High-efficiency air filters exhibit significant differences in filtration effectiveness for particles of varying sizes. This difference stems from the interaction between their filtration mechanisms and the characteristics of the particles. Their core filter material is typically ultrafine glass fiber filter paper, with fiber diameters reaching sub-micron levels. High-efficiency filtration is achieved through a combination of inertial impaction, interception, diffusion, gravitational settling, and electrostatic adsorption. Different particle sizes interact with the fibers differently due to their varying motion patterns, resulting in a non-linear characteristic of filtration efficiency with particle size.
When particle diameters are greater than 0.3 micrometers, inertial impaction becomes the dominant filtration mechanism. These particles have a larger mass and are less likely to bend with the airflow, making them more likely to directly impact and be captured by the fiber surface. As particle size increases, particle inertia strengthens, significantly increasing the probability of collision. Therefore, high-efficiency air filters typically achieve filtration efficiencies of over 99.9% for particles larger than 1 micrometer. For example, in environments such as electronics manufacturing facilities, these filters effectively intercept large particulate pollutants such as metal dust and fiber debris, maintaining the cleanliness of the production environment.
For particles with diameters between 0.1 and 0.3 micrometers, filtration efficiency drops to its lowest point. Particles in this size range are in the transition zone between inertial impaction and diffusion effects; they are neither easily captured by inertia nor easily contact the fiber surface through Brownian motion. This characteristic makes the filtration efficiency of high-efficiency air filters for the most penetrating particle size (MPPS) a core performance indicator. H13-class filters need an MPPS filtration efficiency of over 99.95%, while H14-class filters need to achieve 99.995%.
When the particle diameter is less than 0.1 micrometers, diffusion becomes the dominant filtration mechanism. These ultrafine particles, affected by air molecule impacts, undergo intense Brownian motion, causing them to deviate from the airflow direction and frequently contact the fiber surface. As the particle size decreases, the diffusion coefficient increases, significantly increasing the probability of contact with the fiber. Therefore, high-efficiency air filters can maintain high filtration efficiency for nanoscale particles. This characteristic makes them crucial in scenarios such as biosafety laboratories, effectively intercepting viral aerosols, bacteria, and other microbial contaminants.
The structural design of high-efficiency air filters further enhances their ability to filter particles of different sizes in a tiered manner. High-efficiency air filters use aluminum foil or paper separators to create independent airflow channels, ensuring that large particles are trapped on the surface of the filter media, preventing deep clogging. Separatorless filters, on the other hand, use hot-melt adhesive to separate the filter media, forming a uniform pleated structure. This increases the filtration area and optimizes airflow distribution, improving the capture efficiency of ultrafine particles. This structural difference allows different types of high-efficiency air filters to exhibit unique advantages in specific applications.
In practical applications, high-efficiency air filters are typically combined with pre-filters and medium-efficiency filters to form a multi-stage filtration system. The pre-filter intercepts particles larger than 5 micrometers, extending the lifespan of the high-efficiency filter; the medium-efficiency filter further filters particles from 1 to 5 micrometers, reducing the load on the high-efficiency filter. This staged filtration strategy not only improves the overall system efficiency but also reduces the filtration pressure on the high-efficiency filter for large particles through pre-filtration, allowing it to focus on capturing the smallest particles that are most easily penetrated.
From a performance evaluation perspective, the filtration efficiency of a high-efficiency air filter needs to be rigorously tested using a laser particle counter under MPPS conditions. This testing method can accurately count the number concentration of particles of different sizes. By comparing the particle size distribution of upstream and downstream aerosols, the grading efficiency of the filter for each particle size range can be calculated. This scientific evaluation system ensures that high-efficiency air filters can stably perform as expected in different application scenarios, providing reliable protection for high-cleanliness environments such as cleanrooms and operating rooms.
