Particle collection efficiency

The concept of the start radius and its relation to the volume of su en sion processed is a very inq)ortant one in relation to understanding the collection efficiency of a centrifuge. For exan le, it is possible to rearrange Equation (8.9), using Stokes law for Ut to provide an equation for the particle size when the collection efficiency is 50%, thus  

Considering efficiencies other than 50% Equation (8.6) can be modified to give  

Alternatively, the start radius associated with a given particle size can be calculated by combining the equations for radial and axial residence times and rearrangement to give  

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Collection Efficiency. The classical Deutsch and Anderson equation for predicting particle collection efficiency is... 

Packed fiber bed mist eliminators can be designed to operate at almost any desired particle collection efficiencies, depending on the allowable pressure drop and cost. A good discussion of sulfuric acid mist generation, control, and mist eliminator design is available (109,110). 

FIG. 17-39 Single particle collection efficiency curve. Coutiesy of PSRI, Chicago.)... 

Microscopy Poor for large particles. Collection efficiency increases as particle size decreases. 

PM Impingement-plate tower collection efficiencies range from 50 to 99 percent, depending upon the application. This type of scrubber relies almost exclusively on inertial impaction for PM collection. Therefore, collection efficiency decreases as particle size decreases. Short residence times will also lower scrubber efficiency for small particles. Collection efficiencies for small particles (< 1 fim in aerodynamic diameter) are low for these scrubbers hence, they are not recommended for fine PM control. 

Note that the presented particle collection efficiencies cannot be assumed to be for the best available technology and are shown for equipment existing in industry. Dimensioning of particle removal equipment makes it possible to achieve better removal efficiencies in most cases presented in Table 13.1. All particulate and gas-cleaning equipment must be separately designed to meet specified local conditions. 

A series of theoretical analyses of the fluid and particle collection efficiency of cyclones were performed in the 1970s by Bloor and Ingham " and they have been found to be in good agreement with the experimental data. 

Manufacturer Gas Temp. (Max.) Particle Collection Efficiency Remarks... 

The surface layer composition may influence the effectiveness of pollution control devices. For example, it is apparent that a surface region highly enriched is alkali-alkaline earth sulfates may enhance the fly ash particle collection efficiency of electrostatic precipitators (11, 12, 51-53). 

Most recently the VELUT model has been expanded to handle the problem of simulating the particle collection efficiency of a VE sampling dust-laden air under non-isokinetic conditions... 

Tests of the WWEP were conducted with 4 in, 8 in and 16 in diameter units at flow rates ranging from 100 to 4000 ft /min. Particle collection efficiency of these units was measured with atmospheric dust, AC fine test dust (mass mean diameter (MMD) 12 pm), artificial cotton dust (MMD = 4.0 pm) and cotton dust drawn from the processing area of a card (MMD = 3.0 pm). 

Assuming homogenous expansion of the fluidized-bed the collection efficiency Eg may be calculated as a function of process parameters, for example the size of the collector particle dp or the height of the fluidized-bed z as well as the effective single particle collection efficiency cp and the porosity of the fluidized-bed s ... 

A successful coating process requires that the encapsulation substance adheres sufficiently to the surface of the fluidized-bed material. Of course, the adhesion also affects the collection efficiency. In literature [4,8,9], the impact of adhesion to the coating process is taken into consideration by introduction of the adhesion coefficient X. Thus effective single particle collection efficiency cp may be formulated ... 

Herein, / is the single particle collection efficiency. According to literature [9] for liquids or very soft substances the adhesion coefficient has a value near to one. Another study indicates that for solid aerosols having a diameter in the range of 0.7 pm the adhesion coefficient may vary from 0.001 to 0.01 [4]. 

An estimation of the single particle collection efficiency

collection efficiency /(g and the layer thickness. Using this estimation the time which is necessary to obtain a particular layer thickness can be predicted. 

Particle collection efficiency is a monotonically increasing function of the inertial parameter and has been determined experimentally (1,11,12). Customarily, this function is represented by a single value, that is, the value of the Stokes number (Stk) that corresponds to a collection efficiency of 50%. Thus by rearranging Equation 2), the diameter of the particle collected with 50% efficiency (D50) is... 

FIGURE 3 Particle collection efficiencies for spheres of different diameter and different particle diameters and aerosol flow velocity (Uoo). Particle diameters are given by the values at the upper right of each curve. The diffusion regime is at the left and the inertial impaction regime is at the right. 

Figure 3.8 Fine particle collection efficiencies of the HVS3 and typical home vacuum cleaner...

A sufficient bed length must be kept to insure an appropriate contact time (at least 0.1 to 0.5 s) between the filtering media and the gas-particle flow for an optimum particle collection efficiency ... 

Pilot-scale particle collection efficiency has been found to be similar to the cold and dry experiments over 300 hours filtration time, Figure 12 presents a relatively constant pressure drop over time for the hot and dry experiments conducted on the pilot-scale filter under a gas flowrate of 20 Nm /h (80 Nm /hr/m ), with a particle load of 3000 mg/Nm and using Ottawa sand as the filtering media. Deep holes on Figure 12 are air pulses to back-flush the solids plugging the exits. 

Venturi scrubbers are an enhancement of the spray approach. A contacting liquid is added to enirainment-conlaminated gas stream just upstresm of, or at the throat of, a venturi (Fig. 3.2-16). turbulence of high-velocity gas in the venturi causes break-up of the ini reduced liquid into small drops intercept and coalesce wiih the small, entrained particles. Collection efficiency greater then 90% of parti... 

Pore Radius r Particle Radius q = Face Velocity of Gas Particle Density E Particle Collection Efficiency. 

The previous discussion has concluded that all particles that arrive at a surface do not necessarily remain at the surface. Glen et al [1988, 1992] allow for this phenomenon by the inclusion of a particle collection efficiency rj. defined as the fraction of the free stream particle mass flow (through the projected area of the target body or object, onto which the particles impinge) that actually strikes the body. 

The overall particle collection efficiency can then be written in the following form ... 

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