Agitator Impeller Design Calculations

Impeller Power Equation:

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

Power Number (N_p):

unitless

Density (ρ):

kg/m³

Rotational Speed (N):

rev/s

Impeller Diameter (D):

Impeller Power (P):

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1. What is Impeller Power Calculation?

The impeller power calculation determines the power required to drive an agitator impeller in fluid mixing applications. It is essential for proper motor sizing and efficient mixing system design in chemical, pharmaceutical, and food processing industries.

2. How Does the Calculator Work?

The calculator uses the impeller power equation:

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

Where:

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

Explanation: The power number (N_p) depends on impeller type, geometry, and flow regime (laminar or turbulent).

3. Importance of Impeller Power Calculation

Details: Accurate power calculation ensures proper motor selection, prevents under/over-sizing, optimizes energy consumption, and ensures efficient mixing performance in industrial processes.

4. Using the Calculator

Tips: Enter power number based on impeller type, fluid density in kg/m³, rotational speed in revolutions per second, and impeller diameter in meters. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What is the power number (N_p)?
A: The power number is a dimensionless parameter that relates impeller power consumption to fluid properties and operating conditions. It varies with impeller type and Reynolds number.

Q2: How do I determine the power number?
A: Power numbers are typically obtained from manufacturer specifications, experimental data, or published correlations for specific impeller types.

Q3: What are typical power number values?
A: Common values range from 0.3-5.0 depending on impeller design. For example: Rushton turbine ≈ 5.0, pitched blade turbine ≈ 1.5-2.0, marine propeller ≈ 0.3-0.6.

Q4: Does fluid viscosity affect the calculation?
A: Yes, viscosity affects the power number, especially in laminar flow regimes. The power number becomes constant in fully turbulent flow.

Q5: How accurate is this calculation?
A: The calculation provides theoretical power requirements. Actual power may vary due to mechanical losses, vessel geometry, and other system factors.