3-dimensional diagrams Phase diagram

p–v–t 3d diagram fixed amount of pure material

it possible envision three-dimensional (3d) graphs showing 3 thermodynamic quantities. example, single component, 3d cartesian coordinate type graph can show temperature (t) on 1 axis, pressure (p) on second axis, , specific volume (v) on third. such 3d graph called p–v–t diagram. equilibrium conditions shown curves on curved surface in 3d areas solid, liquid, , vapor phases , areas solid , liquid, solid , vapor, or liquid , vapor coexist in equilibrium. line on surface called triple line solid, liquid , vapor can coexist in equilibrium. critical point remains point on surface on 3d phase diagram.

for water, 3d p–v–t diagram seen here:

an orthographic projection of 3d p–v–t graph showing pressure , temperature vertical , horizontal axes collapses 3d plot standard 2d pressure–temperature diagram. when done, solid–vapor, solid–liquid, , liquid–vapor surfaces collapse 3 corresponding curved lines meeting @ triple point, collapsed orthographic projection of triple line.