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Lost Work and Total Entropy Generated

and

ALL processes:

Multiply by Tsurr :

(for heat exchange with the surroundings)

Big Conclusion :

Notes :

Completely reversible processes:

Real Processes:

Lesson
8D Blog

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Lesson 8D: page 5 of 15

Ok, now we have just derived equations for both lost work and the total entropy generation rate.
Take a close look at these equations.
If we multiply the total entropy generation equation by the temperature of the surroundings, the relationship between lost work and total entropy generation becomes clear.
The rate at which shaft work is lost is equal to the temperature of the surroundings times the total entropy generation rate!
This is an incredibly simple and powerful result.
One word of caution relating to heat exchange with thermal reservoirs…
The equation in the yellow box doesn’t change. You still multiply the total entropy generation rate by Tsurr NOT BY Tres !
However, the way you calculate the total entropy generation does change.
We’ll learn more about this later in this lesson.
Now, let’s learn about the short-comings of the isentropic efficiency and introduce a new and improved efficiency.

Lost Work and Total Entropy Generated

Ch 8, Lesson D, Page 5 - Lost Work and Total Entropy Generated