Home › Calculators › Fluid Mechanics › Ejector & Eductor

Ejector & Eductor Sizing Calculator

A jet pump uses a high-pressure motive fluid to entrain and compress a low-pressure suction fluid. This tool estimates the entrainment ratio, compression ratio, expansion ratio and motive-nozzle throat diameter for a single-phase liquid–liquid eductor.

⚙ In-browser Engine Heat & Momentum Balance Single-phase Liquid

Geometry & Flow Path

Schematic updates with your inputs — pressure labels and throat diameter are live.

Inputs

Enter operating conditions. Results recompute instantly.

🔴 Motive Fluid

Motive pressure (Pm)

bar

Motive flow rate (Qp)

m³/h

🟢 Suction Fluid

Suction pressure (Ps)

bar

Suction flow rate (Qs)

m³/h

🟠 Discharge & Fluid

Discharge pressure (Pd)

bar

Fluid density (ρ)

kg/m³

Results

Ideal single-phase estimate (no losses, uniform density).

Entrainment Ratio (vol)

Qs / Qp

Compression Ratio

Pd / Ps

Expansion Ratio

Pm / Ps

Nozzle Throat Dia.

Throat Velocity

m/s

Throat Area

mm²

Entrainment Ratio (mass)

ms / mp

Suction Share

% of total

Key Formulations

Er = Pm / PsExpansion ratio — motive pressure over suction pressure. Drives the entrainment capability of the nozzle.

Cr = Pd / PsCompression ratio — discharge pressure over suction pressure. Higher Cr means the ejector must lift the suction stream harder.

ω = Qs / QpVolumetric entrainment ratio — how much suction fluid is entrained per unit motive flow (equal to mass ratio at uniform density).

v_t = √( 2·(Pm−Ps) / ρ )Ideal motive-nozzle throat velocity from Bernoulli (neglecting nozzle losses).

d_t = √( 4·A_t / π ) , A_t = Qp / v_tNozzle throat diameter from continuity using the volumetric motive flow and throat velocity.

Calculation Methodology

1Momentum transfer. The motive jet accelerates through a converging nozzle, converting pressure head into velocity. It entrains the low-pressure suction stream by momentum exchange in the mixing section.

2Mixing. Motive and suction streams mix and decelerate in the throat, recovering static pressure.

3Diffusion. The diverging diffuser converts the remaining velocity head back into pressure, reaching the discharge pressure Pd.

!Assumptions. Single-phase, incompressible liquid; uniform density; ideal nozzle (no losses). Real ejectors have nozzle/discharge coefficients (typically 0.85–0.95) that reduce performance — apply a factor when sizing.