气固摆动流化床的气泡运动特性

Bubble motion characteristics of gas-solid rolling fluidized bed

气泡现象是气固流态化的基本现象之一,了解摆动床气泡特性对推动流态化技术的海上应用具有重要意义。采用二维床及B类玻璃球颗粒的摆动床,通过对图像进行分析,研究了气泡在摆动过程中不同时间段的上升特点;提出了“热区图”方法,发现在较高表观气速时存在气泡聚集方向转换“滞后”于床体姿态转换的现象,原因为颗粒所受科氏力使其向摆动反方向聚集,抑制气泡聚集方向的转换;对IOP曲线的分析结果表明,气泡在床内分布位置、气泡平均尺寸及气泡生成与破裂频率等时均特征介于倾斜床与直立床之间;操作气速增加会使摆动床内气泡平均尺寸及气泡生成破裂频率都增加;摆动幅值增加只会使气泡生成与破裂频率明显增加;摆动周期对两者的影响均不明显。

In the marine environment,it is necessary to additionally consider the influence law of the swing movement of the bed with the floating platform on the gas-solid flow.From the previous research,there has been a basic understanding of the phenomena such as uneven gas-solid fluidization,gas-solid phase aggregation and separation in the rolling fluidized bed,but there is still a lack of in-depth understanding of the movement and aggregation characteristics of bubbles.The bubble motion characteristics of twodimensional rolling bed made of transparent plexiglass and Geldart B spherical glass beads are studied in detail based on image analysis and pressure analysis.Through the analysis of the image method,the research results on the spatio-temporal dynamic characteristics of the bubble rising process in the rolling fluidized bed show that when the bed is in the inclined attitude,the bubble rising and aggregation phenomenon is similar to the conventional inclined bed,and the bubble aggregation direction to the wall changes dynamically with the change of the bed attitude.The"hot zone diagram"method is used to analyze the bubble aggregation characteristics in the swing process.It is found that the conversion of bubble aggregation direction obviously"lags behind"the conversion of bed attitude at higher apparent gas velocity.The analysis reason is that the influence of Coriolis force on particles becomes greater at higher gas velocity,which makes particles tend to aggregate in the opposite direction of swing direction,resulting in the delay of gas phase conversion.The analysis results of bubble time averaged characteristics by pressure method show that the swing bed attitude is always"inclined■vertical"dynamic change,the distribution of bubbles in the bed,the average size of bubbles,and the frequency of bubble generation and rupture are between inclined bed and vertical bed.The influence of operating conditions on the bubble characteristics of rolling bed is studied.The increase of operating gas velocity increases the average bubble size and bubble generation and rupture frequency.The increase of oscillation amplitude increases the frequency of bubble formation and rupture,and has little effect on the average bubble size.The influence of rolling period on both is not obvious.