What Is an Agitation Blade?
Agitation blades are the most important component of an agitator because they are responsible for transmitting the rotational energy from the motor into the tank.
The rotational energy is mainly used for the discharge action, which creates a circulating flow throughout the tank, and the shearing action, which applies a local shearing force. The shape of the agitation blade can be optimized depending on whether the discharge or shearing action is desired first.
The agitation blade that best suits the purpose can be selected by determining the maximum capacity that can be achieved within the fixed power of the motor. Typical agitation blades include propeller blades, turbine blades, anchor blades, paddle blades, and ribbon blades.
Uses of Agitation Blades
Agitation blades are used to mix materials in an agitator. In relatively large factories, the capacity of the agitation tank is large, and the time required for agitation increases accordingly. On the other hand, small agitators can be easily used from the laboratory level to the factory floor and can agitate in a short time.
It is common to scale up the shape of agitation blades considered for small agitators so that they can be used with large agitators. However, in some cases, depending on the viscosity range of a substance, simply scaling up the agitation blades may not be sufficient to mix the substance. Scaling up agitation blades must be thoroughly verified.
Principle of Agitation Blades
1. State of Matter Produced by Agitation Blades
Diffusion and convection are necessary for mixing in a tank. Diffusion describes the phenomenon of spontaneous, detailed, and uniform mixing by molecular motion. Convection, on the other hand, is a phenomenon in which different substances are stretched or divided within a tank and dispersed throughout a large space.
2. Agitation Phenomenon Brought About by Agitation Blades
Assume that two kinds of liquids exist in two layers in a tank. When the agitation blades are turned by the power of the motor, they first forcefully disperse the liquids into smaller pieces. This is similar to shaking a dressing before using it.
Depending on the shape of the agitation blade, the liquid in contact with the agitation blade will flow up, down, left, and right, resulting in the unique behavior of the agitation blade. For example, paddle blades are sloped and shaped to form more flow in the vertical direction. Turbine blades, on the other hand, have blades mounted on disks that rotate at high speed in the tank, producing high shearing force.
3. Power of Agitation Blades
As the motor rotates, the power is transmitted to the shaft. At that time, if a reduction gear is attached, deceleration and torque increase according to the reduction gear. In addition, a shaft sealing device can seal the inside of the tank without interfering with rotation. Generally, gland packings and mechanical seals are used as shaft sealing devices.
Types of Agitation Blades
Agitation blades used for low viscosity materials are propeller blades, turbine blades, and paddle blades. The number of agitation blades and the angle at which they are attached can be used to change the mixing state of the substance.
On the other hand, anchor blades and ribbon blades are the agitation blades used in the high viscosity range. They are used for homogenization of high-viscosity liquids and heat exchange.
1. Agitation Blades Used in the Low Viscosity Range
Propeller Blade
This is a common agitation blade, similar in shape to a helicopter propeller. They can form a liquid flow in the axial direction in a tank, enabling efficient agitation in terms of energy.
Turbine Blade
Turbine blades are disks with blades attached to them. They have high shear force and are suitable for droplet refinement and gas-liquid dispersion. The disadvantage is its high power consumption, but it can be used in a wide range of viscosities.
Paddle Blade
The shape is similar to a ship’s oar. Because of its simple structure, it is used as a material for obtaining basic agitation data. It is often used in large agitators at low speeds, and can efficiently agitate liquids because it can generate strong turbulence by attaching baffles.
2. Agitation Blades Used in the High Viscosity Range
Anchor Blade
Shaped like a ship’s anchor. It can mix substances that stay near the wall of the agitation tank, but its disadvantage is that it is difficult to generate flow in the axial direction.
Ribbon Blade
This is a typical agitation blade in the high-viscosity range. It has the same characteristics as the anchor blade, but has a more complex structure. The agitation blade is inclined, which allows the formation of a flow in the axial direction.