This is where the design engineer inputs the fluid properties and tank geometry.
| Parameter | Symbol | Unit | Description | | :--- | :--- | :--- | :--- | | Fluid Density | $\rho$ | kg/m³ | Mass per unit volume of the liquid. | | Viscosity | $\mu$ | cP or Pa.s | Resistance to flow (critical for Reynolds number). | | Tank Diameter | $T$ | m | Inner diameter of the vessel. | | Liquid Level | $H$ | m | Height of the liquid content. | | Impeller Diameter | $D$ | m | Diameter of the agitator blade (usually $D = T/3$ to $T/2$). | | Rotational Speed | $N$ | rpm | Revolutions per minute. | | Number of Impellers | $n$ | - | Single or multiple stages. |
If you cannot find a downloadable file, you can build one easily: agitator design calculation xls repack
| Output | Method | |--------|--------| | Reynolds number ((N_Re)) | ( \frac\rho N D^2\mu ) | | Power number ((N_p)) | From published curves (Rushton, etc.) | | Power draw | ( P = N_p \rho N^3 D^5 ) | | Torque | ( T = P / (2 \pi N) ) | | Shaft diameter | Based on combined bending + torsion (ASME code) | | Impeller stress | For high-speed or large agitators |
Older spreadsheets rely on VBA (Visual Basic for Applications) for iterative solving (e.g., finding the exact impeller diameter for a target power number). When Microsoft updates Excel, these macros often break. A repack fixes these references. This is where the design engineer inputs the
Case: Water (ρ=1000 kg/m³, μ=0.001 Pa·s), Tank T=1.5 m, Rushton turbine D=0.5 m, N=150 rpm.
Matches published data within ±5%.
Turbulent Regime:
P = Np * ρ * N³ * D⁵
Laminar Regime:
P = Kp * μ * N² * D³ (where Kp is the laminar power constant). If you cannot find a downloadable file, you
A repack spreadsheet automates the switch between these equations. You should see a cell that reads: "Calculated Power: 5.2 kW – Recommended Motor: 7.5 kW (SF = 1.4)".