Electrostatics – Richardson and McLeman (1960) explored pneumatic conveying with particles that produced considerable electrostatic forces that presented themselves as an increased in the pressure drop in a recirculation system. See Figure 9. This unique observation focused the community at exploring the cause of such behaviors. Klinzing probed electrostatics first in trying to eliminate the effect but the fascination of the phenomenon led to several experiments trying to establish its amount, direction and conditions for occurrence. Use of the phenomenon in a positive manner was also explored in the metering of flow. Figures 10 shows how the electrostatic effect can give completely different flow behaviors and patterns as such causing considerably more energy to be expended in conveying as well as being dangerous in operation.