Experimental detection of bubble-wall interactions in a vertical gas-liquid flow

Bubble motions and bubble-wall interactions in stagnant liquid were experimentally investigated by high-speed CCD and PIV technique with the main feature parameters such as Eötvös numbers Eo = 0.98-1.10, Morton number Mo = 3.21 × 10− 9 and Reynolds numbers Re = 180 ~ 190. The effect of bubble injecting frequency and the distance S between the gas injection nozzle and the wall on the statistical trajectory of bubbles, average velocity distribution of flow field and Reynolds shear stress were studied in detail. It was shown that the combination of bubble injecting frequency and the distance S caused different bubble motion forms and hydrodynamic characteristics. When the normalized initial distance was very little, like S⁎ ≈ 1.2 (here S⁎ = 2S/de, and de is the bubble equivalent diameter), bubbles ascended in a zigzag trajectory with alternant structure of high and low speed flow field around the bubbles, and the distribution of positive and negative Reynolds shear stress looked like a blob. With the increase of distance S⁎, bubbles' trajectory would tend to be smooth and straight from the zigzag curve. Meanwhile, with the increase of bubble injecting frequency, the camber of bubble trajectory at 20 < y < 60 mm had a slight increase due to the inhibitory effect from the vertical wall. Under larger spacing, such as S⁎ ≈ 3.6, the low-frequency bubbles gradually moved away from the vertical plane wall in a straight trajectory and the high-frequency bubbles gradually moved close to the vertical wall in a similar straight trajectory after an unstable camber motion. Under the circumstances, high-speed fluid was mainly distributed in the region between the wall and the bubbles, while the relative large Reynolds shear stress mainly existed in the region far away from the wall.