Design Calculation Xls Fixed _hot_ - Ejector
: The resulting vacuum draws in a secondary "suction" fluid. In the mixing chamber, momentum is exchanged between the high-velocity motive stream and the lower-velocity suction stream.
Vm=2⋅kk−1⋅R⋅Tm⋅[1−(PsPm)k−1k]cap V sub m equals the square root of 2 center dot the fraction with numerator k and denominator k minus 1 end-fraction center dot cap R center dot cap T sub m center dot open bracket 1 minus open paren the fraction with numerator cap P sub s and denominator cap P sub m end-fraction close paren raised to the the fraction with numerator k minus 1 and denominator k end-fraction power close bracket end-root = Isentropic exponent (Ratio of specific heats, = Specific gas constant ( Tmcap T sub m = Absolute temperature of motive fluid ( Pmcap P sub m = Motive fluid inlet pressure ( Pscap P sub s = Suction fluid inlet pressure ( Entrainment Ratio (
| Mode | Process | Goal | Fixed/Free? | | :--- | :--- | :--- | :--- | | | Input desired flow rates (motive & suction), pressures, & gas properties. | Output the optimal nozzle and mixing chamber diameters. | The geometry is free (to be determined). | | Rating (Performance Prediction) | Input an existing ejector’s geometry (fixed diameters & dimensions). | Predict how the entrained flow will change as suction or discharge pressures vary. | The geometry is fixed (already known). |
A standard XLS for ejector design typically follows these four stages: Step 1: Nozzle Sizing (Isentropic Expansion)
If your suction fluid contains air or CO2, the molecular weight changes, which drastically alters the entrainment ratio. ejector design calculation xls fixed
(but leave input cells unlocked).
= P_d / P_s Example: 1.1 / 0.1 = 11
Often called the "back pressure." If the actual back pressure exceeds the design discharge pressure, the ejector will "break" and lose vacuum rapidly. Step-by-Step Design Logic in XLS
In standard engineering practices, like the Heat Exchange Institute (HEI) standards, the ER is calculated using correction factors for molecular weight and temperature: : The resulting vacuum draws in a secondary "suction" fluid
Then: W_m = W_s / R (kg/h)
If you are looking to design your own calculation, ensure you validate it against established literature (e.g., "Heat Exchange Institute Standards for Steam Jet Vacuum Systems"). If you'd like, I can help you: a specific calculation error.
To understand the XLS, you must understand the underlying physics that the formulas are calculating. A. Core Components
Using this type of spreadsheet is essential for troubleshooting an existing ejector, evaluating its performance under new process conditions, or checking the “turndown” ratio of an installed unit. | | :--- | :--- | :--- |
Ejectors, or steam jet ejectors, are widely used in chemical, oil & gas, and power generation industries to create vacuum conditions by entraining, compressing, and pumping gases or vapors. A critical aspect of ensuring efficient operation lies in precise design calculations.
Many old spreadsheets use a hardcoded nozzle efficiency of and diffuser efficiency of
Replace hardcoded constants with a lookup table ( VLOOKUP or XLOOKUP ) linked to the Reynolds number (
Use =IF(Pm>Ps, LOG(Pm/Ps), 0) to prevent the sheet from breaking during zero-load initialization testing. Handling Circular References in Diffuser Sizing