How to use Industrial Agitator Mixer Shaft Power& Torque Sizing Calculator
- Enter Impeller Type & Hydrodynamic Flow Pattern and adjust the options as needed.
- Run the tool and inspect its results, evidence and limitations.
- Copy or download the result, then verify it against the actual website, source data or business records.
Try a concrete example
In a synthetic polymer reactor (tank ID T = 1200 mm) equipped with 4 standard vertical baffles (120 mm wide) and a 45° 4-pitched blade turbine (PBT, diameter D = 400 mm, D/T = 0.33) rotating at 180 RPM in fluid with 1050 kg/m³ density and 25.0 cP viscosity: Reynolds number is 201,600 (turbulent regime Re > 10,000); with baffles suppressing swirl, turbulent power number Np is 1.27; net fluid shaft power is 0.98 kW; accounting for initial viscosity surges and mechanical seal friction (85% drive efficiency), recommended motor rating is 1.5 kW (35% torque service factor); agitator shaft torque is 79.6 N·m; pumping number Nq is 0.79, generating 182 m³/h circulation pumping flow for a complete tank turnover in just 26.8 seconds, eliminating dead zones with smooth mechanical operation.
How to interpret results
Agitated mixing tanks and chemical reactors serve as core process equipment in fine chemicals, pharmaceuticals, fermentation, polymers, and water treatment. Dynamic sizing adheres to DIN 28131 and Chemineer/Lightnin mixing standards. Hydrodynamic flow regimes are classified by the agitator Reynolds number Re = (ρ·N·D²) / μ: laminar (Re < 10), transition (10 ≤ Re ≤ 10,000), and fully turbulent (Re > 10,000). Net impeller power complies with the dimensionless power number equation P = Np · ρ · N³ · D⁵. In unbaffled vessels, bulk fluid rotates as a solid body, creating a deep central vortex funnel that entrains air and induces severe shaft wobble. Installing 4 standard wall baffles (width W = 0.1T) suppresses swirl, converting circular motion into axial top-to-bottom turnover and radial shear to accelerate heat and mass transfer. Agitator shaft torque T = P / ω dictates gearbox mechanical ratings. Sizing power and RPM prevents motor trip-outs and shaft fatigue failure.
Frequently asked questions
Why is the agitator Reynolds number Re the fundamental criterion for flow regimes and power number Np?
The agitator Reynolds number (Re = ρ · N · D² / μ) evaluates inertial forces relative to viscous shear forces: First, laminar regime (Re < 10): in high-viscosity resins or polymers, viscous shear dominates; power number Np is inversely proportional to Re (Np = K_L / Re), meaning power scales linearly with viscosity and squared with speed. Second, transition regime (10 ≤ Re ≤ 10,000): laminar and turbulent wakes coexist. Third, fully turbulent regime (Re > 10,000): inertia dominates and Np remains constant, rendering fluid viscosity negligible while power scales cubically with speed (N³) and to the 5th power of diameter (D⁵)!
What is the critical role of wall baffles in flow pattern circulation and shaft power consumption?
First, suppressing the air-entraining central vortex: in unbaffled vessels, fluid rotates as a solid body with centrifugal forces depressing the center into a deep funnel, drawing air into the batch and creating foam. Second, forcing 3D top-to-bottom convective circulation: 4 standard vertical baffles (width W = 0.1T) break tangential swirl, forcing fluid into vigorous axial and radial recirculating loops that suspend solids. Third, power impact: eliminating the vortex increases turbulent power number Np by 2x to 4x, requiring motor and gearbox selection to be rated for fully baffled conditions.
How do Rushton radial disc turbines and 45° pitched blade turbines (PBT) differ in flow patterns and applications?
First, Rushton disc turbine (radial flow): consists of a central disc with 6 vertical flat blades. Fluid enters axially from top and bottom and discharges horizontally outward at high velocity, splitting into upper and lower circulating loops. It generates intense localized shear rates, making it standard for gas-liquid dispersion (hydrogenation, aerobic fermentation) and liquid-liquid emulsification. Second, 45° pitched blade turbine PBT (axial-radial flow): blades are inclined at 45°, generating high pumping circulation with moderate shear for bulk blending, solids suspension, and jacket heat transfer.
How are agitator shaft torque and lateral critical speed verified in mechanical drive design?
First, gearbox torque rating: gearboxes are sized primarily by output torque T = 9550 · P / N rather than motor kW. At low speeds (30 to 60 RPM), a modest 5 kW motor produces hundreds to thousands of Nm of torque; gearboxes require a 1.3 to 2.0 service factor. Second, first lateral critical speed verification: overhung agitator shafts act as cantilever beams without bottom steady bearings. Operating speed must stay well outside the resonance window (0.8 to 1.2 times critical speed; typically designed below 60% of critical speed) to prevent shaft deflection from destroying mechanical seals and bearings.