In thermodynamics, a temperatureâÂÂentropy (TâÂÂs) 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 (ideal) processes, the area under the TâÂÂs 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 TâÂÂs diagram.
An isentropic process is depicted as a vertical line on a TâÂÂs diagram, whereas an isothermal process is a horizontal line.