temperature–entropy diagram

{{short description|Graph relating temperature and entropy during a thermodynamic process or cycle}}

{{Other uses|Tanabe–Sugano diagram}}

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In thermodynamics, a temperature–entropy (T–s) diagram is a thermodynamic diagram used to visualize changes to temperature ({{mvar|T }}) and specific entropy ({{mvar|s}}) 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 T–s curve of a process is the heat transferred to the system during that process.{{cite web|url=https://www.engineersedge.com/thermodynamics/temp_enthalpy_th_diagram.htm |title=Temperature Entropy (T–s) Diagram - Thermodynamics - Thermodynamics |publisher=Engineers Edge |date= |accessdate=2010-09-21}}

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.{{cite web|url=https://www.grc.nasa.gov/WWW/K-12/airplane/pvtsplot.html |title=P–V and T–S Diagrams |publisher=Grc.nasa.gov |date=2008-07-11 |accessdate=2010-09-21}}

Image:Ejemplo Diagrama T-S.png taking place between a hot reservoir ({{math|T{{sub|H}}}}) and a cold reservoir ({{math|T{{sub|C}}}}).

For reversible processes, such as those found in the Carnot cycle:

{{legend|#e69ca6|{{math|1=Q{{sub|C}} =}} the amount of energy exchanged between the system and the cold reservoir}}

{{legend|white|{{math|1=W =}} work exchanged by the system with its surroundings}}

{{math|1=Q{{sub|H}} = W + Q{{sub|C}} =}} heat exchanged with the hot reservoir.

{{math|1=η = W / (Q{{sub|C}} + Q{{sub|H}}) =}} 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 {{math|Q{{sub|H}}}} from the cold reservoir to the hot reservoir.]]

Image:Temperature-entropy chart for steam, imperial units.svg

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