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Air Purification Technology

There are several varieties of air filters in the market. These filters are often classified based on the extent to which they can remove a particular size of solid particles present in air. When we say solid particles, it includes dust, pollen, bacteria, mold, etc.

HEPA & ULPA Filter

HEPA (High Efficiency Particulate Air) filters are capable of removing 99.97% of contaminant particles size greater than or equal to 0.3 µm. Most standards also specify that HEPA filters must feature minimal pressure drop and maximum airflow when in operation. There are 2 types of HEPA filter : True-HEPA & HEPA-type. The latter is less efficient (80%).

ULPA (Ultra Low Particulate Air) filters are a step further than HEPA and even more efficient. ULPA filters are specified to remove 99.999% of contaminants particles size greater than or equal to 0.1 µm.

ULPA filters are often used in applications where airborne particles and pathogens are dangerous to human health or essential in manufacturing or assembly operations of sensitive equipment. They are also used in environments that require ultra-pure air to remove the risk of contamination.

What is HEPA & ULPA filter made of?

Both HEPA & ULPA filter media have similar designs.

The filter media is like an enormous web of randomly arranged fibres. When air passes through this dense web, the solid particles get attached to the fibres and thus eliminated from the air.

Porosity is one of the key consideration of these fibres. Lower porosity, while decreases the speed of filtration, increases the quality of filtered air. This parameter is measured in pores per linear inch.

How HEPA & ULPA filter cleans the air?

Most people who are not aware of the air filtration process, believe that filtration works by physically blocking the material by a filter. Particles which are large do not get pass through and smaller one pass.

The above process called sieving is indeed used in air filtration but it is not the only process as it is not possible to use this method to remove smaller size particles.

The cleaning process is based on the particle size of the pollutant.

InertiaLarge particles (about 0.5 to 5 micron) have too much inertia and hence deviate from the air stream around filter fibers, so they impact on the filter fiber and be retained by cohesioninertia
InterceptionMedium particles (about 0.1 to 0.5 micron) follow the air stream around filter fibers, however when they come in *side* contact with a filter fiber they are interceptedinterception
DiffusionSmall particles (below 0.1 micron) oscillate according to Brownian motion due to bombardment by air molecules. When they touch the fiber, they are retained by cohesion.diffusion

What particles can a ULPA filter remove?

ULPA filters can remove from the air a minimum of 99.999% of dust, pollen, mold, bacteria particles at 0.12 microns or larger. These are particles that can pose a threat to sensitive assembly operations, people and the environment.

For example, it can completely remove – dust, bacteria, pigments, pollen, metallurgical dust/fumes, ground talc.

A ULPA filter can remove (to a large extent, not 100%) – oil smoke, tobacco smoke, rosin smoke, smog, insecticide dust.

Uses of ULPA filters

Today, ULPA filters are used widely wherever high level of air purity are required. Some of the most common places they are used are –

  • Biomedical/pharma facilities
  • Electronics / semiconductor manufacturing
  • Airline air filtration
  • Vacuum cleaners
  • Food processing
  • Hospitals
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