Agitator Torque Calculation Formula

Agitator Torque Formula:

\[ T = \frac{P}{\omega} \quad \text{where} \quad P = N_p \rho N^3 D^5 \]

Power Number (N_p):

unitless

Density (ρ):

kg/m³

Rotational Speed (N):

rev/s

Diameter (D):

Angular Speed (ω):

rad/s

Shaft Torque (T):

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1. What is Agitator Torque Calculation?

Agitator torque calculation determines the rotational force required to drive an agitator or mixer in fluid processing. It's essential for proper motor selection and mechanical design of mixing equipment.

2. How Does the Calculator Work?

The calculator uses the agitator torque formula:

\[ T = \frac{P}{\omega} \quad \text{where} \quad P = N_p \rho N^3 D^5 \]

Where:

\( T \) — Shaft torque (N·m)
\( P \) — Power (W)
\( \omega \) — Angular speed (rad/s)
\( N_p \) — Power number (unitless)
\( \rho \) — Density (kg/m³)
\( N \) — Rotational speed (rev/s)
\( D \) — Impeller diameter (m)

Explanation: The power number represents the dimensionless power requirement for a specific impeller geometry and flow regime.

3. Importance of Torque Calculation

Details: Accurate torque calculation ensures proper motor sizing, prevents mechanical failure, optimizes energy consumption, and maintains process efficiency in mixing operations.

4. Using the Calculator

Tips: Enter power number based on impeller type, fluid density, rotational speed, impeller diameter, and angular speed. All values must be positive and in correct units.

5. Frequently Asked Questions (FAQ)

Q1: What is the power number (N_p)?
A: Power number is a dimensionless parameter that depends on impeller geometry, Reynolds number, and flow regime. Typical values range from 0.2 to 5 for common impellers.

Q2: How do I convert RPM to rad/s?
A: Multiply RPM by \( \frac{2\pi}{60} \) to get rad/s. For example, 60 RPM = \( 60 \times \frac{2\pi}{60} = 2\pi \) rad/s ≈ 6.28 rad/s.

Q3: What factors affect agitator torque?
A: Fluid viscosity, density, impeller design, rotational speed, vessel geometry, and presence of baffles all influence torque requirements.

Q4: When is this calculation most accurate?
A: Most accurate for Newtonian fluids in turbulent flow regime. For non-Newtonian fluids or transitional flow, additional corrections may be needed.

Q5: How does torque relate to motor selection?
A: Calculated torque determines the required motor torque capacity. Motors should be selected with 10-20% safety margin above calculated torque.