Steam Turbine Wetness & Condensation Risk Calculator — Steam Quality, Outlet Enthalpy and Specific Work
Calculate steam quality, outlet enthalpy and specific work using inlet pressure, outlet pressure, inlet enthalpy, inlet entropy and turbine efficiency.
Enter the known values and review the calculated result
Input parameters
Use consistent values and select the intended engineering units.
Inlet conditions
Outlet conditions
Turbine performance
Results
Engineering Pro Save, document and continue this calculation
Turn this result into a reusable engineering record with saving, PDF export and reporting workflows.
Method, application and limitations
Review the calculation method, intended application and engineering assumptions before using the result in a design decision.
Formula and calculation method
Steam quality formula:
pbar = p / 100000
T = 1810.94 / (8.14019 − log10(pbar)) − 244.485 + 273.15
hf = 4180 · (T − 273.15)
hfg = 2500000 − 2300 · (T − 273.15)
sf = hf / T
sfg = hfg / T
sg = sf + sfg
Isentropic outlet enthalpy:
If s₁ > sg,2: T2s = T₂ · exp((s₁ − sg,2) / 2100)
If s₁ > sg,2: h2s = hf,2 + hfg,2 + 2100 · (T2s − T₂)
If sf,2 ≤ s₁ ≤ sg,2: x2s = (s₁ − sf,2) / sfg,2
If sf,2 ≤ s₁ ≤ sg,2: h2s = hf,2 + x2s · hfg,2
Outlet enthalpy formula:
Δhis = h₁ − h2s
h₂ = h₁ − ηₜ · Δhis
Specific work formula:
W = h₁ − h₂
Steam quality formula:
hg,2 = hf,2 + hfg,2
If h₂ > hg,2: x₂ = 1
If h₂ ≤ hg,2: x₂ = (h₂ − hf,2) / hfg,2
where:
- x₂ — steam quality at turbine outlet (-)
- h₂ — outlet enthalpy (J/kg)
- W — specific work (J/kg)
- p₁ — inlet pressure (Pa)
- p₂ — outlet pressure (Pa)
- h₁ — inlet enthalpy (J/kg)
- s₁ — inlet entropy (J/kg·K)
- ηₜ — turbine efficiency (-)
- T — saturation temperature (K)
- hf — saturated liquid enthalpy (J/kg)
- hfg — latent heat of vaporization (J/kg)
- sf — saturated liquid entropy (J/kg·K)
- sfg — evaporation entropy difference (J/kg·K)
- sg — saturated vapor entropy (J/kg·K)
- h2s — isentropic outlet enthalpy (J/kg)
- Δhis — isentropic enthalpy drop (J/kg)
- hg,2 — saturated vapor enthalpy at outlet pressure (J/kg)
When to use this calculator
When to use this calculator:
- Estimate turbine outlet steam quality after expansion from a known inlet pressure, outlet pressure, inlet enthalpy and inlet entropy.
- Calculate outlet enthalpy when turbine efficiency is known or selected from the turbine efficiency provider.
- Calculate specific work output from the actual enthalpy drop across the turbine.
- Check whether the outlet state remains superheated or enters the wet steam region.
- Evaluate condensation risk using steam quality, moisture fraction and the pressure ratio between inlet and outlet.
How to interpret the result
Steam quality is defined as the vapor fraction at the turbine outlet. A value of 1 means the outlet state is treated as dry saturated or superheated, while values below 1 indicate moisture in the outlet steam.
Outlet enthalpy depends on inlet enthalpy, isentropic outlet enthalpy and turbine efficiency. Increasing turbine efficiency increases specific work and decreases outlet enthalpy for the same isentropic enthalpy drop.
Specific work is defined as the actual enthalpy drop between turbine inlet and outlet. It increases when the actual outlet enthalpy decreases relative to inlet enthalpy.
- Safe — the outlet state is superheated, or steam quality is x₂ ≥ 0.98.
- Limit — steam quality is 0.95 ≤ x₂ < 0.98.
- Warning — steam quality is 0.90 ≤ x₂ < 0.95.
- Invalid — steam quality is x₂ < 0.90, or one of the validation conditions fails.
The result is used to evaluate outlet wetness, condensation risk and available turbine specific work from the calculated expansion state.
Calculation example
Example:
A user wants to check whether steam expansion through a turbine creates a wet outlet condition and how much specific work is produced.
- p₁ — Inlet pressure = 2000000 Pa
- p₂ — Outlet pressure = 100000 Pa
- h₁ — Inlet enthalpy = 3200000 J/kg
- s₁ — Inlet entropy = 7000 J/kg·K
- ηₜ — Turbine efficiency = 0.85
Result: x₂ = 1.000, h₂ ≈ 2736680 J/kg, W ≈ 463320 J/kg.
Assumptions and limitations
- Inlet pressure must be greater than outlet pressure.
- Turbine efficiency must be greater than 0 and not greater than 1.
- Inlet pressure must be at least 10000 Pa.
- Outlet pressure must be at least 1000 Pa.
- Inlet enthalpy must remain within 100000–4000000 J/kg.
- Inlet entropy must remain within 1000–10000 J/kg·K.
- The inlet state must be superheated according to saturated vapor entropy at inlet pressure.
- Saturation properties are calculated from the pressure-based approximation used in the calculator logic.
- Superheated outlet enthalpy uses a constant heat capacity value of 2100 J/kg·K.