Carnot engine efficiency and exhaust problem

AI Thread Summary
The discussion revolves around calculating the intake temperature of a Carnot heat engine with an exhaust temperature of 121°C and an efficiency of 13.4%. The initial calculation incorrectly used Celsius instead of Kelvin, leading to an incorrect result. The correct approach involves converting the temperatures to Kelvin for accurate calculations. Once the temperatures are converted, the efficiency formula can be applied correctly. This highlights the importance of using the appropriate temperature scale in thermodynamic equations.
lzh
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Homework Statement


The exhaust temperature of a Carnot heat engine is 121◦C. What is the intake temperature if the efficiency of the engine is 13.4 %? Answer in units of ◦C.


Homework Equations


e=1-(Tc/Th)


The Attempt at a Solution


This seems like just a plug and chug problem:
0.134=1-(121/Th)
Th=139.723 ◦C
However, this answer is wrong-according to my Quest web homework. Am I missing something here? Thanks
 
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Hi lzh,

lzh said:

Homework Statement


The exhaust temperature of a Carnot heat engine is 121◦C. What is the intake temperature if the efficiency of the engine is 13.4 %? Answer in units of ◦C.


Homework Equations


e=1-(Tc/Th)


The Attempt at a Solution


This seems like just a plug and chug problem:
0.134=1-(121/Th)
Th=139.723 ◦C
However, this answer is wrong-according to my Quest web homework. Am I missing something here? Thanks

The Celsius scale is not a thermodynamic temperature scale. You need to use a temperature scale such as Kelvin here.
 
Oh! I see! Thanks! I got it now!
 

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