中文摘要：

吸收式换热器是吸收式热泵应用于集中供热的关键核心部件．采用多段吸收式热泵机构可以有效提升机组性能：一次网回水温度一定时可大幅降低总传热面积，更重要的是在机组面积不变情况下显著降低一次网回水温度，实现单段机组无法实现的参数．本文在此技术基础上，设计并制作了三段大温差立式降膜吸收一蒸发器单元，并进行了多组工况的实验，测试其性能．该实验单元可以实现水侧大温差，形成三级蒸发压力梯度，与传统单段吸收机相比．实现了梯级换热，换热过程更加匹配；建立一维吸收器传热传质模型，分析并解释了实验中吸收器出现的冷却水出口温度高于溶液温度的现象．实验单元直接应用于实际供热工程中，在不同供暖工况下取得了良好的效果，一次网回水温度可以低至30℃以下．

英文摘要：

The absorption heat exchanger is a key component in the novel district heating systems based on absorption cycles. It can maintain the primary water return temperature at a quite low level and realize covering more waste heat recycle. Because in most working conditions the temperature drop and rise in a single absorber or evaporator is as high as 20--30 K, the multi-stage structure of this device has been proposed. The theoretical analysis have shown that this kind of structure can make heat transfer process more matched to realize much lower outlet temperature of primary water, while single-stage structure can only achieve a relatively high level. This is because of the multi-stage pressure and temperature gradient. In this study, based on the absorption heat exchanger technology, a vertical three-stage absorber-evaporator experiment unit was designed and built. On a large vacuum test bench, experiments were carried out in different conditions to test the performance. The result shows the experiment unit can achieve large temperature difference on the water side and form three stages of evaporating pressure gradient. With three-stage evaporating pressure gradient, the large triangle heat transfer process disappeared. The most important thing is that it can reduce the water temperature of evaporator side to a low level. Compared with traditional single-stage absorption heat pump, the heat transfer process in the whole absorber and evaporator is more matched and the performance can be better. In the experiment, an important phenomenon shows that the outlet water temperature of the first stage absorber is even higher than the inlet solution temperature. A 1-D differential model was built to analyze and explain the temperature variation inside the device so this experimental phenomenon can be reasonably explained. Finally the experiment unit was directly applied in a real district heating system. It worked as part of a complete multi-stage absorption heat exchanger in one thermal station of the district heating syst