ME300Lecture07

ME300Lecture07 - Lecture 7: Exergy Analysis Note: All...

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Lecture 7: Exergy Analysis Note: All previous analyses considered the isentropic process as the goal to strive for. Maximize adiabatic and isentropic efficiency This approach is short sighted for three reasons: 1. It ignores processes where heat transfer is present. he majority of all practical processes.) (The majority of all practical processes.) 2. It assumes that reversibility can be obtained: Not possible! 3. It assumes that the exit state of a device can “float”, i.e., cases where the exit pressure is fixed, but the exit temperature is allowed to fall below the temperature of 7.1 the surroundings: Not possible!
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Continue Exergy Analysis Need different approach for thermodynamic analysis: Exergy Analysis Notes: » It can be used for both adiabatic and non-adiabatic processes. » It shows how close a device operating between two fixed end states is to its optimum performance. identifies the system components most responsible for » It identifies the system components most responsible for sub-optimum system performance. 7.2
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Continue Exergy Analysis Exergy: » Maximum theoretical work output that could be done by a system if it were to come into equilibrium with its n ironment! environment! » Measure of the quality of energy, or the value of resources! Reasons for exergy analysis: » Match resources to their end use » Identify design improvements 7.3
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Continue Exergy Analysis Exergy Destruction: Air @ T i Air and combustion roducts @ T dT ime uel products @ T i + dT i Burner Time Energy onserved Fuel conserved Exergy destroyed 7.4
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ME300Lecture07 - Lecture 7: Exergy Analysis Note: All...

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