Setting of surface wind speed when detecting high efficiency filter
- Clicks: 4940 Release time: 2017/9/4
Setting of surface wind speed when detecting high efficiency filter
In the purification project, some customers reported that there were more than 100 defects in the gap between the high-efficiency filter and the high-efficiency air supply box. However, the reason has not been found. What is the appropriate value of the surface speed of the high-efficiency filter when it is leak detection? After the high-efficiency filter is installed, what is the range of the high-efficiency filter wind speed when the high-efficiency filter leaks before the shop cleanliness test? The installed high-efficiency filter particles are very leaky, what will be the cause? What caused it?
The high-efficiency filter uses air volume. The experienced design generally takes 80% of the rated air volume. For example, 484*484*220, the rated air volume given by the manufacturer is 1000, and the actual air volume is less than 800. When the filter is leak-detecting and the wind speed is low, the filter may perform better. (especially using dop leak detection) If the filter is determined to be in good condition during the leak detection process, the side seam inspection is unqualified. There are two main reasons for this. One is the reason for the quality of the box, which makes the installation difficult to seal. Another reason is The influence of the environment can be discerned by detecting the windshield.
Efficient filter selection is generally based on the following points
High efficiency filter filtration efficiency
The "filtration efficiency" of the high-efficiency filter is the ratio of the amount of dust collected to the amount of dust in the original air: filtration efficiency = amount of dust collected by the filter / dust content of the upstream air = 1 - downstream air dust content / upstream air content Dust volume
The meaning of efficiency seems simple, but its meaning and value are very different depending on the test method.
Among the factors determining the efficiency of filtration, the meaning of dust "quantity" is various, and the calculated and measured filter efficiency values ​​are also varied. In practice, there is the total weight of dust, the number of particles of dust; sometimes the amount of dust for a typical particle size, sometimes the amount of all dust; and the amount of light that is indirectly reflected by a specific method (colorimetric method), The amount of fluorescence (fluorescence); the instantaneous amount of a certain state, and the weighted average of the efficiency value of the whole process of the dust.
Testing the same high-efficiency filter in different ways will result in different efficiency values. Used by various countries and manufacturers
The test methods are not uniform, and the interpretation and expression of filter efficiency are quite different. Without the test method, there is no way to filter efficiency.
Surface speed and filtration speed of high efficiency filter
The surface speed and filtration rate of the HEPA filter reflect the ability of the HEPA filter to pass air. Face velocity refers to the velocity of the passing airflow on the section of the high-efficiency filter, generally expressed in m/s, V=Q/F*3600. The face wind speed is an important parameter reflecting the structural characteristics of the high-efficiency filter. Filtration speed refers to the velocity of the passing airflow over the area of ​​the filter material, generally expressed in L/cm2.min or cm/s. The filtration speed reflects the passing ability of the filter material, reflecting the filtration performance of the filter material. The filtration rate is low, and generally higher efficiency can be obtained. The filtration rate allowed to pass is low, and the resistance of the filter material is large.
High-efficiency filter penetration, that is, initial resistance
The penetration rate indicates how much dust particles can still pass through the high efficiency filter. K = (1-η) × 100% 3-3 Resistance, high efficiency filter creates resistance to airflow. The resistance of the 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, in the case of determining the performance of the filter material, the resistance of the high-efficiency filter has a great relationship with the structure of the high-efficiency filter, and the resulting effect.
At around 50Pa. The high-efficiency filter accumulates dust and the resistance increases. When the resistance increases to a certain value, the filter is scrapped.
The resistance of the new high-efficiency filter is called "initial resistance"; the resistance value corresponding to the scrap 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 of the initial resistance and the final resistance.
Of course, it can also be tested under the rated air volume, or it can be detected at 0.45M/s. In addition, it is first determined whether the filter is leaking between the frame or the filter and the cabinet. If the former leaks, only the replacement or replacement is required. OK, while the latter looks like the filter is not flattened or the parallelism of the filter is problematic, and the seal is not intact, these may cause leakage, in addition, if the room is positive pressure, in theory, in theory It does not cause pollution indoors, but it can be detected due to the suction force of the sampling pump during the test. It should be the case that the indoor wind is blown out.
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