What is mechanism of HEPA filter?
HEPA filtration : HEPA filter, also known as high-efficiency particulate absorbing filter and high-efficiency particulate arrastance filter, is an efficiency standard of air filters.
HEPA Filters are designed to meet requirements of very fine filtration up to 0.3 micron at high efficiency of 99.99 %. Standing for high efficiency particulate air, HEPA filters trap small, harmful particles, such as pollen, pet dander, smoke and dust mites by forcing air through a fine mesh. In consumer products, these fine mesh filters are most often used in vacuums and air purifiers.
Mechanism
HEPA filters are composed of a mat of randomly arranged fibres. The fibers are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting its functions are fiber diameter, filter thickness, and face velocity. The air space between HEPA filter fibers is typically much greater than 0.3 μm.HEPA filters are designed to target much smaller pollutants and particles.
These particles are trapped (they stick to a fiber) through a combination of the following three mechanisms:
1. Diffusion : The particles traverse the flow stream, they collide with the fiber & are collected.
2. Interception: These mid-sized particles follow the flow stream as it bends through the fiber spaces. Particles are intercepted or captured when they touch a fiber.
3. Inertial impaction : particle inertia causes it to leave the flow streamlines & impact on the fibre.
4. Electrostatic attraction : It contain layers meant to charge particles as they pass through , making the job of attractive layer of filter easier.
