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Selection of high-efficiency filter: filtration efficiency of high-efficiency filter
Selection of high-efficiency filter: filtration efficiency of high-efficiency filterSelection of high-efficiency filter: filtration efficiency of high-efficiency filter Selection of high-efficiency filter: filtration efficiency of high-efficiency filterThe "filtration efficiency" of the high-efficiency filter is the ratio of the amount of dust captured to the dust content of the original air: filtration efficiency = filter dust capture / upstream air dust content = 1-downstream air dust content / upstream air dust content The meaning of efficiency seems simple, but its meaning and value vary greatly depending on the test method. Among the factors that determine the filtration efficiency, the meaning of dust "amount" varies, and the filter efficiency values calculated and measured are also varied. In practice, there are the total weight of dust and the number of dust particles; sometimes it is the amount of dust for typical particle size, and sometimes it is the amount of all dust; there is also the light transmittance (colorimetry) and fluorescence (fluorescence method) that indirectly reflect the concentration by specific methods; there is the instantaneous amount of a certain state, and there is also the weighted average amount of the efficiency value of the whole dust generation process. If different methods are used to test the same high-efficiency filter, the measured efficiency value will be different. The test methods used by different countries and manufacturers are not uniform, and the interpretation and expression of filter efficiency are very different. Without the test method, there is no way to talk about filtration efficiency. Surface velocity and filtration rate of high-efficiency filter The surface velocity and filtration rate of the high-efficiency filter can reflect the ability of the high-efficiency filter to pass air volume. Surface velocity refers to the speed of airflow passing through the cross-section of a high-efficiency filter, generally expressed in m/s, V=Q/F*3600, and surface wind speed is an important parameter reflecting the structural characteristics of the high-efficiency filter. Filtration rate refers to the speed of airflow passing through the filter area, generally expressed in L/cm2.min or cm/s. The filtration rate reflects the passing capacity of the filter material and the filtration performance of the filter material. A low filtration rate generally can obtain higher efficiency. The filtration rate allowed to pass is low, and the resistance of the filter material is large. Penetration rate of high-efficiency filter, that is, initial resistance The penetration rate indicates the degree of dust particles that can still pass through after passing through the high-efficiency filter. K=(1-η)×100%3-3Resistance, high-efficiency filter forms resistance to airflow. The resistance of a high-efficiency filter is mainly composed of two parts: the resistance of the filter material and the resistance of the high-efficiency filter structure. According to experience, when the filter material performance is determined, the resistance of the high-efficiency filter is closely related to the structure of the high-efficiency filter, and the impact caused by this is about 50Pa. When dust accumulates on the high-efficiency filter, the resistance increases. When the resistance increases to a certain specified value, the filter is scrapped. The resistance of a new high-efficiency filter is called "initial resistance"; the resistance value corresponding to the scrapping of the high-efficiency filter is called "final resistance". When designing, a representative resistance value is often needed to calculate the design air volume of the system. This resistance value is called "design resistance. The usual method is to take the average value of the initial resistance and the final resistance. It can also be tested at the rated air volume, or it can be tested at 0.45m/s. In addition, first, determine whether the filter frame is leaking or between the filter and the box. If the former leaks, it can only be repaired or replaced. For the latter, check whether the filter is not laid flat or the parallelism of the filter is problematic, and whether the sealing strip is intact. These may cause leakage. In addition, if the room is under positive pressure, theoretically, it will not cause pollution to the room, but due to the suction of the sampling pump during the test, it can be detected. The situation should be that the indoor wind is blowing outward. |
