Filtration

Filtration

Removal of contaminants from fluids (liquids or gases) using porous media

Micron
1 micron (um) =10－6 m ＝10－3 mm= 3.9×10 -5 inch

Three filtering mechanisms

1.Direct interception
Basic filtration mechanism in liquid
The essence is a sieving effect, mechanical interception of particles
For example: a simple screen can intercept the size, particles larger than their pore size.

When the particles are larger than the flow channel aperture, they are removed by the structure.
The dirt holding capacity can be improved by the curved structure
Screen does not have this effect

Particles smaller than the pore size can also be intercepted by bridging
Irregularly shaped particles / directionality
Multiple particles hit the same filter at the same time

1). Irregular shape bridge

2). Multiple small particles

2.Inertial impact
Auxiliary interception method for particles smaller than the pore size of the filter material
Fluid-carrying particles have linear motion inertia due to mass and line speed
The particles leave the main stream of the fluid and impinge on the filter

The particles are mechanically intercepted or adsorbed and intercepted

It is more effective in gas than in liquid.

It is effective for particles larger than 0.5 - 1.0 microns.

1). Adsorption

Intercepting particles smaller than the filter

Because of 

Surface interaction

Different charge

Van der Waals

2). Surface effect