BASIC STUDIES ON THE DEVELOPMENT OF HIGHLY EFFICIENT COMPACT HEAT EXCHANGER WITH LOW ENVIRONMENTAL LOAD

低环境负荷高效紧凑型换热器开发基础研究

基本信息

批准号：
14550181
负责人：
HAGIWARA Yoshimichi
金额：
$ 1.92万
依托单位：
KYOTO INSTITUTE OF TECHNOLOGY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14550181/
关键词：
liquid-liquid direct contact high-density inactive liquid upward water flow PLIF PTV direct numerical simulation near-wall turbulence structure local heat transfer 局所熱伝導液液直接接触熱交換上昇水乱流粒子画像速度計測法乱流熱流束

项目摘要

The experiments were conducted for the upward water flow in a vertical pipe with falling immiscible droplets of hydrofluoroether (HFE-7200) or perfluorocarbon (FC-72). The visualization of velocity field and temperature field and image processing were carried out.(1) The HFE-7200 droplets fall with noticeable wobbling in the near-wall region of the turbulent upward water flow. On the other hand, the droplets whose specific weight is higher than that of hFE-7200 fall with small-amplitude wobbling in the central region. The increases in the turbulence intensities and the decrease in the mean velocity are measured in the region of droplet passing. The vortices in the wake flow of the droplets cause the change in the turbulence statistics. The outward or wallward flow induced by the flow of HFE-7200 droplets affects the near-wall coherent structure.(2) The Strouhal number for the droplet motion can be estimated from the empirical of rising bubbles. This Strouhal number is lower than the St … More rouhal number of vortex shedding from a solid sphere.(3) The circular fluid motion was observed in the wake flow region. This motion is considered to be the cross sections of the unsteady Ω-shaped vortex tube. The thermal wake region is smaller than the area of passing the Ω-shaped vortex tube in the wake flow. This is because the Prandtl number is high and because high-temperature fluid outside the tube was carried into the wake flow region surrounded by vortex tube.(4) The high velocity flow in the wall jet between the funnel and the pipe inner wall decelerated the droplet falling velocity. The droplet was easily transported in the central region by the wall-normal fluctuating velocity generated by the tripping wire. The funnel and tripping wire allocated near the bottom of the test section worked well for collecting all the descent droplets.The direct numerical simulation was carried out for turbulent upward flow between two heating walls with four immiscible droplets. The main conclusions obtained are as follows.(1) The droplet induced several types of secondary flows. These flows increased the Reynolds shear stress product. These flows were attenuated by the adjacent in the streamwise direction. The small-scale streamwise vortices were attenuated near the droplets. The large-scale developed streamwise vortices were deformed by the droplets.(2) The product of wall-normal velocity fluctuation and the temperature fluctuation increased by the secondary flows. This shows an enhancement of turbulent heat transfer by droplets. Less

对垂直管中的向上水流进行了实验，该垂直管有降落的水氟（HFE-7200）或全氟碳（FC-72）。（1）HFE-7200液滴的可视化速度场和温度场和图像处理。另一方面，特异性重量高于HFE-7200的液滴在中部地区摇摆不定。湍流强度的增加和平均速度的下降是在液滴通过区域中测量的。液滴的尾流中的涡旋导致湍流统计的变化。 HFE-7200液滴流动引起的向外或壁向外流动会影响近壁相干结构。（2）可以从上升气泡的经验中估计液滴运动的曲线数。该曲线数低于ST…从实体球体中脱落的涡旋数量更多。（3）在尾流区域观察到圆形流体运动。该运动被认为是不稳定ω形涡流管的横截面。热唤醒区域小于在尾流中通过ω形涡流管的区域。这是因为prandtl的数量很高，并且由于涡流管周围的尾流区域的高温液体被带入尾流区域。液滴通过绊倒线产生的壁正常波动速度很容易在中央区域运输。在测试部分底部附近分配的漏斗和跳闸线很好地收集了所有下降液滴。进行直接数值模拟，以在两个带有四个不混溶的液滴的加热墙之间进行湍流的向上流动。获得的主要结论如下。（1）液滴诱导了几种类型的二次流。这些流量增加了雷诺剪切应力产物。这些流动在流向方向上被相邻的衰减。小型流向涡流在液滴附近衰减。大规模开发的流涡流被液滴变形。（2）壁正常速度波动的乘积和温度波动随次级流的增加。这显示了液滴湍流传热的增强。较少的