Efficiency tests, filter media

The leak test ( DOP test situ test to verify that filters do not leak on inatidlation. The leak test is not a second efficiency test. It is intended to dis> close leaks around the frames and damage to the filter medium. An aerosol of oil particles with mass median diameter of 0.3 pm is used to challenge the filter deteaion Is by aerosol photometry on the downstream side. Standards of integrity are specified as maximum permissable percentages of the upstream concentration of particles that can be recovered downstream of the filler. 

The authors experimental design included the use of four medium-efficiency fibreglass filter papers of very low variability in order to effectively evaluate filter penetration versus particle diameter. A detailed description of the filters was tabulated and the homogeneity of these samples was demonstrated by the low coefficients of variation shown for both pressure drop and Q127 DOP penetration tests. It was... 

The most representative test is the standard of Underwriters Laboratories Inc. for High Efficiency Particulate Air Filter Units (UL 586). These units will generally consist of a filter medium of glass fiber or other inorganic material and a frame of metal constmction. It is possible to utilize wood but it will have a flame spread of 25 or less. When tested in accordance with UL 723, test method for surface burning characteristics of building materials, UL 586 tests the filter, frame and supports as a unit. It utilizes a 4" blue flame with direct impingement for 3 minutes. It must remain intact. The UL 586 test apparatus units are up to 2 x 2. The typical filter used in the modem cleam-oom are 2 x 4. These units are available in this size from major manufacturers constmcted in an identical fashion to those tested. They will not be labeled since they are beyond the scope of the test. These are the most appropriate units for use in cleam-ooms for the semiconductor industry. 

Very recently, Wang et al. [11] first fabricated PA-66 nanofiber/net (NFN) membranes that comprise common electrospun nanofibers and two-dimensional (2D) spiderweb-like nano-nets via electrospinning/netting (ESN) technique (Fig. 12.3a). As the second doorkeeper, the average pore size of nano-nets (118 nm) is smaller than the size of test NaCl particles (300 nm), so the nano-nets could filter the nanoparticles mainly through interception mechanism. The filtration efficiency of NFN/PP composite filter was 99.9 % (Fig. 12.3b, c), which can be used as the core filter medium in the air filtration field, such as respiratory protection equipment, HEPA filters, and ultralow penetration air (ULPA) filters. 

Very high filtration efficiencies are possible with filter pockets, depending on the filter medium used, e.g. up to 99.8% efficiency with DIN 24 185 test dust. Performance also depends on the pockets remaining rigid and inflated , even at reduced or zero air flow. Most pockets are self-supporting by their very construction, particularly if they are mounted vertically others require hooks, loops or wire mesh for support. 

The very high upstream contaminant concentrations used for such tests are not typical of normal system conditions and produce misleading high-efficiency values. It is common for a wire-mesh filter medium with a mean (average) pore size of 15 pm to pass a 10-pm nominal specification. However, at normal system contaminations, this same filter medium will pass almost all 10-pm particles. 

Individual HEPA filter efficiencies are established by an exacting challenge of the filter frame and medium, usually incorporating a cold-boil, polydisperse aerosol of dioctylpthalate (DOP) or equivalent, which is introduced into the upstream plenum-side of the filter in a manner that ensures even distribution of the test aerosol behind the filter, at its rated airflow. 

Under most application conditions the rate of the SCR reactions exceeds the rate of the soot oxidation. This is especially true under low to medium temperatures as commonly found in Ught-duty emission cycles. Under these conditions, no difference in deNOx efficiency was observed between clean filters and filters loaded with 6-8 g/1 of soot [51, 52], see Fig. 20.19. This was also shown in Ref. [53] under laboratory test conditions with a NO2/NOX ratio of 0. In the same study, either no effect of the presence of 5 g/1 soot or a slightly reduced activity was reported for NO2/NOX = 0.5 and temperatures above 200 °C. At a high NO2/NOX ratio of 1 a beneficial effect of soot was shown for temperatures below 275-300 °C [53]. This could be explained by some consumption of NO2 reacting with soot according to (R3)-(R5) and changing the SCR reaction pathways toward the faster reactions involving NO and NO2. 

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