The relationship between Isentropic and reversible adiabatic processes

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ده كان سؤالي

This was my question 

Why every reversible adiabatic process is isentropic but not every isentropic process is reversible adiabatic?

When we say " isentropic process" ,our mind goes to think internal reversible and adiabatic process. It is right but they aren't two faces for one coin. However the relationship is every reversible adiabatic process is necessarily isentropic process. But not every isentropic process is necessarily reversible adiabatic process. 

That explains to fix entropy values, we have many state

First: reversible adiabatic .reversible to make (entropy generation equals zero) 

What means when I reject heat and absorb it again entropy values don't change. And adiabatic to not making losses or gaining of entropy. 

Second :To make entropy values fixed we should make balance between the increase and decrease of entropy

So the source of increase is entropy generation or gaining heat to system. 

And the source of decrease is lossing heat from the system. So we find that we use the way of lossing heat to decrease entropy values by the same amount we increase entropy by entropy generation. 

Do you agree with me? 

Am I right? 

Can you find another state for Isentropic process? 

If I had a grammatical mistakes because I am not native speaker

وهذا كان جواب أحدهم

And this is the answer

I could not understand you completely but i will try my best to answer.

When a system undergoes an Adiabatic process, the only form of energy interaction across the system boundary is work transfer i.e there is no heat transfer across the system boundary throughout the process. Common misconception is that a process is adiabatic when the net heat transfer is zero which is not correct according to our definition. Since there are no heat transfer interactions across the system boundary, the entropy of the system should remain the same on the condition that the process is reversible ( entropy generation is zero ).

For a system undergoing isentropic process, the entropy remains constant. From second law of thermodynamics we have S(2) - S(1) = S(gen) + integral ( del Q / T).

Here S(2) is the entropy of the system at the end of the process,

S(1) is the entropy of the system at the initial state

S(gen) is the entropy generated due to irreversibilities

integral ( del Q / T) is the entropy transfer due to heat transfer associated with thermal reservoirs of temperature T.

For an isentropic process we have S(2) = S(1). This implies

S(gen) = - integral (del Q / T)

So what do we understand from this ?

A process being isentropic does not say anything about S(gen) which is dependent on reversibility of the process and inegral (del Q / T) which is dependent on the heat transfer interactions between system and thermal reservoirs.

For an adiabatic process del Q / T is zero for

بقية الإجابة

وهذا كان تضميني

I think you have a good answer. 

But until now we find 3 states for isentropic process

1-Reversible Adiabatic process

(2-special)when entropy generation equals to heat losses entropy. In an irreversible and not adiabatic process. 

(2-general) the sum of heat losses and heat gained entropy equals to entropy generation in an irreversible and not adiabatic process. 

3-when heat losses entropy equals to heat gained entropy in an reversible processes like you loss heat from 1 to 2 and gain heat from 2 to 3

Is there any possibility for any state?
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