Temperature–entropy diagram

A temperature vs. specific entropy diagram, or T-s diagram, is used in thermodynamics to visualize changes to temperature and specific entropy during a thermodynamic process or cycle. 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 T-s curve of a process is the heat transferred to the system during that process.

An isentropic process is depicted as a vertical line on a T-s diagram, whereas an isothermal process is a horizontal line.

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