水平管降膜蒸发过程的分区特征与机理研究

This study uses the process of horizontal tube falling film evaporation pipes of desalination technology as the main project, taking the generality of horizontal tube falling film evaporator into account, to study the interface, flow patterns, heat and mass transfer characteristics during the processes of liquid impacting the pipe surface and film-forming, liquid membrane flowing around the pip and liquid gathered tail flow falling in the pipe bottom. The experimental observations and theoretical analysis are mainlu study methods and also include the numerical method. And the study focus on the micro flow phenomena and transfer mechanism under different area and different force potential which have been affected by droplet splashing, temperature difference and concentration difference. The study also discuss the collaborative relationship and the effect of the heat transfer among concentration field, temperature field and velocity field within the liquid film. Through this study, trying to make up an in-depth theory description of film formation and development, and also the influence of impact effect, micro-convection effect, force potential difference effect and scale effect to transfer process. Finally establish the corresponding constitutive relation to provide the basic research and direction for the development of heat transfer enhanced technology of the falling film evaporation.

本研究以海水淡化技术中的水平管降膜蒸发过程为主要研究对象，同时兼顾水平管降膜蒸发的一般性，采用实验观测与理论分析的方法为主，同时辅助数值计算方法，探讨液体冲击管子表面与成膜、液膜绕管流动、液体在管子底部聚集形成尾流与下落的过程中的界面、流型、传热传质特征，重点研究液滴飞溅、温差效应、浓度差效应对管子不同区域、在不同力势作用下的微细流动现象和传递机理，讨论液膜内的浓度场、温度场、速度场之间的协同关系及对换热效果的影响。通过本项目研究，力图对液膜形成与发展、撞击效应、微对流效应、力势差效应和尺度效应对传递过程的影响进行深入的理论描述，建立相应的本构关系，为降膜蒸发传热强化技术的发展提供基础研究依据和方向。

本研究以MED海水淡化技术中的水平管降膜蒸发过程为主要研究对象，通过实验的手段对水平管管间流动形态的特点、各相邻管间流动形态的转变临界雷诺数进行了研究，对水平管外液膜厚度的分布及降膜过程的液滴喷溅量进行了测量，讨论了管间距、管径、喷淋量水平管降膜流动的影响，同时比较了海水与淡水在管外液膜流动状态上的差别。通过理论分析，构建水平管降膜流动了三维数值模型模拟液膜厚度与速度分布，与实验结果吻合较好。通过实验与数值方法对水平管外降膜蒸发传热进行研究，讨论了热流密度、喷淋密度、蒸发温度、盐度、管间距和管径对平均传热系数及局部传热系数的影响。通过实验，观测记录了液体流经竖直常温与加热壁面的流动特点。利用数值方法对水平通道内液体的层流对流进行模拟，研究液膜内部参数对流动及传热的影响。通过以上的研究结果，更加了解了水平管降膜蒸发的流动与传热机理，在研究的条件范围内，提高了水平管降膜蒸发的传热计算精度。