A power cycle operating between two reservoirs receives QH from a hot reservoir at TH = 2000 K and rejects QC to a cold reservoir at TC = 400 K. For each of the following cases, determine whether the cycle is reversible, irreversible or impossible.
a.) QH = 1200 kJ and Wcycle = 1020 kJ
b.) QH = 1200 kJ and QC = 240 kJ
c.) QC = 600 kJ and Wcycle = 1400 kJ
d.) η = 40%
4 comments:
I've found the efficiency of each process, but where does the temperature of the resevoirs factor in, and isn't any process with efficiency less than 1 irreversible and greater than 1 impossible?
To do this problem, I think we need to compare the Carnot Efficiency (pg 160) Rev and Irrev to determine if the HE is rev, irrev or impossible. If its impossible, the thermal efficiency will be above nrev, right?
Washburn 2:56 PM
The key here is that the efficiency of ANY power cycle is 1-Qc/Qh but the efficiency of any reversible cycle is 1-Tc/Th.
NO cycle EVER has an efficiency of 1 and never will.
Compare the efficiency of each cycle to the efficiency of a reversible (Carnot) cycle operating between the same two reservoirs. DO NOT compare efficiencies to 1.0, that is irrelevant because it is impossible.
Steve 3:23 PM
Exactly.
All reversible HE's have the same efficiency as Carnot. All real, irreversible HE's have efficiencies less than Carnot. Any HE with efficiency greater than Carnot are impossible.
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