Filter panels

Air-Filter Types Air filters may be broadly divided into two classes (1) panel, or unit, filters and (2) automatic, or continuous, filters. Panel filters are constructed in units of convenient size (commonly 20- by 20-in or 24- by 24-in face area) to facilitate installation, maintenance, and cleaning. Each unit consists of a cleanable or replaceable cell or filter pad in a substantial frame that may be bolted to the frames of similar units to form an airtight partition between the source of the dusty air and the destination of the cleaned air. 

Mechanical filtration systems are intended to limit the introduction of pollutants from outdoors to indoors. The efficiency of such systems generally depends on the filter properties and the aerodynamic properties of filtered particles [26]. The efficiency of filters varies from 5% to 40% for low-efficiency filters, such as dry media filters, panel and bag filters, from 60% to 90% for electrostatic precipitators to over 99% for high-efficiency particulate air filters. Not only the filters, but the whole heating, ventilation and air-conditioning system contributes to particle reduction, owing to particle losses on the cooling/heating coil and other parts of the system. The selection of a system depends on the type of indoor environment, outdoor and indoor sources, the demand on the level of reduction of pollutant concentrations and the cost associated with purchase, operation and maintenance of the system. 

Figure 3.3-2 shows typical results. The simple first-order averaging filter, panel (c) in Fig. 3.3-2, is most effective in reducing the noise, but also introduces the largest distortion, visible even on the broadest peaks. This is always a trade-off noise reduction is gained at the cost of distortion. The same can be seen especially with the narrower peaks, where the higher-order filters distort less, but also filter out less noise. In section 10.9 we will describe a more sophisticated filter, due to Barak, which for each point determines the optimal polynomial order to be used, and thereby achieves a better compromise between noise reduction and distortion. 

The injection-molding process provides low cost fabrication of large and small parts to precision tolerances. Many of these parts are nearly impossible to make in production voliunes by other techniques. Injection molding can form parts as small as a cubic milUmeter (micromolding), and parts as large as garbage dumpsters and 1.2 x 2.4 m (4 x 8 ft) filter panels are in production. A wide range of... 

Research has shown that flooded-bed scrubbers can remove more than 90% of respirable-sized coal and silica dust (Colinet et al. 1990). However, the collection efficiency is affected by the density of the fQter panel. The original filter panel was fabricated with 40 layers of fine stainless steel mesh. Filter panels containing 30, 20, and 10 layers of stainless steel mesh are now available. The reduced fQter density allows larger quantities of air to be moved by the scrubber, potentially improving capture efficiency, but can reduce the collection efficiency. In one study, the 30-layer panel was shown to maintain respirable dust collection efficiency above 90% but the collection efficiency dropped when less dense panels were used (CoHnet and Jankowski 2000). When using flooded-bed scrubbers, the balance between the capture efficiency and collection efficiency must be optimized to minimize dust levels. 

Shiba, S. Color filter panels for liquid-crystal display devices and ink-jet printing process for their manufacture. Jpn. Kokai Tokkyo Koho JP 2002196126, 2002 Chem. Abstr. 2002, 137, 80398. 

The applications and efficiencies of dust collecting filters are given in more detail in Section 6, where it will be seen that filter panels can achieve very high filtration efficiencies. Such high efficiency filters are normally installed in series with a prefilter, using coarser filter medium, to remove larger particles from the inlet air, which would block the fine filter too quickly. 

Although filter pockets can also be used singly, they are much more often found in groups of 4 to 8, mounted side by side in a rigid front member, which holds the pockets open, and from which they can be withdrawn for disposal (see Figure 3.46). This holding frame is made to the same size as the filter panels, so that the pocket panel can be clipped into the same sized space. 

Increasingly, the V-block filter panels, with mini-pleated nonwoven media (shown earlier in Figure 6.8), are being used for machine air intakes, especially for gas turbine systems. 

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