Mechanisms of mixing | Equipment used for liquid mixing

There are 4 main mechanisms of mixing

1)Bulk transport

2)Turbulent mixing

3)molecular diffusion

4)Laminar mixing

1)Bulk transport:

Movement/transfer of large portion (bulk form) or large quantity of liquid from one position (point) to another position with in a system is called bulk transport.

•movement/transport of portion of liquid in all directions.

Bulk transport is occur by paddle or rotating blades.

E.g. mixing of miscible liquids.

2)molecular diffusion:

Movement of individual molecule from one location to another location within a system by diffusion method (from higher concentration to lower concentration) is molecular diffusion.

E.g. mixing of one drop of colour in liquid.

3)Turbulent mixing:

Turbulent flow:

Random fluidization of fluid at any given point . There is continuous change is instantaneous velocity. There is formation of eddies.


Portion of liquid flow as unit, mainly flow in direction opposite to direction of flow of liquid.

Turbulent mixing:

In turbulent mixing there is formation of large eddies used for the mixing of thin liquid.

In turbulent mixing mix with high velocity and rapid action of mixing. Turbulent mixing in short time give effective mixing. Give efficient mixing.

4)Laminar mixing:

Laminar mixing is also called streamline mixing. In laminar mixing instantaneous velocity is same and no random fluidization of fluid.

Laminar mixing is used for viscous liquids, mixing of dissimilar liquids. Mixing occur in the form of layers. Layer of one liquid mix with the layer of other liquid.

Equipment used for liquid mixing:

1)propeller mixer

2)turbines mixer

3)paddle mixer

1)propeller mixer:

Propeller mixer

three blade propeller mixer. Blades are attached to shelf which is attached to motor. When motor is on the blades will rotate.

Propeller mixer is used for thin liquids e.g. water and alcohol.

The velocity is high in propeller mixer. Rotation of propeller mixer is 8000rpm .

The one drawback of propeller mixer is that there is the formation of vortex. Air inside the Thin layer of liquid.

2)turbines mixer:

Turbines mixer

Turbines mixer contain number of blades and these blades are attached to the circular disc. The circular disc is attached to the shaft which is attached to the motor. When motor is on this will rotate the circular disc.

Turbine mixer is used for the viscous liquid for example syrups , emulsions, castor oil, liquid parafin, suspension.

Speed of rotation is low as compared to propeller mixer.

3)paddle mixer:

Paddle mixer

In the paddle mixer the blades are large sized or increase surface area. The blade may be one or may be multiple blades.

Paddle mixer is used for highly viscous liquids for example semi solid materials like ointment,  gels, pastes.

Speed of rotation is very low . Speed of rotation of paddle mixer is 100rpm.

The drawback of paddle mixer is formation of dead spot which is unmixed liquid .

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