Experimental investigation on integrated two-stage evaporators for CO2 heat-pump chillers

In this experimental study the performance of novel compact evaporator configuration was investigated. What makes this evaporator configuration unique is the integration of a gravity-fed/ self-circulation evaporator loop on one side of a plate heat exchanger (pre-cooling the secondary flow) and an ejector-assisted circulation loop on the other side (after-cooling the secondary flow). The secondary loop is internally connected, which means that larger temperature differences can be obtained with less connection work and space required, compared to previous heat exchanger models. Current CO2 heat-pump chillers available on the market utilize two evaporators to achieve high energy efficiency values. Space saving of the new compact design is a desired solution from vendors. When using this new concept, only one ‘three-circuit’ brazed heat exchanger is needed. The experimental campaign proofed that an ejector integration enables the two-stage evaporation configuration which significantly elevates the compressor suction pressure and improves the overall system performance. These systems can be applied in several market sectors including industrial chillers with high-capacity demands, where the secondary fluid is cooled even below 0°C. An image of the prototype heat exchanger with measuring instruments is shown in the attached figure. The experimental tests are carried out to investigate the performance under different conditions of evaporation pressure, secondary fluid temperature, and secondary fluid flowrate. The results are uploaded here in two files.

本实验研究针对新型紧凑型蒸发器构型的性能展开了探究。该蒸发器构型的独特之处在于，其在板式换热器（plate heat exchanger）的一侧集成了重力供液/自循环蒸发器回路，用于对二次流（secondary flow）进行预冷；另一侧则搭载了喷射器辅助循环回路，用于对二次流实施后冷却（after-cooling）。该二次回路采用内部连通设计，相较于传统换热器模型，可在更少连接工序与更小空间占用的前提下实现更大的温差。当前市面上在售的二氧化碳热泵冷水机组（CO2 heat-pump chiller）需配备两台蒸发器以实现较高的能效值，而这款新型紧凑型设计的空间节约优势正是厂商所亟需的解决方案。采用该新型设计理念时，仅需一台“三回路”钎焊换热器（three-circuit brazed heat exchanger）即可。本次实验测试证实，喷射器的集成可实现两级蒸发构型，此举能够显著提升压缩机吸气压力（compressor suction pressure）并优化系统整体性能。该系统可应用于多个市场领域，其中包括对二次流体冷却至0℃以下的大容量工业冷水机组场景。附随图示展示了搭载测量仪器的换热器原型机图像。本次实验测试针对不同蒸发压力、二次流体温度以及二次流体流量工况下的性能展开了探究。相关实验结果已以两份文件的形式上传至本页面。