离子液体-水工质对太阳能吸收制冷两相流动热质传输特性研究

In view of the toxicity, corrosion, negative effects of crystallization and many other issues of the traditional refrigerating working fluid pairs, the research on the new green refrigerating working fluid pair of ionic liquid and water in the application of absorption refrigeration cycle is growing. This project mainly deals with the flow characteristics, heat and mass transfer and the refrigeration circulation characteristics in solar absorption refrigeration cycle. First, the falling film flow characteristics down along the heated/cooled horizontal tubes with a countercurrent absorbable gas were studied. The effect of the temperature difference between the liquid and the substrate and the countercurrent absorbable gas on the mechanism and regularity of the flow pattern transition were revealed. Also, the relationship between the flow/fluctuation and the heat transfer was established. On this basis, the absorption of water vapor with ionic liquid was studied and the relationship between the flow pattern and the mass transfer was established. Also, the model of the falling film flow and the heat and mass transfer with ionic liquid-water vapor was built. Finally the coupling relationship between the heat and mass transfer performance and the refrigeration performance were discussed. The impact of the operating parameters on the performance of the solar absorption refrigeration cycle with ionic liquid-water was revealed. This work will provide a good theoretical guidance on improving the performance of the absorption refrigeration cycle.

鉴于传统制冷工质对有毒性、腐蚀性及易结晶等诸多问题，对新型绿色制冷工质对离子液体-水在吸收式制冷循环中的研究与日俱增。本项目以可再生能源太阳能为驱动热源，针对制冷循环吸收器与发生器中离子液体水平管间降膜流动-热质传递性能-制冷循环特性三个相互关联的过程进行研究。首先，研究可吸收逆流气体吹扫下离子液体沿冷却/加热水平管间的降膜流动特性，揭示降膜液体与壁面存在温差及可吸收逆流气体促进/阻碍流型转换的机理和规律，建立降膜流动/波动与热量传递之间的关系。在此基础上，研究离子液体吸收/解吸水蒸汽特性，揭示降膜流型与质量传递之间的关系，建立离子液体-水蒸汽气液两相降膜流动与热质传递耦合理论模型。最后，研究太阳能吸收制冷循环系统内热质传递-制冷性能之间的相互耦合关系，揭示运行工况参数对离子液体-水工质对太阳能吸收制冷循环系统性能的影响规律。研究工作将为提高吸收制冷循环系统性能提供很好的理论指导。

吸收器/发生器的流动及热质传递性能已成为影响吸收制冷系统效率的关键因素，但目前对新型绿色离子液体-水制冷工质对在吸收器和发生器中复杂的流动-热质传递-循环性能及机理缺乏充分认识，从而缺乏性能强化的理论指导方法。本项目针对吸收器和发生器中的降膜流动及热质传输问题，系统研究了[EMIm]Ac纯离子液体、离子液体水溶液、离子液体基纳米流体及石墨烯-[EMIm]Ac/水三元溶液的密度、粘度、导热系数、比热容和表面张力，确定了最佳含水量，获得了离子液体基纳米流体的热物性预测模型，完善了离子液体吸收剂的热物性数据；通过研究管壁与液膜之间存在温差下离子液体水溶液沿水平管间的降膜流动及传热特性，明晰了热Marangoni效应对降膜流型及液膜铺展特性的影响规律，揭示了降膜流体与管壁之间存在温差促进及阻碍液膜铺展的机理；基于VOF模型，建立了水平管外降膜流动与传热的耦合模型，获得了不同工况下的液膜流动规律及不同工况下的液膜表面温度分布以及局部传热系数；对比分析了纯[EMIm]Ac离子液体液滴、60%wt[EMIm]Ac离子液体水溶液液滴及水滴撞击加热铜板后的液滴表面温度、蒸发时间、铺展直径等的变化规律，明晰了离子液体液滴与水滴在加热平板上不同的铺展动力学特点；通过分析蒸发温度、冷凝温度、发生温度对性能系数和循环倍率这两个性能参数的影响，揭示了运行工况参数对吸收式制冷循环系统性能的影响规律。项目的顺利实施能为极具前景的新型离子液体吸收式制冷系统性能强化提供理论指导。