Carnot Engine: Finding Final Temperature Attained

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Homework Help Overview

The discussion revolves around a Carnot engine operating between two thermal reservoirs at temperatures T1 and T2, where T1 is greater than T2. The problem involves finding the final temperature attained when the heat capacities of both reservoirs are equal.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the implications of heat transfer between the reservoirs and the resulting changes in temperature and entropy. Questions arise regarding the total change in entropy when the reservoirs reach thermal equilibrium and how this relates to the final temperature.

Discussion Status

Some participants have provided initial reasoning involving infinitesimal heat changes and the relationship between heat transfer and temperature changes. There is an ongoing exploration of the entropy changes in the reservoirs, with suggestions to integrate to find the total change in entropy over the process. The discussion reflects a mix of interpretations and approaches without a clear consensus yet.

Contextual Notes

Participants are working under the assumption that the temperature changes during a single cycle are very small, and they are considering the implications of the Carnot engine's reversible nature on the total change in entropy.

junfan02
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A Carnot engine is operating between a source and a sink at temperatures T1 & T2 (T1>T2) respectively..
The heat capacities of the source and the sink are equal.
Find the final temperature attained.
 
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junfan02 said:
A Carnot engine is operating between a source and a sink at temperatures T1 & T2 (T1>T2) respectively..
The heat capacities of the source and the sink are equal.
Find the final temperature attained.
You have to show us what you have done to solve the problem. Please follow the homework template.

What can you say about the change in total entropy of the two reservoirs at the end when they reach the same temperature? Does that help you find the temperature?

AM
 
I assumed an infinitesimal amount of heat dQ taken away from the reservoir.. So the amount of heat dumped into the sink is T2*dQ/T1.
I couldn't proceed further.
 
dQ amount of heat taken away from the aource reduces its temperature by dQ/c.
Assuming c to be the common heat capacity. And the increase in temperature of the sink for this cycle is T2*dQ/(T1*c)
How do I proceed after this?
 
junfan02 said:
dQ amount of heat taken away from the aource reduces its temperature by dQ/c.
Assuming c to be the common heat capacity. And the increase in temperature of the sink for this cycle is T2*dQ/(T1*c)
How do I proceed after this?

Assume that the temperature changes of the reservoirs during a single cycle are very small. In one cycle the heat flow (out) of the hot reservoir will be dQh = mcdTh. The heat flow (into) the cold reservoir will be dQc = mcdTc.

What is the change in entropy in one cycle?

Can you integrate to Tfinal to determine the total change in entropy over the whole process? Since this is a Carnot engine, what can you say about the total change in entropy?

AM
 
The total change in entropy obviously has to be zero since this is a reversible process!
 
junfan02 said:
The total change in entropy obviously has to be zero since this is a reversible process!
So work out the expression for the change in entropy of each reservoir and set their sum equal to 0!

AM
 
Last edited:
Thanks a lot!
Will give it a try, please be there if I am stuck somewhere..
 

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