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Unformatted text preview: ME320 Thermodynamics Homework set #9 Due: Wednesday 11/19/03 at the start of class 1. Someone claims to have developed a new reversible heat-engine cycle that operates between two temperature reservoirs has a higher oper- ating efficiency than a Carnot cycle operating between the same two reservoirs. How do you evaluate this claim? Solution: The claim violates the second Carnot principle and thus is false. 2. An inventor claims to have developed a heat engine that receives 750 kJ of heat from a source of 400 K and produces 250 kJ of net work while rejecting waste heat to a sink at 300 K. Is this a rasonable claim? Why? Solution: The highest thermal efficiency possible for a heat engine operating be- tween two specified temperature limits is the Carnot efficiency, which for T L = 300 K and T H = 400 K yields th,max = 1- T L T H = 1- 300 K 400 K = 1 4 . However, using directly the given values W net = 250 kJ and Q H = 750 kJ for the net work and waste heat yields a thermal efficiency...
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- Spring '08