Isentropic
Definition
... a process at constant entropy, denoted by a curve on a pV diagram and a vertical line on a Ts diagram.
Where it occurs.
In the theoretical Carnot, Otto and Diesel Cycles, working gas is compressed or expanded isentropically.
Special features
There is no heat addition (adiabatic) and no gas friction. An isentropic process is said to be "reversible".
How to draw it
Locate the POI and press the isentropic button.
The theory
The isentropic relationship follows
$$ p V^{\gamma}= constant $$
For a specified temperature and entropy the derived expression for the entropy of an ideal gas follows integration of the Gibbs Equation. It is rearranged to yield:
$$ p = 1.013 \, bar \times exp(- s/R) (T/273.)^{\gamma/(\gamma-1)} $$
where \( \gamma = 1.4 \) is the ratio of heat capacities and \(R=0.287 kJ/kg\) is the specific gas constant.
The derviation of
$$ p V^{\gamma}= constant $$
is given here.
Exercises
Click on the graph to get a POI and plot an isentropic line through it. Click along the line to get new POIs and note the way that pressure and volume change with temperature.
Links
... to follow.