Which input pair should I use?
Use P–T for single-phase lookups, P–h when enthalpy is known or conserved through ideal throttling, and P–s for an ideal isentropic outlet at a specified pressure. Use h–s, T–h, or T–s to reconstruct a state from those known properties. T–h and T–s inputs with multiple solutions are rejected.
For saturated states below the critical point, use P–x or T–x. Pressure and temperature are dependent on the saturation curve, so P–T alone cannot determine vapor quality.
What does vapor quality (x) mean?
Vapor quality x is the vapor mass fraction in a saturated liquid–vapor mixture. Enter x = 0 for saturated liquid or x = 1 for saturated vapor.
Wet-steam results show Sat. liquid, Sat. vapor, and Mixture side by side, plus the vaporization differences h_fg, s_fg, and v_fg. Specific volume, internal energy, enthalpy, and entropy are weighted by vapor mass fraction. Mixture density is calculated from ρ = 1/v.
Why is a property shown as a dash (—)?
A dash means a property is not applicable, is not calculated for the bulk two-phase mixture, or exceeds a correlation limit used by PhaseGauge. It never means zero. Vapor quality applies to saturated states; surface tension describes the liquid–vapor interface.
For wet steam, cₚ, cᵥ, w, β, κₜ, μ, λ, ε, and pK_w are shown for the liquid and vapor endpoints. Their mixture values are shown as dashes because simple mass-weighted averaging does not determine them.
PhaseGauge stops reporting viscosity and thermal conductivity above 1173.15 K (900 °C), dielectric constant above 873 K (599.85 °C), and pK_w above 1273.15 K (1000 °C).
How are gauge pressures (barg and psig) converted?
PhaseGauge adds a fixed standard atmosphere of 101.325 kPa (≈ 14.69595 psi) to convert gauge pressure to absolute pressure.
If your measurement uses local atmospheric pressure, calculate p_absolute = p_gauge + p_atmosphere and enter the result in an absolute unit: MPa, bar, kPa, atm, or psi. For a positive vacuum reading below atmosphere, use p_absolute = p_atmosphere − p_vacuum.
Why do results differ from NIST WebBook or older steam tables?
PhaseGauge uses IAPWS-IF97, the industrial formulation for fast water and steam property calculations. The NIST Chemistry WebBook uses IAPWS-95 for water, the reference formulation for general and scientific use. Differences depend on the state and property, especially near the critical point.
For older tables, check the formulation, reference convention, units, and interpolation or rounding. Methodologylists PhaseGauge's verification coverage and test tolerances.
How do I compare two states?
Calculate your reference state, then your current state. In Recent, select Compare on the reference entry. The table shows both states and signed property differences: current minus reference, using your selected unit system and display precision.
To check an ideal isentropic outlet, calculate it with P–s using the outlet pressure and inlet entropy, then compare it with the inlet state.
Are my inputs or calculation history sent to a server?
The solver runs in your browser. Ordinary calculations do not upload your inputs or saved history. Browser storage holds your preferences and up to 200 recent and 100 pinned calculations.
Opening a shared link sends its encoded inputs in the URL to the hosting infrastructure. The site also uses usage analytics; see Privacy for details.
How should I archive a calculation for engineering review?
Use Export → Print for a record with the inputs and units, property table, record time, permalink, and engine version. CSV uses calculation units such as MPa and K, with your selected display precision. JSON preserves the stored values without display rounding and includes result snapshots.
Re-import JSON and select Restore to recalculate with the current engine. PhaseGauge reports changes visible at the selected precision. Equipment limits, applicable codes, and safety factors still need separate engineering review.