Structure of Heat and Mass Transfer process in Turbulent Bubbly Flow by Combined Laser Imaging.

分散两相流的一个重要方面是分散两相与湍流的相互作用，它控制着许多工程装置的性能。在气液两相流动中，许多实验证据表明，湍流强度随空隙率和气体流速的增大而增大或减小。然而，气泡对湍流调制的机理，特别是气泡间相互作用的微观结构仍未得到充分的研究。本研究的目的是阐明分散两相流湍流和传热传质过程中气泡和微观结构相互作用的机理。本文对单个上升气泡的简单剪切层流湍流微结构进行了实验研究。采用一台高速CCD数字粒子图像测速仪（DPIV）与荧光示踪粒子（PIV/LIF）进行速度测量。采用互相关技术对记录的图像数据进行分析。另一台CCD摄像机通过方形红外LED背光阵列（红外阴影技术IST）来检测气泡的形状和平移运动。通过PIV/LIF/IST技术对气泡运动对周围流体湍流结构的影响进行了定量测量。对于剪切层中单个气泡的实验，我们估计了各种作用力对气泡的作用、气泡轨迹以及相互作用对流动结构的影响。此外，在向上的气泡通道流动中，可以看到当空隙率为低时，气泡附近单独出现了涡度值，而当空隙率为高时，颗粒间距出现了涡度值。这些实验结果与气泡湍流中输运现象的详细机理有关。

One of the most important aspects of dispersed two-phase flow is the interaction of dispersed phase with turbulent flow, which controls the performance of many engineering devices. In gas-liquid two-phase flow many experimental evidence indicated that the turbulent intensity became decreased or increased according to dependence on the void fraction and gas flow rate. However the mechanisms of turbulent modulation by bubbles are still unexplored, especially microstructure of the interaction between bubbles. The objective of the present study is to elucidate the mechanism of interaction of bubbles and microstructure of turbulence and heat and mass transfer process in dispersed two-phase flow. Experiments have been performed on turbulent microstructures in a simple shear layer flow involving a single rising bubble, an upward bubbly channel flow. Velocity measurements were made using one digital high-speed CCD camera for Digital Particle Image Velocimetry (DPIV) with fluorescent tracer particles (PIV/LIF). The recorded image data were analyzed by cross-correlation technique. A second CCD camera was used to detect the bubble's shape and translational motion via backlighting from a square array of infrared LED's (Infrared Shadow Technique IST). We clarified turbulent structures of surrounding fluid that was influenced by the bubble motion, quantitatively measured by PIV/LIF/IST technique. For the experiments of single bubble in shear layer, we estimated various forces on the bubble, bubble trajectory, and the interactive influence on flow structure. Further more, in upward bubbly channel flow, it can be seen that when the void fraction was low vorticities appeared in the vicinity of the bubble individually, while when the void fraction was high value of vorticities appeared in inter-particle spacing. These experimental results have been related to detailed mechanism of transport phenomena in bubbly turbulent flows.