HEPA filter

HEPA filters are composed of a mat of randomly arranged fibres

Detailed Product Description:

  HEPA filters can remove at least 99.97% of particle 0.3μm in diameter.Particles of this size are the most difficult to filter and are thus considered the most penetrating particle size(MPPS). Particles that are larger or smaller are filtered with even higher efficiency.

  HEPA filters are composed of a mat of randomly arranged fibres.Key metrics affecting function are  fibre density and diameter,and filter thickness.The air space between HEPA filter fibres is much greater than 0.3μm.The common assumption that a HEPA filter acts like a where particles smaller than the largest opening can pass through is incorrect.Just as for,particles so large that they are as wide as the largeset opening or distance between fibres can not pass in between them at all.But HEPA filters are designed to target much smaller pollutants and particles are mainly trapped(they stick to a fibre)by one of the following three mechanisms:

1.       Interception,where particles following a line of flow in the air stream come within one radius of a fibre and adhere to it.

2.      .Impaction,where larger particles are unable to avoid fibres by following the curving contoursp of the air flow velocity.

3.      Diffusion,an enhancing mechanism is a result of the collision with gas molecules by the smallest particles,especially those below 0.1μm in diameter,which are thereby impeded and delayed in there path through the filter,this behaviour is similar to and raises the probability that a particle will be stopped by either of the two mechanisms above,it becomes dominant at lower air flow velocities.

Diffusion predominates below the 0.1μm diameter particle size.Impact and interception predominate above 0.4μm.In between, near the 0.3μm MPSS.diffusion and interception predominate.

 The initial filter air flow resistance and final filter air flow resistance are typically measured as drop across the filters.

HEPA filter