HEPA filter consists of randomly arranged fiber mats. The key indexes affecting the function are fiber density, diameter and filter thickness. The space between HEPA filter fibers is more than 0.3 micron meters. * * It is incorrect to assume that HEPA filters filter particles smaller than the maximum like a sieve. As for the membrane filter, the particles are very large, as wide as the maximum starting point or distance between fibers, and it is impossible to pass between them. However, the design goal of HEPA filter is smaller pollutants, and particles are mainly captured through one of the following three mechanisms (they insist on fibers):
Intercept particles, make the airflow enter the fiber radius and follow the fiber radius. The larger packed particles can't avoid the fibers and are forced to be directly buried in one of the fibers along the curved contour of the airflow; This increases with the decrease of fiber separation and higher air velocity. An improved diffusion mechanism is that the smallest particles, especially those with a diameter less than 0. 1 micron, are hindered and delayed in the process of passing through the filter as a result of collision with gas molecules; This behavior is similar to that of Scottish botanist robert brown, and it is possible that the cultivation of particles will be through one of two mechanisms; It becomes dominant at low air speed. Diffusion is dominant below 0. 1 micron, tightening and interception are dominant above 0.4 micron, and diffusion and interception are dominant near 0.3 micron MPPS.
The initial filter airflow resistance and the final filter airflow resistance are usually measured by the pressure drop across the filter. The original HEPA filter was designed and used in the Manhattan Project in the 1940s to prevent the diffusion of radioactive pollutants in the air. It was commercialized in 1950s and became a registered trademark. General terms are very effective filters. In the past ten years, filters have been continuously developed to meet the increasing demand for air quality in various high-tech industries, such as aerospace, pharmaceutical processing, hospitals, medical care, nuclear fuel, nuclear energy and electronic microcircuits (computer chips).
The specified value of HEPA filter for artificial respiration machine: the efficiency performance standard and minimum value I of the filter are equivalent to NIOSHN 100. The US Department of Energy (DOE) has specific requirements for HEPA filters in the specified applications of DOE. Products marked with "HEPA type", "HEPA" or "99% HEPA" may not meet these requirements in independent laboratories and may not be tested.