制冷工质降膜蒸发过程气液两相相互作用和气泡流动特性研究

Falling film evaporation is a phase change convective heat transfer process characterized by multi-influencing factor coupled each other, high random fluctuation and complicated heat transfer mechanism. Many difficulties and uncertainties exist in theoretical analysis of the process. In this program, the falling film evaporation of refrigerant outside horizontal tube bundles with more than 8 tube rows is investigated. The major research contents include: (1) Experimental study on the characteristics of the coupled effect between liquid-vapor two-phase flow and liquid film in falling film heat transfer; (2)Visualization investigation on the fluctuation behavior of bubbles outside the heating surface. The implementation of this program is based on the falling film heat transfer apparatus established in the applicant group, further measurement and analysis will be performed by flow rate, pressure and temperature measurement instruments of high accuracy and flow visualization facility. The critical scientific problems to be solved are: preliminary mechanism of dry-out in falling film heat transfer with the influence of vapor flowing from different directions and velocities; bubble behavior and distributing characteristics outside the heating surfaces. The influencing factors of falling film heat transfer can be further understood through this research. And the results of this program may have an important significance to the development of high efficiency central air conditioning system and the intellectual property of our own country.

降膜蒸发是多因素相互耦合作用的相变对流传热过程，随机性强，换热机理复杂。理论分析存在众多难点和不确定性。本项目以制冷工质在8排以上水平管束表面降膜蒸发过程为研究分析对象。主要研究内容包括：（1）降膜蒸发过程中气液两相流动和液膜之间相互作用特性的实验研究；（2）降膜蒸发传热表面气泡的流动及分布规律的可视化研究。本课题的实施以课题组已经建成的降膜蒸发传热测试系统为基础，利用高精度的流量、压力、温度测试仪表及可视化设备进行深入的实验测试与分析。拟解决的关键问题包括：降膜蒸发过程受不同大小以及方向气流影响传热表面的局部蒸干特性和传热面上气泡的变化和分布规律。通过研究，进一步掌握降膜蒸发传热的主要影响因素。研究结果对于我国开发高效的中央空调系统和掌握该领域自主知识产权有重要意义。

降膜蒸发是多因素相互耦合作用的相变对流传热过程，随机性强，换热机理复杂。理论分析存在众多难点和不确定性。为了更好地研究降膜蒸发传热过程的规律和气流对相变传热过程的影响，本课题设计了蒸气气流对降膜蒸发传热影响的测试装置，利用高精度的流量、压力、温度测试仪表及可视化设备，对制冷工质在6-8排水平管束外的降膜蒸发过程进行了深入的实验测试与分析。具体包括：研究了三个方向气流对蒸发器内气液两相流动、气液两相相互作用、传热管表面气泡的产生规律和流动状况进行了研究。完成了上、下、侧三种独立工况气流对降膜蒸发传热系数的影响测试。并开发出了适用于光管降膜蒸发传热系数的预测公式并进行了准确性验证。研究了不同强化传热表面的降膜蒸发传热特性，获得了强化管外降膜蒸发干蒸的临界液膜雷诺数，基本掌握了在附加气流影响下降膜蒸发的流动及传热特性。通过可视化研究，了解了传热管表面液膜的分布和受气流影响液膜的波动和流动规律，进一步掌握了降膜蒸发传热的主要影响因素。研究结果对于我国开发高效的中央空调系统和掌握该领域自主知识产权有重要意义。