Motor Power Calculation for Agitator

Agitator Power Equation:

\[ P = \rho N^3 D^5 N_p \]

Density (ρ):

kg/m³

Rotational Speed (N):

rev/s

Impeller Diameter (D):

Power Number (N_p):

unitless

Motor Power (P):

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1. What is the Agitator Power Equation?

The agitator power equation calculates the power required to drive an agitator or mixer in fluid processing applications. It is based on the relationship between fluid properties, impeller geometry, and rotational speed.

2. How Does the Calculator Work?

The calculator uses the agitator power equation:

\[ P = \rho N^3 D^5 N_p \]

Where:

\( P \) — Motor power (W)
\( \rho \) — Fluid density (kg/m³)
\( N \) — Rotational speed (rev/s)
\( D \) — Impeller diameter (m)
\( N_p \) — Power number (unitless)

Explanation: The equation shows that power consumption is proportional to the cube of rotational speed and the fifth power of impeller diameter, making these the most significant factors in power requirements.

3. Importance of Motor Power Calculation

Details: Accurate motor power calculation is essential for proper agitator selection, energy efficiency optimization, process design, and preventing motor overload or underutilization.

4. Using the Calculator

Tips: Enter fluid density in kg/m³, rotational speed in revolutions per second, impeller diameter in meters, and power number (dimensionless). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the power number (N_p)?
A: The power number is a dimensionless parameter that depends on impeller type, geometry, and flow regime (Reynolds number). It typically ranges from 0.3 to 6 for common impellers.

Q2: How does fluid viscosity affect power requirements?
A: Higher viscosity fluids generally require more power due to increased resistance to mixing. The power number varies with Reynolds number in transitional flow regimes.

Q3: What are typical power number values?
A: For standard impellers: Rushton turbine N_p ≈ 5, pitched blade turbine N_p ≈ 1.5, marine propeller N_p ≈ 0.3-0.6.

Q4: Should I include a safety factor?
A: Yes, typically add 10-20% safety margin to account for startup torque, fluid property variations, and potential fouling.

Q5: How does baffling affect power consumption?
A: Baffled tanks typically require 2-3 times more power than unbaffled tanks at the same conditions due to prevented vortex formation and improved mixing efficiency.