What materials are HEPA filters made of? Is the denser the air purifier filter material the better?

HEPA filterWhat materials are they made of? Is the denser the air purifier filter material the better?

Nowadays, air purifiers are becoming more and more important for every home user due to well-known reasons. Many of our friends are aware of theHEPA filterIt can be called the heart of the air purifier, and the material it's made of directly affects the performance and longevity of the air purifier. But what is HEPA made of? What is its purification principle? How should we distinguish the quality of HEPA? Many people may not be able to tell.

What is a HEPA filter

Speaking of HEPA filters, HEPA has basically become the standard configuration of air purifiers, from a few hundred dollars to tens of thousands of dollars of purifiers HEPA filters carry a very large number of filtration roles.
High-Efficiency Particulate Air, or High-Efficiency Particulate Air Filter, or HEPA for short, is made of very fine fibers interwoven with a strong ability to capture particles, small pore size, large adsorption capacity, and high purification efficiency. According to the single filter net rate calculation, the standard HEPA filter can filter the air from small to 0.3 micron (hair diameter of 1/200) particles, filter net rate of at least 99.97%, is the haze, as well as bacteria, viruses, fungal spores and other pollutants of the most effective filtration medium, the best filtration performance can be 99.999995%, that is, every 20 million particles, can only have 1 particle, but not 1 particle. In other words, for every 20 million particles, only 1 particle can penetrate the HEPA filter membrane. At present, it is internationally recognized as a high-efficiency filtration material.

HEPA is a high tech black technology, what is the basic principle?

HEPA filters are not high tech, but they are by no means technology-free. It was invented by scientists at the U.S. Department of Energy during the Manhattan Project, which developed the atomic bomb during World War II, to filter contaminated air with radiation particles. Initially, HEPA was only used in classified nuclear research protection, but later commercialized in the 1950s and quickly spread to industrial applications in precision laboratories, pharmaceutical production, electronic instruments and surgical procedures that require high levels of cleanliness.

Nowadays, with the growing concern about air pollution and living health problems. This technology is brought into the civilian field, HEPA into the ordinary people's field of vision. With the popular imagination is different, HEPA filter air is not exactly like a fishing net for fish, sieve sieve stone general, with a small size mesh to directly "block". In fact, HEPA filters rely on the adsorption of fibers to "stick" the PM2.5 dust.

With an electron microscope to observe the microstructure of HEPA, it will be found that it is a diameter of about 0.2 to 2.0 micron fibers interwoven flocculent network. The diameter of the fibers and dust is almost as large as the "mesh" between the fibers of the gap is more "large", between the fibers of the "wide" space to allow the smooth passage of airflow. However, due to the layer by layer arrangement, fine particles are still inevitably hit the messy intertwining of one of the fibers, so as to be adsorbed.

What are HEPA filters made of?

Currently on the market HEPA material is mainly divided into PP (polypropylene) high-efficiency filter paper, PET filter paper, PP and PET composite high-efficiency filter paper and glass fiber high-efficiency filter paper. Among them, PP (polypropylene) is paper, therefore, generally can not be washed!

1、PP high efficiency filter paper

It is a new type of filtration material made of polypropylene by special hot melt method, the product is acid and alkali resistant, corrosion resistant, high melting point, stable performance, non-toxic, odorless, uniform distribution, low resistance, high efficiency, high strength, environmental protection, etc. The filtration effect of PP fiber can be achieved at the highest level of H14.

2、PET filter paper

It is made of polyester resin and other materials meltblown, high hardness, good stiffness, corrosion resistance, high temperature resistance, stable performance, but PET single filtration is relatively low, generally can only do H10-H11 level (90% ~ 99.5%), commonly used in sweepers, vacuum cleaners and other filtration precision requirements of the household electrical appliances or large-scale cleaning machine above.

3、Glass fiber high efficiency filter paper

Glass fiber high-efficiency filter paper, a very high gold content filter paper, has previously been used in the nuclear industry. Compared with plastic fibers, glass fibers are characterized by high temperature resistance, high dust holding capacity, good stability, durability and long life. Its most important advantage, however, lies in the fact that it guarantees a sufficiently high filtration efficiency in a single pass. Until today, the highest efficiency of the U15 ~ U17 filter, basically still mainly glass fiber. But the improvement of the filtration effect also brought about by the increase in wind resistance, normally more than 200Pa, can only rely on the increase in fan power to alleviate the lack of air volume.

How HEPA filters work
1. Sieve effect

When the size of the gap between media compositions (fibers, sieves, corrugated metal, etc.) is smaller than the particle diameter, the filter is designed to capture these particles. This principle is widely used in most filter designs and is entirely dependent on particle diameter size, media spacing and media density.

2. Inertia effect

The rapid change in air direction and the principle of inertia are utilized to separate large quantities (particles) from the air stream. Microparticles at a certain velocity tend to maintain that velocity and continue in the same direction. This principle is generally applied if the process particle concentration is high. And, in many cases, both the pre-filter mode and the more efficient final filter use this principle.

3. Interception effect

In order to achieve interception, a particle must enter from within a distance of a fiber radius. The particle thus comes into contact with the fiber and adheres to it. The difference between the interception principle and the embedding principle is that the intercepted particles are small and their inertia is not sufficient for the particles to continue in a straight line. They therefore flow with the air until they come into contact with the fibers.

Dust smaller than 1μm does not move with the airflow, but does "Brownian motion" due to the impact of air molecules. If it hits on the filter fiber, it will be captured. Therefore, the smaller the particle, the more intense the Brownian motion, the better the filtration effect.

Particles are filtered by van der Waals forces, also known as electrostatic adsorption. The filtration of particles below 0.3 microns, such as viral bodies, relies mainly on this effect.

Is the denser the air purifier filter media the better?

Many friends will think that the filter air purifier selection of filter material density the greater the effect of its filter pollutants will be better, but the truth is really so?

Filter for general ventilation in the purifier, the velocity of airflow through the filter material in the range of 0.13 ~ 1.0m / s, resistance and air volume is no longer a linear relationship, but an upward arc, the air volume increased by 30%, the resistance may increase by 50%, the filter can capture any form of particulate matter, including liquid droplets. The filter material is generally porous and more or less anechoic. Filters create resistance to airflow and have some equalizing effect. The higher the density of the filter to filter out the dust particles the smaller the diameter, the better the purification effect, but will produce a strong resistance, reduce wind speed, affecting the purification efficiency, and thus rely solely on the filter to purify certain limitations (need to increase fan power, but the noise is easy to exceed the standard, energy consumption, and high-efficiency filters should be replaced frequently, more consumables). Its reasoning is very much like we wear masks, really effective protection against PM2.5 masks to wear up often very breathable.