3 factors affecting HEPA efficiency

HEPA filter is one of the most important components of the cleanroom. HEPA filter is high efficiency particulate air filter. The efficiency of HEPA filter is affected by many factors. What are these factors? This article will clarify 3 main factors affecting HEPA filter efficiency.

1. Resistance

The air through the filter will create resistance and reduce the air velocity at a certain level.

The air filter is dense and tightly knit, so it is hard for the air to come through. Resistance is created. It means that the filter is more efficient in filtering particles.

When the filter reaches a certain critical pressure value (final pressure drop), it should be replaced.

The dirtier the air filter, the higher the resistance.

Read more: Pressure drop in air filtration

2. Air velocity

Generally, the lower the air velocity, the higher the efficiency.

At a low air velocity, the flow remains in the filter longer, then particles will collide more with filter media.

If the air velocity reduces a half, the probability of dust passing through the filter media reduces, and the efficiency increases by 9 times (according to MERV). If the air velocity doubles, the probability of dust passing through the filter media doubles, and the efficiency decrease by 9 times.

When the air velocity is low, the probability of large particles hitting the filter during inertial motion is reduced. These effects are not obvious in practical applications, because the air velocity is reduced, and resistance is also reduced. Dust collects more easily and the filtration efficiency is greatly improved. Therefore, in practical applications, try to set reasonable air velocity filter parameters. It has great benefits for better filtration performance.

3. Filter area

The filter resistance increases when the air flow and velocity increase. Trapped or attached dust increases the resistance of the filter.

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HEPA filters can be used on air cleaning equipment in clean environments. Therefore, if HEPA filters in a clean environment, just filter small particles, the life of the filter will be longer and the filter performance will be better. On the contrary, if it is used in environments with many large dust particles, the life will be short and the filtration efficiency is not high.

Read more: What is HEPA filter?