot showed that:
3 Numerical example This formula is in fact the maximum value that can be attained for a reversible process . At a power plant, superheated steam (560 o C) is used to drive turbines for electricity generation. Estimate the engine efficiency if the temperature of the cooling tower is 38 o C. ... .......... 833 311 833 = = efficiency

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4 Cycles of a Carnot engine http://www.shermanlab.com/xmwang/myGUI/CarnotG.html Let’s look at an animation of a Carnot engine (for an ideal gas): Step 1: Isothermal expansion Step 2: Adiabatic expansion Step 3: Isothermal contraction Step 4: Adiabatic contraction 4 steps are performed: Gas expansion (isothermal and adiabatic) Gas contraction (isothermal and adiabatic) What is the amount of work performed?
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110124_new - 2nd Law of TD Carnot engine entropy...

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