To build a robust calculation sheet, you must define the following input variables: A. Motive Fluid Properties Usually high-pressure steam or air. Temperature ( Tmcap T sub m ): Needed to determine specific volume. Flow Rate ( Wmcap W sub m ): The mass flow available to do the work. B. Suction Fluid Properties Suction Pressure ( Pscap P sub s ): The vacuum level you aim to maintain. Entrainment Ratio ( ): The ratio of suction gas to motive gas ( ). This is the most critical output of your calculation. C. Discharge Conditions Discharge Pressure ( Pdcap P sub d ): The pressure the ejector must overcome (back-pressure). 3. The Step-by-Step Calculation Process
Where the low-pressure fluid is entrained.
Converts high-pressure energy into high-velocity kinetic energy.
A is a vital tool for process engineers. By utilizing a structured XLS approach, you can predict how changes in utility headers will affect your vacuum system. Always validate your spreadsheet results against manufacturer curves to account for specific friction losses unique to their casting designs.
) does not exceed the "critical discharge pressure." If it does, the shockwave will move back into the throat, and the ejector will stop suctioning (breaking the vacuum). 4. Structuring Your XLS for Accuracy
A standard XLS for ejector design typically follows these four stages: Step 1: Nozzle Sizing (Isentropic Expansion)
The diffuser must slow the mixed fluid down to recover pressure.
Use conditional formatting to highlight if the Compression Ratio ( ) exceeds stable limits (typically 10:1 for single stage).