Discharge Measurement
Inlet (Ambient) Conditions
Validation & Checks
Calculation Results
Free Air Delivery (FAD)
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Vapor Pressure (Psat)
-
Volume Expansion Ratio
i
Ratio of Discharge Volume to Inlet Volume.
-
Equivalent Standard Flow
SCFM (14.7 psi, 60°F)
-
Nm³/min (1 bar, 0°C)
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Technical Notes
Variable Definitions
- Qmeas: measured discharge volumetric flow at meter (compressed volume).
- Pdis,g: discharge gauge pressure at meter.
- Pdis: discharge absolute pressure, Pdis=Pdis,g+Pamb.
- Tdis: discharge absolute temperature (K).
- Pamb, Tamb: inlet/ambient suction pressure (absolute) and temperature.
- RH: inlet relative humidity (%).
- Psat: saturation vapour pressure of water at Tamb.
- Pw: water vapour partial pressure, Pw=RH·Psat.
- Pdry: inlet dry-air partial pressure, Pdry=Pamb−Pw.
- FAD: Free Air Delivery corrected to inlet dry-air reference basis (reported in selected flow units).
Formulas / Logic
- Humidity correction (Annex C concept): compute dry-air partial pressure at inlet Pdry.
- Ideal-gas reference correction: QFAD = Qmeas · (Pdis/Pdry) · (Tamb/Tdis).
- Saturation pressure: calculated from a standard engineering correlation for water vapour pressure vs temperature (used for inlet humidity correction).
- Equivalent standard flows: Qstd = QFAD · (Pdry/Pstd) · (Tstd/Tamb). This tool reports SCFM (14.696 psia, 60°F) and Nm³/min (1.01325 bar(a), 0°C).
FAD here is a dry-air corrected reference flow based on ideal-gas
relationships. For acceptance tests, follow ISO 1217 definitions,
instrument requirements, and correction procedures applicable to the
compressor type and test setup.
Assumptions / Notes
- Pressures are treated as: discharge = gauge input; inlet = absolute input.
- Humidity correction is applied at the inlet only (dry-air partial pressure).
- Gas is assumed ideal; compressibility (Z) is not applied (screening). For high pressures, consider Z correction as per test method/vendor.
- Ensure discharge temperature is measured at the same point as discharge pressure/flow measurement.
Standards / References
- ISO 1217 — Displacement compressors: Acceptance tests (see Annex C for water vapour correction concept).
- Standard psychrometric relationships for water vapour partial pressure from RH and saturation pressure.
- For certified results, follow ISO 1217 instrumentation, uncertainty, and test setup requirements.