CORRELATING FRACTIONAL COLLECTION EFFICIENCY

The traditional (Rosin, et al., 1932) mechanistic approach equates the time necessary for a particle to settle at a Stokes law velocity across the width of a cyclone s inlet duct, to the available residence time of the carrier gas stream in its number of spiral traverses within the barrel. With reference to Fig. 1, this permits solving for the smallest particle size able to cross the entire width and reach the wall in the available time. 

On the inherent assumptions that (a) all entering particles are uniformly dispersed over the area of the inlet duct, (b) the barrel is a perfect cylinder with a straight inlet duct entering tangentially, (c) the trajectory of die incoming particles will not result in any impingement on the gas outlet duct, (d) that the velocity of the downwardly spiraling gas 

Unfortunately the literature is rampant with data obtained from cyclones of so wide a variety of deviating dimensional ratios and ill defined particle properties, sizes and loadings, that full agreement between designers, theorists and practitioners has not yet been achieved. However, in practice, the enormous number of cyclones installed in identical industrial process applications in the petroleum and petrochemical industries (Zenz, A P I., 1975) throughout the world and spurred by a common interest in economics and environmental regulations, has led to the correlations shown as the solid curves in Figs. 2 and 3. 

The broad spectrum of derived fractional efficiency curves in Fig. 2 simply reflects the effects of cyclone designs deviating from consistence with the basic premises and from ill defined particle characteristics. 

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The theory of diffusion through the screens in diffusion batteries, as described by a semi-empirical equation derived by Cheng and Yeh (1980) correlating the screen fractional efficiency with experimental parameters, does not strongly differ from that formulated by Thomas and Hinchliffe (1972) as the penetration of particles through the screen (or the screen collection efficiency) is also an exponential function of the above parameters. 

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