EXPERIMENTS IN TRICKLE BEDS AT THE MICROSCALE AND MACROSCALE - FLOW CHARACTERIZATION AND ONSET OF PULSING

A randomly packed bed of nearly uniform spherical particles is employe d to study cocurrent air/water downflow. Using a high-speed video came ra, observations are made in the interstices close to the bed wall. Pa tterns in the microscale (in constrictions and pores), similar to thos e recently reported for a two-dimensional test section, combine to yie ld macroscopically observed flow regimes. A gas penetration mechanism is identified as a dominant feature at incipient as well as in well de veloped pulsing flow. Special attention is paid to pulse formation and growth. A new, nonintrusive conductance technique appears to hold dis tinct advantages, over other methods, for on-line detecting the onset of the pulsing regime. Time records obtained with this technique compl ement information from flow visualization, shedding light on the mecha nism of transition. Measurements of the trickling/pulsing transition b oundary are in fair agreement with other data and model predictions fr om the literature.