Correlation for Predicting Choking Flowrates in Vertical Pneumatic Coveying

A mathematical definition of choking phenomenon and a mathematical model for predicting choking velocity and choking voidage

“…Recently Leung et al (1971) reviewed the existing correlations and pointed out the inadequacy of the correlations by Zenz and Othmer (1960) and by Doig and Roper (1963). In turn, they proposed a method for calculating solid flow sates at the onset of choking based on two assumptions: the voidage at the onset of choking eC is equal to a constant value of 0.97, and the slip velocity Us* = ( U f ) , -( U p ) at the onset of choking is equal to Ut, the terminal velocity of a single particle.…”

ECT studies of the choking phenomenon in a gas–solid circulating fluidized bed

“…Various assumptions were made in modeling efforts. For example, by assuming the voidage and the slip velocity at the onset of choking to be 0.97 and the terminal velocity of a single particle, respectively, Leung et al (1971) derived a correlation that predicts the choking velocity of solids in vertical pneumatic systems. Capes and Nakamura (1973), on the other hand, noted that the slip velocity at the onset of choking could be greater than the terminal velocity of a single particle because of the particle-wall friction and particle recirculation effects.…”

“…They noted, then, that the choking data were difficult to obtain accurately because the occurrence of the choking spans over a range of gas and solids velocities in a vertical pneumatic system. Using the same assumption concerning the slip velocity at choking as that of Leung et al (1971), Yang (1975) considered the choking point in a CFB riser to be reached when the solids friction factor was equal to 0.01. Yang (1983) further modeled the choking point by using a correlation to describe the solids friction factor.…”

Choking Affects the Operation Diagram of a CFB Riser

“…(4) is illustrated in Figure 3 for the 84 m rounded sand. For all powders, Leung et al [7] and Matsen [8] underestimate Ch . The Yousfi and Gau [9] prediction is fair at lower and/or values.…”