Verification method of filtration efficiency1

Air filtration efficiency generally refers to the“Filtration efficiency is the ratio of the amount of dust captured to the dust content of the original air. The actual meaning and specific value of filter efficiency vary greatly depending on the test method. The general ventilation filter test method is similar to that used in the gravimetric method and the colorimetric method, and the high-concentration test dust used for dust generation is also similar to that used in the gravimetric method and the colorimetric method. dusty“quantity”is the number of particles in the micro-size segment. The instrument for measuring dust is a laser particle counter. During the test, before and after each dust emission test, count measurement was performed, and the filtration efficiency of the filter for various particle sizes was calculated. The test is stopped when the conditions for terminating the test are reached. The typical efficiency value of the filter is within the specified particle size range, and the instantaneous efficiency of each stage is the weighted average of the amount of dust generated. The European standard specifies that specific polydisperse phase droplets are used for counting measurements, such as a DEHS spray blown with a Laskin nozzle, or the same Latex latex spheres used to calibrate the counters for standard particles. The U.S. states that counting measurements use bleaching powder. Counting efficiency is no longer a single value, but a filtration efficiency curve along different particle sizes. The European test shows that when the final resistance of the test is 450Pa, the counting efficiency value at 0.4 μm is close to that of the traditional colorimetric method. The American standard stipulates that the efficiency values ​​of different particle size ranges are measured for different grades of filters, and the final resistance of the test is still“2x initial resistance or higher”. The complete counting efficiency test is a destructive test and cannot be used for routine inspection of products. The dust source of the gravimetric test is the standard dust with large particle size and high concentration. The main components of the dust are the screened and specified areas of floating dust, and then mixed with a specified amount of fine carbon black and short fibers. Most countries prescribe the use of Arizona desert“road dust”, the Chinese standard once stipulated the use of dust from a village on the Loess Plateau, and the Japanese standard stipulated the use of“Off East Asian Clay”. measured“quantity”is the dust weight. The filter is installed in the standard test wind tunnel, and the upwind end continuously generates dust. At regular intervals, measure the weight of dust passing through the filter or the amount of dust collected on the filter, thereby obtaining the filtration efficiency of the filter calculated by the weight of dust at this stage. The final weighing efficiency is the weighted average of the efficiency in each test stage according to the amount of dust generated. The conditions for the termination of the gravimetric test are: the agreed final resistance value, or when the efficiency drops significantly. here so-called“convention”Refers to the agreement between the customer and the tester, or the tester's own regulations. Obviously, different conditions for terminating the test will lead to different weighting efficiency values. When the test is terminated, the weight of the test dust contained in the filter is called“Dust holding capacity”. The gravimetric method is used to measure low-efficiency filters, which are typically used for pre-filtration in central air-conditioning systems. The gravimetric test is a destructive test and cannot be used for the daily product performance inspection of the manufacturer. Atmospheric dust counting method The dust source is the natural atmosphere“atmospheric dust”. dusty“quantity”is the total number of particles greater than or equal to a certain particle size. The instruments for measuring dust are ordinary optical or laser dust particle counters. The efficiency value is the initial efficiency of the new filter. The atmospheric dust counting method is used to measure filters for general ventilation. Its efficiency values ​​represent only the performance of the new filter. China's efficiency classification is based on the atmospheric dust counting method. The colorimetric test bench and test dust are the same as those used in the gravimetric method. dust“quantity”It is the light flux of the high-efficiency filter paper at the sampling point. Sampling before and after the filter, there is high-efficiency filter paper on the sampling head. Obviously, the pollution degree of the high-efficiency filter paper at the sampling point before and after the filter will be different. In the test, after each period of dust emission test, measure the light transmission of the high-efficiency filter paper at the sampling points before and after the filter under the condition of no dust emission.“Filtration efficiency”. The final colorimetric efficiency is the weighted average of the efficiency values ​​of each stage in the whole process of the test according to the amount of dust generated. The conditions for terminating the test are similar to those of the gravimetric method: the agreed final resistance value, or when the efficiency drops significantly. Colorimetry is used to measure general ventilation filters with high efficiency, and most filters in air conditioning systems belong to this type of filter. Colorimetry used to be a common test method abroad, and this method was gradually replaced by counting method. Strict colorimetry is a destructive test. More about Filter Efficiency Tester: http://www.standard-groups.com/FilterMaterial/

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