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

通过组合激光成像研究湍流气泡流中的传热传质过程结构。

基本信息

批准号：
11450088
负责人：
HISHIDA Koichi
金额：
$ 6.53万
依托单位：
Keio University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11450088/
关键词：
Laser technique Image Processing PIV Bubbly Flow Turbulence

项目摘要

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.

分散的两相流量最重要的方面之一是分散相与湍流的相互作用，它控制着许多工程设备的性能。在气体液体两相流中，许多实验证据表明，根据对空隙分数和气体流速的依赖性，湍流强度降低或增加。然而，气泡调制的湍流调制机制仍未开发，尤其是气泡之间相互作用的微观结构。本研究的目的是阐明气泡相互作用的机理以及分散两相流中的湍流，热和传质过程的微观结构。在简单的剪切层流中，已经对湍流微观结构进行了实验，涉及单个上升气泡，一个向上起泡的通道流。使用一台用于数字粒子图像速度测定（DPIV）的数字高速CCD摄像头（荧光示踪剂颗粒（PIV/LIF））进行速度测量。通过互相关技术分析记录的图像数据。第二台CCD摄像头用于通过从红外LED的平方阵列（红外阴影技术）的背光来检测气泡的形状和翻译运动。我们阐明了受气泡运动影响的周围流体的湍流结构，该结构通过PIV/LIF/IST技术定量测量。对于剪切层中单个气泡的实验，我们估计了气泡，气泡轨迹以及对流动结构的相互作用的各种力。此外，在向上起泡的通道流动中，可以看出，当空隙分数为低涡度时，在气泡附近单独出现，而当空隙分数为高涡度值时，则出现在颗粒间间距中。这些实验结果与气泡湍流中的转运现象的详细机制有关。