Chemical Tank Agitator Calculation

Power Number 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):

Power (P):

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1. What is the Power Number Method?

The Power Number Method is used to calculate the power required for agitators and mixers in chemical tanks. It relates the power consumption to the impeller geometry, fluid properties, and operating conditions through the power number (N_p).

2. How Does the Calculator Work?

The calculator uses the power number equation:

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

Where:

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

Explanation: The power number is a dimensionless parameter that characterizes the power consumption of an impeller in a given fluid system.

3. Importance of Agitator Power Calculation

Details: Accurate power calculation is crucial for proper agitator selection, motor sizing, energy efficiency optimization, and ensuring adequate mixing performance in chemical processes.

4. Using the Calculator

Tips: Enter power number (typically 0.5-5 for different impeller types), 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 typical range for power numbers?
A: Power numbers range from about 0.3 for marine propellers to 5 for anchor impellers, depending on impeller type and geometry.

Q2: How does fluid viscosity affect power consumption?
A: Higher viscosity fluids generally require more power for the same mixing intensity due to increased resistance to flow.

Q3: What are common impeller types and their power numbers?
A: Rushton turbine (N_p ≈ 5), pitched blade turbine (N_p ≈ 1.5), marine propeller (N_p ≈ 0.3), anchor (N_p ≈ 0.35).

Q4: When is this equation most accurate?
A: The equation is most accurate in the turbulent flow regime (Re > 10,000) where power number becomes constant.

Q5: How does tank geometry affect power consumption?
A: Baffles, tank diameter, liquid height, and impeller position all influence power consumption and should be considered in detailed design.