Pressure fluctuations and choking criterion for vertical pneumatic conveying of fine particles

Pressure fluctuations and bed voidages are obtained in the dilute phase flow and dense phase flow regimes of vertical pneumatic conveying systems of fine particles. Statistical parameters of the pressure fluctuations are utilized to study the transition from the dilute phase flow to the dense phase flow. Out of the four types of fine particle used in the experiments, three types of fine particle exhibit a choking transition, which is characterized by a sharp change in the bed voidage. At the choking transition, sharp changes in the power spectral density function and standard deviation of the pressure fluctuations are also observed. The fourth type of fine particle does not exhibit any sharp changes in bed voidage, power spectral density function, or standard deviation of the pressure fluctuations over a wide range of air velocities used in the experiments. It is shown that the power spectral density function and the standard deviation of pressure fluctuations can be effectively used to accurately determine the choking transition. The experimentally determined choking velocities and bed voidages in the slugging dense phase flow are compared with available correlations.