基于盐溶液温差效应的多孔介质蒸馏热质传递机理研究

This project is to reveal mechanism of heat and mass transfer of porous media distillation based on salt-solution temperature gradient effect as the objective, to analyze the mechanism of heat and mass transfer on the evaporation interface of gas and liquid, to establish a dual component-three district model for porous media distillation based on salt-solution temperature gradient effect. Analysis of evolution law of gas-liquid interface and flow characteristics of two-phase flow are completed through visual experiment and transition criterion of evaporation pattern is proposed. Based on the dual component-three district evaporation model, evaporation is numerically simulated for experiment case, and then characteristics of temperature and pressure fluctuations are characterized. Evaporation pattern map and correlations of mass and heat transfer coefficient are developed for falling film flow and evaporation in porous media on vertical plate. With difference from the mechanism in AGMD (air-gas membrane distillation), this project focuses on mechanism reveal of the effects on the dual component-three district evaporation model with structural parameter of porous media, physical parameter of dual component solution and geometric parameter in air-gas space during the distillation as key scientific problem, which causes change of heat and mass transfer. Establishment of internal connection of falling film flow and evaporation phenomenon in porous media on vertical plate, characteristics of temperature and pressure fluctuations, and rule of heat and mass transfer forms the research feature and innovation to explore the nature cause and to establish some theoretical foundation of structural characteristics of porous media and effect parameter, and then to enhance of heat and mass transfer.

本项目以基于盐溶液温差效应的多孔介质蒸馏热质传递机理揭示为目标，剖析多孔介质气液蒸发界面处热质传递机制，构建基于盐溶液温差效应的多孔介质蒸馏“二元三区”蒸发模型。通过可视化实验，分析气液界面演变规律、两相流流动特征，提出蒸发流型转捩判据。基于“二元三区”蒸发模型，对实验工况下的蒸发过程进行数值模拟，进而对温度和压力波动特征进行表征，发展适用于竖板多孔介质降膜流动蒸发相图、传热传质系数关联式。与气隙式膜蒸馏机制不同，本项目紧密围绕“二元三区”蒸发模型中随着多孔介质结构参数、二元工作溶液物性参数和气隙中几何参数的影响，导致蒸发界面热质传递特性的机理揭示这一关键科学问题。在构建多孔介质降膜流动蒸发现象、温度和压力波动特征、热质传递规律的内在关联方面，形成研究特色和创新，为探究与基于盐溶液温差效应的强化热质传递过程相适应的多孔介质结构特性及其影响因素奠定一定的理论基础。

本项目以基于盐溶液温差效应的多孔介质蒸馏热质传递机理揭示为目标。通过可视化实验，分析了汽液界面演变规律和两相流流动特征。提出了超亲水多孔介质降膜流动蒸发传热临界饱和度概念，剖析了多孔介质汽液蒸发界面处热质传递机制。.构建了基于盐溶液温差效应的超亲水多孔介质降膜流动蒸发模型，获得多孔介质结构参数、工作溶液运行参数和气隙中几何参数等表征的蒸发通量、传热传质系数关联式。发现了大孔隙率超亲水性多孔介质内易生成优先流的特性和高饱和度下的优先流复发现象，扩展了优先流理论的适用范围。.定量分析了相互关联的多孔介质参数对优先流发展和蒸发热质传递特性的影响规律，解决了实验难以直接区分多孔介质多参数对优先流和热质传递特性具体贡献的问题。通过逐步多元回归分析方法筛选出了影响优先流和热质传递特性的关键因素，通过路径分析和决策系数方法揭示了多孔介质主要参数在渗流和蒸发过程中的影响机制。.扩展了多孔介质水分特征van Genuchten模型，建立了适用于超亲水性多孔介质内热湿耦合传递的气隙扩散蒸馏过程数学模型。该模型能够解决气隙扩散蒸馏脱盐过程参数的分析与优化等实际问题，具有良好的预测精度。.本项目在构建多孔介质降膜流动蒸发现象、温度和速度波动特征、热质传递规律的内在关联方面形成研究特色和创新，为探究与基于盐溶液温差效应强化热质传递过程相适应的多孔介质结构特性及关键因素提供了一定的理论基础。