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: 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.
Formula and source
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.
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