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For turbulent: ( t_b = 5.2 \cdot \left(\fracTD\right)^2 \cdot N^-1 )
This verified guide walks you through practical agitator design calculations for mixing, suspension, and aeration. It includes step-by-step formulas, a complete worked example, design tables, and a downloadable PDF template you can use for engineering or academic projects.
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Designing an industrial agitator requires balancing fluid dynamics with mechanical integrity. The primary goal is to determine the power needed to achieve a specific mixing intensity while ensuring the shaft can withstand the resulting torque and bending forces. 1. Fluid Dynamics & Power Calculation
The first step is determining the motor power based on the fluid's properties and the chosen impeller. Reynolds Number ( NRecap N sub cap R e end-sub
): Identifies the flow regime (laminar, transition, or turbulent). agitator design calculation pdf download verified
NRe=D2⋅N⋅ρμcap N sub cap R e end-sub equals the fraction with numerator cap D squared center dot cap N center dot rho and denominator mu end-fraction : Impeller diameter ( ) : Rotational speed ( RPScap R cap P cap S ) : Fluid density ( ) : Dynamic viscosity ( ) Power Consumption ( ): Calculated using the Power Number ( Npcap N sub p ), which is specific to the impeller type.
P=Np⋅ρ⋅N3⋅D5cap P equals cap N sub p center dot rho center dot cap N cubed center dot cap D to the fifth power
Total Motor Power: Includes losses from the gearbox and seals (typically 10-20% additional). 2. Mechanical Shaft Design
Once the power is known, the shaft must be sized to prevent failure from torque and vibration. Torque ( ): Derived from the power and speed.
T=P⋅602π⋅Ncap T equals the fraction with numerator cap P center dot 60 and denominator 2 pi center dot cap N end-fraction Shaft Diameter (
): Based on the maximum shear stress and bending moments. Engineers often use the equivalent bending moment ( Mecap M sub e ) to find a safe diameter.
ds=(32⋅Meπ⋅σall)1/3d sub s equals open paren the fraction with numerator 32 center dot cap M sub e and denominator pi center dot sigma sub a l l end-sub end-fraction close paren raised to the 1 / 3 power Due to copyright and engineering ethics, we do
Critical Speed Check: The operating speed must avoid the shaft's natural frequency (usually or of critical speed) to prevent violent vibrations. Verified PDF Resources
For detailed step-by-step calculations and spreadsheets, you can download verified technical guides from these platforms:
Agitator Design and Power Calculations | PDF | Viscosity - Scribd
Verified Guide to Agitator Design Calculation Agitator design is a critical engineering process in chemical, pharmaceutical, and food industries to ensure homogeneous mixing of substances. This guide provides the verified mathematical framework for calculating power requirements, shaft dimensions, and structural safety. 1. Agitator Power Requirement Calculation
The power required by an agitator depends on fluid properties (density and viscosity), impeller geometry, and rotational speed. The governing formula for power is:
P=Np⋅ρ⋅N3⋅Da5cap P equals cap N sub p center dot rho center dot cap N cubed center dot cap D sub a to the fifth power : Power required (Watts) Npcap N sub p : Power Number (dimensionless), determined by impeller type : Density of the liquid ( : Rotational speed (revolutions per second, RPS) Dacap D sub a : Agitator/Impeller diameter ( Step-by-Step Power Verification: Calculate Reynolds Number ( NRecap N sub cap R e end-sub
): Determine the flow regime (laminar, transition, or turbulent). For turbulent: ( t_b = 5
NRe=Da2⋅N⋅ρμcap N sub cap R e end-sub equals the fraction with numerator cap D sub a squared center dot cap N center dot rho and denominator mu end-fraction (where is the dynamic viscosity in Determine Power Number ( Npcap N sub p
): Use standard charts based on the impeller type (e.g., Rushton turbine, pitched blade) and the NRecap N sub cap R e end-sub
Account for Power Losses: Add mechanical losses from seals and gearboxes (typically 5–20%) to find the total motor power required. 2. Mechanical Design of the Shaft
The shaft must be strong enough to transmit the required torque and resist bending moments caused by hydraulic forces. Study the Effect Of Impeller Design On Power Consumption
Given:
Tank T = 1.8 m, liquid Z = 1.8 m, ρ = 1000 kg/m³, μ = 0.001 Pa·s, D = 0.6 m (D/T = 0.33), N = 3 rps (180 rpm), Rushton turbine (Np=5.5).
Re: ( 1000 * 3 * 0.6^2 / 0.001 = 1.08 \times 10^6 ) (turbulent)
Power: ( P = 5.5 * 1000 * 27 * 0.6^5 ) → 0.6^5 = 0.07776 → ( P = 5.51000270.07776 = 11,548 , W ) (~11.5 kW)
Torque: ( T_q = 11548 / (2π3) = 612.6 , Nm )
Shaft dia: Assume τ_allow = 50 MPa → ( d_s = (16612.6 / (π50e6))^1/3 = 0.0397 , m ) → ~40 mm (add corrosion allowance).