Introduction to the main parameters of air filters

1、 Rated Airflow

The air flow rate of a certain volume that the filter passes through in a unit of time is generally expressed in m3/h in China, and in foreign countries, it is also expressed in cubic foot per minute (cfm), which is equivalent to ft3/mim cubic feet per minute. The two are converted to 1cfm ≈ 1.7m3/h. Of course, we hope that the filter can pass through as much air as possible under the same windward cross-section, indicating its high filtration capacity, but it is mainly determined by its filtering material and structure.

2、 Face velocity and filter velocity

Speed refers to the velocity of the airflow passing through the windward section, generally expressed in m/s;

Face velocity=air volume ÷ windward cross-sectional area

The filtration speed refers to the velocity of the airflow passing through the filter material, generally expressed in cm/s;

Filtering speed=air volume ÷ filtering area

The filtering area refers to the area of the filtering material used. Only when the filtering material is flat and perpendicular to the airflow direction, the windward cross-sectional area and filtering area of the filter are the same. However, the filtering material installed in vacuum cleaners is often folded and shaped.

Foreign countries also use the British wind speed unit: fpm (foot per minute)

Feet per minute, 1000 fpm ≈ 5.08m/s

3、 Filtering Efficiency

1) Definition: Filtration efficiency=amount of dust captured by the filter ÷ upstream air dust content=(upstream air dust content - downstream air dust content) ÷ upstream air dust content

The definition of efficiency may seem simple, but its meaning and value are closely related to the testing method. The efficiency values obtained by different testing methods cannot be directly compared, so when it comes to efficiency, it is necessary to explain what testing method is used to determine the efficiency. Sometimes in foreign countries, penetration rate or penetration rate is also used to represent filtration performance, where penetration rate=1- filtration efficiency

2) Specification:

a、 Chinese specifications: Course, Medium, High Medium, Sub HEPA, HEPA

b、 European specifications: using G-F-H-U level four