Submersible mixer sizing requires a defined mixing duty, tank geometry, liquid data, and a suitable method for assessing thrust. Calculate the tank’s geometric quantities first, then review the hydraulic assumptions and model data before deciding on equipment size or quantity.
Two tanks can hold the same volume and have different shapes. A power label doesn’t describe that difference, and a volume calculation doesn’t tell you how liquid will move around a partition. The useful question is which inputs are ready for calculation and which still need a design decision.
This guide makes that distinction practical. You’ll get formulas for simple tank geometry, a worked comparison, and a submersible mixer sizing worksheet. The result is a clearer design brief, not an automatic model recommendation.
Key Takeaways
- Use the operating liquid depth, not the full structural height, for tank calculations.
- Keep volume in m³, wetted area in m², thrust in N, and power in kW.
- Separate geometric calculations from hydraulic sizing and equipment selection.
- Compare model data using clear definitions and relevant test conditions.
- Record missing inputs before accepting a final mixer quantity or layout.
Preparing a shortlist? Review Kairun’s published mixer specifications alongside your tank data. Use this guide for sizing inputs and the mixer overview and selection background for the wider equipment decision.
Submersible Mixer Sizing Starts With Defined Inputs
Name the task before choosing a calculation
State whether the mixer must maintain solids in suspension, blend incoming liquids, or support circulation through a basin. Include the process conditions in which that task must be achieved. A tank name alone leaves too much open.
For submersible mixer sizing, separate normal use from a future design case. If liquid levels, solids, or inflow change, name the cases the designer must check. Don’t combine values from different cases into one unexplained calculation.
Record the liquid composition and available solids, density, and viscosity data. Show their source and whether they are measured or assumed. Include fibers, grit, and internal structures in the design description rather than treating the tank as an empty container.
Keep dimensions and units together
| Input or quantity | Symbol used here | Unit | What it describes |
|---|---|---|---|
| Tank length and width | L, W | m | Internal plan dimensions |
| Operating liquid depth | H | m | Liquid depth for the stated case |
| Circular tank radius | r | m | Half the internal diameter |
| Liquid volume | V | m³ | Volume under the stated geometric assumptions |
| Wetted area | A | m² | The surfaces included in the chosen geometric model |
| Mixer thrust | F | N | Force data or an assessed requirement, clearly identified |
| Electrical input power | P input | kW | Input at the stated operating or test condition |
This unit table supports submersible mixer sizing by making the quantities distinct. A value in m³ cannot be substituted for an area in m², and a motor’s rated kW is not a measured thrust value.
Illustrative scenario: A buyer has a tank capacity figure but no confirmed operating depth. The drawing shows the structural height, while the process team expects a lower liquid level. The buyer marks the depth as unresolved before preparing the sizing sheet. This is a teaching example, not a customer project or an installed result.
Calculate Tank Geometry Before Comparing Mixers
Rectangular tanks: volume and wetted area
For a simple rectangular tank, use internal length L, width W, and uniform liquid depth H. The liquid volume is:
V = L × W × H
For an open tank, the bottom-plus-wetted-walls area is:
A = L × W + 2 × H × (L + W)
The first term is the bottom area. The second is the perimeter multiplied by liquid depth. These are geometry formulas for the stated shape; they do not calculate required mixer thrust.
Submersible mixer sizing needs the assumptions beside the result. These expressions describe a flat-bottomed rectangle and exclude partitions, equipment displacement, and extra internal surfaces. A covered roof is not included as a wetted surface in this open-tank model.
Circular tanks: check radius and liquid depth
For a simple cylindrical tank with a flat bottom and vertical walls:
V = π × r² × H
A = π × r² + 2 × π × r × H
The area includes the bottom and wetted sidewall, not a top surface. Confirm that r is the radius, not the diameter. Entering diameter in place of radius changes both calculations and produces the wrong geometric record.
For submersible mixer sizing, list a sloping bottom, channels, baffles, or a fully flooded roof as separate features. A simple formula won’t describe them unless the model includes them. The flow assessment still needs a drawing of the real tank.
Worked comparison: equal volume, different geometry
Illustrative scenario: Compare two open rectangular tanks. Both have a uniform liquid depth of 3 m, with no internal structures included in this geometric exercise. All dimensions below are assumed for teaching, not measurements from a Kairun installation.
| Calculation | Tank A | Tank B |
|---|---|---|
| Length × width × liquid depth | 8 m × 5 m × 3 m | 10 m × 4 m × 3 m |
| Volume | 8 × 5 × 3 = 120 m³ | 10 × 4 × 3 = 120 m³ |
| Bottom area | 8 × 5 = 40 m² | 10 × 4 = 40 m² |
| Wetted wall area | 2 × (8 + 5) × 3 = 78 m² | 2 × (10 + 4) × 3 = 84 m² |
| Bottom plus wetted walls | 40 + 78 = 118 m² | 40 + 84 = 124 m² |
The volumes match, while the wetted areas differ. That is a useful finding for submersible mixer sizing, but it is not a rule saying Tank B needs a stated percentage more thrust. The mixing task, medium, hydraulic method, and equipment position remain unresolved.
The worksheet should therefore contain both the geometric result and the next design questions. Don’t turn the area difference into a power, energy, or mixer-count claim.
Catch input errors before the hydraulic assessment
Keep a brief calculation check beside the drawing:
- Are all lengths in metres, rather than a mixture of metres and millimetres?
- Does the depth represent the stated liquid level?
- For a round tank, is the entered value a radius or a diameter?
- Does the area model include the surfaces it claims to include?
These checks improve the submersible mixer sizing record without adding an assumed design coefficient. Have a second person check the geometry and units against the same drawing revision. If the liquid level changes, recalculate the volume and wetted area before reusing the worksheet.
Keep the old and revised cases separate. Submersible mixer sizing becomes harder to trace when a new depth is entered but an old result remains in the next row.
Separate Required Thrust From Motor Power
Geometry is an input to a method
After calculating geometry, identify how the proposed hydraulic sizing method uses it. Xylem’s discussion of mixer size presents a manufacturer approach involving wetted area and an assessed shear-stress value. That approach has its own application conditions; it is not established here as a Kairun design method.
In submersible mixer sizing, the distinction matters. Geometry can be checked directly from dimensions. A required thrust value also depends on the method, its inputs, and its applicability to the duty. Naming a coefficient without those conditions does not complete the design.
If a proposal includes a thrust calculation, record the method reference, assumptions, and responsible reviewer. Keep any unsupported coefficient marked as an open item. This guide provides no universal value to multiply by every tank’s volume or area.
Separate required thrust from published equipment data
Required thrust is a design assessment for a stated application. Published mixer thrust is equipment data that needs its own definition and conditions. Submersible mixer sizing must connect the two without treating them as interchangeable labels.
Kairun’s public table lists these examples:
| Model | Rated power | Published “Water pushing” | Propeller diameter | Speed |
|---|---|---|---|---|
| QJB4/6-400/3-980/S | 4 kW | 1,100 N | 400 mm | 980 r/min |
| QJB4/12-620/3-480/S | 4 kW | 1,200 N | 620 mm | 480 r/min |
These are catalog values from the linked Kairun specification page, checked October 13, 2026. They do not identify the better model for either illustrative tank. The table shows why a 4 kW motor label alone leaves other data to compare.
Use the right power definition
Xylem’s explanation of mixer performance distinguishes produced thrust from the electrical input used to produce it. If comparing thrust per input power, request the relevant input data and test conditions. Don’t divide the table’s thrust by rated motor power and call the result measured efficiency.
ISO 21630:2007 addresses acceptance test methods for submersible mixers in wastewater and similar applications. Its published scope does not prove that a quoted unit has been tested to it. Keep the exact model and supporting document in the submersible mixer sizing record.
Review Mixer Quantity and Layout as a System
Total thrust does not settle the arrangement
A proposed total thrust value is not a complete layout. Submersible mixer sizing also needs the arrangement that applies the proposed equipment to the real tank. Review inlets, outlets, partitions, columns, and other installed systems with the project designer.
Avoid choosing a unit count simply by dividing one total-force figure by a catalog number. That arithmetic does not show whether the arrangement serves the required flow path. Nor does it establish that a different number of units with the same summed catalog thrust is equivalent.
Keep hydraulic concerns separate from installation details
Record the position and orientation assumed by the hydraulic assessment. Then identify which mounting and service-access details still need design confirmation. Submersible mixer sizing explains the input to that review; it does not supply a universal mounting angle or clearance.
For a settling concern, use the guide to sludge suspension and dead zones to describe the process observation. Keep the observed problem separate from an assumed solution, so the designer can review the cause.
Build a Submersible Mixer Sizing Worksheet
Keep inputs, calculations, and decisions separate
Copy the fields below into your project record. Enter a value, its unit, and the document or person supporting it. A blank field should stay visibly unresolved rather than receive a convenient default.
| Worksheet field | Value or entry | Unit or document | Status |
|---|---|---|---|
| Mixing task | [Suspension, blending, or circulation] | Duty description | [Confirmed / open] |
| Tank dimensions and liquid depth | [L, W, H, or r and H] | m; drawing revision | [Confirmed / open] |
| Geometric model | [Shape and included surfaces] | Calculation assumptions | [Confirmed / open] |
| Calculated volume | [Result] | m³ | [Checked / open] |
| Calculated wetted area | [Result, if relevant to method] | m² | [Checked / open] |
| Liquid and solids properties | [Available values and range] | Report or process data | [Confirmed / open] |
| Hydraulic sizing method | [Method, applicability, and reviewer] | Design reference | [Reviewed / open] |
| Required thrust assessment | [Result and stated conditions] | N; supporting calculation | [Reviewed / open] |
| Proposed units and arrangement | [Model, quantity, and layout] | Equipment schedule / drawing | [Reviewed / open] |
| Equipment performance data | [Definitions and test conditions] | Supplier document | [Matched / open] |
This is a submersible mixer sizing record, not a calculator that returns a model. It keeps a verified dimension, a calculated geometric quantity, and an assessed hydraulic requirement in separate rows. That separation makes later changes easier to trace.
Compare proposals against the same inputs
First check that the offers use the same duty, liquid levels, and drawing revision. Next compare the method and assumptions. Finally match the test data to the exact models and layout.
If one supplier changes an input, record the reason before comparing the resulting equipment. Submersible mixer sizing should not rank two offers as equivalent when they answer different design cases. Keep alternatives on separate lines with their differences visible.
Close the gaps before final model confirmation
Illustrative scenario: An engineer fills in Tank A’s dimensions and checks the 120 m³ volume. The liquid-property report and proposed mixer’s test conditions are still missing. The worksheet marks those items as open rather than using the geometric result to select a model. This example gives no installed outcome or final equipment recommendation.
Name the owner of each open item and the document needed to close it. Once an input changes, revisit any calculation or proposal that depends on it. A traceable submersible mixer sizing sheet should show the revision, not just the latest number.
Have tank data ready for review? Send Kairun your drawings and sizing inputs, including the available liquid data and unresolved fields. Use the worksheet to make the request specific; do not treat a preliminary reply as a completed design approval.
Submersible Mixer Sizing FAQs and Next Steps
Is W/m³ enough to size a mixer?
No. Power density describes power relative to volume but leaves out the method’s other inputs and the proposed arrangement. For submersible mixer sizing, document how a value is being used and what conditions support it. This guide does not provide a universal W/m³ target.
Do equal-volume tanks need the same mixer?
Not necessarily. The illustrative tanks both hold 120 m³, but their dimensions and wetted areas differ. Geometry, duty, medium, and layout still need review. Equal volume alone cannot establish equal equipment needs.
Can I calculate thrust directly from wetted area?
Area is a geometric result, not a force. Any method that converts it into a thrust requirement needs a justified coefficient and defined conditions. Submersible mixer sizing should state that method’s source and limits rather than apply an unexplained multiplier.
How is required thrust different from a catalog value?
Required thrust belongs to the assessed design case. A catalog value describes the proposed equipment under its stated conditions. Check both definitions and the supporting documents before deciding that the proposed unit meets the requirement.
Can I determine quantity by adding catalog thrust values?
Not on that basis alone. A sum of values does not show the effect of the proposed positions, tank structures, or process conditions. Review the quantity and layout with the hydraulic assessment instead of treating addition as a completed system design.
What can a sizing worksheet calculate?
It can record inputs and show geometry calculations for a defined shape. Without a validated hydraulic method, it cannot choose a mixer, establish a unit count, or guarantee circulation. Keep those outputs separate in the submersible mixer sizing record.
Move from calculations to a reviewable proposal
Start with reliable dimensions and a defined task. Calculate the geometric quantities you can verify, then connect them to a documented hydraulic assessment and the exact equipment data. Keep every open input visible until it is resolved.
For the wider system scope, review Kairun’s wastewater treatment equipment. To discuss a proposed unit, send your tank drawings, liquid data, and worksheet. A useful submersible mixer sizing request makes the assumptions clear and gives the supplier a consistent case to assess.
