Steam Ejector Calculator | Suction, Discharge & Steam Flow
Steam Ejector Calculator
Performance Analysis based on Equivalent Air Load & Rload Correlations
Inlet Stream (Suction)
Motive Steam
Outlet Stream (Discharge)
Required Steam Flow
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Performance Diagnostics
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Equivalent Air Load (kg/h)
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Entrainment Ratio (Rload)
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Steam Press. Ratio Factor
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MW Ratio Factor
Technical Notes
Variable Definitions
- αΉtot: suction total load (kg/h) = water vapour + noncondensables.
- αΉw: suction water vapour (kg/h); αΉnc = αΉtot β αΉw.
- MW: molecular weight of suction noncondensable gas mixture.
- Ts: suction temperature (Β°F).
- Ps: suction pressure (mmHg abs).
- Pd: discharge pressure (mmHg abs).
- Pstm: motive steam supply pressure (psig).
- EqAir: equivalent air load (kg/h) used for correlation.
- Rload: entrainment ratio (dimensionless) in this correlation set.
- αΉstm: motive steam mass flow (kg/h).
Formulas / Logic
- Equivalent air load: converts water vapour and noncondensables to an βair-equivalentβ basis using temperature-dependent factors and MW correction.
- MW ratio factor: computed from an empirical function of MW: mwRatio = exp(aΒ·MWΒ² + bΒ·ln(MW) + c/MW + d).
- Steam pressure ratio factor: empirical function of motive steam pressure: stmRatio = exp(aΒ·PΒ² + bΒ·ln(P) + c/P + d).
- Pressure correlation: discharge and suction are related by a log-linear form using slope/origin parameters that vary with Rload.
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Solve modes:
- Solve steam rate: iterate Rload so calculated discharge matches target; then αΉstm = RloadΒ·EqAirΒ·stmRatio.
- Solve suction: compute Rload from entered steam flow, then invert correlation to obtain Ps.
- Solve discharge: compute Rload from entered steam flow, then compute Pd.
These correlations are screening/curve-fit relations and are not a
substitute for manufacturer performance curves.
Assumptions / Notes
- Pressures are in mmHg absolute (not gauge). Ensure vacuum readings are converted to absolute before entry.
- Correlation validity is limited; warnings appear for high Rload values where multi-stage ejectors are commonly required.
- Does not model nozzle/choke limits, condensation within ejector, inter/after-condenser effects, or non-equilibrium flashing.
- Use as preliminary estimate; finalize using vendor curves per project vacuum system design basis.
Standards / References
- Heat Exchange Institute (HEI) β Standards for Steam Jet Vacuum Systems (selection, terminology, typical performance basis).
- Perryβs Chemical Engineersβ Handbook β vacuum systems/ejector sizing background (for general guidance).
- Vendor performance curves and datasheets remain governing for final sizing and guarantees.