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Simple thermal efficiency check 1

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jmoth79

Automotive
Joined
Dec 9, 2009
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US
The working fluid of a power plant executes a thermodynamic cycle with thermal efficiency of 40%. The working fluid is heated by the hot gases in a coal-fired furnace, and cooled by water from a river. How much heat transfer from the hot gases occurs, for each joule of heat transfer to the river water?

So, I just used the thermal efficiency equation: n = 1 - Q out / Q in. Plugging in 0.4 for n , and 1 Joule for Q out.
I calculated 0.714 Joules for an answer. Is this correct?
 
No. Your method is ok but your math is bad 1-1/.714 = -.4. Answer should be 1.67

Qin > Qout Unless you are measuring the water at the inlet and outlet?

How and where you measure Qin and Qout would be interesting.
 
Yes, silly math mistake. Thanks for correcting!
 
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