Temperature–entropy diagram

In thermodynamics, a temperature–entropy 'diagram' is a thermodynamic diagram used to visualize changes to temperature and specific entropy during a thermodynamic process or cycle as the graph of a curve. It is a useful and common tool, particularly because it helps to visualize the heat transfer during a process. For reversible processes, the area under the T–s curve of a process is the heat transferred to the system during that process.
Working fluids are often categorized on the basis of the shape of their T–s diagram.
An isentropic process is depicted as a vertical line on a T–s diagram, whereas an isothermal process is a horizontal line.
Image:Ejemplo Diagrama T-S.png|thumb|left|Example T–s diagram for a thermodynamic cycle taking place between a hot reservoir and a cold reservoir.
For reversible processes, such as those found in the Carnot cycle:
heat exchanged with the hot reservoir.
thermal efficiency of the cycle
If the cycle moves in a clockwise sense, then it is a heat engine that outputs work; if the cycle moves in a counterclockwise sense, it is a heat pump that takes in work and moves heat from the cold reservoir to the hot reservoir.
[Image:Temperature-entropy chart for steam, imperial units.svg|thumb|T–s diagram for steam, US units]