Saturated steam
Dry saturated steam from 100 to 200 °C — saturation pressure, vapour density and latent heat along the boiling line that low and medium pressure steam heating runs on.
| Phase | Gas — saturated state |
| Temperature range | 100 to 200 °C |
| Source | IAPWS-95 / ASME Steam Tables |
Validated from 100 to 200 °C along the saturation curve.
| Density | 2.548 kg/m³ |
| Dynamic viscosity | 0.01419 mPa·s |
| Specific heat | 2.314 kJ/(kg·K) |
| Thermal conductivity | 0.0288 W/(m·K) |
| Vapour pressure | 476.16 kPa |
| Latent heat of vaporisation | 2,113.7 kJ/kg |
| Kinematic viscosity ν = µ/ρ | 5.5691 mm²/s |
| Prandtl number Pr = cpµ/k | 1.14 |
Saturated state only. On the saturation curve temperature and pressure are locked together, so one input fixes everything — but sub-cooled liquid and superheated vapour need two, and these values do not describe them.
Learning zone
Saturated steam is the fluid the entire steam-heating trade is built around, and it has one variable. Pick the pressure and the temperature follows; pick the temperature and the pressure follows. That is why a steam system is controlled by a pressure gauge and why a trap, a coil and a main can all be sized from a single number.
Latent heat is the reason to use it at all. Condensing one kilogram of steam at 100 °C releases 2256 kJ — about 970 BTU per pound — at CONSTANT temperature, with no flow-rate and ΔT juggling of the kind a water loop demands. A steam coil delivers heat isothermally, which is exactly what a process that needs a held temperature wants.
The trade-off appears as pressure rises. Latent heat FALLS with temperature: 2256 kJ/kg at 100 °C, 2114 at 150 °C, 1940 at 200 °C, and eventually zero at the critical point, 373.95 °C and 22.064 MPa, where liquid and vapour stop being distinguishable. Running a system at higher pressure to get higher temperature buys less heat per kilogram, so mass flow rises faster than the temperature gain suggests. Meanwhile vapour density climbs by a factor of thirteen across this range, from 0.598 to 7.86 kg/m³, which is why high pressure steam mains are so much smaller than low pressure ones for the same duty.
Everything here is DRY saturated steam. Real steam carries entrained water — a dryness fraction of 0.95 is normal and delivers 95 % of the latent heat — and superheated steam is off the saturation curve entirely, where temperature and pressure become independent again and these values no longer apply.
The constants library carries these at a single stated temperature, with their uncertainty and provenance. The table above is the same substance as a function.