High-efficiency particulate air ( HEPA ), originally called high efficiency particulate absorbers but also sometimes called high efficiency retaining particulates or high efficiency particulate containment , is a type of air filter. Filters that meet HEPA standards have many applications, including clean indoor use for IC fabrication, medical facilities, cars, airplanes and homes. Filters must meet certain efficiency standards as set by the US Department of Energy (DOE).
To qualify as HEPA by industry standards, air filters must remove (from air passing) 99.97% of particles having sizes greater than or equal to 0.3 Âμm. Although the ASME industry standard is not published by any government, it is recognized as an authoritative standard by many governments.
HEPA was commercialized in the 1950s, and the original term became a registered trademark and then a general term for highly efficient filters.
Video HEPA
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The HEPA filter consists of a randomly arranged fiber mat. Fiber usually consists of fiberglass and has a diameter between 0.5 and 2.0 micrometers. The key factors that affect its function are fiber diameter, filter thickness, and facial velocity. The air space between the HEPA filter fibers is usually much larger than 0.3 m. The general assumption that HEPA filters act like a filter in which particles smaller than the largest opening can pass wrong and are not practical. Unlike membrane filters at these pore sizes, where the widest particles of opening or the greatest distance between the fibers can not pass through at all, the HEPA filter is designed to target the smaller pollutants and particles. These particles are trapped (they stick to the fiber) through a combination of the following three mechanisms:
- Interception
- in which the particle follows the flow line in the flow of air coming in one fiber radius and obeying it.
- Impaction
- where larger particles can not avoid fibers by following the airflow curve contours and being forced to implant one of them directly; this effect increases with reduced fiber separation and higher airflow rates.
- Diffusion
- an increase mechanism that is the result of a collision with a gas molecule by the smallest particle, especially those below 0.1 Ã,Âμm in diameter, thus hampered and delayed in its path through a filter; this behavior is similar to Brownian motion and increases the probability that the particle will be stopped by one of the two mechanisms above; this mechanism becomes dominant at lower airflow velocities.
Diffusion dominates below the particle size of 0.1? Diameter. Impaction and interception dominate above 0.4 m? In between, near the most penetrating particle size (MPPS) 0.21 m ?, Both diffusion and interception are relatively inefficient. Since this is the weakest point in the filter performance, the HEPA specification uses particle retention near this size (0.3 m) to classify the filter. However it is possible for smaller particles of MPPS to have no greater filtering efficiency than MPPS. This is due to the fact that these particles can act as nucleation sites for most of the condensation and form particles near the MPPS.
Gas filtration
HEPA filters are designed to capture very fine particles effectively, but they do not filter out gas and odor molecules. Circumstances which require the filtering of volatile organic compounds, chemical vapors, cigarettes, pets, and/or bloating stomachs calling for the use of activated carbon (charcoal) or other types of filters, not or in addition to HEPA filters. The carbon cloth filter, claimed to be much more efficient than the granular activated carbon form in gas pollutant adsorption, is known as the HEGA (" H igh E b> G as A dsorption ") and was originally developed by the British military as a defense against chemical warfare.
Maps HEPA
Specifications
The HEPA filter, as defined by the US Department of Energy (DOE) standard adopted by most American industries, eliminates at least 99.97% of airborne particles of 0.3 micrometers (Âμm) in diameter. Minimal filter resistance to airflow, or pressure drop, is usually determined about 300 pascal (0.044 psi) at its nominal volumetric flow rate.
The specifications commonly used in the European Union are the European Norms EN 1822: 2009. It defines several classes of HEPA filters by their retention at the most penetrating particle size (MPPS):
- See also different classes for the air filter as a comparison.
Currently, the HEPA filter rating applies to any highly efficient air filter that achieves the same standard of efficiency of the filter as a minimum and is equivalent to the newer National Institute for Occupational Safety and Health N100 ratings for respirator filters. The US Department of Energy (DOE) has special requirements for HEPA filters in DOE-regulated applications. In addition, the company has begun to use a marketing term known as "True HEPA" to provide assurance to consumers that their air filters are indeed certified to meet HEPA standards.
Products claiming to be "HEPA-type", "HEPA-like", "HEPA-style" or "99% HEPA" do not meet these requirements and may not be tested in independent laboratories. Some of the quality filters below may be quite close to HEPA filtering, while others will be very short, making it really lower.
Security
HEPA screening works in a mechanical way unlike ion and ozone filtration, each of which uses negative ions and ozone gas. Thus, the likelihood of lung side effects such as asthma and allergies is much lower with HEPA cleansers.
Biomedical app
HEPA filters are very important in preventing the spread of bacterial organisms and viruses in the air and, therefore, infection. Typically, the HEPA used medical filtration system also incorporates a high-energy ultra-violet light unit to kill live bacteria and viruses trapped by the filter media. Some of the best HEPA units are rated to have an efficiency rating of 99.995%, which ensures a very high level of protection against the transmission of airborne diseases.
Vacuum cleaner
Many vacuum cleaners also use HEPA filters as part of their filtering system. This is helpful for people with asthma and allergies, because HEPA filters trap fine particles (such as pollen and dust mites) that trigger allergic and asthma symptoms. For a HEPA filter in a vacuum cleaner to be effective, a vacuum cleaner must be designed so that all air drawn into the engine is removed through the filter, without any air leaking through it. This is often referred to as "Sealed HEPA" or sometimes "True HEPA" which is more vague. A vacuum cleaner labeled "HEPA" may have a HEPA filter, but not all air must pass through it. Finally, vacuum cleaner filters marketed as "HEPA-like" will usually use a similar construction filter to HEPA, but without filtering efficiency. Due to the correct HEPA excess filter density, HEPA vacuum cleaners require a stronger motor to provide adequate cleaning power.
Some newer models claim better than the first model because the filters are "washable". Generally, washable HEPA filters are expensive. Some manufacturers claim a filter standard such as "HEPA 4", without explaining the meaning behind it. This refers to the rating of the Minimum Efficiency Rating (MERV). This rating is used to assess the ability of air purifier filters to remove dust from the air as it passes through the filter. MERV is the standard used to measure the overall efficiency of filters. The MERV scale ranges from 1 to 20, and measures the filter's ability to remove particles from 10 to 0.3 micrometers in size. Higher ratings filters not only remove more particles from the air, but also eliminate smaller particles.
Vehicles
Airlines
Modern aircraft use HEPA filters to reduce the spread of airborne pathogens in the air that are recirculated. Critics have expressed concern about the effectiveness and state of improvement of air filtration systems, as they think that most of the air in the aircraft cabin is recirculated. Almost all the air inside the pressurized aircraft is actually carried from the outside, circulated through the cabin and then runs out through the outgoing valves at the rear of the aircraft.
Motor vehicles
Some cars have cabin air filters that look like HEPA filters but do not work at that level. This confusion is perpetuated by a guide to replace a car filter that incorrectly identifies the filter as a HEPA filter. The actual performance of these filters is obscured by the manufacturer and difficult to evaluate, since they are not rated with the MERV system, although they usually result in a performance equivalent to 8 MERV.
Recently, Tesla Model X has been linked to having the world's first HEPA filter class. After the release of Model X, Tesla has updated Model S to also have an optional HEPA air filter.
History
The original HEPA filter was designed in the 1940s and is used in the Manhattan Project to prevent the spread of radioactive contaminants in the air. It was commercialized in the 1950s, and the original term became a registered trademark and then a general term for highly efficient filters.
Over the past decades filters have evolved to meet higher and higher demands for air quality in a variety of high-tech industries, such as aerospace, pharmaceutical drug processing, hospitals, health care, nuclear fuel, nuclear power, and integrated circuit fabrication.
See also
- Air purifier
- Clean Air Delivery Rates
- Clean room
- Electrostatic precipitator - trap particles with high voltage
- A hypoallergenic vacuum cleaner - a vacuum cleaner with a high efficiency air filter
- Minimum efficiency reporting value (MERV)
- Respirator
- ULPA - Eliminates 99.999% of dust, pollen, mold, bacteria, and particles larger than 120Ã, nm
References
General reference
- ITSI-041 Application Note: Filtration Mechanism for High Efficiency Fiber Filters
External links
- Recommended Practices on HEPA and ULPA Filters
Source of the article : Wikipedia
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