Polytropic Process

Many processes can be approximated by the law:

where,
P= Pressure,
v= Volume,
n= an index depending on the process type.

Polytropic processes are internally reversible. Some examples are vapors and perfect gases in many non-flow processes, such as:

n=0, results in P=constant i.e. isobaric process.
n=infinity, results in v=constant i.e. isometric process.
n=1, results in P v=constant, which is an isothermal process for a perfect gas.
n=, which is a reversible adiabatic process for a perfect gas.
Some polytropic processes are shown in figure below:

The initial state of working fluid is shown by point 0 on the P-V diagram. The polytropic state changes are:

0 to 1= constant pressure heating,
0 to 2= constant volume heating,
0 to 3= reversible adiabatic compression,
0 to 4= isothermal compression,
0 to 5= constant pressure cooling,
0 to 6= constant volume cooling,
0 to 7= reversible adiabatic expansion,
0 to 8= isothermal expansion.
Related topic:

Polytropic Efficiency