基于制冷剂超润湿特性的竖直管内薄液膜降膜蒸发换热机理

As CFC elimination deadline is approaching, it becomes one of the technical route to deal with CFC elimination that the refrigerant filling quantity and usage are reduced by improving the structure of heat exchanger and refrigerant side heat transfer mode. Based on the super wetting characteristics of the refrigerant, the vertical falling film phase change heat transfer technology is adopted to reduce the liquid hold up in the outdoor unit of the air conditioner to reduce the quantity of refrigerant. The basic coupling law of the flow and heat transfer will be obtained by studying the falling heat transfer of the refrigerant in the vertical tube. The formation conditions and evolution regularity of homogeneous liquid films under non - dynamic liquid separation conditions are investigated. Considering the effect of gas tangent stress on the thickness of the liquid film during the evaporation, the theoretical model of the falling film evaporation of the refrigerant on the vertical surface will be established. The main influence rule will be concluded that the film thermal conductivity and gas-liquid interface shear affect the liquid film thickness, heat transfer coefficient and flow characteristics. The rule of enhanced surface effect on liquid film evaporation is clarified. The criteria for judging the film break up and the minimum total energy criteria of the thin liquid film break up will be obtained. The theory of vertical falling film evaporation heat transfer will be established which will provide a theoretical basis for heat transfer technology of low refrigerant charge in refrigeration system. The research of this project has important social significance and scientific value to solve the problem of alternative refrigerants in our country and the world.

氟氯烃类制冷剂淘汰限期日渐临近，通过改进换热器的结构及制冷剂侧换热模式、减少制冷剂的充灌量和使用量，成为应对氟氯烃类制冷剂限期淘汰的技术路线之一。基于制冷剂的超润湿特性，采用竖直降膜相变换热技术来减小空调器室外机中的液相积存量从而减少制冷剂的使用量。研究制冷剂在竖管内的降膜蒸发换热过程，获得其流动与传热的基本耦合规律。探寻非动力分液条件下均匀液膜的形成条件和演化规律。考虑蒸发过程中气相切应力对液膜厚度影响，构建制冷剂在竖直表面降膜蒸发理论模型，阐明制冷剂蒸发过程中液膜导热和气液相界面切应力对液膜厚度、传热系数、以及流动特征的主要影响规律。阐明扩展表面强化降液膜蒸发换热的规律。获得薄膜破裂的判断准则表达式及降膜破裂时的降膜能量临界值。确立竖管降膜蒸发换热分析理论，为掌握低制冷剂充灌量的制冷换热技术提供理论基础。本项目的研究对解决我国乃至世界制冷剂替代难题具有重大的社会意义和科学价值。

氟氯烃类制冷剂淘汰限期日渐临近，替代的制冷剂较难在降低温室效应、非易燃易爆性能以及高制冷循环性能三个方面达成一致。通过改进换热器的结构及制冷剂侧换热模式、减少制冷剂的充灌量和使用量，成为应对氟氯烃类制冷剂限期淘汰的技术路线之一。通过对制冷剂降膜蒸发过程接触角变化特性及换热特性的研究，获得了接触角随壁面过热度增大而增大的关系式，在过热度较小时，饱和制冷剂降膜蒸发过程中宏观液膜的温度Marangoni效应几乎可以忽略。由Young-Laplace方程计算的液膜形状得出的液膜宽度最接近实验数据。相界面传热模型运用Wayner模型会使液膜宽度的计算结果更接近实验数据。证明了制冷剂与换热表面具有超润湿特性，不需再进行材料的表面改性处理提高其润湿特性。对制冷剂在微肋管内两相流特性、环状液膜蒸发的研究结果表明，光滑管中主导流型为间歇流和环状流，其它流型只占全部工况中很小的一部分。而在微肋管中，环状流的起始发生在更低的干度。由于螺旋微肋表面对流动液相的离心作用使液膜分布均匀，因而提早进入环状流区域。提出的传热系数预测模型的误差在30%以内。采用螺旋微肋扩展表面可有效增加其换热系数。通过对水在竖直管壁降膜流动蒸发的换热特性的研究，获得了液膜覆盖率与喷淋水流量、空气流量的关联式、管外液膜对流换热系数和液膜流动雷诺数以及喷淋水普朗特数的关联式。开发了竖管型蒸发式冷凝器，已在和珠海格力电器股份有限公司联合开发的蒸发式冷凝器冷水机组项目中应用，生产销售制冷量在300kW~900kW的冷水机组60余台机组，广泛应用于轨道交通、数据中心、学校、工业厂房等多项工程。开发了竖管降膜冷凝器，能够同时满足环保、安全和能效要求，为R290房间空调器的推广应用提供了新的技术方案。开展了水在竖直孔板上静止和流动液膜特性的研究、用于高热通量散热的制冷剂环路重力热管的传热性能的研究以及制冷剂泵增压的机房空调系统性能的研究，对提高制冷系统的性能有一定的参考价值。