Temperature–entropy diagram

The Ts diagram is a common addition to the pv diagram in thermodynamics and in energy technology state diagram representation of processes. Its abscissa ( X-axis) is the entropy of either S or - as in the figures - the specific entropy s, its ordinate axis ( y axis) the absolute temperature T.

Description

The importance of this diagram is that the area under the curve corresponding to the curve in the reversible state changes on the system or to limit heat loss. Thus, the efficiency of the two- isentropic and two isotherms Carnot cycle, which is represented in the Ts diagram as a rectangle, read directly from the area ratio.

For non- adiabatic irreversible processes the area of ​​the sum of the heat and dissipated within the system work, such as friction work ( see Figure 1). The individual components can not be determined solely from the Ts diagram. This requires at any given time, the knowledge of more than the system limit the transmitted process variables and heat work ( the integral value of the work is obtained, for example, by measurement of speed and torque ). For adiabatic processes, such as in a steam turbine, the surface alone represents the dissipated work is the state curve by measuring the state variables (generally pressure and temperature ) is known, from which of the condition equations, the corresponding entropy can be calculated ( as the difference from that of the triple point ), are obtained by the representation in the Ts diagram a good overview of the quality of the process (see " adiabatic engine").

Figure 2 shows the Ts diagram frequently used for water vapor with isobars and isochores and the phase boundary. The ordinate is the Celsius temperature here. Therefore, the graph is adjacent to the hs diagram particularly suitable for representation of state behavior in the technically important area above the freezing point and to represent the processes in this area, but not to identify the heating and the dissipated work.