Conditions are adiabatic and reversible about a turbine

[scott_for_the_game]

Why is it when the conditions are adiabatic and reversible about a turbine, the assumption is its isentropic?

 

[Astronuc]

What does the term 'adiabatic' mean?

Then see the definition of change in entropy.

http://hyperphysics.phy-astr.gsu.edu/hbase/therm/entrop2.html#c2

Discussion of adiabatic
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/adiab.html

and the First Law of Thermodynamcis
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/firlaw.html

 

[Andrew Mason]

Why is it when the conditions are adiabatic and reversible about a turbine, the assumption is its isentropic?

If dQ = 0, then dS = dQ/T = 0.

This would seem to imply that all adiabatic processes are isentropic (constant entropy - ie dS = 0) which is not true. The relation: dS = dQ/T assumes a quasi static process in which the system is always at equilibrium. If the process is quasi-static and adiabatic, the process is isentropic.

I don't see how this would apply to a turbine, however. The expanding gas is necessarily dynamic (in order to drive the turbine), not quasi-static/reversible.

AM

 

[sicjeff]

you are missing a few terms in your entropy equation. You can't simply assume that dS=dQ/T.

 

[Andrew Mason]

you are missing a few terms in your entropy equation. You can't simply assume that dS=dQ/T.

I am not assuming that dS = dQ/T. That is the thermodynamic definition of dS.

"[URL
Quantitatively, entropy, symbolized by S, is defined by the differential quantity dS = δQ / T, where δQ is the amount of heat absorbed in a reversible process in which the system goes from one state to another, and T is the absolute temperature.[3][/URL]

AM