析湿工况换热通道凝结水运动特性及其对传热性能影响的研究

Tube bank fin heat exchangers are widely used in a variety of applications in the air-conditioning, refrigeration, and process industry. The application may involve condensation of humid air on the heat transfer surfaces when the surface temperature is below the corresponding dew point temperatures. Thus, simultaneous heat and mass transfer occurs during the dehumidifying process. The presence of water condensation makes the heat and mass transfer process even more complicated since it may bridge the fin spacing and change the airside heat transfer and pressure drop characteristics of the tube bank fin heat exchangers. Furthermore, the condensated water may corrode fins and produce corrosion problems, and result in a series of health problems when heat excahnger used as air conditioner of daily life. Therefore, it is very important to obtain the mechanism how the condensated water affects the heat transfer and friction characteristics of heat exchanger, and to obtain effective method to control the movement of condensated water under wet conditions. However, the reported results can not deeply reveal main mechanism which causes the change of heat transfer and friction characteristics under wet conditions. Thus, equipped with theoretical analysis, numerical and experimental methods, under wet conditions, this project will try to investigate: (1) the probability distribution of condensate water on the fin surface of heat exchanger and the influence factors on condensation rate will be studied; (2) the kinematic characteristics of condensate water on the fin surface and in the channel formed by the fins, and critical air flow velocity and other influence factors for water droplet to departure from the fin surfaces; (3) through what mechanism the condensated water affects heat transfer and friction performance. The following results are expected to be obtained: the kinematic characteristics of condensated water on the fin surface and in the channelformed by the fin surfaces, and its effect on the air side heat transfer and friction performances; establishing the coupling model considering gas-liquid two-phase flow, heat transfer, mass transfer, heat transfer of the tube and the fin and movement of condensated water; exploring the effective measures to control the movement of condensated water. The research results not only can strengthen the understanding of the mechanism of heat transfer and friction performance of heat exchanger under wet conditions, but also can form the theoretical base to optimize the heat exchanger under wet conditions. Therefore，to carry out this project has not only great academic significance, but also high application value.

翅片管换热器在湿工况下运行时，水的凝结过程及运动特性直接影响着换热器的传热与阻力性能，并造成换热器腐蚀及带来一系列卫生问题。从而获得换热器在湿工况下对传热与阻力性能的影响机理、探索控制凝结水运动的有效措施非常重要。国内外现有研究结果还不能深刻揭示湿工况下引起换热器传热及阻力性能变化的主要机理。为此，项目采用理论分析、实验测试、数值分析相结合的方法拟对换热器在湿工况下开展三方面研究工作：（1）凝结水在换热表面发生位置的概率分布；（2）凝结水在换热通道内的运动特性及其描述；（3）凝结水通过何种机理对传热和阻力产生影响。目标是获得凝结水在换热表面、通道内的运动特性及其对传热与阻力性能的影响机理；建立气液两相流动、传热、传质及与管壁和翅片间传热的耦合模型；探索控制凝结水运动的有效措施。项目研究结果不仅可以增进对湿工况下换热器传热与阻力性能变化机理的认识，还可为优化湿工况下换热器设计奠定理论基础。

翅片管换热器在湿工况下运行时，水的凝结过程及运动特性直接影响着换热器的传热与阻力性能，并造成换热器腐蚀及带来一系列卫生问题。从而获得换热器在湿工况下对传热与阻力性能的影响机理、探索控制凝结水运动的有效措施非常重要。国内外现有研究结果还不能深刻揭示湿工况下引起换热器传热及阻力性能变化的主要机理。为此，项目采用理论分析、实验测试、数值分析相结合的方法拟对换热器在湿工况下开展三方面研究工作：（1）凝结水在换热表面发生位置的概率分布；（2）凝结水在换热通道内的运动特性及其描述；（3）凝结水通过何种机理对传热和阻力产生影响。通过深入细致研究获得的主要学术进展是：得到了典型结构翅片上凝结水析出与生长的特性规律；获得了不同条件下，凝结水脱离翅片表面的临界空气流速；建立了凝结水凝结速率与换热器入口空气温度、入口空气相对湿度以及入口空气流动速度关系的经验公式；分析出了典型结构换热通道中入口空气流速、相对湿度等因素对换热器传热和阻力特性影响关系；找出了控制凝结水运动的有效措施。项目研究结果不仅可以增进对湿工况下换热器传热与阻力性能变化机理的认识，还可为优化湿工况下换热器设计奠定理论基础。