Collecting surface area

Collecting surface area The actual surface area of a filter on which particulate matter is collected, normally greater than the filter face area. 

Talc samples which were deaerated at 100°C and 1ft4 mm of Hg for 1 hr reported surface areas in the range of 4-8 m2/g [30]. However, talc samples outgassed at 200°C for 5 hours resulted in a surface area of 20 m2/g [31]. Outgassing conditions should be carefully chosen when collecting surface area data for these materials. 

Calculate the collection efficiency, remembering the collection surface area per duct remains the same ... 

Larger collection surface area and lower gas flow rates increase efiiciency because of the increased residence time available for electrical charging and subsequent collection of the dust particles. 

Dinitrogen adsorption measurements were performed at 77.3°K. on a Micromeritics TriStar porosimeter. Samples were degassed at 150 C overnight prior to data collection. Surface area measurements utilized a five-point adsorption isotherm collected over 0.05 to 0.20 p/po and analyzed via the BET method. Results are shown in Table 2. 

Dry filters are usually deeper than viscous filters. The dry filter media use finer fibers and have much smaller pores than the viscous media and need not rely on an oil coating to retain collected dust. Because of their greater resistance to air flow, dry filters must use lower filtration velocities to avoid excessive pressure drops. Hence, dry media must have larger surface areas and are usually pleated or arranged in the form of pockets (Fig. 17-64), generally sheets of cellulose pulp, cotton, felt, or spun glass. 

The surface area of a spill should be minimized for materials that are highly toxic and have a significant vapor pressure at ambient conditions, such as acrylonitrile or chlorine. This will make it easier and more practical to collect vapor from a spill or to suppress vapor release with foam. This may require a deeper nondrained dike area than normal or some other design that wilfminimize surface area, in order to contain the required volume. It is usually not desirable to cover a diked area to restric t loss of vapor if the spill consists of a flammable or combustible material. 

HEPA (high-efficiency particulate air) filters Also known as absolute filters, the large collection filter surface area provides a high collection efficiency for particulate matter. 

The felted fabrics are generally used for maximum recovery of product and are used at high face velocity for airflow-to-cloth-area ratio. The felt promotes the greatest dust collection surface. 

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