Rising Behavior Of Bubbles And Hydrodynamic Characteristics Of Gas-liquid Two-phase Flow Nearby The Vertical Plate

In the near wall gas-liquid two-phase flow,there are many important parameters such as bubble trajectory,size and shape.The different bubble trajectories will lead to different flow state of the liquid phase.Consequently,further investigations regarding to motion characteristics of the bubble and hydrodynamics of liquid in the near wall gas-liquid two-phase flow could act as guidance for solving many practical engineering problems.In the research,selecting bubble chains in the glycerol aqueous,the main feature parameters are E?tv?s numbers Eo=1.14¹.28,Morton number Mo=5.422X10-4 and Reynolds number Re=181¹91,which belong to classic cases.The near-wall behavior of bubbles and hydrodynamics of liquid are the main research contents.Firstly,we design and build an experimental platform based on gas-liquid two-phase flow,which has such these virtues as visualization and non-contact measurements.The 16cases of bubble motion are captured by the high-speed photography.These situations include the frequency of bubbles are f₁=47 Hz、f₂=126 Hz、f₃=157 Hz、f₄=210 Hz,besides bubbles rise freely and the distance between nozzle and vertical plate are S₁=1.5 mm、S₂=3mm、S₃=4.5 mm respectively.Meanwhile,based on MATLAB image processing toolbox,an algorithm is given to analyze the various images.It mainly consists of image preprocessing,computing the binary image,bubble edge detection and extraction of bubbles characteristics.By analyzing of a lot of data from experiments shows trajectories of the bubbles,which include zigzag,far away from and towards the vertical plate.In the experiments,all the freely rising bubbles in every frequency ascend at a straight trajectory in different frequencies.But combination of distance between the nozzle and the plate and frequencies of bubbles can cause different forms of bubbles motion.When the normalized initial distance S*=1.2,bubbles ascend in a zigzag trajectory.But when S*=1.2the low frequencies bubbles gradually move away from the vertical plate in a straight trajectory and the high frequencies bubbles gradually move close to vertical plate in a similar straight trajectory after an unstable motion.Particle Image Velocimetry（PIV）is employed to measure the velocity field of liquid around the bubbles.And instantaneous velocity,average velocity field,Reynolds stress and the turbulence intensity are analyzed.Result reveals that the velocity of liquid got bigger with the increase of the bubble frequency.Meanwhile,flow field of liquid near the vertical wall is not of similar radiation distribution in the condition of high bubble frequency.When bubbles ascend at zigzag trajectory,flow field of liquid near the vertical wall is of similar snake flow and the distribution of positive and negative Reynolds shear stress looked like a blob.The results of turbulence intensity shows that the value of turbulent intensity along the wall have not obvious changed in different situations and the bubbles rising in zigzag trajectory facilitates the uniformity of turbulence distribution.