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Unformatted text preview: ME320 Thermodynamics Homework set #8 Due: Wednesday 11/11/03 at the start of class 1. Consider the problem of baking a turkey in a conventional oven. Can the hot air in the oven be treated as a thermal reservoir? Solution: Yes. Because the temperature of the oven remains constant no matter how much heat is transferred to the turkey. 2. Explain why it is not possible for a heat engine to operate without ejecting any waste heat to a low-temperature reservoir. Solution: A heat engine that ejects no waste heat into a low-temperature reser- voir violates the second law of thermodynamics as expressed in the Kelvin–Planck statement. 3. A 600 MW steam power plant, which is cooled by a nearby river, has a thermal efficiency of 40 %. Determine the rate of heat transfer to the river water. Will the actual heat transfer rate be higher or lower than this value? Why? Solution: By the first law, ˙ Q L = ˙ Q H- ˙ W net,out . Thus, using the relation η th = ˙ W net,out / ˙ Q H for the thermal efficiency, it follows that...
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- Spring '08
- Heat, Ql, low-temperature reservoir, kW QL