Filtration efficiency charged

Electrostatic and electrical double-layer forces play a very important role in a number of contexts in science and engineering. As we see in Chapter 13, the stability of a wide variety of colloids, ranging from food colloids, pharmaceutical dispersions, and paints, to colloidal contaminants in wastewater, is affected by surface charges on the particles. The filtration efficiency of submicron particles can be diminished considerably by electrical double-layer forces. As we point out in Chapter 13, coagulants are added to neutralize the electrostatic effects, to promote aggregation, and to enhance the ease of separation. 

The application of external electrical fields can enhance filtration efficiency beyond a simple system. Bipolar electrostatic charge between the fabric and the particles can induce migration to the filter surface and particle agglomeration in the aerosol. 

In the present paper our previous analysis of fluidized bed filtration efficiencies has been extended by considering more realistic methods for estimating the single collector efficiencies as well as more recently reported experimental results. In general the predicted values of the fluidized bed filtration efficiencies compare favorably to the experimental values. For electrically active fluidized beds, direct measurements of the particle and collector charges would be necessary to substantiate the results given here. 

High-efficiency particulate air (HEPA) filtration seems to be the most cost-effective approach to nanoaerosol removal from the air. Although charging nanoaerosol particles is likely to improve the filtration efficiency by ESP effect, diffusion is the dominating mechanism for nanoaerosol filtration. Conventional filtration theory indicates that nanoaerosol filtration efficiency increases inversely with particle size. Base on this hypothesis, filtration efficiency of nanoaerosol particles can reach 100 % for a properly designed filter. In reality, however, there should be a critical size from which filtration efficiency drops with the decrease of particle diameter (see Fig. 2). Otherwise, gas molecules, which are indeed extremely small particles,... 

During processing, multiple treatments can alter the nature of the final product. Additives can be directed into the hot air attenuating stream. Various surface modifications can be sprayed onto the web before winding to impart desired characteristics. Substrates can be placed under the melt-blown web to create composite structures. Electrostatic charging units can be integrated to provide improved filtration efficiency [3]. 

From Figure 6.32a and b, several observations can be made. First, the filtration efficiency to charged particles is higher than the filtration efficiency to reneutralized particles. Second, the filtration efficiency of charged particles is observed to decrease over time (data trend not observable in Figure 6.32a due to y-axis scale selection), whereas with the reneutralized particles, the filtration efficiency is often observed to increase over time. 

By incorporating nanofibres into particulate filter media, companies were able to get higher particulate filtration efficiency for particulate sizes less than 2.5 pm with almost negligible effect on pressure drop or often less pressure drop across the filter. This is because nanofibre layer is non-woven and has controllable nanometre range pore size that is distributed evenly. Furthermore, each individual nanofibres has van der Waals forces which attract charged particles towards themselves. Table 11.3 shows the list of popular companies that have successfully commercialized air filter media and products. 

Hydrolysis of benzyl cyanide to phenylacetamide. In a 1500 ml. three-necked flask, provided with a thermometer, reflux condenser and efficient mechanical stirrer, place 100 g. (98 ml.) of benzyl]cyanide and 400 ml. of concentrated hydrochloric acid. Immerse the flask in a water bath at 40°. and stir the mixture vigorously the benzyl cyanide passes into solution within 20-40 minutes and the temperature of the reaction mixture rises to about 50°, Continue the stirring for an additional 20-30 minutes after the mixture is homogeneous. Replace the warm water in the bath by tap water at 15°, replace the thermometer by a dropping funnel charged with 400 ml. of cold distilled water, and add the latter with stirring crystals commence to separate after about 50-75 ml. have been introduced. When all the water has been run in, cool the mixture externally with ice water for 30 minutes (1), and collect the crude phenylacetamide by filtration at the pump. Remove traces of phenylacetic acid by stirring the wet sohd for about 30 minutes with two 50 ml. portions of cold water dry the crystals at 50-80°. The yield of phenylacetamide, m.p. 154-155°, is 95 g. RecrystaUisation from benzene or rectified spirit raises the m.p. to 156°. 

Application of charges and filtration may separate protein very efficiently. Electro-kinetic deposition uses voltage gradients of 1050V/cm to produce solid biomass with densities of up to 40% w/v. 

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