What is HEPA

What is HEPA
 
The filtration method is the most common purification method. The main components of the air purifier using the filtration method are the filter screen and the fan. The filter screen is the key to the purification effect. In air purification, fiber filtration technology is mainly used. The fiber can filter most of the particles smaller than 10μm, mainly including plant fiber, polyester fiber, polypropylene fiber, and glass fiber.
 
When choosing an air purifier, we often see products claiming to use a certain level of HEPA filter, so what exactly is HEPA?
 

HEPA filter
HEPA (High Efficiency Particulate Arrestment) is the abbreviation of High Efficiency Particulate Arrestment, and is usually called High Efficiency Particulate Filter. As early as 1942, the United States implemented the Manhattan Project in order to block nuclear radiation particles. After research, the HEPA theory was established. It was determined that the most difficult to capture particles in the diffusion motion was 0.3μm particles. Relying on this theory, glass fibers were used to make HEPA filters and apply them. In the aviation industry, medical, precision manufacturing, and households were also increasingly used later, so HEPA filtration is actually not a high-tech. It has been applied decades ago.
 
HEPA filter is mostly composed of polypropylene breast filter paper or glass fiber filter paper. The working principle of HEPA high efficiency filter is mainly that the dust particles in the air move inertially or irregularly Brownian motion with the airflow. When moving by a certain force and move, the particles will move in the following 5 types The form collides with other obstacles, and the gravitational force on the surface of the particle will make it stick to the obstacle. This is the process by which air dust is adsorbed. The five filtering forms are: diffusion, interception, inertia, van der Waals force and Brownian motion.
 

 

The filtering principle of HEPA air filter
The filtering principle of HEPA is mainly to filter the particulate matter in the flowing air through the sieve effect, inertia effect, interception effect and diffusion effect. The substances smaller than 1μm are mainly based on Brownian motion and are easily adsorbed on large particles and fibers. Therefore, some bacteria, viruses, and VOCs can also be filtered out when filtering large particles, while most of the small particles are still unblocked. Unimpeded.
 
1. Diffusion effect: Dust particles smaller than 1um do not move with the airflow, but move irregularly due to the impact of air molecules, which is called "Brownian diffusion motion". , If it hits the filter fiber, it will be caught. The smaller the particle, the more violent the diffusion movement, the more chances of hitting the fiber, and the better the filtering effect.
2. Interception effect: In the interception mechanism, small and light dust particles move with the airflow. When bypassing the fiber, particles that are too close to the fiber surface will be intercepted.
3. Inertia effect: The larger dust particles move inertially in the airflow. When the airflow bypasses the fiber, the particles with large inertia have no time to bypass and directly hit the fiber. The larger the dust, the stronger the inertial force and the impact on the fiber. The greater the possibility, the better the filtering effect.
4. Van der Waals force and Brownian motion: The ultrafine particles make Brownian motion and hit the hepa fiber layer, and are purified by the influence of Van der Waals force. Here, it is easy to have a misunderstanding in understanding, that is, HEPA has a stronger ability to remove particles with a larger volume. In fact, HEPA relies on the Van der Waals force between fine particles and solids to work, so it is for 0.5 microns. The filtration efficiency of particles above and below 0.1 micron is very good. Because 0.1 micron particles do Brownian motion, the smaller the particle, the stronger the Brownian motion, and the more times the particles are hit, the better the adsorption effect. The particles move inertially, the greater the mass, the greater the inertia, so the filtering effect is better. In comparison, particles with a diameter of 0.1-0.3 microns have become a difficulty for HEPA removal.
5. Finally, let's talk about the sieve effect: if the diameter of the dust is larger than the gap between the fibers, it will be blocked. Generally, the dust diameter is much smaller than the fiber gap, so the sieve effect rarely occurs.
 



 
HEPA filter replacement
The substances attached to the fibers will become more and more due to accumulation for a long time. On the one hand, it increases the resistance of the air to pass through. On the other hand, various substances will react chemically, breed bacteria and cause secondary pollution. Therefore, for purifiers that use filtration technology, the filter screen must be replaced regularly to ensure the air volume and cleanliness effect.