Pressure volume diagram

The PV diagram is a special form of a phase diagram in which the pressure p of a system of the specific volume v is applied. Is used instead of the specific volume v, the volume V, so it is also called a pV diagram; in this case, the reference is no longer a constant amount of substance or mass, and may need to be charged as an additional requirement.

The pv diagram is often used to process sequences - with or without phase change - to illustrate, such as in the adjacent diagram, the diesel process.

According to the Gibbs phase rule has a pure fluid or a fluid mixture of constant composition exactly two degrees of freedom. It follows that described in the function of the pressure p by the unique specific volume v and the temperature T.

Plotting this relationship in a three-dimensional diagram a, then a PVT diagram. By projecting this surface in the pV plane one obtains a pV diagram. Here, the pressure p is the ordinate, the specific volume V and the abscissa represents the temperature T is chosen to be constant depending on the application for the graph ( isothermal ) or neglected.

In this diagram are often also the limits of physical states "solid", "liquid" and " gas " or entered each phase of the fluid.