Page 11 - dust collection systems

Fabric filters can also collect very small particles, less than 1
µm in aerodynamic diameter. One would think that this size

particle would be carried right along with the gas stream. In

fact, these particles are so small, they just sort of bounce

around and deflect slightly when they are stuck by gas

molecules. This individual or random motion causes them to

be distributed throughout the gas as shown in above figure

and is known as Brownian Motion or Brownian Diffusion.

The particle may have a different velocity than the gas

stream and at some point, could come in contact with the

fibre and be collected. This behaviour is called diffusion.

Fabric Filtration Mechanisms

A fibre is any long, thin (length / diameter ≥ 100) hair-like

material. A fabric is a stable collection of fibres attached to

each other so as to retain a permanent structure.

Woven fabrics are the traditional textile fabric. Fibres are

first formed into yarns (threads) and the yarns are then

woven together to make a woven fabric. Woven fabrics have

a definite repeated weave pattern. Various weaving patterns

(for example, plain weave, twill weave, etc.) increase or

decrease the amount of space between yarns and affects the

permeability of the fabric. A tighter weave has lower

permeability and, therefore, captures fine particles more
efficiently. A nonwoven (felted) fabric is made from long