Mixing Design Calculator

Power equals specific weight times flowrate times headloss

Solution

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How It Works

Mixing injects energy into water to blend chemicals, suspend solids, or transfer oxygen. Static mixers dissipate energy through headloss as water flows through baffles or orifices. Mechanical impeller mixers operate in either laminar or turbulent regimes, and their power draw depends on rotational speed, impeller diameter, and fluid properties.

Rapid mixing (G > 300 s−1) disperses coagulant chemicals in seconds, while slow mixing (G = 20–80 s−1) promotes gentle flocculation over 20–40 minutes.

Example Problem

A static mixer treats 0.2 m³/s of water with a specific weight of 9,810 N/m³ and a headloss of 0.5 m. What power is dissipated?

  1. P = γ × Q × h = 9,810 × 0.2 × 0.5
  2. P = 981 W

Frequently Asked Questions

What is the difference between rapid mix and slow mix?

Rapid mix uses high energy (G > 300 s−1) for 10–30 seconds to uniformly distribute coagulant. Slow mix applies gentle energy (G = 20–80 s−1) for 20–40 minutes to build flocs without breaking them.

What mixing constant should I use for an impeller?

The mixing constant k depends on impeller type and Reynolds number. For a standard Rushton turbine in turbulent flow, k is about 5.0. Propeller-type impellers in turbulent flow typically use k ≈ 0.3–0.4.

How do I choose between a static mixer and a mechanical mixer?

Static mixers are ideal for rapid blending of chemicals in pressurized pipelines with no moving parts. Mechanical mixers are better for basins where you need adjustable intensity and longer detention times, such as flocculation tanks.

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