带有离子液体溶液回路的CO2压缩-吸收耦合制冷循环降压机理研究

In recent years, CO2 as a natural working substance is catching the attention of people in the study of alternative refrigerants. The application and development of CO2 refrigeration technology has an important significance for environmental protection. However, the transcritical CO2 refrigeration cycle has the disadvantages of high manufacturing costs, heavy equipments and large energy consumption for its high operating pressure which is up to 10-12 MPa. Some scholars have already proposed CO2 vapor compression cycle with solution circuits to make the circulating pressure be significantly reduced. But the related research at home and abroad is still very limited so far, and its depressurization mechanism is unclear. The project proposal intends to make absorbent of ionic liquid and CO2 be mixed refrigerants and conduct a study on the key influential factors of reducing the operating pressure of refrigeration cycles under the background of air conditioning/heat pump applications by combining theoretical and experimental analysis. Research contents include: (1) The CO2 solubility in ionic liquids and the viscosity characteristics of the binary mixtures at equilibrium are to be studied; (2) The effects of absorption/desorption rate of ionic liquids for CO2 and their mass ratio on the operating pressure of the cycle under the flow regime are to be studied; (3) The best condition points of reducing the cycle operating pressure by the synergy of absorption and desorption processes are to be theoretically predicted. The implementation of this project will contribute to promote the understanding of the compression and absorption coupling characteristics of CO2-ionic liquid mixed refrigerants and the depressurization mechanism of the CO2 vapor compression refrigeration cycle. Thereby the study in this project will lay theoretical and technical foundation for the subsequent system optimization and performance improvement, and has important theoretical significance and practical value.

近年来CO2作为天然工质在制冷剂替代研究中再次受到人们关注。CO2制冷技术的应用和发展对保护环境具有重要意义。然而跨临界CO2制冷循环因具高达10-12MPa运行压力导致系统制造成本高、设备笨重、能耗较大等问题。已有学者提出采用带有溶液回路CO2蒸气压缩制冷循环，以使循环压力大幅降低。但目前国内外相关研究还很局限，其降压机理尚不明确。本项目以离子液体为吸收剂与CO2构成混合工质，理论和实验相结合，围绕空调/热泵应用背景下循环运行压力降低的关键影响因素展开研究：⑴处于静止平衡态时离子液体对CO2的溶解和粘度特性；⑵流动状态下CO2-离子液体吸收/解吸速率及循环质量比对运行压力的影响规律；⑶吸收-解吸过程协同对循环压力降低的最佳状态点理论预测。最终揭示带离子液体溶液回路的CO2压缩和吸收耦合特性及其对CO2制冷循环压力降低的内在机理。对推动CO2制冷技术的应用和发展，具有重要的理论和应用价值。

CO2作为环保型制冷工质有望成为现行制冷工质的主要替代品之一，但运行压力过高一直制约着CO2在制冷领域的发展。采取吸收和压缩耦合的方法来降低CO2制冷循环运行压力的CO2-离子液体压缩-吸收式制冷循环为CO2制冷剂的发展带来了新的思路，但目前国内外有限的研究导致其降压机理尚不明确。鉴于CO2在离子液体中的溶解特性及其混合物的粘度特性对整个循环的压力降低以及能效提高具有重要影响，本课题首先实验测定了CO2在离子液体中的溶解度以及CO2-离子液体体系达到相平衡时粘度，并分析了温度、压力、离子结构及搅拌对CO2溶解度的影响以及压力、温度、离子结构和CO2溶解度对体系粘度的影响；利用K-K方程关联实验数据计算得到了CO2在三种离子液体中的溶解Gibbs自由能、溶解焓和溶解熵，进一步了解了CO2在离子液体中的溶解过程；确定聚乙二醇（PEG200）作为助溶剂，实验分析了助溶剂PEG200的添加对CO2溶解度和体系粘度值的影响，探究了助溶剂助溶、降粘的实际应用效果；设计并搭建了一套研究流动状态下CO2-离子液体相平衡及压缩-吸收式制冷系统的实验台，进行了CO2-离子液体在流动状态下的相平衡实验研究，分析了离子液体循环流量、进气温度、压力和系统压比对系统高压侧降压幅度、流动态实际吸收效果以及蒸发温度的影响规律，结果显明系统高压侧压力得到显著降低（降压幅度最大达到30%）且具有较好的吸收效果（吸收完成度约70%）；基于实验数据建立了“吸收-解吸”流程模拟，分析了进气压力、吸收器温度、解吸效果以及混合工质气液流量比对系统高压侧降压幅度的影响规律，揭示了压缩-吸收式循环压力降低的内在机理；实验分析了冷却水进口温度、冷却水流量与载冷剂进口温度对系统各部件温度压力、制冷制热量、实际吸收效果、系统压比、功耗以及COP的影响规律，探究了CO2-离子液体压缩吸收式循环压力降低和能效提高的关键影响因素及规律。在本项目支持下，发表各类学术论文22篇，其中SCI/EI收录19篇；累计获授权专利3项；培养博士研究生1名，硕士研究生7名。