多效蒸发海水淡化技术中的关键热科学问题

The low temperature multi-effect distillation has become one of the main technologies for the desalination. However, until now the knowledge on the thermal physical process in this technology is limited in macro and equilibrium state. There are lots of micro phenomena and non-equilibrium process involved in it, which are lack of being acquainted together with technical feature sensitivity. That reveals the deficiency of basic scientific research related to LT-MED. In this project, the basic physical characteristics and key scientific problems involved in the LT-MED process will be studied, which includes the falling seawater (brine) film hydrodynamics under the actions of multi potential difference and outer impact, the distribution of temperature and concentration in the film and micro convection, the dependence of film evaporation mechanism on temperature difference, the flow pattern of steam in horizontal tubes during condensation and the phase interface characteristics, the scale and boundary effects when steam supersonic flows in adjustable TVC and their functions to condensation, shock wave, droplet self-evaporation and non-equilibrium thermodynamic process, and heat mixing features, etc. By combining the experimental examination, theoretical analysis and simulation calculation, the heat and mass transfer mechanism in desalination would be revealed comprehensively and accurately. The integrated theoretical system about non-equilibrium thermodynamic process in MED desalination would be built. Based on the analysis on basic thermodynamic process, the optimization of advanced MED desalination would be suggested. It is expected to promote the conformation and development of advanced desalination technology by applying the basal research achievements.

低温多效蒸发正成为海水淡化的主流技术之一。但迄今人们对该技术中的热物理过程仅限于宏观、平衡状态的认识，对其中微细传递现象、非平衡过程、技术特征的敏感性认识不足，显示出基础研究的不足。本项目拟对多种势差和外部冲击作用下的海水（浓盐水）降膜动力学过程和蒸发、液膜内部温度和浓度分布及微对流、液膜蒸发机理对温差的依赖性、蒸汽在水平管内凝结时的流型分布和相界面特征对凝结传热的影响、可调节TVC内部蒸汽超音速流动的尺度和边界效应及其对凝结/激波/液滴自蒸发和非平衡热力学过程的影响及热混合特性等MED海水淡化的基本物理过程和关键科学问题进行深入研究，采用实验测试、理论分析和模拟计算相结合的手段，全面准确揭示海水淡化热质传递过程机理，建立较完整的MED海水淡化非平衡热力过程理论体系，提出基于基本热力过程分析的先进MED海水淡化装置优化理论，争取实现基础研究成果推动先进海水淡化技术的形成与发展。

低温多效蒸发海水淡化装置的关键技术是节能和高效传热，其中的热力过程包括多种气液两相流动、溶液的蒸发和凝结相变传热、多效蒸发器之间的参数关联、蒸汽超音速喷射及其伴随的特殊过程等，对其中的一些基础问题缺乏足够的研究和认识是导致我国海水淡化装置在工程中屡屡出现失误的根本原因。本项目从多效蒸发海水淡化装置中的基本热力过程入手开展研究，包括从降膜流动过程、气液两相流在除沫器中的流动与分离过程、海水喷嘴布液等过程中抽象出液滴对不同壁面的撞击效应、多种势差和外部冲击作用下的流体降膜动力学过程等科学问题，对管外的降膜蒸发过程凝练为液膜内部温度、浓度、速度分布和微对流、传热温差分布、压差分布、气流速度以及蒸发界面等对液膜蒸发机理的作用的科学问题，对蒸汽在水平管内凝结过程凝练出凝结液的流型分布、相界面特征、不凝结气体含量及其分布、结构与界面效应对凝结传热机理影响的科学问题，对大型TVC工作过程凝练出内部蒸汽超音速流动的尺度和边界效应及其对凝结/激波/液滴自蒸发和非平衡热力学过程的影响及热混合特性等科学问题，以及多效蒸发系统参数关联与优化的科学问题。对上述科学问题做出了深入系统的阐述，解释说明了海水淡化装置中的基本现象，提出了对装置性能有重要影响的传热临界点、传热性能分区等概念，给出了海水淡化置中的热力学损失分布，全面准确揭示海水淡化热质传递过程机理，建立了较完整的MED海水淡化非平衡热力过程理论体系，提出基于基本热力过程分析的先进MED海水淡化装置优化方法。上述基础研究成果推动了先进海水淡化技术的形成，在工程项目中得到了应用。