Submersible mixers are integral to numerous industrial processes, including wastewater treatment, chemical processing, and food production. To ensure these mixers perform optimally, precise design and calculation are essential. The first step involves assessing the mixing requirements, including the tank's shape and size, to determine the appropriate mixer specifications. Key calculations focus on power requirements, factoring in the tank volume, liquid properties, and desired mixing intensity. Selecting the right impeller design and speed is crucial, as it influences the flow pattern and mixing efficiency. Engineers must also consider material selection for durability and resistance to the specific conditions of the environment, ensuring that seals and shafts are robust enough to handle operational stresses. Safety and maintenance are paramount; incorporating features like over-temperature protection and ensuring ease of access for routine inspections can prevent operational disruptions. Prototype testing is the final step, validating design calculations and performance under actual conditions to ensure reliability. By meticulously following these design and calculation steps, engineers can achieve highly effective and reliable submersible mixers that meet the rigorous demands of diverse industrial applications.

Determine Power Requirement

The first step in designing a submersible mixer is determining the power requirement. This calculation depends on several factors, including the volume of liquid to be mixed, the viscosity of the fluid, and the desired level of agitation. Engineers typically use empirical formulas or computational fluid dynamics (CFD) simulations to estimate the power needed.

One common method is to use the power number (Np) and Reynolds number (Re) relationship. The power number is a dimensionless quantity that relates the mixer's power consumption to its rotational speed and impeller diameter. The Reynolds number, on the other hand, characterizes the flow regime in the mixing vessel.

Select Impeller Type

Choosing the right impeller type is crucial for achieving the desired mixing performance. Different impeller designs are suited for various applications, depending on factors such as fluid viscosity, tank geometry, and mixing objectives.

Common impeller types for submersible mixers include:

Hydrofoil Impellers: Ideal for low-viscosity fluids and large tanks

Pitched Blade Turbines: Suitable for a wide range of applications, offering good flow and moderate shear

Radial Flow Impellers: Effective for high-shear applications and gas dispersion

When selecting an impeller, consider its pumping capacity, shear characteristics, and energy efficiency. Consulting impeller performance curves and manufacturer recommendations can help in making an informed decision.

Calculate Impeller Diameter

The impeller diameter is a critical parameter that affects mixing performance and power consumption. A general rule of thumb is to size the impeller diameter between 0.3 to 0.6 times the tank diameter for most applications. However, this ratio may vary depending on the specific mixing requirements and tank geometry.

To calculate the impeller diameter, you can use the power number relationship mentioned earlier. Rearranging the power equation, we get:

D = (P / (Np * ρ * N^3))^(1/5)

This calculation provides a starting point for impeller sizing. Fine-tuning may be necessary based on CFD simulations or pilot-scale testing.

Determine Rotational Speed

The rotational speed of the impeller affects the mixing intensity and power consumption. Higher speeds generally result in better mixing but also increase energy usage. The optimal speed depends on the application, fluid properties, and impeller design.

For submersible mixers, typical rotational speeds range from 100 to 1500 RPM. The specific speed can be determined using the power equation or by consulting impeller performance curves provided by manufacturers.

It's important to consider the tip speed of the impeller, which is the velocity at the outer edge of the impeller blade. Excessive tip speeds can lead to cavitation or damage to sensitive materials in the mixture.

Select Motor And Gearbox

Once the power requirement and rotational speed are determined, the next step is to select an appropriate motor and gearbox combination. The motor should be sized to provide the required power with a safety factor to account for potential overloads or startup conditions.

For submersible mixers, it's crucial to choose a motor with proper ingress protection (IP) rating to ensure reliable operation in submerged conditions. Most submersible mixer motors have an IP68 rating, which provides complete protection against dust and long-term immersion in water.

The gearbox, if required, should be selected to match the desired output speed and torque. Factors to consider include gear ratio, efficiency, and durability in the operating environment.

Design Shaft And Bearing

The mixer shaft and bearings must be designed to withstand the loads and environmental conditions of the application. Key considerations include:

Shaft Diameter: Calculated based on the transmitted torque and bending moments

Shaft Material: Selected for corrosion resistance and strength (e.g., stainless steel)

Bearing Type: Typically, sealed bearings are used for submersible applications

Seal Design: Mechanical seals are often employed to prevent fluid ingress

Engineers should perform stress analysis and fatigue calculations to ensure the shaft and bearings can handle the operational loads and have an adequate service life.

Submersible Mixer Manufacturers

When choosing a submersible mixer manufacturer, it is important to choose a reputable company with a solid reputation for quality and reliability. Tianjin Kairun is one such manufacturer and we supply electric submersible mixers and electric submersible agitators. Our products are certified to ISO 9001 quality management system, ensuring consistent quality and performance.

Tianjin Kairun's commitment to quality and its range of submersible mixing solutions make it a strong choice for a variety of industrial applications. If you are interested in submersible mixers, you can contact us at catherine@kairunpump.com for more information or to discuss your specific requirements.

Designing a submersible mixer requires careful calculation and consideration of various factors to ensure optimal performance and reliability.

References:

1. Paul, E. L., Atiemo-Obeng, V. A., & Kresta, S. M. (2004). Handbook of Industrial Mixing: Science and Practice. John Wiley & Sons.

2. Weetman, R. J. (2008). Fluid Mixing Technology. Handbook of Industrial Mixing: Science and Practice, 1-23.

3. Uhl, V. W., & Gray, J. B. (1986). Mixing: Theory and Practice. Academic Press.

4. McCabe, W. L., Smith, J. C., & Harriott, P. (2005). Unit Operations of Chemical Engineering. McGraw-Hill Education.

5. Oldshue, J. Y. (1983). Fluid Mixing Technology. McGraw-Hill.