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1) Does an isentropic process have to be a quasistatic one? What is the relation between equilibrium and reversibilty?

2) Naturally, there are revesible processes involving control volumes. A gas can go through an isentropic process in a reversible turbine, but as we know, turbines in a steady state have siginficant gradient of pressure inside them- the properties of the gas inside the turbine are not uniform.

How can the gas go through a reversible process in the turbine if it is not in equilibrium? (the gas in the turbine is not in equilibrium because it's properties are not unfiorm)

Also, it is said that the gas goes through an isentropic prcess, and let's say it goes through a turbine, what system is regarded? Is it the gas inside the control volume (always looking at the gas in the control volume- open system) ? is it a closed system that goes through the turbine, exits it and than moves on (following the gas- closed system)?

For example: if you have an ideal gas going through a quasistatic adiabatic process, than the process can be described by the equation: (pV)^k=const

if you have an ideal gas going through a revesible adiabatic process (isentropic)- the process can be described by the equation: (pV)^k=const

The same equation. So does this mean any isentropic process is quasistatic? If so how can the process in the turbine can be quasistatic if the properties of the gas in the trubine are not uniform. If not any isentropic process is quasistatic ,than how can both be equations be the same?

Generaly, how can a process in a control volume be reversible and adiabatic, if the properties of the gas are not uniform?

I must say I am very confused about this, and it's not the first time I took this course.

Thanks, Erez.