流体机械

2020, v.48;No.579(09) 1-5

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布液器入口参数对竖直管外降膜流动特性的影响
Effect of Inlet Parameters of Liquid Distributor on Falling Film Flow Characteristics Outside Vertical Tube

张天娇;马良栋;张吉礼;张继谊;
Zhang Tianjiao;Ma Liangdong;Zhang Jili;Zhang Jiyi;Faculty of Infrastructure Engineering,Dalian University of Technology;

摘要(Abstract):

布液器是实现液体降膜的关键部件,为了改善竖直管外降膜的布液效果,试验研究了布液器上方静液柱高度及布液器与布液管间环隙间距对降膜流量、雷诺数、流量系数以及液膜厚度的影响。通过研究发现:降膜流量和雷诺数随着环隙间距的增大呈线性趋势增加,但受静液柱高度影响较小,为了避免换热管外有"干斑"出现,降膜雷诺数应保证在1 000以上,同时布液器环隙间距不应小于0.5 mm;流量系数随着环隙间距的增加而增大并趋于稳定,但随着静液柱高度的增大,流量系数却有所下降,表明静液柱高度的增加会增大布液器出口的局部阻力,不利于布液;布液器出口处液膜厚度与布液器环隙间距直接相关,环隙间距越大,出口处膜厚越大;而布液器出口到液膜流动稳定这一过渡段内液膜厚度是逐渐减薄的,且随着环隙间距的增大膜厚变化幅度也逐渐变大;此外,布液器出口处的波动强度不受布液器入口参数变化的影响。
Liquid distributor is a key component of falling film equipment.In order to improve the liquid distribution effect of falling film outside the vertical tube,an experiment was conducted to study the influences of hydrostatic liquid height and annulus spacing between the distributor and the vertical tube on flow rate,Reynolds number,flow coefficient and falling film thickness.The study found that the falling film flow rate and the Reynolds number increase linearly with the increase of annulus spacing.However,these two parameters are less affected by hydrostatic liquid height.Furthermore,in order to avoid the appearance of dry spots outside heat exchanger tubes,the Reynolds number must be ensured to be more than 1 000 and the annulus spacing should not be less than 0.5 mm as well.In addition,the flow coefficient increases with the increase of annular spacing and becomes constant at the final stage,however,the flow coefficient decreases with the increase of hydrostatic liquid height,indicating the increase of the liquid height will increase local resistance at the outlet of the distributor,which is unfavorable to liquid distribution.Finally,the results show that the film thickness at the distributor outlet is directly affected by the annular spacing.The larger the annular spacing,the greater the film thickness at the outlet.Whereas in the transition section from the distributor outlet to the location where the liquid film flows stably,the film thickness gradually becomes thinner,and the change amplitude of film thickness gradually becomes larger with the increase of annulus spacing.In addition,the fluctuation intensity at the outlet is not affected by changes of inlet parameters of the distributor.

关键词(KeyWords): 竖直降膜;布液器;环隙间距;静液柱高度
vertical falling film;liquid distributor;annular spacing;hydrostatic liquid height

Abstract:

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基金项目(Foundation): 国家自然科学基金项目(51676026)

作者(Author): 张天娇;马良栋;张吉礼;张继谊;
Zhang Tianjiao;Ma Liangdong;Zhang Jili;Zhang Jiyi;Faculty of Infrastructure Engineering,Dalian University of Technology;

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