Analysis of pulsating electric signals generated in gas–solids pipe flow

In gas–solids pipe flow, particles are electrostatically charged as a result of repeated impacts on the inner walls. When a section of the pipe made of metal is electrically isolated and the charge leakage to the ground is monitored, pulsating electric signals are detected. In the present work, these signals have been studied both experimentally and theoretically. Micrometer-sized alumina particles were dispersed through an ejector and continuously transported in dilute phase. The pipes used were 6 mm in inner diameter, and a pre-charging pipe and detection pipes were installed in the particle transport system. The pulsating electric signals were found to vary in a wide range from positive to negative. The variation of the electric signals was attributed to two electrostatic phenomena (i) the induced current caused by the transport of a cloud of charged particles and (ii) the particle charging caused by repeated impacts on the inner wall. Based on analyses of these phenomena, the total charge, transferred charge, and particle concentration of the cloud can be evaluated. Furthermore, the average velocity of the cloud flowing in the pipe can be obtained from the time interval between peak signals measured with a detection pipe or using a two-detection pipe system based on the correlation method.