How to Choose the Right Impeller Size for 2900mm Dosing Tanks with Solid Particles?

When designing a top entry mixer for industrial applications, many customers focus solely on the tank volume. However, at LJ Water Treatment Equipment Co.,Ltd, we believe the secret to long-term efficiency lies in the details of fluid dynamics—specifically the D/T ratio.

Recently, we worked with a client from Africa who required a mixing solution for a large dosing tank. The project presented unique challenges that required a professional recalibration of their original specifications.

The Case Study: Mixing 5mm Solid Particles

The client’s project involved a dosing tank with the following dimensions:

• Tank Diameter (T): 2900mm

• Tank Depth: 2200 mm

• Medium: Liquid containing approximately 5 mm solid particles.

• Material Requirement: All wetted parts in AISI 316L stainless steel.

Initially, the client requested a 600 mmdiameter impeller (double-layer, 3-blade type) powered by a 3.7 kW motor with a 60 mm shaft.

Why a 600mm Impeller Was Not Enough

In mixing technology, the D/T Ratio is the ratio between the Impeller Diameter and the Tank Diameter :

For applications involving solid suspension (keeping particles from settling at the bottom), the industry standard D/T ratio usually falls between 0.25 and 0.45.

The client's original 600mm proposal resulted in a ratio of:

A ratio of 0.20 is at the absolute critical minimum. For 5 mm solid particles, this small "footprint" would likely result in "dead zones" near the tank walls, leading to particle buildup and inconsistent dosing.

Our Engineered Solution: Optimizing for Performance

To ensure the solids remain fully suspended and to prevent equipment fatigue, our engineering team suggested a more robust configuration:

1. Increasing the Impeller Diameter

We recommended upgrading to an 800 mm diameter impeller. This brings the D/T ratio to 0.27, safely within the optimal range for solid suspension.

2. Upgrading Power and Stability

Increasing the blade size increases the torque and resistance. Therefore, we adjusted the mechanical specs to ensure durability:

• Motor Power: Upgraded from3.7 kW to 4 kW.

• Shaft Diameter: Increased from 60 mm to 76 mm to handle the higher bending moments.

• Output Speed: Optimized at 130 rpm.

  
  

The Result

By choosing a larger top entry mixer configuration, the client achieved a higher flow capacity (pumping rate) without needing excessive RPM. This not only ensures a homogeneous mix of the 5 mm particles but also extends the lifespan of the seals and bearings due to the sturdier 76 mm shaft.

At LJ Water Treatment Equipment Co.,Ltd , we don't just take orders; we optimize your process. Whether you are dealing with simple liquid blending or complex solid-liquid suspension, our team is here to provide the right calculation for your success.