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垂直管内弹状流壁面传递是诸多工业应用中需研究的重要问题之一。今用极限扩散电流技术,对弹状气泡上升时瞬时壁面剪应力和传质系数进行了测定,结果显示:当基于表观气速的Froude数FrG < 0.74时,壁面剪应力随弹状气泡和液塞的到来呈现方向相反的交替变化,壁面传质系数亦相应变化;而当FrG > 0.74时,剪应力方向一直向下,说明液膜向下流动,且弹状气泡和液塞的到来对壁面传质系数的影响很小。这说明下落液膜射流穿透了液塞段,控制了整个壁面传递过程。研究还对下落液膜区、尾迹区及液塞段的不同传递特征及机理进行了分析, 并结合气泡塔熔融结晶器中弹状气泡上升时的传热,对结晶操作条件的合理选择进行了讨论。
The transmission of wall-shaped wall flow in vertical tubes is one of the most important issues to be studied in many industrial applications. The instantaneous wall shear stress and mass transfer coefficient at the rising time of the elastic bubble were measured by the limit diffusion current technique. The results show that when the Froude number FrG <0.74 based on the superficial gas velocity, the wall shear stress increases with the deformation of the bubble and The arrival of liquid slug showed alternating changes in the opposite direction, and the wall mass transfer coefficient also changed accordingly. When FrG> 0.74, the direction of shear stress was always downward, indicating the downward flow of the liquid film and the coming of the elastic bubbles and liquid slugs The effect of wall mass transfer coefficient is small. This shows that the falling liquid film jet penetrates the liquid plug section and controls the entire wall surface transfer process. In addition, the different transfer characteristics and mechanisms of the falling liquid film zone, the wake zone and the liquid plug segment were also analyzed. The reasonable choice of crystallization operating conditions was also studied in combination with the heat transfer during the rise of the slug bubble in the bubble melting crystallizer discuss.