Prediction of the choking velocity and voidage in vertical pneumatic conveying of coarse particles

A method for predicting the choking velocity and voidage in vertical pneumatic conveying of coarse particles is developed and verified using the data obtained in this study as well as the data of Capes and Nakamura [C.E. Capes, K. Nakamura, Vertical pneumatic conveying: an experimental study with particles in the intermediate and turbulent flow regimes, Can. J. Chem. Eng. 51 (1973) 31–38]. The method is based on momentum equation, variational expression for the fluid–particle interphase drag coefficient and empirical correlation for the slip velocity at choking. New experimental data for choking velocity and voidage in vertical pneumatic conveying of monosized glass spheres (1.2, 1.94 and 2.98 mm in diameter) in a 30 mm in diameter tube are presented. Different published methods for the prediction of the choking velocity and voidage are compared with available data for coarse particles. The average agreement for choking velocity between proposed method and experimental values is within ± 7.2%. It was found that the simplest method to measure regime transition points in vertical pneumatic conveying is to measure pressure fluctuations in the transport line.