Steam Jet Ejector Calculator | HEI Vacuum System Design
HEI Steam Jet Ejector Calculator
π Sizing based on Heat Exchange Institute (HEI) Standards for Equivalent Air Load & Critical Flow
1. Process Conditions
Usually 101.3 kPa for single stage venting to atm.
2. Gas Properties (HEI)
Used for HEI Equivalent Air Load (Air MW=29).
3. Motive Steam Supply
Leave blank for Saturated Steam.
4. Performance Tuning
Leave blank to estimate based on Comp. Ratio.
Primary Outputs
Required Motive Steam:
--
kg/h
HEI Equivalent Air Load:
--
kg/h (Dry Air @ 70Β°F)
System Analysis
Compression Ratio (Pd / Ps):
--
Expansion Ratio (Pm / Ps):
--
Entrainment Ratio (Ra):
--
Recommended Stages:
--
HEI Correction Factors
MW Factor (Fm):
--
Temp Factor (Ft):
--
Motive Nozzle Sizing
Throat Diameter:
-- mm
Critical Flow Status:
--
Technical Notes
Variable Definitions
- Ps: Suction absolute pressure.
- Pd: Discharge absolute pressure.
- Pm: Motive steam absolute pressure.
- CR: Compression ratio = Pd/Ps.
- ER: Expansion ratio = Pm/Ps.
- MW: Gas molecular weight.
- Fm, Ft: HEI correction factors for molecular weight and suction temperature.
- EAL: Equivalent Air Load (kg/h of dry air at 70Β°F reference).
- Ra: Entrainment ratio (kg motive steam / kg EAL).
- αΉs: Motive steam mass flow rate.
- At: Motive nozzle throat area.
Formulas / Logic
- HEI Equivalent Air Load (screening): EAL = αΉgas / (FmΒ·Ft)
- Motive steam load: αΉs = EAL Β· Ra
- Nozzle throat sizing (critical flow screening): implemented using a common HEI-style correlation in US units with a superheat correction factor Ksh.
- Critical (sonic) check: Ps < 0.546Β·Pm (rule-of-thumb screening for choked flow at the motive nozzle).
- Stage estimate: If CR is high (e.g., > 8), multi-stage system typically required; this tool warns and reports an approximate stage count.
This calculator is intended for preliminary checks only; final
ejector selection should use HEI curves/vendor software and confirm
non-condensables, suction temperature effects, and intercondensers
(if multi-stage).
Assumptions / Notes
- Pressures are treated as absolute at suction and discharge; motive pressure converts to absolute when entered as barg/psig.
- HEI correction factors used here are simplified screening relationships; verify with HEI tables for the project edition and gas composition.
- If suction temperature is not entered, EAL cannot be corrected reliably; enter the best-estimate suction temperature.
- Critical flow and throat sizing are screening-level; real nozzle sizing depends on steam quality, nozzle efficiency, and geometry.
Standards / References
- HEI Standards: Steam Jet Ejectors / Steam Jet Vacuum Systems (use project-approved edition).
- ASME Steam Tables / IAPWS for saturation temperature reference (recommended for final design).
- Vendor curves/software should be used to confirm stages, intercondenser loads, and steam consumption.