An investigation of the prevailing flow patterns and pressure fluctuation near the pressure minimum and unstable conveying zone of pneumatic transport systems

The magnitude and frequency of pressure fluctuations were measured during the conveying of polymer pellets in a variety of flow conditions. The steady state range of the fluctuations was minimized at gas velocities that correspond to the pressure minimum of the typical state diagram. A reduction of the gas velocity from the pressure minimum value resulted in repeatable fluctuations at frequencies below 1 Hz. Analysis of the pressure traces shows that the system must go through an initial pressure peak before the system achieves a lower steady state value of pressure drop. An examination of this phenomena and unstable flow conditions is presented, which serves as a useful device for the operator attempting to optimize system performance.