液-液气隙膜接触器传递过程热力学特性研究

The atmospheric absorption heat pumps based on the liquid-liquid membrane contactors have several advantages of atmospheric operation, compact structure, strong extensibility, energy conservation, environment protection, etc. Therefore this technology has wide application prospects in the distributed energy systems. However, the thermodynamic properties of the heat and mass transports in the system of “water-membrane-air-gap-membrane-salt solution” in these new membrane contactors have not been fully understood at home and abroad. In present project, the mathematical model of the heat and moisture diffusions inside the membranes will be established. The heat and moisture diffusions inside the membranes will be disclosed. The mathematical models describing the momentum, heat and mass transports in the air-gap membrane contactors will be established and numerically solved. The fundamental data of the Nusselt and Sherwood numbers in the channels and air-gaps will be then obtained and analyzed. The coupled heat and mass transfer mechanisms in the system of “water-membrane-air-gap-membrane-salt solution” will be disclosed. The plug flow mathematical models of the fluid flow, heat and mass transfer in the air-gap membrane contactors will be established. The criteria correlations of the heat and moisture transfer effectivenesses and entropy generations-Number of Transfer Units in the air-gap membrane contactors will be derived. The internal relationship between the heat and moisture transport effectivenesses and entropy generations will be disclosed. Also the mechanism of the energy consumption generated in the air-gap membrane contactors will be disclosed. The matching properties of the thermal parameters will be obtained. The energy transfer law will be analyzed. The heat and moisture recovery experimental device based on the air-gap membrane contactors will be built up and tested. The above established models will be validated by using the experimental results. The optimization principles of the thermodynamic performances will be disclosed, which will provide the fundamentals for performance optimizations of the air-gap membrane contactors. This project will expand a new direction of the researches on the absorption heat pump. Further, they will promote the new developments of the interdisciplinary researches of the membrane science, heat and mass transfer, and thermodynamics.

基于液-液气隙膜接触器的新型常压吸收式热泵具有结构紧凑、易于扩展、节能环保等显著优点，在分布式能源系统应用前景广阔。目前，国内外对这种新型接触器中“水-膜-气隙-膜-盐溶液”复杂热湿传递过程中的热力学特性的认识还很不充分。本项目拟建立膜本体热湿扩散数学模型，揭示膜本体热湿传输机理；建立液-液气隙膜接触器中的动量、热量与质量传递数学模型，获得流道和气隙中的努塞尔数、舍伍德数等准则数，揭示其热湿耦合传递机理；建立液-液气隙膜接触器中的热湿传递活塞流模型，导出其热湿传递效率及熵产数-传递单元数准则式，揭示热湿传递效率和熵产数之间的内在联系及其能耗产生的机理，分析其能量传递规律，探明其热力参数匹配特性，提出热力学性能优化的原理；开展膜式常压吸收式热泵实验装置的搭建、测试和模型验证研究，为液-液气隙膜接触器性能优化提供依据。本项目拓展了吸收式热泵研究的新方向，促进膜科学与热力学学科交叉研究的新发展。

基于液-液气隙膜接触器的新型常压吸收式热泵具有结构紧凑、易于扩展、节能环保等显著优点，在分布式能源系统应用前景广阔。目前，国内外对这种新型接触器中“水-膜-气隙-膜-盐溶液”复杂热湿传递过程中的热力学特性的认识还很不充分。本项目建立了逆流式液-液气隙膜接触器传热传质数学模型，发现热质传递在膜液界面附近和整个气隙区域表现活跃，气隙内以热传导和质量扩散方式为主，气隙起到了有效的隔热屏障作用，最大限度地减少了溶液的显热损失，采用0.5 mm的最佳气隙宽度可达到10.84°C的最大温升值，相比无气隙提高了99.6%；建立了中空纤维膜接触器的熵产模型和㶲损模型，发现在大多数情况下，当不可逆损失最小时，膜接触器的传热传质性能最佳，在通过增加水与溶液流之间的传热传质驱动力来改善接触器性能的过程中，熵产率和㶲损将不可避免地随着两流之间能量等级的增加而增加，最大的水蒸气转移速率对应最大的熵产率，入口水温和流量越大，水蒸气传质速率越大，熵产率越大，㶲损越大；建立了逆流式/顺流式平板膜模块集总参数数学模型，通过简单的代数变换，导出了热质耦合输运归一化方程的解析解，发现随着水流质量流速增加，溶液能量转化率和能效均增大，温升先增大后减小，逆流模块的性能优于顺流模块，当溶液入口质量分数为0.55，溶液入口温度为25℃左右时，膜组件的性能最佳，气隙长径比建议设置为50左右，以获得最佳性能，逆流模块的溶液温升比顺流模块大3.3% ~ 16.3%；通过将错流式液-液气隙膜接触器等效地转换为平行板液-液气隙膜接触器，建立了从水到溶液的热量和质量传输的方程，用新定义的无量纲参数对方程进行了归一化，当填料分数大于0.262时，错流式液-液气隙膜接触器的溶液温度提升大于平板式液-液气隙膜接触器，填料分数在0.48左右可能是一个很好的选择。中空纤维膜管的外径1.2mm左右可能是最佳值。本项目拓展了吸收式热泵研究的新方向，促进膜科学与热力学学科交叉研究的新发展。