NAFA Guide To Air NAFA Guide To Air FiltrationFiltration

Chapter 3Chapter 3

Impingement FiltersImpingement Filters

presented by thepresented by the

National Air Filtration AssociationNational Air Filtration Association

Fourth Edition

Impingement FiltersImpingement Filters

• Impingement- The process in which Impingement- The process in which larger particles are removed from larger particles are removed from an air stream because of their an air stream because of their (weight or size) inertia. (weight or size) inertia.

• Mechanical filtersMechanical filters whose principal whose principal mechanism of dust mechanism of dust capture is impingement.capture is impingement.

Impingement FiltersImpingement Filters

Most impingement filters are Most impingement filters are characterized by relatively characterized by relatively high media velocities and by high media velocities and by low pressure drops.low pressure drops.

Impingement Filter Impingement Filter CategoriesCategories Panel Filters

Roll Filters Lint Filters

Washable Metal-Panel Filters

Panel FiltersPanel Filters Fixed-media air Fixed-media air

filters in which filters in which the face velocity the face velocity and the media and the media velocity are velocity are essentially the essentially the same.same.

Panel FiltersPanel Filters

•Media velocity-the speed of the Media velocity-the speed of the air as it moves through the filter air as it moves through the filter media.media.

Face velocity-the speed of Face velocity-the speed of the air as it approaches the the air as it approaches the filter face.filter face.

Panel Filters: Materials of Panel Filters: Materials of ConstructionConstruction

•Metals Metals

•Spun-glass fiber mediaSpun-glass fiber media

•Synthetic FibersSynthetic Fibers

•FoamFoam

Metal Washable FiltersMetal Washable Filters

Spun-glass mediaSpun-glass media• Used extensively in Used extensively in

Impingement FiltersImpingement Filters

• Usually adhesive Usually adhesive coated to improve coated to improve retentionretention

• Media density Media density varies ¼” to 5”varies ¼” to 5”

• Can be used in pads Can be used in pads or cardboard framesor cardboard frames

Synthetic FibersSynthetic Fibers• Polyester- Most popular material – Polyester- Most popular material –

ring and link panels, pocket filtersring and link panels, pocket filters

• Also Polypropylene, NylonAlso Polypropylene, Nylon or other synthetic or other synthetic (usually meant to be(usually meant to be washed)washed)

Synthetic Fibers• Fiber Fiber weight weight is measured in denier.is measured in denier.

• As a rule smaller denier fibers will As a rule smaller denier fibers will do a better job capturing small dust do a better job capturing small dust particles.particles.

• Dual denier media is commonlyDual denier media is commonly

used. It incorporates a largerused. It incorporates a larger

fiber on the air entry side andfiber on the air entry side and

a smaller fiber on the exit side.a smaller fiber on the exit side.

Characteristics of Characteristics of Synthetic Fiber MediaSynthetic Fiber Media

• Fiber distribution consistency is the most Fiber distribution consistency is the most important consideration when making important consideration when making synthetic media.synthetic media.

• Tackifiers are commonly applied to the Tackifiers are commonly applied to the air exit side of some synthetic medias to air exit side of some synthetic medias to prevent dust migration.prevent dust migration.

• Electrostatic charge is present in some Electrostatic charge is present in some types of synthetic media to aid in particle types of synthetic media to aid in particle capture.capture.

FoamFoam

•Usually polyurethaneUsually polyurethane

•Classified by pore sizeClassified by pore size

•The more pores per inch (PPI) the The more pores per inch (PPI) the higher the efficiencyhigher the efficiency

•Can be washed and reusedCan be washed and reused

Impingement Filter Media Impingement Filter Media PerformancePerformance

•Determined from independent Determined from independent filter testingfilter testing

•ASHRAE standard 52.1 (now ASHRAE standard 52.1 (now obsolete)obsolete)

•ASHRAE standard 52.2 (MERV)ASHRAE standard 52.2 (MERV)

Method of RenewalMethod of Renewal

• Filter banks using panel filters are Filter banks using panel filters are renewed by washing or replacing renewed by washing or replacing dirty filter media.dirty filter media.

• The use of disposable The use of disposable materials has become materials has become the predominant method of renewal.the predominant method of renewal.

Filter Holding SystemsFilter Holding Systems

Roll Filters Roll Filters • Devices in which clean Devices in which clean

filter media is unrolled filter media is unrolled at one end,exposed to at one end,exposed to a dirty air stream, and a dirty air stream, and advanced at intervals advanced at intervals to keep the pressure to keep the pressure drop through the drop through the exposed air stream exposed air stream within a desired within a desired operating range.operating range.

Roll Filters: Media Roll Filters: Media Advance and ControlAdvance and Control

•A motor driven system.A motor driven system.

•Manually operated chain drive.Manually operated chain drive.

•Can be controlled by an Can be controlled by an adjustable timer.adjustable timer.

Roll Filter MediaRoll Filter Media

•Fiberglass roll (infrequent)Fiberglass roll (infrequent)

•Synthetic fiber rollsSynthetic fiber rolls

Lint FiltersLint Filters

•Use the automatic roll filter Use the automatic roll filter principle.principle.

•Filter materialFilter material– Glass media with spun-bond backingGlass media with spun-bond backing– Thin 1,2, or 3 ply cellulose mediaThin 1,2, or 3 ply cellulose media

Grease FiltersGrease Filters

• Devices installed in kitchen range hoods Devices installed in kitchen range hoods to prevent the accumulation of grease in to prevent the accumulation of grease in hood exhaust ducts.hood exhaust ducts.

• Usually made of steel Usually made of steel or aluminumor aluminum• Grease filters do notGrease filters do not aid in smoke removal.aid in smoke removal.• They can be washed.They can be washed.• Must meet NFPA Std. 96Must meet NFPA Std. 96

Sample QuestionsSample Questions

The velocity of the air through any one The velocity of the air through any one square foot of media in an extended square foot of media in an extended surface filter is called?surface filter is called?

Media VelocityMedia VelocityHaving larger fibers on the air entering Having larger fibers on the air entering

side and smaller fibers on the air exit side and smaller fibers on the air exit side is called?side is called?

Graduated densityGraduated density

Thank you.Thank you.

Other QuestionsOther Questions