Maximum Work Theorem : Herbert Callen

[mayank pathak]

Hi, I have been studying thermodynamics from Herbert Callen's "Thermodynamics : an introduction to the physical theories of equilibrium thermostatics and irreversible thermodynamics"
In Chapter 4, Section 4.4, he writes : "
all processes occurring between a given initial and a given final state of a system, the flux of heat to an associated reversible heat source is minimum and the flux of work to an associated reversible work source is maximum for reversible processes."

Now he also describes what a reversible heat source is : "
A reversible heat source is defined as a system enclosed by a rigid
impermeable wall and characterized by relaxation times sufficiently short
that all processes of interest within it are essentially quasi-static."

I understand his argument. But I fail to understand why is the heat source required to be reversible ? According to me, as long as the heat source(or sink) is constrained to have constant volume and constant mole numbers, same heat input will lead to same rise in internal energy and hence same increase in entropy in accordance with the fundamental equation of the heat source. And that is all that we need to prove maximum work theorem. And we don't actually need the heat source to be reversible.

Am I missing something ?

Edit : I have uploaded the relevant text from the book.

 

[Chestermiller]

For what it is worth, none of it makes any sense to me.

 

[mayank pathak]

For what it is worth, none of it makes any sense to me.

does my question sound incomplete ? Let me share some pages from the book to make it easy for others.

 

[Chestermiller]

None of it makes any sense to me. It is well known that, for two specified thermodynamic equilibrium states of a closed system, there are an infinite number of reversible paths, and they don't all involve the same work and heat.

As an alternate to Callen, might I suggest Fundamentals of Engineering Thermodynamics by Moran et al. I think you will find it much easier to understand.