水平螺旋翅片管外降膜蒸发传热传质性能研究
发布时间：2018-12-12 22:41
【摘要】：淡水资源的匮乏和能源的紧缺导致利用可再生能源的淡化水技术越来越受到重视。内蒙古地区水资源天然紧缺,地下水是主要的供水水源,但地下水普遍是含盐、含氟量较高的苦咸水。因此结合该地区太阳能资源丰富的特点,设计了将太阳能蒸馏系统和水平管降膜蒸发系统相结合的新系统,为该地区的淡水供应提供一种新的水淡化途径。水平管降膜蒸发技术因存在相变过程具有传热温差小、传热系数高且能够利用低品位能源的优点,成为一种节能型蒸馏淡化技术。本文通过搭建水平管降膜蒸发传热试验平台重点研究降膜蒸发过程。利用搭建的试验平台,研究喷淋密度、蒸发温度、热流密度等因素对蒸发量及降膜蒸发传热系数的影响规律。研究结果表明:(1)蒸发量:在实验参数范围内,随着蒸发温度的提高、热流密度的增大,螺旋翅片管束和普通光管管束的单位时间蒸发量均增加;对于前者,蒸发温度为40℃和50℃时,喷淋密度0.060kg/(m·s)时对应的单位时间蒸发量大;蒸发温度为60℃和70℃,喷淋密度0.072kg/(m·s)时单位时间蒸发量大;对于后者,热流密度在3.91kw/m2~7.69 kw/m2之间时,喷淋密度0.072kg/(m·s)时单位时间蒸发量大;热流密度在10.11kw/m2~16.05kw/m2之间时,喷淋密度0.060kg/(m·s)时对应的单位时间蒸发量大。(2)降膜蒸发传热系数:在实验参数范围内,随蒸发温度的提高,螺旋翅片管和普通光滑圆管的降膜蒸发传热系数都增大;对于螺旋翅片管,随着热流密度的增大,降膜蒸发传热系数增大,但降膜蒸发传热系数几乎不受喷淋密度的影响;对于普通光滑管,热流密度变化对降膜蒸发传热系数产生的影响很小;蒸发温度为40℃时,降膜蒸发传热系数随喷淋密度的变大先变大,后减小;蒸发温度为70℃时,降膜蒸发传热系数随喷淋密度的变大而略微减小。当喷淋密度0.064kg/(m·s)、蒸发温度50℃、热流量193.2W~394W时,螺旋翅片管的降膜蒸发传热系数大约为普通光滑管的2倍。本文利用Fluent软件对管外液膜的分布情况进行了三维数值模拟,发现布液孔的纵向开孔间距影响管外液膜的分布情况。布液孔纵向开孔间距s=8mm时,管外液膜最均匀;s=10mm时,管子中间位置处形成的液膜较均匀,两端位置处形成的液膜不均匀。在实际应用中,应适当减小两端的布液孔纵向间距。研究轴向中间位置处管外的液膜厚度,得到该处的液膜厚度值沿管壁周向角呈先变小后变大的趋势,但总的变化幅度不大,大约在120°附近,液膜厚度达到最小值。换热管上下部分的X方向速度分布和Y方向速度分布基本一致,在管子壁面存在粘性底层。
[Abstract]:The shortage of fresh water and energy makes desalination of renewable energy more and more important. There is a natural shortage of water resources in Inner Mongolia, and groundwater is the main source of water supply, but the groundwater is generally brackish water containing salt and high fluorine content. Therefore, a new system combining solar distillation system and horizontal tube falling film evaporation system is designed to provide a new way for freshwater supply in this area. The horizontal tube falling film evaporation technology is a kind of energy saving distillation desalination technology because of the advantages of small heat transfer temperature difference, high heat transfer coefficient and the ability to make use of low grade energy in the process of phase change. In this paper, the process of falling film evaporation is studied by setting up the experimental platform of falling film evaporation heat transfer in horizontal tube. The effects of spray density, evaporation temperature and heat flux on evaporation rate and heat transfer coefficient of falling film were studied by using the test platform. The results show that: (1) evaporation: in the range of experimental parameters, with the increase of evaporation temperature and heat flux, the evaporation of spiral fin tube bundle and ordinary light tube bundle increase in unit time; For the former, when the evaporation temperature is 40 鈩，
本文编号：2375362
[Abstract]:The shortage of fresh water and energy makes desalination of renewable energy more and more important. There is a natural shortage of water resources in Inner Mongolia, and groundwater is the main source of water supply, but the groundwater is generally brackish water containing salt and high fluorine content. Therefore, a new system combining solar distillation system and horizontal tube falling film evaporation system is designed to provide a new way for freshwater supply in this area. The horizontal tube falling film evaporation technology is a kind of energy saving distillation desalination technology because of the advantages of small heat transfer temperature difference, high heat transfer coefficient and the ability to make use of low grade energy in the process of phase change. In this paper, the process of falling film evaporation is studied by setting up the experimental platform of falling film evaporation heat transfer in horizontal tube. The effects of spray density, evaporation temperature and heat flux on evaporation rate and heat transfer coefficient of falling film were studied by using the test platform. The results show that: (1) evaporation: in the range of experimental parameters, with the increase of evaporation temperature and heat flux, the evaporation of spiral fin tube bundle and ordinary light tube bundle increase in unit time; For the former, when the evaporation temperature is 40 鈩，
本文编号：2375362
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