Characteristics of Air Filters
Air filter is the main equipment in the field of air cleaning technology, and it is an indispensible equipment to create the clean air environment. So it is necessary to know the characteristic of air filters and its design principle so as to use it corre
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Characteristics of Air Filters
Air filter is the main equipment in the field of air cleaning technology, and it is an indispensible equipment to create the clean air environment. So it is necessary to know the characteristic of air filters and its design principle so as to use it correctly and effectively.
4.1
Function and Classification of Air Filtration System
In 1992 and 1993, China has issued two national standards “Air Filters” (GB/T 14295-93) and “High-Efficiency Particulate Air Filter” (GB13554-92), respectively. They are revised in 2008. According to GB/T 14295-2008, air filters could be divided into four types, shown in Table 4.1. According to GB13554-2008, high-efficiency air filters could be divided into HEPA filter and ULPA filter, which are shown in Tables 4.2 and 4.3. According to standard, HEPA filter product must pass the leakage test before delivery. The test method and judgment criterion are presented in Table 4.4. Coarse Air Filter. It is mainly used as prefilter to capture large particles and prevent them from entering the system, especially these airborne particles with diameter larger than 5 μm, settling particles larger than 10 μm and various foreign materials. Medium-Efficiency Air Filter. Since roughing air filter has been placed to filter large particles, medium-efficiency air filter can be used as the final filter in general ventilation system and prefilter for HEPA filter. It is mainly used to capture airborne particles with diameter between 1 and 10 μm. High-Efficiency Filter. It is used as final filter for ordinary cleaning ventilation system and as intermediate filter to protect HEPA filter and improve the cleanness of supply air. It is mainly used to capture airborne particles with diameter between 1 and 5 μm. Z. Xu, Fundamentals of Air Cleaning Technology and Its Application in Cleanrooms, DOI 10.1007/978-3-642-39374-7_4, © Springer-Verlag Berlin Heidelberg 2014
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4 Characteristics of Air Filters
Table 4.1 Efficiency and pressure drop of air filters at nominal airflow rate Index Initial resistance Face with nominal velocity Efficiency with nominal flow rate Type Label (m/s) flow rate (E) (%) (△Pi) (Pa) Sub-high YG 1.0 Particle size 99.9 > E 95 120 efficiency 0.5 μm High and GZ 1.5 95 > E 70 100 medium efficiency Medium effi- Z1 2.0 70 > E 60 80 ciency 1 Medium effi- Z2 60 > E 40 ciency 2 Medium effi- Z3 40 > E 20 ciency 3 Coarse 1 C1 2.5 Particle size E 50 50 2.0μm Coarse 2 C2 50 > E 20 Coarse 3 C3 Arrestance E50 efficiency 50 > E 10 Coarse 4 C4 with standard artificial dust
Final resistance with nominal flow rate (△Pt) (Pa) 240 200
160
100
Note: When the measured efficiency value meets the requirement for two types at the same time, the higher type is used for assessment
Table 4.2 Performance of HEPA filter Efficiency with sodium flame Efficiency with sodium flame method under 20 % of nominal flow Resistance under method under nominal flow rate rate nominal flow rate Type A B C
% 99.99 > E 99.9 99.999 > E 99.99 E 99.999
% No requir
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