Discussion on air filtration detection technology

Discussion on air filtration detection technology

With the increase of smog in the north, filtration and purification industries such as air purification and fresh air have ushered in a new spring, which also detonated the entire filter industry.

　　Because of the many uses of filter materials, there are air purifiers, fresh air systems, cabin air conditioning filters, car filters, and general ventilation filters. The author recently visited some filter material manufacturers and found that chaos was reborn while communicating about filter material testing methods.

As far as the author is concerned, the main standards for air filtration include ISO 16890 test standard for general ventilation filters (replaced EN 779 and ASHRAE 52.2 in 2018), ISO 11155 test standard for air-conditioning filters in automobile cabins (particulate matter) And gas adsorption part), EN 779: 2012 General Ventilation Air Filter Test Standard, EN 1822 High Efficiency Filter Test Standard, ISO 5011 Automobile Air Filter Test Standard, ISO 11057 Cleanable Filter Material Test Standard, VDI Cleanable Ash filter material test standard, ISO 20564 CD oil mist separator test standard, etc.

　　The challenge aerosol and test conditions used in each test standard are different. Almost all test methods involve the testing of the following main indicators:

　　 1) Flow-resistance curve. This indicator is the simplest and most overlooked. Under normal circumstances, the flow-resistance curve of a clean sheet filter has a good linear relationship. At present, when most people compare the resistance of the filter media, they will directly say what is my resistance in Pa, which confuses me a bit. Later, I found out after inquiring that everyone was comparing under the conditions of TSI 8130. In fact, the common flow rate of TSI 8130 is 32L/min, and the surface wind speed is 5.33cm/s, which is far lower than most practical working conditions at present. For example, the surface wind speed of the cabin air conditioner filter is about 0.3m/s, and it is generally ventilated. The wind speed of the filter surface used may be higher. Personally think that TSI 8130 is only suitable for mask testing.

　　 It is recommended to measure the filter material flow-resistance curve. The range of the selected surface wind speed is 25%, 50%, 75%, 100%, 125% of the actual working condition wind speed of the filter material for comparison. Make the whole curve;

　　 2) Dust holding capacity. To reach a certain resistance can hold the quality of dust. According to their respective standards, it can be A2 dust, A4 dust, ASHRAE dust, Pural NF (ISO 11057), talcum powder, etc. The dust holding capacity reflects the life of the filter material or filter, and the entire filter system cannot work normally due to the increase in resistance. When the resistance of the filter material or filter exceeds the designed range, either discard the filter material or filter, or remove the filter cake on the surface by back-blowing to reduce the system resistance.

　　 In addition, the dust concentration defined by different standards is also different, and some are in order to obtain a more uniform and stable dust holding capacity result. Some in order to accelerate the aging or reach the set final resistance. Generally speaking, when other conditions are the same, the higher the dust concentration, the faster the formation of filter cake on the surface of the filter material or filter, resulting in a higher dust holding capacity value than the value obtained with a low dust concentration. Is low. At the same time, environmental temperature and humidity, especially humidity, have a significant impact on the dust holding capacity test. The main reason is that humidity will make dust agglomerate and not easily diffuse, resulting in significant differences in the final test results of z* due to humidity.

　　3) Weight efficiency test. It is mainly calculated by weighing, that is, the ratio of the mass of dust trapped by the sample to be tested to the total mass loaded on the sample to be tested. When the sample to be tested is small, especially when testing the filter material, the accuracy of the balance and the artificial influence factors are relatively large. When testing the weight efficiency of the filter material, because the sample itself is small, the quality of the dust collected on the filter material itself and the absolute filter material is less, and the difference before and after the test is small. If the environmental conditions are a little worse, the test The repeatability is even worse.

　　 It is recommended that when doing this test, define the same test conditions, weighing operation process, and operator training to ensure the stability and repeatability of the test.

　　4) Hierarchical counting efficiency. Generally speaking, the commonly used challenge aerosols for grading counting efficiency are DEHS, A2 dust, KCl, NaCl (due to its small crystal particles and the peak value is at the nanometer level, the recommended measurement method is SMPS, but sometimes it is found that everyone is using OPC for testing. , Personally do not recommend). This indicator can be quickly obtained through testing, but it is the most difficult to understand. It is recommended that relevant practitioners read the aerosol measurement principle carefully.

　　 Generally speaking, the standards for filter material testing are mostly the filter standards of the application industry. During the test, we need to follow the actual application environment and simulate the working conditions as much as possible. At the same time, we also need to understand the limitations of current detection technology. In this way, the filter material can be better developed and applied.