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

• 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

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

研究了垂直管内上升水流中不混溶的HFE-7200和FC-72液滴的下落特性。进行了速度场和温度场的可视化及图像处理。(1)HFE-7200液滴在湍流向上水流的近壁区域中以明显的摆动落下。另一方面，比重高于hFE-7200的液滴在中心区域以小幅度摆动落下。在液滴通过的区域，测量到湍流强度的增加和平均速度的降低。液滴尾流中的旋涡引起湍流统计特性的变化。由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)液滴运动的Strouhal数可以从上升气泡的经验估计。这个Strouhal数低于St ...更多信息 从固体球体上脱落的旋涡的鲁哈尔数。(3)在尾流区观察到了圆形的流体运动。这种运动被认为是非定常Ω形涡流管的横截面。热尾流区小于尾流中通过Ω形涡流管的面积。这是因为普朗特数较高，管外的高温流体被带入涡流管周围的尾流区。(4)漏斗与管道内壁之间的壁面射流中的高速流动使液滴下落速度减慢。通过触发线产生的壁面法向脉动速度，液滴容易在中心区域被输送。在试验段底部附近布置漏斗和绊线，可以有效地收集所有下降液滴。对两壁面间四种不混溶液滴的湍流上升流动进行了直接数值模拟。主要结论如下。(1)液滴引起了几种类型的二次流。这些流动增加了雷诺剪应力积。这些流动在流向上被相邻的边界层衰减。小尺度流向涡在液滴附近衰减。液滴的存在使大尺度流向涡发生了变形。(2)二次流使壁面法向速度脉动与温度脉动的乘积增大。这表明液滴增强了湍流传热。少

项目成果

Hagiwara Y., Takagaki S., Yuge T.: "Effects of a droplet on near-wall transport phenomena in turbulent downward liquid-liquid flow"J. Enhanced Heat Transfer. Vol.10. 81-93 (2003)

Hagiwara Y.，Takagaki S.，Yuge T.：“液滴对向下湍流液-液流中近壁传输现象的影响”J。

T.Yuge, Y.Hagiwara: "The Modifications of Near-wall Turbulence Structure and Heat Transfer by Immiscible Droplets in Turbulent Liquid-liquid Two-phase Flow"Int.J.Heat and Fluid Flow. Vol.25(in print). (2004)

T.Yuge、Y.Hagiwara：“湍流液-液两相流中不混溶液滴对近壁湍流结构和传热的修改”Int.J.热与流体流动。

Goto M., Matsukura N., Hagiwara Y.: "Heat transfer characteristics of warm water flow with cool immiscible droplets in a vertical duct"Experimental Thermal and Fluid Science. Vol.28 (to appear). (2004)

Goto M.、Matsukura N.、Hagiwara Y.：“垂直管道中温水流与冷不混溶液滴的传热特性”实验热与流体科学。

M.Goto, N.Matsukura, Y.Hagiwara: "Heat Transfer Characteristics of Warm Water Flow with Cool Immiscible Droplets in a Vertical Pipe"Proc.3rd European-Japanese Two-phase Flow Group Meeting. (CD-ROM). 1-7 (2003)

M.Goto、N.Matsukura、Y.Hagiwara：“垂直管道中冷不混溶液滴温水流的传热特性”Proc.第三届欧洲-日本两相流小组会议。

田島正博, 松倉紀行, 後藤雅志, 萩原良道: "沈降する不溶性液滴を含む鉛管内上昇水乱流の計測"第40回日本伝熱シンポジウム講演論文集. (2003)

Masahiro Tajima、Noriyuki Matsukura、Masashi Goto、Yoshimichi Hagiwara：“含有沉降不溶液滴的铅管中湍流上升水的测量”第 40 届日本传热研讨会论文集（2003 年）。