Pressure Drops in the Pneumatic Conveyance of Solids

Abstract

Abstract With the object of studying the characteristics of the horizontal flow of a mixture of solids and air a theoretical analysis of the flow pattern was attempted. Experiments were performed whose object was to determine the relationship between pressure loss, solids flow rate, and air velocity, and to obtain values for the frictional constants involved in the analysis. A justification for the developed equations was sought. It was found that the presence of the solid phase causes an appreciable pressure loss which is a linear function of both solid and gas flow rate. This justified the theoretical equations which predicted such a relationship. Experiments with two sizes of the same sand showed a higher pressure drop for the larger particles, other conditions being equal. These experiments, however, question the validity of applying the Fanning equation to a solid phase. The equation holds for a given solid but does not take into account variations in its size. The introduction of the dimensionless group d/D is proposed. On the basis of this investigation, it is concluded that the drag coefficient C is a function of the Reynolds number. The ratio of solids velocity to gas velocity is 0.5–0.6 for the small and 0.3 for the large sand. Following results of this work it would seem desirable to operate pneumatic systems at low gas velocities and high solid rates. Recommendations for further investigations are made.