From Selection to Application: Technical Matching Analysis of Agitators with Fluids of Different Viscosities

Stirring plays a crucial role in both experimental processes and industrial production. Its primary function is to ensure thorough contact and mixing of two or more different media or to facilitate complete reactions.

Currently, common stirring methods include traditional mechanical agitation, airflow agitation, and ultrasonic oscillation. Among these, mechanical agitation is widely used across various processes due to its simple structure, ease of operation, and well-established manufacturing techniques.

Agitators primarily facilitate thorough mixing of two or more different media, enabling physical interactions or complex chemical reactions while also enhancing mass and heat transfer. They ensure uniform dispersion in liquid-liquid, solid-liquid, gas-liquid, or solid-liquid-gas systems. The selection of an appropriate agitator depends on the viscosity of the fluid in the preparation system to achieve the desired reaction outcome.

Selection of Agitators for Medium- to Low-Viscosity Fluids

Viscosity is a key parameter that characterizes a fluid’s resistance to flow, representing the internal friction between liquid molecules when subjected to external forces. For medium- to low-viscosity fluids, the following types of agitators are commonly used:

1. Propeller Agitator

A propeller agitator typically consists of three blades with relatively short lengths, with a blade-to-reactor diameter ratio of 0.2 to 0.5. During agitation, the fluid enters the blades, is expelled through a cylindrical helical motion, and returns to the bottom of the container in an axial circulation pattern. Due to its simple structure and ease of fabrication, it is suitable for low-viscosity, high-flow systems, particularly in liquid-liquid systems and low-concentration solid-liquid systems.

2. Paddle Agitator

Paddle agitators have a simple structure, typically consisting of two to four blades. These blades can be either straight or inclined, with their surfaces oriented perpendicular or at an angle to the direction of rotation. The fluid moves downward along the shaft and then rises along the inner wall of the reactor, forming a continuous circulation pattern. With relatively small blade diameters and high rotational speeds, paddle agitators are ideal for low-viscosity (≤20 Pa·S) liquid-liquid and solid-liquid systems.

3. Turbine Agitator

Turbine agitators can be classified into disk-type and open-type designs. The disk-type turbine consists of a central disk attached to the shaft, typically with six blades, which can be straight, inclined, or curved. The blade diameter is generally one-third of the reactor’s internal diameter. In this system, the fluid exits the turbine and spreads horizontally along the blade surfaces, ensuring excellent dispersion.

4. Three-Blade Backward Curved Agitator

This type of agitator has a more complex structure and requires sophisticated manufacturing techniques. Similar to turbine agitators, it generates radial flow within the reactor, drawing fluid in through the impeller and expelling it tangentially along the blades. This design provides excellent circulation and uniform mixing, making it particularly suitable for medium- to low-viscosity suspensions or fluids experiencing viscosity increases during reactions.

Selection of Agitator Blades for High-Viscosity Fluids

High-viscosity fluids exhibit greater internal friction, requiring higher mechanical energy to induce relative motion between molecules during agitation. This imposes specific strength requirements on the agitator. Commonly used agitators for high-viscosity fluids include: anchor agitator, frame agitator, sawtooth disc agitator, ribbon agitator, screw agitator, screw-ribbon agitator.

Due to space limitations, a detailed discussion of these agitators is omitted here.

Figure 1. Types of Agitator Blades and Corresponding Structural Diagrams

Image Source: 

The Function and Types of Agitator Blades

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Agitator Selection: A slight mistake in selection can lead to significant inefficiencies, similar to using a spoon to mix cement. An agitator with a diameter that is too small cannot generate effective circulation. Industry recommendations suggest that the agitator blade diameter should be 30%-50% of the tank diameter.

BioLink offers mixing systems suitable for different volumes, such as 2L, 5L, 10L, 15L, and 20L, designed for laboratory-scale preparation of small volumes or precious solutions. These systems feature high mixing power and are suitable for preparing medium- to low-viscosity liquids, with adjustable speeds based on actual needs.

The 50L-3000L mixing systems are designed for large-scale commercial production, with a variety of blade types that can be selected based on the type of liquid being prepared. The systems are flexible and customizable to meet customers’ specific liquid preparation requirements.

BioHub® DS Single-use Desktop Mixing System

• The modular design allows for a single control cabinet to manage multiple mixers, reducing production costs.

• The mixing support tanks are available in various specifications: 2L, 5L, 10L, 15L, and 20L, meeting the needs for mixing small volumes of precious liquids.

• The tanks are available in two material options: stainless steel and acrylic.

• The system complies with the data integrity requirements of 21 CFR Part 11, making them suitable for GMP production standards.

BioHub® BM Single-use Magnetic Mixing System

Application Fields:

• Medium preparation

• Buffer solution preparation

• Downstream intermediate product processing

• Bulk solution purification

• Semi-finished product preparation

• Other applications

Features:

• Highly customizable to meet specific needs

• Wide range of standard volume specifications from 50L to 3000L

• Modular design, allowing for flexible selection of modules

• Precise and stable stirring with a speed tolerance of ±2 rpm

• High mixing efficiency

• Stable hardware design and reliable software design

BioHub® UM Top-driven Mixing System

BioHub® UM Series Open-Top Agitation System

BioHub® UM Top-driven Mixing System features an aesthetically pleasing and clean design, with equipment that is easy to clean and operate. It is designed for common stirring applications in biotechnology and pharmaceuticals, supporting research laboratories and process development stages.

Product Features:

• Ergonomically designed for easy and quick use

• The stirring motor is adjustable in height, adaptable to different liquid preparation volumes, covering mixing capacities from 50L to 500L.

• The agitator blades rotate freely, with an angled insertion stirring method that creates irregular circular motion, enhancing mixing efficiency.

• SS316 material blades are quickly connected via a clamp for efficient use.

• Stainless steel blades paired with an open mixing bag to meet low-cost, high-quality mixing needs.