HEPA/ULPA Definition - Specifications and Industry Applications

HEPA filter [https://www.kscracfilter.com/hepa-filter/]efficiency requires no less than what value? Countries have their own regulations, and with the different test methods without full agreement.

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Based on China GB13554-92 standard, high efficiency filter is:

(1) according to GB6165 sodium flame method prescribed test its efficiency greater than or equal to 99.9%.

(2) the particle size of greater than or equal to 0.1m, which greater than or equal to 99.999%.

The former refers to the HEPA filter, due to sodium flame method NaC1 solution atomized median particle size of about 0.5m, and thus corresponds to greater than or equal to 99.9% (0.5m). The latter refers to the ULPA filter. In contrast, foreign general definition of HEPA filters greater than or equal to 99.97% (0.3m); ULPA filters greater than or equal to 99.999% (0.1-0.2m), has often been applied to 0.12m determination. The test method notifies DOP. European EN1882-1 (1998 year) using the MPPS method tests the efficiency greater than or equal to 99.5% (MPPS) filter quite greater than or equal to 99.97% (0.3m) a file of the HEPA filter, the efficiency greater than or equal to 99.995% (MPPS) filters considerably greater than or equal to 99.999% (0.1-0.2m) a file ULPA filters.

There are two different views:

Common to be:

(1) inertial impaction effect on the 0.1-0.5m particle effect is very small;

(2) diffusion of collision, the 0.1-0.5m particle major role;

(3) blocking effect;

(4) sedimentation of 0.1-0.5m particle is negligible;

(5) electrostatic effect on the non-special treatment of the media with a static fiber, may be considered;

(6) sieve hindrance, nor much impact.

So that is mainly (1), (2) and (3) on the filtration efficiency work.

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Another view is:

Blocking mechanism is not filtered, it is a small particle size, the inertia of its single fiber filtration efficiency tends to the ideal intercept, mathematical formulas have been reflected in the inertia; the large particles, diffusion effect disappears, there will be zero spread, single fiber filtration efficiency transformed into an ideal interception efficiency. Therefore, for the efficiency should be:

E = EDR EIR-E

EDR-diffusion filtration efficiency

EIR-inertia filtration efficiency

E-ideal intercept filtration efficiency

Regardless of how the views of filtering mechanism, and practical efficiency filter in influencing the efficiency factors are the following:

(1) and the average particle diameter of the particle velocity, flow velocity, filtration efficiency is low, high long-term path;

(2) the thickness of the filter media and filtration efficiency is proportional;

(3) fiber diameter and distribution of filter media and filtration efficiency is inversely proportional;

(4) medium filling density (fiber percentage ratio of the volume of the entire filter, HEPA filters are generally less than 0.1).

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