Two (equivalent?) versions of Clausius-Duhem inequality?

In summary, the Clausius-Duhem inequality shown in the book and the one discussed in class are equivalent, with the only difference being the representation of temperature.
  • #1
honululu
2
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Homework Statement


Hello everyone,
I have a problem to solve, which I found hard and so looked for help on the web. Finally found this:
https://books.google.co.uk/books?id...E#v=onepage&q=clausius-duhem inviscid&f=false
which is great as on page 183 is the EXACT question I am supposed to solve. It's not fully shown on google but I can do the rest.

There a a few differences:
I have

T=T(F,Θ,gradΘ)
q=q(F,Θ,gradΘ)
η=η(F,Θ,gradΘ)

rather than
T=T(ρ,Θ,gradΘ) etc. as in the link above.

The Clausius-Duhem inequality shown throughout the book has terms a term

+T⋅D

in it. We learned this differently in class: Our inequality read the exact same as in the link above but had a term

+tr(TD)

instead.

I would really like to understand why these two forms are equivalent before just using the form I found on the web and assuming it's correct. Is this to do with T vs. T?

I feel like such a beginner (which I am!) :D

Thank you so much for any advice!
 
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  • #2
Homework EquationsClausius-Duhem Inequality: ΔS ≥ ∑ i (∂q i /∂T) ΔT + ∑ i (∂q i /∂x j ) Δx j where S is entropy, q i is heat flux in direction i, T is temperature and x j is the spatial coordinate in direction j.The Attempt at a SolutionThe two forms of the Clausius-Duhem inequality are equivalent because they both account for the same physical processes. The first form has a term +T⋅D which accounts for the change in entropy due to a change in temperature. The second form has a term +tr(TD) which accounts for the change in entropy due to a change in the heat flux, which is related to the temperature gradient. Thus, both forms are equivalent as they both account for the same physical processes.
 

Related to Two (equivalent?) versions of Clausius-Duhem inequality?

1. What is the Clausius-Duhem inequality?

The Clausius-Duhem inequality is a fundamental law of thermodynamics that describes the relationship between energy transfer and entropy change in a system. It states that in any spontaneous process, the total entropy of the system and its surroundings will always increase or remain constant.

2. What are the two versions of the Clausius-Duhem inequality?

The two versions of the Clausius-Duhem inequality are the integral form and the differential form. The integral form expresses the inequality as a change in entropy over a finite process, while the differential form expresses it as a change in entropy over an infinitesimal process.

3. Are the two versions of the Clausius-Duhem inequality equivalent?

Yes, the two versions of the Clausius-Duhem inequality are equivalent. This means that they are different mathematical expressions of the same fundamental principle and can be interchanged in any thermodynamic calculation without affecting the final result.

4. How is the Clausius-Duhem inequality related to the second law of thermodynamics?

The Clausius-Duhem inequality is a mathematical representation of the second law of thermodynamics, which states that the total entropy of a closed system will always increase or remain constant in any spontaneous process. The inequality provides a quantitative measure of this law and is used to analyze and predict the behavior of thermodynamic systems.

5. How is the Clausius-Duhem inequality used in practical applications?

The Clausius-Duhem inequality is used in various practical applications in the fields of engineering, chemistry, and physics. It is essential in the design and optimization of heat engines, refrigeration systems, and other thermodynamic processes. It is also used in the study of chemical reactions and phase transitions to determine the conditions under which they occur spontaneously.

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