Characterization of Bubble Properties in Slurry Bubble Columns Using a Triple Electroresistivity Probe

A triple electroresistivity probe was newly developed to detect the bubbles whose centers moved upwards through it and to measure their rise velocities and sizes (central chord lengths). The probe was designed based on the directional coincidence of the probe axis with the bubble motion, as required to determine the bubble velocity, as well as on the positional determination of the bubble chord detected, as required to obtain the chord length. The conventional double probe has a difficulty in sampling its signals for the bubbles moving vertically and in determining which chord of the individual bubble is detected. The measurements of the behaviors of bubbles with the triple probe were made for two different sizes of normal bubble columns and an external loop airlift bubble column with the liquid and solid phases performed batchwise under a wide range of operating conditions. An analysis of the signal sequences obtained by the probe was proposed which considered the effects exerted by the complicated behaviors of both bubbles and particles. The method gave the results on the local bubble frequency and gas holdup, as well as on distributions of the bubble central chord length and bubble rise velocity at a given radial position of the column. These results suggested an enhanced interaction between bubbles, such as their coalescence and breakup, due to the presence of solid particles. The radial profiles of the bubble frequency, the gas holdup and the mean bubble size and rise velocity, were found to depend on the bubble column type, operating conditions and physical properties of liquid and solid particles.