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GE Healthcare Life Sciences

March 2015

Filtration mechanisms

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Content

Filtration mechanisms

- in liquids

- in gases

Filtration Mechanisms in liquids

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Physical entrapment on surface

Pore

Physical entrapment - particles larger than

the pores trapped. Particles smaller than

pore size passes through the filter

Particle

Filter material

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Physical entrapment within pore

Physical entrapment can happen on filter material’s

surface or within the pores

Pore within filter material

Particle trapped in

the pore

Filter material surface

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Adsorption

Adsorption can occur due to electrostatic interaction or

van der Waals forces. Can removes particles smaller

than the pore size.

Pore

(Most Filter have a negative charge if the wetting

liquid pH >2-3)

Filter material surface

Filtration Mechanisms in liquids

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Filtration mechanisms - gases

Direct interception

• Particles larger than the pores removed and those

smaller than pore size passes through

Inertial impaction (or Inertial collection)

• Arises due to inertia of particles

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Inertial impaction

Air flow

If the particle has no inertia, the it will follow the air flow path and pass through

the filter (as long as the particle is smaller than the pore)

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Inertial impaction

Air flow

In reality the particle has inertia. Hence it may escape from the air flow path,

impact the surface of the filter and get trapped.

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Filtration mechanisms - gases

Diffusion

• Only important for very small particles (<0.1 micron)

Electrical attraction

• Charge differences between filter and particles

Gravitational Sedimentation

• Only important for large particles

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Air filtration

Due to these mechanisms air filtration is efficient and

particle sizes much smaller than the pore size will be

removed by the filter

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First published. October 2014

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