Fractional collection efficiency

Mathematically expressed, NT = Pf, where NT is the number of particulate transfer units achieved and PT is the total energy expended within the collection device, including gas and liquid pressure drop and thermal and mechanical energy added in atomizers. NT is further defined as NT = In [1/(1 -1 )], where Tj is the overall fractional collection efficiency. This was intended as a universal principle, but the constants and y have been found to be functions of the chemical nature of the system and the design of the control device. Others have pointed out that the principle is applicable only when the primary collection mechanism is impaction and direct interception. Calvert (R-10, R-12) has found that plotting particle cut size versus pressure drop (or power expended) as in Fig. 14-129 is a more suitable way to develop a generalized energy-requirement curve for impaction... 

The fractional collection efficiency at each size interval, rid, is calculated by using a similar formula, and the results are given in Table E7.2. 

In terms of the averaged particle diameters and the corresponding fractional collection efficiency, the fractional efficiency curve is obtained as shown in Fig. E7.1, from which the cut-off size of this cyclone is estimated as 9 pm. 

Table E7.2. Fractional Collection Efficiency for Dust Collection in Each Particle Size Range...

Highly friable particles may fracture and malleable particles may deform when thrown onto the cyclone wall. The nature of inertial separation based technologies impose the limitation that larger and more dense particles will be more readily separated from the continuum and therefore obtain higher collection yields compared to smaller less dense panicles. Various analytical semi-empirical and CFD-ba.sed methods exist for predicting cyclone fractional collection efficiency and yield (44). However, the ability to a priori predict full cyclone performance from first principles for applications involving inhalation panicles is still a considerable challenge. 

The current measured by an amperometric electrode is directly proportional to the flux described in Eq. 7.11, with proportionality constants n (electrons in the stoichiometric electrochemical reaction), F (Faraday s constant, 96,487 C/mol), A (electrode area) and B (fractional collection efficiency) ... 

Calculate the fractional collection efficiency for die particle diameter dp-. 

Typical fractional collection efficiencies for gas-solid filters are indicated in Fig. 3.5-4. Below a particle size of 2-5 pm, where even banks of small-diameser cyclones are ineffective, filters are often the most economical equipment. A filter can often be selected with a irdnumim of experimental wortt. The availability of standard equipment to handle capacities up to 100.000-200,000 ftVmin is very good. Consequently, filters are normally the equipment that is given first conadesratton after a determination has been made that neither gravity settlers nor cyclones are economical. 

Values of C are presented in Fig. 3.5-2. Note that C appears on both sides of the equation. 6. Calculate the fractional collection efficiency for the particle diameter... 

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