EMA_4314_HW3_solutions

EMA_4314_HW3_solutions - EMA 4314 HW 3 Solutions Discussion...

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EMA 4314 HW 3 Solutions Discussion Questions 3.2 The device proposed uses geothermal heat (energy) and appears to be similar to devices currently in existence for heating and lighting homes. As long as the amount of heat extracted from the hot source (the ground) is not less than the sum of the amount of heat discarded to the surroundings (by heating the home and operating the steam engine) and of the amount of work done by the engine to operate the heat pump, this device is possible; at least, it does not violate the first law of thermodynamics. However, the feasibility of the device needs to be tested from the point of view of the second law as well. There are various equivalent versions of the second law, and some are more directly useful in this case than others. On first analysis, it might seem that the net result of the operation of this device is the complete conversion of heat into the work done by the heat pump. This work is the difference between the heat absorbed from the surroundings and the heat discharged to the surroundings, and all of that difference has been converted to work. We might, then, conclude that this device violates the second law in the form stated in the introduction to Chapter 3 and therefore that it cannot operate as described. However, we must carefully examine the exact wording of the second law. The key
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EMA_4314_HW3_solutions - EMA 4314 HW 3 Solutions Discussion...

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