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

对垂直管道内向上流动的氢氟醚(HFE-7200)或全氟化碳(FC-72)不混溶液滴进行了实验，进行了速度场和温度场的可视化和图像处理。(1) HFE-7200 液滴在湍流向上的水流的近壁区域下落时有明显的摆动，而比重大于 HFE-7200 的液滴。 hFE-7200 在中心区域发生小幅度摆动，在液滴经过的区域测量到湍流强度的增加和平均速度的降低。液滴尾流中的涡流导致了液滴的变化。 HFE-7200 液滴流动引起的向外或向壁流动影响近壁相干结构。(2) 可以估计液滴运动的斯特劳哈尔数。根据上升气泡的经验，该斯特劳哈尔数低于固体球体涡流脱落的圣劳哈尔数。(3) 在尾流区域观察到圆周流体运动，该运动被认为是十字运动。非定常Ω型涡流管的热尾流区域小于尾流中通过Ω型涡流管的面积，这是因为普朗特数较高且外部有高温流体。 (4)漏斗与管道内壁之间的壁射流中的高速流动降低了液滴的下落速度，液滴很容易在中心区域被输送。触发线产生的壁法向脉动速度分布在测试段底部附近的漏斗和触发线能够很好地收集所有下降的液滴。对两个具有四个加热壁的湍流向上流动进行了直接数值模拟。得到的主要结论如下： (1) 液滴引起了几种类型的二次流，这些流增加了流向的小尺度流向涡流。 (2)壁面法向速度脉动与温度脉动的乘积因二次流而增大。液滴增强湍流传热。