HEPA filter efficiency η requires no less than what value? Countries have their own regulations, and with the different test methods without full agreement.

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

(1) according to GB6165 sodium flame method prescribed test its efficiency η ≥ 99.9%.

(2) the particle size of ≥ 0.1μm, which η ≥ 99.999%.

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

There are two different views:

Common to be:

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

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

(3) blocking effect;

(4) sedimentation of 0.1-0.5μm 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.

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-ΔE

EDR-diffusion filtration efficiency

EIR-inertia filtration efficiency

ΔE-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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