To build a scalable and error-free ejector design tool in Excel, structure your tabs and cells systematically. Tab 1: Input Parameters
| Pitfall | Solution in .xls | |---------|------------------| | (nozzle area depends on ṁ_s which depends on area) | Enable iterative calculation: File → Options → Formulas → Enable iterative calculation (max 100 iterations). | | Using wrong fluid properties | Always use absolute pressure (bar(a)), not gauge. Add validation rules. | | Neglecting two-phase flow | If motive fluid is saturated steam, check quality at nozzle exit. Use IF condition: if quality < 0.9, warn user. | | Manual lookup errors | Replace all manual chart lookups with FORECAST.LINEAR or VLOOKUP approximate match. | | Unit mix-up (mm vs m) | Use named constants: mm_to_m = 0.001 . Always convert inside formulas. |
Motive Fluid (High Pressure) | v [ Motive Nozzle ] ---> (Converts Pressure to Supersonic Velocity) | Suction Fluid ------------> [ Mixing Chamber ] (Fluids mix at constant pressure) (Low Pressure) | v [ Diffuser ] ---> Discharge (Intermediate Pressure)
Ejectors, also known as jet pumps or eductors, are simple devices that use a high-pressure fluid (motive fluid) to entrain, mix, and compress a secondary fluid (suction fluid), achieving a pumping effect without any moving parts. Because of their simplicity, reliability, and low cost, they are widely used in industrial processes for creating vacuum, pumping gases, and handling corrosive or hazardous materials. ejector design calculation xls
This article explores the fundamentals of ejector design, the critical parameters required for calculation, and how to utilize a spreadsheet tool to automate the design process. 1. What is an Ejector? (Fundamentals)
Calculate:
Dtn=4⋅Atnπcap D sub t n end-sub equals the square root of the fraction with numerator 4 center dot cap A sub t n end-sub and denominator pi end-fraction end-root Calculated using the Mach number ( Mecap M sub e ) at the expansion pressure. Step 4: Mixing Chamber and Diffuser Sizing The mixing throat area ( Atdcap A sub t d end-sub ) can be estimated using momentum balance principles: Calculate the momentum of the entering motive gas. To build a scalable and error-free ejector design
Rm=α⋅(PsPd)⋅MsMm−1cap R m equals alpha center dot open paren the fraction with numerator cap P sub s and denominator cap P sub d end-fraction close paren center dot the square root of the fraction with numerator cap M sub s and denominator cap M sub m end-fraction end-root minus 1 (Note:
Calculates the ratio of motive pressure to suction pressure: $$ER = \fracP_mP_s$$
A standard engineering spreadsheet for ejectors follows these sequential steps: : Motive Pressure ( Ppcap P sub p ) : High-pressure steam or fluid entering the nozzle. Suction Pressure ( Pecap P sub e ) : Low-pressure entrained vapor. Discharge/Exit Pressure ( Pccap P sub c ) : Pressure at the condenser or outlet. Calculate Ratios : Expansion Ratio ( Ercap E sub r = ) : Determines how much the motive fluid can expand. Compression Ratio ( Crcap C sub r = Add validation rules
To create or use an Excel spreadsheet for ejector design, you need to input several key parameters. An effective tool should include cells for the following: Input Data Motive Fluid Properties: Pressure ( Pmcap P sub m ), Temperature ( Tmcap T sub m ), Molecular Weight, Ratio of Specific Heats (γ). Suction Fluid Properties: Pressure ( Pscap P sub s ), Temperature ( Tscap T sub s ), Molecular Weight, γ. Discharge Pressure ( Pdcap P sub d ): The required backpressure. Desired Capacity: Suction mass flow rate ( Wscap W sub s Calculated Outputs (Optimized by XLS) Motive Mass Flow Rate ( Wmcap W sub m ): Usually determined by the nozzle throat area. Entrainment Ratio (R):
Below are essential equations often incorporated into VBA or formula cells in a design XLS:
Comprehensive Guide to Ejector Design and Excel Calculation Methodologies
This is why a simple hand calculation fails. An XLS spreadsheet iterates these equations at each section.
