|
Partilce Size
Ø Smallest visible particle 50micron
Ø Human hair 60-80micron
Ø Blood cells 10-30micron
Ø Yeast cells 5-10micron
Ø Small bacteria 0.3micron
Ø Virus 0.03micron
What Influences Filter Retention Mechanisms?
Ø Fluid
Ø Particle
Ø Operating Conditions
Filter
Retention Mechanisms-Fluid
Viscosity
Ø High viscosity means low flowrate
Ø Slow flow allows more filter contact
Ø Increased adsorptive soft pargicle capture
Ø Low fiscosity means high flowrate
Ø Increased momentum based hard particle capture
Ø Temperature effect on viscosity
Ø Chemical/Ionic content
Ø Colloids can aggregate or move apart
Mixing/Contact time can be critical
Types of Particles
Deformable types
Ø Ie gels,sols ,protein ,lipid ,or suger complexes
Ø Change shanpewigh flow/pressure
Ø Intrude into filter struclure
Ø ¡°Slime¡± the filter
Ø Difficult to filter Non-deformable types
Ø Ie resin beads,crystals,carbon fines,D.erth
Ø Usually irregular shape
Ø Build an open cake
Easier to filter
Retention Mechanisms-Operating Conditions
Particle speed/velocity
Ø Particle speed/velocity
Ø Flow fate lower enhances retention and filter life
Applied pressure
Ø Depth matrix movement is bad
Ø Depth media can detatch and pass down stream
Ø Keeps particles lightly packed
Particles can bleed through filter
Retention Mechanisms-Filter
Pore rating
Ø Sterilizing filter is the only common rating
Ø Prefilter ratings not standardized
Ø Compare manufacturers rating method &particle with your use
Structure
Ø Depth structures change characteristics
Membranes and surface filters maintain integrity
| 
