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Plant Engineering Calculator

Updated Sep 18, 2026

Flash Steam Percentage Calculator — Condensate Letdown & Flash Flow

Calculate flash-steam fraction and mass flow from high-pressure condensate liquid enthalpy and low-pressure saturated liquid/latent enthalpy.

Live calculationWorking shownPrivate in browser

Inputs

Results

Flash fraction 15.20 %
Flash steam 152.0 kg/h
Remaining condensate 848.0 kg/h
Flash ratio 0.1520 kg/kg feed
More actions

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Formula

x=(hf,high−hf,low)/hfg,low; mflash=x·mcond.

Your calculation, step by step

These steps use the values currently entered above so the result can be checked independently.

  1. 1.Available enthalpy above downstream saturated liquid = hf,high − hf,low = 762.00 − 419.00 = 343.00 kJ/kg.
  2. 2.Flash fraction x = 343.00 ÷ 2257.00 = 0.15197 = 15.20%.
  3. 3.Flash steam = 1000.00 × 0.15197 = 151.97 kg/h.
  4. 4.Remaining liquid condensate = 1000.00 − 151.97 = 848.03 kg/h.

How to use this calculator

  1. Enter measured or design values using the units shown beside each field.
  2. Review the live results and the substituted calculation steps before using the estimate.
  3. Check the assumptions below, then continue to a related calculator when the next engineering decision needs another model.

Worked example

With hf,high=762, hf,low=419 and hfg,low=2257 kJ/kg, about 15.2% of saturated condensate flashes after letdown.

Assumptions and limits

  • Enter validated steam-table enthalpies for both pressure states.
  • Assumes adiabatic throttling and saturated liquid upstream; subcooling changes the result.

How to interpret the result

Treat the primary result as an engineering screening value, then use the secondary outputs to understand scale, energy or operating impact. Confirm site measurements, equipment limits and applicable standards before making a design or control change.

Questions engineers ask

Why does flash-steam percentage use enthalpy instead of pressure directly?

The letdown is modeled as throttling, so the upstream liquid enthalpy is conserved across the pressure drop. At the lower pressure, the excess above saturated-liquid enthalpy supplies the latent heat needed to vaporize part of the condensate.

Where should the hf and hfg values come from?

Use a consistent steam-table or standards-backed property source for the actual upstream and downstream pressures. This calculator intentionally does not invent steam properties from pressure because trustworthy production work needs validated property data.

What if the enthalpy inputs imply more than 100% flash?

That is not a valid saturated-condensate flash result. It indicates inconsistent state assumptions or property inputs; check the pressures, upstream liquid condition and steam-table values rather than clipping an impossible result.

Continue the calculation

Use the next calculator in the same engineering workflow instead of restarting from search.

steam qualitycondensate returnsteam vent loss
Methodology. MAXScanner shows the governing formula, entered values and calculation outputs so the estimate is auditable. The calculator is a screening aid; assumptions and equipment-specific limits remain part of the engineering review.