腈纶溶剂回收降膜蒸发强化研究

发布时间：2018-01-30 03:35

  本文关键词： 降膜蒸发 纵槽管 布膜器 强化传热 改进Wilson图解法　出处：《华东理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：竖管式降膜蒸发器相比于其他类型的换热设备具有传热系数高、传热温差损失小、可处理热敏性物料、易于实现多效操作、结构简单等优点,因此广泛应用于各类行业。本文针对腈纶溶剂回收多效蒸发装置存在因液体不易成膜且小传热温差下传热效率低,并基于节能减排的目的,旨在开发出新型高效降膜蒸发装置。论文主要工作及成果如下:1.本文开发出矩形、椭圆形和圆形开口三种类型布膜器,对其最小降液流率进行测量,结合Hartley所提出的理论公式,优选出椭圆形开口布膜器,并利用Nusselt模型和Wilke模型对液膜平均厚度进行计算,最后验算布液盘液位高度,为降膜流动实验结果提供保证。2.对新开发的纵槽管进行降膜蒸发传热实验,在热通量q=13.2-56.52kW/m2,液体周边进料流量T=0.419-1.112kg/m·s,传热温差△T=2.02-9.87℃时以浓度为19.4%的NaSCN溶液为实验介质进行研究,结果表明:纵槽管强化传热效果在一定范围内随着管内雷诺数增大而增大;在热通量相同时,纵槽管的传热温差仅为光管的51%;纵槽管管外冷凝传热系数为光管的约2.07倍,总传热系数为光管的约1.73倍,强化效果显著。3.根据改进Wilson图解法,结合实验所测数据对纵槽管和普通光管计算结果进行线性回归,得到管外冷凝传热系数,结果表明威尔逊图解法线性回归关系很好,回归结果与实验所测结果吻合,说明了实验数据的可靠性。结合相关传热学原理,建立了不锈钢纵槽管降膜蒸发传热时管外冷凝传热的特征关联式,为工程应用提供一定的参考。
[Abstract]:The vertical tube falling film evaporator has the advantages of high heat transfer coefficient, small loss of heat transfer temperature difference, easy to realize multi-effect operation, simple structure and so on. Therefore, it is widely used in various industries. In this paper, there is a low heat transfer efficiency due to the liquid is not easy to form film and small heat transfer temperature difference, and based on the purpose of energy saving and emission reduction, the multi-effect evaporator for polyacrylonitrile solvent recovery. The main work and results of this paper are as follows: 1. In this paper, three types of film dispensers, rectangular, elliptical and circular, are developed, and the minimum downflow rate is measured. According to the theoretical formula proposed by Hartley, the elliptical open film distributor is selected, and the average thickness of liquid film is calculated by Nusselt model and Wilke model. Finally, the liquid level height of the liquid plate is checked to guarantee the results of the falling film flow experiment. 2. The heat transfer experiment of falling film evaporation of the newly developed longitudinal groove tube is carried out at the heat flux qn 13.2-56.52 kW / m ~ 2. The liquid circumferential feed flow rate is 0.419-1.112 kg / m 路s. The heat transfer temperature difference between 2. 02 and 9. 87 鈩，

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