The spreadsheet must contain a fixed internal lookup table for saturated steam, superheated steam, or ideal gas constants. Unlike dynamic databases, a fixed XLS uses embedded arrays covering 0 to 500°C and 0 to 100 bar. This allows the engineer to select a fluid by index number, preventing VLOOKUP errors.
This section calculates the pressures, areas, and velocities. This logic assumes an ideal gas and isentropic flow (standard for first-pass design).
A. Critical Flow Constants These are required to check if the flow is sonic (choked).
B. Nozzle Calculations (Motive Fluid) Calculates the area required for the motive fluid to expand and create a vacuum. ejector design calculation xls fixed
C. Mixing Chamber & Diffuser (The "Fixed" Iteration Logic) This is where most spreadsheets break. To avoid circular references, calculate velocity directly.
If your application involves liquid-gas ejectors (e.g., slurry transport or refrigeration), a standard fixed XLS for gases will fail. You need a fixed two-phase model using the homogeneous equilibrium model (HEM). In this case, the "fixed" aspect means the spreadsheet uses a locked density correction factor:
ρ_mix = 1 / ( (x/ρ_g) + ((1-x)/ρ_l) )
where x is the quality. Ensure your fixed XLS has cells for liquid surface tension and nozzle cavitation index.
Ejector formulas come from three different origins: API 619 (American), ESDU (European), or empirical steam tables. A fixed spreadsheet hardcodes unit conversions (psi to bar, °F to °C, lb/hr to kg/s) into protected cells, ensuring you don’t accidentally multiply pressure by density logarithmically. The spreadsheet must contain a fixed internal lookup
Thermophysical Properties
Performance Correlations & Theory
Geometry Sizing Calculations
Loss Models & Efficiency Estimates
Checks & Outputs
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Ejector design relies on matching the motive nozzle expansion to the mixing chamber shock wave. This requires solving for Mach numbers, isentropic efficiencies, and entrainment ratios simultaneously. Most casual spreadsheets use circular references or broken GOAL SEEK macros. A fixed XLS eliminates circular logic by using direct algebraic approximations or single-variable solvers with convergence limits.