Fast, automated testing of different air filter media

Abstract

Air filters are used in many fields and for totally different applications. There are at least two different categories — high efficiency filters (HEPA), used for example in clean room technology, and gas cleaning filters, used in emission control and also in vacuum cleaners. The efficiency of HEPA filters is better than 99.97 % for particles of approximately 0.1 μm in diameter. The efficiency of gas cleaning filters is between 0 and 100 % and particle sizes are generally between 0.3 μm and 100 μm. The measurement of the fractional penetration and of the pressure drop is essential for the characterisation and quality control of both HEPA and gas cleaning filters. A common test procedure has been developed and two different test rigs have been built. By simultaneously measuring the fractional penetration and the pressure drop, loading studies can be done within a time scale of only a few minutes. Measurements under various conditions have shown the influences of face velocity, upstream concentration, test dust material, filter material and electrostatic charge of the particles and filter fibres. The time and size dependent penetration and pressure drop of electret fibre, glass fibre and paper media are discussed.