Frequent impacts of bubbles on tubes immersed in bubbling fluidized beds can lead to excessive rates of tube erosion and vibration, with correspondingly high maintenance costs. The rate of erosion depends on the velocity of impact of the bubble wake on the tube, with bubbles striking the tube as they are in the process of coalescing (referred to as double bubbles) resulting in particularly high velocity wake impacts. In assessing the degree of erosion damage which occurs in a tube bundle in a bed operating at a given set of conditions, information is needed on the relative frequencies of impact of different types of bubbles and on their respective sizes and velocities. The characteristics of the dynamic loading on a tube also determines its vibration characteristics, thus governing the requirements for the tube support structure. A tube instrumented with strain gages was used to obtain data on impact dynamics. From these data, it was determined that the important features that distinguish a single bubble from a double bubble are the energy absorbed by the tube during the impact of the wake, the impulse transferred to the tube, and in the case of a pair of bubbles coalescing at the level of the tube, the interval of time between the impact of the leading wake and the trailing wake on the tube. A pattern recognition technique was adapted to utilize these criteria to distinguish between single bubbles and double bubbles in a freely bubbling bed. The method gave results which were in good agreement with visual observations made from the video screen. This technique can be used to help determine relative rate of erosion at a specific location in the bed. The results also can be helpful in developing information for use in design of tube supports and tube configurations.
