Principle, Construction, Working, Uses, Merits and Demerits of Paddles

Paddles

Principle

An agitator works with a paddle to produce a laminar flow of liquid. The paddles push the liquid in radial and tangential directions, with little or no axial movement unless the blades are pitched. As the blades possess a large surface area relative to the container, they are able to rotate in close proximity to the container walls for effective mixing of viscous liquids or semisolids.

Construction

Long flat blades are attached vertically to a central hub in the middle of the paddle. Figure in the picture below shows a two-bladed or four-bladed fan. It is not uncommon for blades to have different shapes, such as dish-shaped or hemispherical, and to have an increased surface area relative to the tank in which they are used. Paddles rotate at 100 r.p.m. they are attached to shafts one above the other in deep tanks. In tanks without baffles, it gives mild agitation at very low speeds, but at high speeds, baffles are required.

Working

To mix materials, the material is placed at the top of the trough. It is possible to spray liquids if needed. It is typical to fill the shafts slightly above the level of the liquid. Thus, there is excess space in the mixer through to allow air to surround each particle, allowing them to move freely. It results in a mixing homogeneity of 98 - 99%, based on random movements in the trough. Each paddle rotates at about 100 rpm.

Uses

• An acidic suspension and antidiarrhea mixture such as bismuth-kaolin mixture use paddles.
• When super saturated cooling is occurring, these systems are used to mix solids, slurries, and crystals forming phases.

Merits

• Due to the low speed at which paddle-impellers mix liquids, vortex formation is least likely.
• Suitable for slow operation, these mixers are heavy-duty.
• With 2 or 4 blades, they are able to mix systems effectively.

Demerits

• A baffled tank is required due to the poor mixing of the suspensions.
• Due to their heavy-duty nature, they consume a lot of power.
• Mixing different materials with different consistencies is difficult with them.

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