3: Isentropic Flow Relations for a Perfect Gas

Assuming reversible processes (no losses), and with the only work being that due to volume change against a pressure,

, so that

Integrating from one state to another,

Define

Then

If is constant

=

Isentropic Process

or

Note: This is the relation between the pressure ratio and temperature ratio for an isentropic change from one state to another at constant specific heats.