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# HW8_Problems.pdf

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Department
Mechanical Engineering
Course
MECHENG 235
Professor
Donald Siegel
Semester
Winter

Description
THE UNIVERSITY OF MICHIGAN Department of Mechanical Engineering ME 235 Thermodynamics I / Winter 2014 / Section 002 HW 8 Due date: Mar. 20 2014 5.30 In a Rankine cycle steam power plant 0.9 MW is taken out in the condenser, 0.63 MW is taken out in the turbine, and the pump work is 0.03 MW. Find the plant thermal efficiency. If everything could be reversed find the COP as a refrigerator. 5.51 The lowest temperature that has been achieved is about 1 × 10 K. To achieve this, an additional stage of cooling is required beyond that described in the previous problem, namely nuclear cooling. This process is similar to magnetic cooling, but it involves the magnetic moment associated with the nucleus rather than that associated with certain ions in the paramagnetic salt. Suppose that 10 μJ is to be removed from a specimen at an average temperature of 10 K (10μJ is about the potential energy loss of a pin dropping 3 mm). Find the work input to a Carnot heat pump and its coefficient of performance to do this assuming the ambient is at 300 K. 5.72 A sales person selling refrigerators and deep freezers will guarantee a minimum coefficient of performance of 4.5 year round. How would you evaluate that? Are they all the same? 5.73 A cyclic machine, shown in Fig. P5.73, receives 325 kJ from a 1000 K energy reservoir. It rejects 125 kJ to a 400 K energy reservoir and the cycle produces 200 kJ of work as output. Is this cycle reversible, irreversible, or impossible?
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