The working principle of air filters primarily encompasses various technologies and mechanisms aimed at removing impurities from the air, including dust, solid particulates, as well as liquid water and oil droplets (though it cannot eliminate gaseous water and oil). Below is a detailed analysis of the working principles of air filters:
I. Primary Filtration Techniques
Mechanical Filtration:
Principle: Captures particles through direct interception, inertial impaction, and Brownian diffusion mechanisms. As dust particles in the air move with the airflow and encounter obstacles like fibers, they adhere to the obstacles due to gravitational forces, achieving filtration.
Characteristics: Effective in collecting fine particles but with relatively high air resistance. To achieve high purification efficiency, the filter element needs to be dense and replaced regularly.
Adsorption:
Principle: Utilizes the large surface area and porous structure of materials to capture particulate pollutants. The adsorbent can absorb pollutants from the air, thereby purifying it.
Characteristics: Remarkable in removing gaseous pollutants but prone to clogging, requiring periodic replacement or regeneration of the adsorbent material.
Electrostatic Precipitation, Negative Ion and Plasma Methods, and Electret Filtration:
Principle: Leverages electrostatic forces to adsorb particles onto dust collection plates or makes particles easier to capture by charging them. These technologies enhance particle capture capability by generating electrostatic fields or negative ions.
Characteristics: Capable of efficiently removing particles from the air but necessitates a stable power supply and regular maintenance to ensure effectiveness.
II. Specific Types and Working Principles
Dry Inertial Air Filter:
Composition: Dust shroud, deflector, dust outlet, dust cup, etc.
Working Principle: Utilizes suction generated by cylinder intake to create a pressure difference inside and outside the air filter. External air enters the air filter at a high speed under pressure, throwing heavier dust particles mixed in the air into the dust cup, achieving air filtration.
Wet Inertial Air Filter:
Composition: Central tube, oil bath, etc.
Working Principle: Air enters the filter and descends rapidly along the central tube, rushing violently into the oil surface of the oil bath, where its direction of motion abruptly changes to ascend and generate rotational motion. Some heavier dust particles, due to inertia, cannot reverse direction with the air and adhere to the oil, completing air filtration.
Dry Filtration Air Filter:
Composition: Paper filter element and sealing gasket, etc.
Working Principle: As air passes through the paper filter element, dust is separated or adheres to the filter element, achieving air filtration.
Wet Filtration Air Filter:
Composition: Oil-impregnated metal filter screen.
Working Principle: After oil bath filtration, when air passes through the oil-impregnated metal filter screen, fine dust particles are retained and adhere to the screen, with some particles dripping off with the oil.
III. Other Considerations
Resistance: During filtration, filters create resistance to airflow, which increases with airflow volume. Resistance can be reduced by increasing the filter material area.
Filtration Efficiency: The ratio of the amount of dust captured by the filter to the amount of dust in the air before filtration is known as "filtration efficiency." Filtration efficiency varies for particles of different sizes, with a Most Penetrating Particle Size (MPPS) existing.
Filter Disposal: When the filter resistance increases to a specified value (typically 2-4 times the initial resistance), the filter needs to be replaced to ensure the system operates normally.
In conclusion, air filters effectively remove impurities from the air through the comprehensive application of various technologies and mechanisms, providing clean air environments for various application scenarios.