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Steam Heat Engine Question

  • Thread starter GreenPrint
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I'm getting tired of pointing out careless mistakes.

In the first post you said the power plant puts out 900 MW of power. Alright, great. In post #17 you used 500 MW. In the answer in post #20, it's 600 MW. I mean, what the heck?

Also, I'm disappointed at the answer in post #20. It's wrong, period. They took into consideration the fact that the second engine is 0.65 times the Carnot efficiency, but didn't do the same for the first. I mean, what the heck?
hmm do you mean they took into consideration that the engine is .65 times the Carnot efficiency in the first and not the second becasue for some reason I'm not getting .128
 
1,196
0
for the second engine I'm getting about .0588

here's what I did

.65 (1 - 553.16/608.16)
 

ideasrule

Homework Helper
2,266
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First, can you please tell me whether it's 900 MW, 500 MW, or 600 MW? Second, e = 1 - TL/TH = 1 - 553.16/608.16 is not right because the bottom should NOT be 608.16 K. Recalculate, and make sure you get 0.128 before making another post.
 
1,196
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oh sorry 688 gee I'm really tired sorry
 
1,196
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in book it's 900 MW
 
1,196
0
ok i get 12.8

what were you saying about the first one not taking into account that it was .65 Carnot efficiency because I don't see how this is so
 
1,196
0
I'm getting tired of pointing out careless mistakes.

In the first post you said the power plant puts out 900 MW of power. Alright, great. In post #17 you used 500 MW. In the answer in post #20, it's 600 MW. I mean, what the heck?

Also, I'm disappointed at the answer in post #20. It's wrong, period. They took into consideration the fact that the second engine is 0.65 times the Carnot efficiency, but didn't do the same for the first. I mean, what the heck?
i don't see how

e (Carnot) = 1 - 703.16 K/953.16 K = .2623
e = .65 e Carnot = .65(.2633) = .1705

what am I doing wrong
 

ideasrule

Homework Helper
2,266
0
Sorry, my mistake. Ignore that comment; the answer's correct.
 
1,196
0
Wait so then...

I got e_system to be .0217
because I did

e_system = e_first intersection e_second = .1705(.1275) = .0217

now

e_system = |W|/|Q_H|

Therefore

|Q_H|= |W|/e_system
= (900 MJ)/.0217
= 4.147 E 10 J
what am I doing wrong now
 
1,196
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So I got the wrong input heat and don't see why...
 
1,196
0
please anyone
 

ideasrule

Homework Helper
2,266
0
OH. So this is what's happening.

The first engine spits out some work, which is part of the electricity generated. It also spits out waste heat, which is used to power the second engine. I thought the first engine's work was used to power the second engine; in fact, it's the waste heat.
 
1,196
0
so what do i do
 

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