低品位热与动力驱动的喷射/压缩复合制冷循环研究

Jet refrigeration can achieve the refrigeration effect by utilizing low grade heat sources, such as solar energy and waste heat. However, its refrigeration temperature is high( always above 0℃), which limits its application in the domain of cryogenic freezing. Autocascade refrigeration can achieve lower refrigeration temperature below -50℃ easily, but it totally consumes high grade energy and its COP is low. In view of the advantages of above two kinds of refrigeration cycles, the project presents jet/compression hybrid refrigeration cycle with mixed refrigerants driven by low grade heat and power. In the new cycle, in order to improve the efficiency of refrigeration significantly and achieve low temperature refrigeration, the jet refrigeration driven by low grade heat supplies the cooling capacity for the condensation of low boiling point component, reduces the compressor compression ratio, and recovers waste heat of discharge gas of the compressor, making a contribution to optimize the comprehensive efficiency for energy utilization in the domain of refrigeration and cryogenics. In this project, the performance characteristic of the new cycle and the optimum choice of refrigerant mixtures are investigated. Besides, the key scientific problems involved in this cycle are studied intensively, namely, energy coupling mechanism problem of jet/compression hybrid refrigeration cycle with mixed refrigerants and intrinsic mechanism of supersonic flow of mixed refrigerants in ejector under off-design conditions. In the meantime, experimental study is conducted to verify theoretical research results. The research results can not only provide fundamental data for the design of the new cycle, but also establish theoretical basis for heat and mass transfer mechanism research of heat and mass exchange equipments in this cycle.

喷射制冷可利用太阳能、废热或余热等低品位热来获得制冷效果，但制冷温度较高（通常在0℃以上），不适用于低温冷冻领域；自行复叠制冷循环很易获得低于-50℃低温，但完全消耗高品位能且制冷效率较低。结合上述两种循环优点，本项目提出一种低品位热与动力驱动的混合工质喷射/压缩复合制冷循环，该新循环以低品位热所驱动喷射制冷提供低沸点组分冷凝所需冷量、降低压缩机压缩比及回收压缩机排气余热，以期显著提高制冷效率和达到深度制冷目的，为提高低温制冷领域的能源综合利用效率做出贡献。本项目既对该新循环工作特性及混合工质优化选择进行理论研究，又对该循环所涉及的关键科学问题进行深入研究，即混合工质喷射/压缩复合制冷循环能量耦合机理问题、混合工质在喷射器中超音速流动传热传质机理问题。同时，开展实验研究进行理论验证。研究成果为该低温制冷系统设计提供基础数据，也为系统内各热质交换设备的传热传质机理研究奠定理论基础。

为解决喷射制冷循环制冷温度偏高及自行复叠制冷循环制冷效率偏低问题，本项目提出混合工质喷射/压缩复合制冷循环，建立喷射/压缩复合制冷循环热力学数学模型，研究混合工质配比、环境温度、蒸发压力、冷凝压力、压缩比等与喷射器特性及系统循环特性之间关系，对循环能效进行综合评价；提出进一步改进的新循环流程以实现更低制冷温度，优化选择两组混合工质研究喷射器喷射比和压缩机压缩比对改进新循环的热性能系数和机械性能系数影响；提出混合工质双级分离喷射制冷循环，研究基于单级分离及双级分离的混合工质喷射制冷循环热力学特性及能效分析，获得-30℃制冷温区，这是首次在喷射制冷循环中获得最低制冷温区突破；开展混合工质喷射器传热传质特性数值模拟研究；建立混合工质喷射器理论一维模型，进行喷射器结构优化设计，搭建喷射器性能测试实验平台进行喷射器性能初步实验。在发生温度74.0℃、发生压力1254KPa、冷凝温度21.0℃、冷凝压力450KPa、压缩机压比3.0，喷射器压比1.95时，获得新系统机械性能系数5.16，热力学性能系数0.60，最低制冷温度222.3K；本项通过课题组对该喷射/压缩复合制冷循环进一步改进基础上，在上述相同条件下，采用混合工质R170/R600比采用R23/R236fa该改进后循环所获得制冷温度更低，最低制冷温度达到195.1K；在相同外界环境条件和相同制冷温度条件下，采用R170/R600混合工质时，复合制冷循环的平均制冷效率较传统自行复叠制冷循环平均制冷效率提高60%以上。. 本项目已经在国内外期刊和会议上发表论文共20篇，其中在国际期刊上发表论文1篇，被SCI收录1篇，被EI共收录8篇，申请发明专利6项，实用新型3项，其中已经获得授权发明专利11项，培养在读博士研究生2名、在读硕士研究生4名。