Nonintrusive monitoring of slug sequence and flow stability in dense-phase pneumatic conveying
This article presents three sensing methods developed for the nonintrusive monitoring of important flow parameters in dense-phase pneumatic conveying. With the optical measurement system, images of the flow are acquired and an image analysis is used to determine the sequence, length, and velocity of slugs for given materials and operating conditions. The conveying parameters of interest are also monitored with a capacitive sensor by means of exploiting electrical properties of the flowing media. The charge-based measurement system uses a field meter to determine the electric field strength caused by charged particles and provides information about the sequence and regularity of the moving slugs. The noninvasive principle of all three methods avoids concerns about particle contact effects (e.g., wear of the measurement equipment or interference with the flow). All three prototype sensors have been tested under slug flow conditions. A comparison of the three sensing methods against key requirements in pneumatic conveying reveals that capacitive sensing seems to be best suited for reliable flow determination in slug flow.