Vortex Formation Quiz: Learn about Mixing and Liquid Mixing

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Questions and Answers

What is the primary mechanism of mixing in liquids that involves the movement of a large amount of material from one position to another?

Viscous flow

Turbulent mixing

Bulk transport (correct)

Molecular diffusion

What type of mixing is characterized by small groups of molecules moving together as a unit?

Molecular diffusion

Turbulent mixing (correct)

Viscous flow

Bulk transport

Which of the following is NOT a mechanism of liquid mixing?

Molecular diffusion

Turbulent mixing

Vortex formation (correct)

Bulk transport

What is the result of vortex formation in mixing liquids?

No good mixing Signup and view all the answers

What is the effect of air entering into the material during mixing?

Decomposition of substances by oxidation Signup and view all the answers

How can vortex formation be suppressed in small tanks?

By moving the impeller to an off-center or inclined position Signup and view all the answers

What is the advantage of bulk transport in mixing liquids?

It produces a large degree of mixing fairly quickly Signup and view all the answers

What is the primary mechanism of mixing that occurs at the molecular level?

Molecular diffusion Signup and view all the answers

What is the primary function of an impeller in liquid mixing?

To provide the necessary shear forces Signup and view all the answers

What happens when the centrifugal force produced by the impeller is greater than the liquid resistance to flow due to viscosity?

The liquid discharges from the impeller at a right angle to its shaft Signup and view all the answers

What occurs in most mixers due to the movement of a stirrer or mixer paddle at a suitable speed?

Both bulk transport and turbulence occur Signup and view all the answers

What is the purpose of axial flow in liquid mixing?

To suspend solids in the liquid Signup and view all the answers

What is the main purpose of sigma mixers in semi-solids mixing?

To provide a pulling and kneading action Signup and view all the answers

What is the result of a correct balance of the three types of liquid flow?

Good mixing of liquids Signup and view all the answers

What is the characteristic of the blades in a sigma mixer?

They rotate at different speeds, one usually about twice the speed of the other Signup and view all the answers

What is the direction of the tangential component of liquid flow?

In a direction that is a tangent to the circle of rotation around the impeller shaft Signup and view all the answers

What is the main application of planetary mixers in the pharmaceutical industry?

Low-shear granulation Signup and view all the answers

What is the effect of rotational flow predominating in liquid mixing?

Formation of a vortex Signup and view all the answers

What is the characteristic of the double planetary mixer?

It has two blades that rotate at their own axis, clockwise and in opposite directions Signup and view all the answers

What is the role of baffles and agitators in liquid mixing?

To change the flow pattern of the liquid Signup and view all the answers

What is the advantage of the double planetary mixer?

It has no dead spot in the vessel Signup and view all the answers

What are the three velocity components of liquid flow in a mixing tank?

Radial, axial, and tangential Signup and view all the answers

What type of mixers are sigma mixers and planetary mixers classified as?

Agitator mixers Signup and view all the answers

What is the main characteristic of turbulent mixing in miscible fluids?

It produces a well-mixed product eventually Signup and view all the answers

Study Notes

Vortex Formation

Vortex formation occurs when the shaft of the impeller is vertical and centrally located in the tank, leading to tangential flow predominance.
As velocity increases, the vortex increases, causing disadvantages such as:
- No good mixing due to swirling of liquid layers
- Air enters the material, causing:
  - Decomposition of substances by oxidation
  - Excessive foaming with certain products, affecting further processing (e.g., accurate filling into containers)

Suppression of Vortex Formation

Suppression methods include:
- Moving the impeller to an off-center or inclined position in small tanks
- Installing vertical baffles (strips perpendicular to the wall) in large tanks to reduce tangential flow without affecting radial and axial flow
- Mounting the impeller on the side of the tank in very large tanks

Mechanisms of Liquid Mixing

Three main mechanisms of liquid mixing:
- Bulk transport: movement of a large amount of material from one position to another, producing a large degree of mixing quickly
- Turbulent mixing: small groups of molecules moving together as a unit (eddy)
- Molecular diffusion: mixing of individual molecules, occurring with miscible fluids and eventually producing a well-mixed product

Mixers for Semi-solids

Divided into:
- Agitator mixers:
  - Sigma mixers
  - Planetary mixers
- Shear mixers:
  - Colloidal mill
  - Triple roller mill

Sigma Mixers

Feature:
- Agitator arms designed for pulling and kneading action
- Two mixer blades resembling the Greek letter σ (sigma)
- Rotation towards each other at different speeds, resulting in lateral pulling of material

Planetary Mixers

Features:
- Used for mixing and beating viscous and pasty materials
- Suitable for wetted powder during tablet granulation
- Often used in the pharmaceutical industry for mixing, blending, and low-shear granulation
Double planetary mixer:
- Two blades rotate at their own axis, clockwise and in opposite directions, while orbiting the mix vessel on a common axis
- Blades continuously advance along the periphery of the vessel, removing material from the vessel wall and transporting it to the interior, with no dead spot in the vessel

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Description

Understand the concept of vortex formation in mixing, its causes, and disadvantages. Learn how tangential flow and shaft location affect vortex formation and its effects on mixing and substance decomposition.