Introduction In the world of fluid dynamics and process engineering, the ejector (or eductor) is a deceptively simple device. With no moving parts, it uses a high-pressure motive fluid to entrain, compress, or pump a secondary low-pressure fluid. From vacuum distillation in oil refineries to chemical dosing in water treatment, ejectors are indispensable.
While empirical, this is highly reliable for preliminary sizing and is easily embedded in XLS. The diffuser converts velocity head back to pressure. Efficiency ($\eta_d$) typically 70-85%: ejector design calculation xls
$$P_{discharge} = P_{throat} + \eta_d \cdot \frac{1}{2} \rho_m (V_2^2)$$ Introduction In the world of fluid dynamics and
Where $V_2$ is velocity at end of throat (subsonic after shock). Your XLS must solve for $V_2$ iteratively. While empirical, this is highly reliable for preliminary
But wait – if $P_m/P_s$ exceeds the critical pressure ratio (approx 1.89 for air), Mach is >1. Most ejectors operate supersonically (M=1.5 to 4.0). Your XLS should cap Mach using the critical ratio. $$V_m = M_m \times \sqrt{k \cdot R \cdot T_m}$$
A simplified practical approach used in industry XLS templates: Use the by El-Dessouky (2002) for steam-jet ejectors: $$Er = 0.85 \times \left( \frac{P_m}{P_s} \right)^{0.77} \times \left( \frac{P_d}{P_s} \right)^{-1.13}$$
This allows you to required nozzle area if $W_m$ is given. Step 3: Momentum Balance in the Mixing Section (Most Critical) This is where spreadsheets shine. Assuming constant-area mixing (most common model), apply conservation of momentum: