A tank mixing eductor sizing calculator should produce a first-pass circulation requirement, not a final model guarantee. Enter the working tank volume, desired nominal turnover time, available motive flow and pressure at the eductor header, liquid properties, solids information and the selected model’s verified performance data. The final quantity must also be checked against tank geometry, flow-field coverage and the pump operating point.
This worksheet is for engineers comparing options before requesting a model-specific selection. It separates the process requirement from the manufacturer’s performance curve so a generic entrainment ratio is never treated as universal.
Inputs for a first-pass eductor calculation
| Input | Symbol | Use |
|---|---|---|
| Working liquid volume | V | Volume that must be circulated at the actual operating level. |
| Nominal turnover time | T | A project target used to compare concepts; it is not automatically the true blend time. |
| Motive flow per eductor | Qm | Flow supplied by the pump at pressure available at each eductor. |
| Total circulation per eductor | Qc | Model-specific circulation from verified performance data at the operating pressure. |
| Tank geometry | D, H, internals | Controls quantity, placement, orientation and dead-zone risk. |
| Liquid and solids data | ρ, μ, T, particle data | Changes hydraulics, settling behavior, material choice and validation. |
For a vertical cylindrical tank, a geometric estimate is V = πD²H/4. Use the actual working level and subtract major internal displacement when it is material to the result. For rectangular tanks, use length × width × liquid depth. Convert every value to one consistent unit system before continuing.
Step-by-step sizing calculation
1. Define the process acceptance condition
State what success means: concentration variation, temperature uniformity, suspension at defined particle size, or another measurable outcome. “Mix the tank” is not an acceptance criterion.
2. Calculate the preliminary circulation target
For a nominal turnover approach, calculate Qrequired = V/T. If V is in cubic metres and T is in hours, Qrequired is in m³/h. This is a screening value. Actual blend time also depends on jet direction, tank proportions, internals, density or viscosity differences and where material enters the tank.
3. Establish pressure available at the eductor
Start with the pump operating point, then subtract losses through pipe, fittings, valves, filters, elevation and the distribution header. Pump discharge pressure measured at a different location is not the same as pressure at the eductor inlet.
4. Read total circulation from model data
Use the selected model’s performance curve at the calculated inlet pressure. A published product example from Spraying Systems shows circulation rate and effective flow field changing with pressure, which demonstrates why one fixed multiplier should not be used across sizes or conditions.
5. Calculate preliminary quantity
Calculate N = ceiling(Qrequired ÷ Qc). Round up, then check whether that number can physically sweep the tank. A calculation that meets total circulation but leaves an isolated corner or short-circuits into the pump suction is not complete.
6. Check pump capacity
The pump must provide approximately N × Qm at the required header pressure after system losses. Plot the system requirement against the pump curve rather than selecting from motor power or nominal connection size alone.
Worked hypothetical example
The following values demonstrate the method and are not Jeltecn product performance data.
- Working volume: 30 m³
- Nominal turnover target: 15 minutes, or 0.25 h
- Required circulation: 30 ÷ 0.25 = 120 m³/h
- Hypothetical verified circulation per selected eductor at its actual inlet pressure: 24 m³/h
- Preliminary quantity: ceiling(120 ÷ 24) = 5 eductors
The next checks are whether five jets cover the liquid volume across minimum and maximum operating levels, whether the header distributes motive flow evenly, and whether the pump supplies the combined motive flow at pressure. If placement requires six units to avoid dead zones, the layout requirement controls even though the turnover calculation returned five.
Checks that can change the result
- Viscosity: higher viscosity can reduce entrainment and slow bulk circulation.
- Solids: settling velocity, particle size, concentration, abrasion and free passage matter.
- Level variation: minimum liquid level can change submergence and jet coverage.
- Header balance: unequal branches can starve distant eductors.
- Short-circuiting: pointing discharge toward the pump suction can circulate a local loop instead of the tank.
- Heat or reaction limits: turnover is not the same as reaction, dissolution or heat-transfer completion time.
Continue with how to determine eductor quantity, placement and orientation, and pump sizing.
Information to send for model selection
Provide a tank drawing, operating levels, working volume, liquid density and viscosity at temperature, solids details, pump curve or measured operating point, piping layout, connection standard, material restrictions and the required process result. Jeltecn can then compare the calculation with model-specific data.
Review the Mixing Eductor range or send the calculation inputs for an engineering review.
Technical reference
Model-specific examples and performance boundaries: Spraying Systems Co. 46550 Tank Mixing Eductor product data; specification and installation scope: Guide to Optimizing In-Tank Agitation and Mixing Using Eductors.