Flash Steam Percentage Across a Pressure Drop
The fraction of condensate that re-boils to steam when it drops across a trap from a high pressure to a lower one.
Example
You enter
- Liquid enthalpy hf at high pressure (Btu/lb) 309
- Liquid enthalpy hf at low pressure (Btu/lb) 180
- Latent heat hfg at low pressure (Btu/lb) 970
You get
- Flash steam 13.3
Details, formula, and sources
flash = (hf_high - hf_low) / hfg_low, from the saturated-water enthalpies at the two pressures (100-to-0 psig -> ~13.3%). Drives flash-tank and vent-line sizing and the 'why is my return full of steam' diagnosis. A thermodynamic-ideal fraction; trap subcooling and line losses move the field value, and a flash-recovery vessel is sized from the manufacturer's data.
flash_fraction = (hf_high - hf_low) / hfg_low; flash_pct = flash_fraction x 100. hf and hfg are saturated-water enthalpies (Btu/lb) at the two pressures.
First-principles steam thermodynamics; the bundled saturated-water enthalpy points are from the ASME steam tables, by name. Not edition-bound.
The flash relation is public thermodynamics; the enthalpies come from the published ASME / IAPWS saturated-water steam tables.
Estimate. AHJ and licensed professional govern.
Field names used by the API: hf_high, hf_low, hfg_low, flash_pct
- Enthalpies saturated-liquid enthalpies hf and latent heat hfg from the ASME steam tables at the two pressures (user-supplied for an off-table pressure)ASME steam tables
- Ideal flash the fraction is the thermodynamic ideal; trap subcooling and line losses lower the field valuesteam thermodynamics