A standard agitator design spreadsheet is not a monolithic black box. Instead, it is organized into logical modules, typically including the following key sections:
). In laminar regimes, power is directly proportional to viscosity and calculated as Kpcap K sub p is a laminar power constant. Motor Horsepower (HP) Selection
Re=ρ⋅N⋅d2μcap R e equals the fraction with numerator rho center dot cap N center dot d squared and denominator mu end-fraction Power Number (
While the specific layout may vary, most agitator design spreadsheets follow a similar logical flow. We will use the example of a typical Agitator Power Requirement and Mixing Intensity Calculation.xls file to illustrate the process. agitator design calculation xls
is a dimensionless constant unique to each impeller type (e.g., Rushton turbine, hydrofoil, pitched blade) and is found using empirical charts embedded into your XLS via lookup tables. The Power Equation The basic shaft power ( ) delivered to the fluid is calculated as:
Use Excel’s data validation to ensure inputs remain within practical, physical limits.
| Formula | Calculation | Result | |---------|-------------|--------| | N (rev/sec) = N_rpm / 60 | =150/60 | 2.5 rps | | Reynolds number, Re = (ρ × N × D²) / μ | =1000×2.5×0.67²/0.001 | 1,122,250 | | Flow regime | If Re<10: laminar; 10<Re<10k: transition; >10k: turbulent | Turbulent | A standard agitator design spreadsheet is not a
): This is a dimensionless constant specific to your impeller type, often found in lookup tables or generic curves. Calculate the actual shaft power.
For comprehensive safety, your sheet should also incorporate bending moments caused by hydraulic dynamic forces acting abnormally on the impeller blades. 6. Structuring the Excel Spreadsheet (XLS) Layout
| | Input Parameters | Calculations / Outputs | | :--- | :--- | :--- | | Reactor Geometry | Diameter (T), Height (H), Liquid Level (Z) | Total Volume, Liquid Volume | | Agitator Specs | Impeller Type (selection), D/T Ratio, RPM, Number of Impellers | Impeller Diameter (D), Tip Speed | | Fluid Properties | Density (ρ), Viscosity (µ) | | | Hydraulic Performance | | Reynolds Number (Re), Flow Regime, Power Number (Np), Power Required (P), Pumping Number (Nq), Pumping Capacity (Q), Bulk Fluid Velocity | | Mechanical Design | Shaft Material Properties | Required Shaft Diameter, First Critical Speed | | Summary / Sizing | | Recommended Motor HP/kW, Gearbox Ratio, Agitator Selection | The Power Equation The basic shaft power (
If you want to refine this model, let me know you are dealing with, your preferred impeller type , or if you need the formulas for calculating bending moments caused by fluid hydraulic forces.
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Calculate the minimum shaft diameter based on combined torque and bending moments to prevent failure. Critical Speed ( Nccap N sub c
). These are critical for determining the flow regime (laminar vs. turbulent). : Tank diameter ( ), total liquid height ( ), and bottom shape (flat, dished, or conical).