Properties of filter media

Machine-orientated properties of filter media - which restrict the use of a medium to specific types of filter 

Resistance to creep/stretch Stability of edges Resistance to abrasion Stability to vibration Dimensions of available supplies Ability to be fabricated Sealing/gasketing function 

Note Many of these mechanical properties are determined by the structure of the medium and its methods of manufacture only limited use is made of much of this information, and some of it may not be readily available. 

Application-orientated properties of filter media medium with the process environment 

Chemical and thermal stability The resistance of a medium to specified chemical and thermal environments is usually available in published technical data. 

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TABLE XI.3. Adhesion as Affected by Properties of Filter Media... 

Table 2.4 Filtration-specific properties of filter media (Purchas, 1980 Flardman, 1994). ...

Porosity and pore size are crucial properties of filter media, which determine efficiency as well as pressure drop and permeability. Small pore sizes at high porosity of a textile filter medium depend on the fiber size. A reduction of the pore size below the fiber diameter greatly reduces the porosity and diminishes the permeability, which means the filtration efficiency increases with a reduction in the fiber diameter. 

Table 2.4 Comparative properties of filter media fabrics... 

Due to the wide variety of filter media, filter designs, suspension properties, conditions for separation and cost, selection of the optimum filter medium is complex. Filter media selection should be guided by the following rule a filter medium must incorporate a maximum size of pores while at the same time providing a sufficiently pure filtrate. Fulfilment of this rule invokes difficulties because the increase or decrease in pore size acts in opposite ways on the filtration rate and solids retention capacity. 

Optical interference generated by the variations of the optical properties of the media at the excitation or emission wavelength (inner filter effect). 

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. 

Pihlajamaki A. (1998), Electrochemical characterisation of filter media properties and their exploitation in enhanced filtration, PhD Thesis, Lappeenranta University of Technology, Finland. 

PPS fiber has excellent chemical resistance. Only strong oxidising agents cause degradation. As expected from inherent resia properties, PPS fiber is flame-resistant and has an autoignition temperature of 590°C as determined ia tests at the Textile Research Institute. PPS fiber is an excellent electrical iasulator it finds application ia hostile environments such as filter bags for filtration of flue gas from coal-fired furnaces, filter media for gas and liquid filtration, electrolysis membranes, protective clothing, and composites. 

There are many filter media from which to choose from however, the optimum type depends on the properties of the suspension and specific process conditions. Filter media may be classified into several groups, however the two most common classes are the surface-type and depth-media-type. 

Table 7 provides some literature reported measurements of the properties discussed for common filter media and aids as loose materials. You might try an experiment and measure the various angles. In developing your data base, obtain the measurements in triplicate, and calculate a standard deviation for each angle measurement. 

Different filter media, regardless of the specific application, are distinguished by a number of properties. The principal properties of interest are the permeability of the medium relative to a pure liquid, its retention capacity relative to solid particles of known size and the pore size distribution. These properties are examined in a laboratory environment and are critical for comparing different filter media. 

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