Engineering Thermodynamics: Phase Diagrams

Comprehensive vocabulary flashcards covering pure substance phase changes, critical and triple points, supercritical fluids, and regions of P-T, T-v, and P-v diagrams from Claire Yu Yan's Introduction to Engineering Thermodynamics.

Pure substance

A substance that may exist in any of three distinct phases—solid, liquid, and vapour—at specific temperatures and pressures.

Phase change

The transition of a pure substance from one physical state to another resulting from a change in temperature or pressure, such as water turning to ice at $1\,\text{bar}$ and $0^\circ\text{C}$.

P-T diagram

A pressure–temperature phase diagram illustrating the equilibrium phase boundaries between solid, liquid, and vapour, as well as the triple point, critical point, and supercritical fluid region.

Triple point

The unique thermodynamic condition on a P-T diagram where the solid, liquid, and vapour phases coexist simultaneously in equilibrium.

Critical point

The thermodynamic state defined by the critical pressure ($P_c$) and critical temperature ($T_c$), beyond which distinct liquid and gas phases cannot coexist.

Supercritical state

A thermodynamic state at a pressure and temperature above the critical point.

Supercritical fluid

A substance existing at a supercritical state, characterized by the absence of distinct liquid and gas phases within the supercritical zone.

Subcritical fluid

A substance existing at thermodynamic states below its critical point, where distinct liquid and vapour/gas phases can exist.

Working fluid

A substance that undergoes phase transitions between liquid and vapour within an engineering system, such as water in a steam plant or R134a in a refrigeration system.

Compressed liquid region

The region located to the left of the saturated liquid line on a T-v or P-v diagram where the substance exists entirely as a liquid.

Saturated liquid line

The curve on a phase diagram that marks the onset of vaporization, separating the compressed liquid region from the saturated liquid-vapour mixture region.

Saturated liquid-vapour region

The two-phase coexistence region located beneath the saturation dome between the saturated liquid line and the saturated vapour line.

Saturated vapour line

The curve on a phase diagram that marks the boundary between the two-phase saturated liquid-vapour region and the single-phase superheated vapour region.

Superheated vapour region

The region located to the right of the saturated vapour line on a T-v or P-v diagram where the substance exists entirely in the vapour state.

T-v diagram

A temperature versus specific volume diagram featuring the saturation dome, the critical point, and constant pressure lines that remain horizontal across the two-phase mixture.

P-v diagram

A pressure versus specific volume diagram featuring the saturation dome, the critical point, and constant temperature lines that remain horizontal across the two-phase mixture.