基于吸收式换热技术的多段立式吸收-蒸发器的实验研究与应用
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 o