Submersible Mixer Sizing

Submersible mixers play a crucial role in various industrial applications, from wastewater treatment to food processing. Proper sizing of these mixers is essential to ensure optimal performance and efficiency. This article will guide you through the key factors to consider when sizing a submersible mixer, including application requirements, thrust calculations, positioning, and manufacturer selection.

Application Requirements

When sizing a submersible mixer, it's vital to first understand the specific needs of your application. The type of media being mixed, the desired level of mixing, and the mounting location of the mixer all play significant roles in determining the appropriate size and configuration.

Media type and characteristics are fundamental considerations. Different substances have varying viscosities, densities, and particle sizes, which directly impact the mixing process. For instance, mixing a low-viscosity liquid like water requires less power than blending a high-viscosity fluid or a mixture containing solid particles. The specific gravity of the media also affects the required mixer power and impeller design.

The extent of mixing required is another pivotal consideration, as it significantly influences the final product's quality, consistency, and performance. Ensuring the right level of blending ensures that all ingredients are uniformly distributed, allowing for optimal chemical reactions, physical properties, and ultimately, satisfying the desired outcome. Some applications may need only gentle blending to maintain suspension, while others might demand vigorous mixing to achieve homogeneity or prevent settling. The mixing intensity directly influences the required mixer power and impeller speed.

The submersible mixer's mounting location within the tank or vessel is equally important. Factors such as tank geometry, available mounting points, and potential obstructions can impact the mixer's performance and efficiency. Proper placement ensures optimal flow patterns and prevents dead zones where mixing may be inadequate.

Thrust - Key Performance Indicator 

Thrust is a key performance indicator for submersible mixers, representing the force that creates bulk flow in the mixed media. The International Organization for Standardization (ISO) recognizes the importance of thrust in mixer performance through the ISO 21630 standard.

To estimate the required thrust for your application, you need to consider the tank dimensions and the desired shear stress. For example, in an anoxic tank measuring 12 m x 6 m with a liquid level of 5 m, the bottom area would be 72 m², and the wet wall area would be 180 m². This gives a total wet area of 252 m².

For rectangular tanks, the pool shear stress typically ranges from 1.5 to 3 N/m². Assuming a shear stress of 2 Pascals (N/m²), you can calculate the required thrust as follows:

Required Thrust = Shear Stress x Total Wet Area

Required Thrust = 2 N/m² x 252 m² = 504 N

This calculation provides an approximation of the thrust needed to achieve adequate mixing in the given tank.

Submersible Mixer Sizing

Once you've determined the required thrust, you can proceed with sizing the submersible mixer. Several factors influence the mixer's ability to generate the necessary thrust, including impeller diameter, number of blades, and blade shape.

The impeller diameter is perhaps the most critical factor in mixer sizing. Generally, larger impellers can generate more thrust at lower speeds, which can lead to improved energy efficiency. However, the impeller size must be appropriate for the tank dimensions to ensure proper flow patterns.

The number of blades on the impeller also affects mixer performance. More blades typically result in higher thrust but may also increase power consumption. The optimal number of blades depends on the specific application and media characteristics.

Blade shape is another important consideration. Different blade designs are suited for various mixing tasks. For example, hydrofoil blades are often used for low-viscosity fluids and gentle mixing, while pitched blade turbines are better suited for more intense mixing and solids suspension.

When sizing a submersible mixer, it's crucial to balance these factors to achieve the required thrust while optimizing energy efficiency and mixing effectiveness. Many mixer manufacturers provide sizing tools or software to help determine the most suitable mixer configuration based on your specific application requirements.

Positioning And Layout 

The positioning and layout of submersible mixers significantly impact their performance and efficiency. Proper placement ensures that the mixer's jet creates maximum bulk flow, adapting to the tank's shape and dimensions.

In rectangular tanks, mixers are often positioned at an angle to create a circular flow pattern that reaches all corners of the tank. For circular tanks, mixers may be placed off-center to generate a swirling motion throughout the tank volume.

The mixer's depth and angle of installation are also crucial. Generally, they should be positioned below the liquid surface to prevent vortexing and air entrainment. The optimal depth and angle depend on the tank geometry and the desired flow pattern.

In larger tanks or complex applications, multiple mixers may be necessary to achieve uniform mixing. The layout of multiple mixers requires careful consideration to ensure that their flow patterns complement each other rather than interfere.

It's important to note that the positioning and layout of submersible mixers often involve some degree of trial and error. Computational Fluid Dynamics (CFD) simulations can be helpful in predicting flow patterns and optimizing mixer placement, but on-site adjustments may still be necessary to achieve the best results.

Submersible Mixer Manufacturers

Tianjin Kairun is one such manufacturer that has obtained ISO 9001 certification for its quality management system. When selecting a submersible mixer manufacturer, it's advisable to consider factors such as product range, technical support, after-sales service, and industry experience. you can reach out to them at :catherine@kairunpump.com.

In conclusion, proper sizing of submersible mixers involves careful consideration of application requirements, thrust calculations, impeller design, and mixer positioning. By taking these factors into account and working with reputable manufacturers, you can ensure optimal mixing performance and efficiency in your industrial processes.

References:

1. Pumps - Testing - Submersible mixers for wastewater and similar applications. International Organization for Standardization.

2. Oldshue, J.Y. Fluid Mixing Technology. McGraw-Hill.

3. Paul, E.L., Atiemo-Obeng, V.A., & Kresta, S.M. (Eds.). Handbook of Industrial Mixing: Science and Practice. John Wiley & Sons.

4. Weetman, R.J. Optimization of large agitators. Chemical Engineering Progress.