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ENGR5003 / Week 3
L8 slide 7: Triple state? Reading the water p-v and T-s diagramsFrom lectureCurrent specThird4 marks5 min

ENGR5003 Lecture 8, slide 7 (T-v diagram of constant-pressure phase change processes, "Triple state ?")

The p-v and T-s diagrams of water on Lecture 8 slide 7 are summarised as "one point, two lines, three regions, five states", and the dashed line at the bottom of the p-v diagram is labelled "Triple state ?".

Formulas you may need
  • Critical point of water: pcr=22.12p_{cr} = 22.12 MPa, tcr=374.15t_{cr} = 374.15 C, vcr=0.00317 m3/kgv_{cr} = 0.00317\ \mathrm{m^3/kg} (steam tables)
  • Triple point of water: p=0.006112p = 0.006112 bar, T=273.16T = 273.16 K (steam tables; first row of the saturation table)
  1. (a)
    Name the one point, the two lines, the three regions and the five states, giving the critical-point values for water.
    [3]
  2. (b)
    What is the "triple state" (the dashed line at the bottom of the p-v diagram), and what are the triple-point pressure and temperature of water?
    [1]