![]() Sub-high-efficiency particulate air filter media used here is not only polypropylene fiber filter paper, but it is composed of prefilter layer, main filter layer, and enhanced gauze. Inside medium-efficiency air filter media, fibers near the rear are relatively dense and they will interference with the airflow. ![]() Inside the coarse filter media, fibers are inherently large and spaces between fibers are loose, so difference is small between front and rear. In these figures there are “front and rear.” Fibers near the front side are relatively large. Relationship between pressure drop and filtration velocity for sub-high-efficiency particulate air filter media Generally speaking, extreme small fiber and low filtration velocity will result in extreme small Re number, so airflow is laminar.įor the isolated cylinder with unit length, when its long axis is perpendicular to the airflow, the force acting on its surface is a function of the cross section and dynamic pressure, i.e., Pressure drop depends on whether the airflow through fibrous layer is laminar or turbulent. ![]() In some literature and monograph, actually only the pressure drop of filter media layer is mentioned during the introduction of pressure drop of air filter, which will cause misconception to readers.įor fibrous filter, pressure drop of filter media is caused by the frontal resistance during the airflows through fibrous layer. The following part will emphasize on the aforementioned two parts of pressure drop. Pressure drop of airflow entering and exiting air filters is usually constant, which is about 5 Pa and could be added as a fixed value. Pressure drop of air filter is composed of two components: filter media and structure of air filter. Tables 4.5, 4.6, 4.7, and 4.8 are four examples of foreign standards. There are several types of HEPA filters, such as folded media-type filter which could be classified as separator HEPA filter and no-separator HEPA filter. The former is a type of low-pressure drop, which is a patent product of Institute of HVAC of China Academy of Building Research. There are several types of sub-high-efficiency particulate air filters, such as cartridge air filter and folded media-type filter. There are several types of high-efficiency filters, such as bag filter, cartridge air filter, and folded media-type filter. It’s better to choose air filters with larger filtration area. There are several types of roughing air filters and medium-efficiency air filters, such as panel-type air filter, bag air filter, and folded media-type filter. If cleanness class corresponding to 0.1 μm is needed, its efficiency should be tested with particle diameter 0.1 μm and it is called ULPA filter. The purpose is to provide various cleanness classes corresponding to 0.5 μm, while its efficiency is usually tested with particle diameter 0.3 μm. It is mainly used as final filter in cleanroom. It is mainly used to capture submicron particles with diameter less than 1 μm, which is similar as that of high-efficiency filter. It is used as final filter in the cleanroom to obtain a certain class of air cleanness (please refer to 10.1007/978-4-7_7), prefilter for HEPA filter to further improve the cleanness of supply air, and final filter of fresh air system to improve the fresh air quality. Sub-high-Efficiency Particulate Air Filter. It is mainly used to capture airborne particles with diameter between 1 and 5 μm. ![]() 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 10 μm. 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 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.
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