# A New Phase Diagram: The T-S Diagram

The

### TS Diagram

:
• We only consider pure substances
• Two-phase envelope, similar to PV Diagram

or

#### compressed liquids

have lower entropy than saturated liquids
• #### Superheated vapors

have higher entropy than

#### saturated vapors

• The entropy of a

#### saturated vapor-liquid mixture

lies below the entropy of the saturated vapor (at the same T & P) and above the entropy of the saturated liquid at the same T & P.
Compressed or
Subcooled Liquid:
Superheated Vapor:
Saturated
Vapor -Liquid Mixture:
Subcooled Liquid
Superheated Vapor
Saturated Vapor - Liquid Mixture
Critical
Point
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### Ch 7, Lesson B, Page 8 - A New Phase Diagram: The T-S Diagram

• We will use the TS Diagram more often than any other phase diagram in the remainder of this course.
• So, let’s begin with a proper introduction.
• First of all, T is always on the vertical axis and S or Shat is always on the horizontal axis.
• The main feature of the TS Diagrams that we will use is our old friend the two-phase envelope.
• Just as in the PV Diagram, the saturated liquid curve lies to the left of the critical point and the saturated vapor curve lies to the right.
• States that lie beneath the saturation curve consist of a mixture of saturated liquid and saturated vapor.
• We will not consider regions of the diagram in which a solid phase appears.
• Just as in a PV Diagram, states to the left of the saturated liquid curve are subcooled or compressed liquids and states to the right of the saturated vapor curve are superheated vapors.
• Notice that at the same temperature, vapor phases have greater specific entropies than liquid phases.
• Now, let’s take a look at a real TS Diagram that has a little more detail.