Polytropic equation

1. jaredokie

21
Is temperature constant in a polytropic thermodynamic process? The equation pv^n=c leads me to believe so. But logic tells me otherwise. Its not isothermal or adiabatic. Did they derive this equation from using log transforms when analyzing gas experiments?

2. CFDFEAGURU

763
A polytropic process does not require the heat transfer to be negligible. The process is following a relationship between equilibrium states. The equation is restricted to a quasistatic process for a simple compressible gas system.

The above is taking from "Thermodynamics" 5th Edition by Wark. Page 664

3. jaredokie

21
But how did they come up with the equation pV^n=c?
I can find any derivation for that equation. I'm trying to understand how the equation was formed.

Staff: Mentor

People noted that, for an isothermal process, n=1 and for an adiabatic process, n=γ. So they figured that, if the temperature is controlled properly, there can be other processes which satisfy a p-v equation of the specified mathematical form. They coined the term "polytropic" to refer to such processes.