降膜溶液除湿空调系统中的液膜动态波动及其传热传质研究

Buildings are an indispensable part of people’s lives as people spend 70-90% of their time in the built environment. The traditional dehumidification technology for indoor air has been proved to have many limitations such as energy waste and spread of harmful microbes. By handling the extra humidity independently with desiccant absorption, the liquid desiccant air-conditioning system (LDAC) has been regarded as a promising alternative. Internally cooled falling film dehumidification is an effective type to improve the system efficiency, which also avoid the corrosion of ventilation system and pollution of indoor air. During the dehumidification process, the film surface is not smooth and has many small waves due to the high liquid and gas velocity. The enhancement of surface waves was expected to be useful for improving the heat and mass transfer between air and desiccant. However, due to the complexity of the film flow, research on the film dynamic waves is limited, especially in the area of LDAC. The existing theoretical models are mostly steady state and fail to predict the effect of dynamic waves on the heat and mass transfer..This project aims to investigate the dynamic film surface waves theoretically, numerically and experimentally, including the shape determination and local turbulent flow on the side of interface, and its effect on the heat and mass transfer during the falling film dehumidification process. The unsteady-state model for film surface waves as well as heat and mass transfer of falling film LDAC will be developed ,verified and improved with experiments. Besides, to improve the accuracy of the model, the effect of contact angle of desiccant on the dehumidifier surface and surface roughness would be tested. With the research, measures for improving system efficiency, such as enhancing film waves and reducing the contact angle, will be proposed accordingly. This research is useful for predicting and optimization the system performance of LDAC and other falling film applications.

现代社会中人在室内时间达70-90%，中国建筑能耗接近社会总能耗三成。除湿方式严重影响室内空气品质及人员健康，亦对建筑能耗起决定作用。目前普遍使用的冷凝除湿技术效率低、能耗高，且存在滋生、传播有害微生物等诸多问题。溶液除湿空调系统被认为是解决上述不足的有效技术。降膜型内冷除湿可有效提高热湿交换效率，更可减少溶液飞沫腐蚀通风系统及污染空气。降膜除湿过程中液膜表面动态波动，对热湿传递有显著影响，增加波动可提高除湿性能。而目前研究还局限在平滑液膜稳态模型，未考虑传热传质过程中液膜表面动态波动的影响，不能解释实验与实际现象。本项目旨在研究溶液除湿过程中的液膜动态波动规律，探讨实际波动形态和其导致的界面局部紊流，研究波动与传热传质的相互耦合作用，并进行实验验证。本项通过理论及实验研究，建立针对降膜溶液除湿的非稳态传热传质模型，提出优化系统性能的实际解决措施及方法，推进溶液除湿空调系统的产业化进程。

现代社会中人在室内时间达70-90%，中国建筑能耗接近社会总能耗三成。除湿方式严重影响室内空气品质及人员健康，亦对建筑能耗起决定作用。目前普遍使用的冷凝除湿技术效率低、能耗高，且存在滋生、传播有害微生物等诸多问题。溶液除湿空调系统被认为是解决上述不足的有效技术。降膜型内冷/内热除湿系统可有效提高热湿交换效率，更可减少溶液飞沫腐蚀通风系统及污染空气。降膜除湿过程中液膜发生动态形变，对热湿传递有显著影响，特别是部分负荷下降膜不完全润湿极其常见，热质传递效果不佳，严重影响了系统性能。而目前研究对溶液除湿过程中降膜形变机理阐述不清，多为黑箱模型，应用范围窄，不能解释实验与实际现象。因此，本项目以液固相互作用为切入点，针对液膜形变与传热传质的相互耦合作用展开研究，取得如下成果：1）建立了降膜除湿液膜形态理论模型，获得了降膜扩散解析解，小流量下预测精度可提升80%；2）建立了基于液固相互作用的降膜除湿理论模型，部分负荷下热质传递性能预测精度可提高达30-50%；3）建立降膜溶液除湿非稳态CFD数值模型，预测液固表面参数对降膜除湿性能的影响：4）阐明了降膜除湿性能调控机理，提出基于TiO2涂层表面改性的热质传递强化实际解决方法。在完成上述项目预期目标外，继续对降膜溶液除湿展开深入研究，建立了太阳能辅助的内冷/热型降膜除湿空调系统热力学模型，并针对不同真实工况进行了运行优化。项目开展过程中发表相关学术论文12篇，其中SCI检索国际论文6篇（第一作者5篇），于国际/国内会议发表特邀报告2次，申请专利4项（授权1项），培养研究生5名，协助培养博士生1名。这一研究切实推进了溶液除湿空调系统的产业化进程。