Single-Fiber Efficiency

The single fiber efficiency by diffusion can be estimated from Eq. (8.37),... 

The efficiency of a filter depends on fiber diameter df (or the dimensionless projected area S) and the single fiber efficiency Es (Davies 1973) ... 

However, if we use the single-fiber efficiency / due to inertial impaction, then, from definition (6.3.42a), 2b = Eis 2rf. 

The same approach has been used successfully for aerosol filtration in a fibrous filter bed. Rubow (1981) has developed the following expression for the single-fiber efficiency for fibers of radius Tf when Brownian diffusion and interception operate simultaneously ... 

Here, Q/. and Qg are the volumetric liquid and gas flow rates, respectively, in m /s ddr aud Udr are the diameter and velocity of the drop falling in a gas moving with a velocity Vg, so that (Vg-Udr) is the relative velocity between the drop and the gas q is the particle collection efficiency of an individual droplet, somewhat analogous to the single fiber efficiency E,s due to inertial impaction, (6.3.42a). Calvert (1984) has obtained the following expression for the overall Venturi scrubber efficiency Ep after incorporating an appropriate expression for the individual drop collection efficiency q ... 

This equation is a reasonable basis for air sterilizing filter design. The single fiber efficiency, n, to use in this equation when experimental data are lacking is that based on collection due solely to interception effects estimated at an air velocity where minimal filtration efficiency is expected. 

K Proportionality constant, for target efficiency of a single fiber in a bed of fibers Dimensionless Dimensionless ... 

Therefore, from Eq. (8.33), the single fiber collection efficiency by inertial impaction is... 

Consider a clean house bag filter filled with randomly assembled fibers. The porosity of the filter is 0.97, and the fibers have an effective diameter of 10 pm. The length of the filter is 0.1 m. The viscosity of air is 1.8 x 10-5 kg/m s. For a velocity of the dust-laden air of 0.2 m/s, and a collection efficiency of a single fiber of 1.50 percent, estimate the overall efficiency of the filter. To reach a collection efficiency of 99.99 percent, what is the minimum length of this type of filter At this minimum length, what is the overall pressure drop ... 

The already fairly efficient collection efficiency of parallel n-around-1 probe has been further improved by modifications to the probe tip, four of which are shown in Figure 12.12. The single-fiber configuration has the advantage of complete overlap of excitation and collection regions and has been used successfully for fluorescence experiments. However, the background scattering... 

Figure 3.6 Efficiency minlmuni for single fiber removal efficiency for particles of finite diameter. For very small particles, diffusion controls according to f3.38) and ijr The different curves nesuli from the effects of velocity. In the interception range according to (3.39), rjtt is...

Fibrous deep bed fillers can be modeled as a collection of single cylindrical fibers set normal to the Row of an aerosol. The removal efficiency for the single fibers cun be e.stimated from theory if the gas velocity distribution around the fibers (cylinders) is known. 

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