Air filter

A particulate air filter is a device composed of fibrous, or porous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal may also remove odors and gaseous pollutants such as volatile organic compounds or ozone. Air filters are used in applications where air quality is important, notably in building ventilation systems and in engines.

HEPA Filters

High efficiency particulate arrester (HEPA), originally called high-efficiency particulate absorber but also sometimes called high-efficiency particulate arresting or high-efficiency particulate arrestance, is a type of air filter. Filters meeting the HEPA standard have many applications, including use in clean rooms for IC fabrication, medical facilities, automobiles, aircraft and homes. The filter must satisfy certain standards of efficiency such as those set by the United States Department of Energy (DOE).

Varying standards define what qualifies as a HEPA filter. The two most common standards require that an air filter must remove (from the air that passes through) 99.95% (European Standard) or 99.97% (ASME standard) of particles that have a size greater than or equal to 0.3 μm.

Automotive Cabin Air Filters

The cabin air filter is typically a pleated-paper filter that is placed in the outside-air intake for the vehicle's passenger compartment. Some of these filters are rectangular and similar in shape to the engine air filter. Others are uniquely shaped to fit the available space of particular vehicles' outside-air intakes. The first automaker to include a disposable filter to keep the ventilation system clean was the Nash Motors "Weather Eye", introduced in 1940.

Clogged or dirty cabin air filters can significantly reduce airflow from the cabin vents, as well as introduce allergens into the cabin air stream. Since the cabin air temperature depends upon the flow rate of the air passing through the heater core, the evaporator, or both, clogged filters can greatly reduce the effectiveness and performance of the vehicle's air conditioning and heating systems.

Internal Combustion Engine Air Filters

The combustion air filter prevents abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination. Most fuel injected vehicles use a pleated paper filter element in the form of a flat panel. This filter is usually placed inside a plastic box connected to the throttle body with duct work.

Older vehicles that use carburetors or throttle body fuel injection typically use a cylindrical air filter, usually between 100 millimeters (4 in) and 400 millimeters (16 in) in diameter. This is positioned above or beside the carburetor or throttle body, usually in a metal or plastic container which may incorporate ducting to provide cool and/or warm inlet air, and secured with a metal or plastic lid. The overall unit is called the air cleaner.

Bulk Solids Handling Filters

Bulk solids handling involves the transport of solids which may be in a powder form. Many industries are handling bulk solids which requires the treatment of air streams escaping the process so that fine particles are not emitted, for regulatory reasons or economical reasons. As a consequence, air filters are positioned at many places in the process, especially at the reception of pneumatic conveying lines where the quantity of air is important and the load in fine particle quite important.

Filters can also be placed at any point of air exchange in the process to avoid that pollutants enter the process, which is particularly true in pharmaceuticals and food industries. The physical phenomena involved in catching particles with a filter are mainly inertial and diffusional.