Enthalpy–entropy chart

An enthalpy–entropy chart, also known as the h–s chart or Mollier diagram, plots the total heat against entropy, describing the enthalpy of a thermodynamic system. A typical chart covers a pressure range of 0.01 - 1000 bar, and temperatures up to 800 degrees Celsius. It shows enthalpy in terms of internal energy , pressure and volume using the relationship .

History

The diagram was created in 1904, when Richard Mollier plotted the total heat against entropy. At the 1923 Thermodynamics Conference held in Los Angeles it was decided to name, in his honor, as a “Mollier diagram” any thermodynamic diagram using the Enthalpy h as one of its axes.

Details

On the diagram, lines of constant pressure, constant temperature and volume are plotted, so in a two-phase region, the lines of constant pressure and temperature coincide. Thus, coordinates on the diagram represent entropy and heat.

The work done in a process on vapor cycles is represented by length of 'h', so it can be measured directly, whereas in a T–s diagram it has to be computed using thermodynamic relationship between thermodynamic properties.